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NORTH DAKOTA CLOUD MODIFICATION PROJECT

OPERATIONSMANUAL

A Program Designed for the

Seeding of Convective Cloudswith Glaciogenic Nuclei to

Increase Rainfall and

Diminish Hail Damage on theNorthern Great Plains

North Dakota Atmospheric Resource Board

State Water Commission

900 East Boulevard AvenueBismarck, ND 58505-0850

voice: (701) 328-2788

fax: (701) 328-4749

May 1993, May 2005Revised May 2010


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NORTH DAKOTA CLOUDMODIFICATION PROJECT

OPERATIONS

MANUAL

RevisedMay 2010

NORTH DAKOTAATMOSPHERIC RESOURCE BOARD

State Water Commission900 East Boulevard AvenueBismarck, ND 58505-0850

voice: (701) 328-2788fax: (701) 328-4749

Darin Langerud, DirectorMark Schneider, Chief Meteorologist

Kelli Schroeder, Business ManagerDan Brothers, Meteorologist

Matt Ham, Meteorologist


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ii


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North Dakota Cloud

Modification Project

OPERATIONS MANUALMay 2010 Revision

TABLE OF CONTENTS

1. INTRODUCTION ...................................................................................1

1.1 Operations History ......................................................................1

1.2 Research ......................................................................................2

2. PROJECT ORGANIZATION.................................................................3

2.1 Organizational Structure .............................................................32.2 Cloud Seeding Operations........................................................... 4

2.3 Project Equipment Locations ......................................................4

2.4 NDCMP Operations Area ...........................................................5

2.5 Statement of Equal Opportunity.................................................. 5

3. EVALUATION .......................................................................................6

3.1 Rainfall........................................................................................6

3.2 Crop Hail Damage....................................................................... 7

3.3 Other Studies ...............................................................................9

3.4 Urban Effects ..............................................................................10

4. RESPONSIBILITIES............................................................................ 124.1 Radar Meteorologists ................................................................ 12

4.2 Intern Meteorologists ................................................................ 12

4.3 Pilot - Meteorologist Joint Responsibilities .............................. 13

4.4 Pilots-In-Command................................................................... 14

4.5 Intern Copilots........................................................................... 14

4.6 Safety..14

4.7 General Responsibilities............................................................ 15

5. SEEDING CONCEPTUAL MODEL.................................................... 18

5.1 Seeding for Rainfall Increase .................................................... 18

5.2 Hail Suppression and the Conceptual Model ............................ 18

6. IDENTIFICATION OF SEEDING OPPORTUNITIES ....................... 23

6.1 Targets Suitable for Rainfall Increase Seeding......................... 23

6.2 Hail Suppression Opportunities ................................................ 24


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iv

TABLE OF CONTENTS,

continued

7. DELIVERY TECHNIQUES ................................................................. 25

7.1 Rain Augmentation Seeding Procedures................................... 25

7.1.1 Seeding in the Absence of Shear .................................. 26

7.1.2 Forward-Shear Seeding ................................................ 26

7.1.3 Reverse-Shear Seeding ................................................. 27

7.1.4 Embedded Cumulus...................................................... 27

7.2 Hail Suppression Seeding Techniques ...................................... 28

7.2.1 Squall Lines .................................................................. 28

7.2.2 Multicell Storm Techniques ......................................... 31

7.2.3 Supercell Seeding Techniques...................................... 32

7.3 Considerations for the Deployment of Aircraft......................... 33

7.4 Targeting Upwind of the Project and Broadcast Seeding ......... 35

7.5 Aircraft Sharing Between Districts ........................................... 36

8. DECISION MAKING ........................................................................... 388.1 Daily Strategy............................................................................ 38

8.2 Conditions Control Decision Ladder ........................................ 39

8.3 Seeding Strategy........................................................................ 39

8.4 Rainfall Increase........................................................................ 40

8.5 Hail Suppression ....................................................................... 40

8.6 Seeding Suspension Criteria ..................................................... 41

9. SEEDING EQUIPMENT ...................................................................... 45

9.1 Efficiency of Seeding Agents.................................................... 45

9.2 Hazardous Materials.................................................................. 46

9.3 Handling, Use and Storage of Flares......................................... 47

9.4 Preparation and Handling of Acetone Solution......................... 47

9.5 Handling, Use and Storage of Dry Ice ...................................... 48

9.6 Seeding Equipment Maintenance and Troubleshooting............ 49

10. PROJECT DOCUMENTATION .......................................................... 52

10.1 Aircraft Flight Forms ................................................................ 52

10.2 Flight Track Maps ..................................................................... 54

10.3 Chemical Inventory Form ......................................................... 54

10.4 NDCMP Records Distribution and Quality Control ................. 55

10.5 Archival of NDCMP Records ................................................... 55

APPENDICES.................................................................................................. 58I. Mixing Chemical....................................................................... 58

II. Seeding Opportunities and Methods ......................................... 59

III. Burn In Place Flare Usage......................................................... 60


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NDCMP Operations Manual 1

1. INTRODUCTION

The North Dakota Atmospheric Resource

Board (ARB) has prepared this operations manual for

the North Dakota Cloud Modification Project

(NDCMP). The manual draws extensively upon

previous operations manuals dated February, 1980 and

May, 1984. This manual contains information most

likely to be needed on a day-to-day basis by project

personnel. [The radar meteorologists will also receive a

Radar Manual, which includes information needed to

operate and interpret the radar and IRIS/TITAN software

programs. The PICs and ICPs will receive a PARS

manual that includes instructions necessary for operating

the Palm devices.]

The Operations Manual is both informative and

directive in nature. Information given represents asummary of detailed laboratory and field work, and the

reader must make use of the references listed to obtain

more complete information. The procedures described

are required for use by all project personnel. It is thus

important for each project person to become as familiar

with this manual as possible.

Teamwork is essential for quality operation.

This teamwork extends from the cooperation required

between meteorologists and pilots, to the relationship

between the Atmospheric Resource Board and the cloud

seeding contractor. Open communication among field

personnel, county weather modification authoritymembers and ARB office staff is essential.

Project personnel having ideas as to how to

improve any aspect of the NDCMPare strongly urged to

communicate such ideas to Bismarck staff. Continuous

quality improvement is a primary objective of the project

and only through the sharing of constructive ideas can

this be realized.

Because of the NDCMPs 24/7 around-the-

clock operational nature, project personnel shouldnt

hesitate to contact the ARB office or staff at home after

hours to discuss any real or potential problem that might

affect the project or the performance of their job.The Atmospheric Resource Board

acknowledges with deep appreciation the efforts of those

individuals who contributed to the earlier versions of this

manual: Merlin C. Williams, Dr. Pierre St. Amand,

Wilbur E. Brewer, Robert D. Elliott, Chester Wisner,

Jackson Pellet, John A. Donnan, Dr. D. Ray Booker, Leo

F. Ritter, Martin Schock, Jim Miller, John Thompson,

Mark Schultz, R. Lynn Rose, James Scarlett, Bruce Boe,

and Brenda Hove, among others.

This version reflects the present knowledge of

storms, storm structure and cloud physics, as interpreted

by the Executive Director of the Board. Additional

operational insights have been provided by North

Dakota Atmospheric Resource Board and State Water

Commission Staff and by Hans Ahlness and the staff of

Weather Modification, Inc., Fargo, North Dakota.

1.1 Operations History

Operational cloud seeding got its start in North

Dakota in the 1950's, when ground-based seeding

activities began in the western part of the state. By the

late 1950's, hail was recognized as the greatest weather-related threat to small grain crops; many growers

suffered significant hail damage or total losses in back-

to-back years.

The beginnings of what is today'sNorth Dakota

Cloud Modification Projectcame about when Bowman

County farmer-rancher Wilbur Brewer joined forces

with pilot neighbors, Bill Fisher and Bill Mazaros, to

form Weather Modification, Incorporated (WMI), the

state's first all-airborne commercial cloud seeding

company. Seeding first for just a few townships, then

later entire counties, the program expanded and spread

eastward throughout much of North Dakota. Theprogram at that time was entirely locally sponsored.

In the early years, silver iodide was the seeding

agent released into the updrafts of mature storms

perceived to pose a hail threat. Though little was known

about how the hail suppression effect came about within

the clouds, the results were positive (Butchbaker 1973).

In 1975, support from the State of North Dakota was

sought and the North Dakota Weather Modification

Board was created as a division of the Aeronautics

Commission. In 1976, state cost sharing was available

for the program for the first time and a total of 17

counties participated in the NDCMP.Within the next few years, participation

diminished sharply in the eastern portion of the state but

remained in the west. The eastern half of North Dakota

receives significantly more rainfall, which lessens the

desire for more moisture and hence the program. It was

noted by Dr. Archie Kahan, while director of the United

States Bureau of Reclamation's cloud seeding research


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Introduction2

program, that "Interest in weather modification is

soluble in rain water." In Dr. Kahan's words lies a basic

truth about humanity, that being when one has an

abundant supply of an essential commodity, they lose

interest in acquiring more-- at least until they run short

again.

As cost-sharing dollars were pared from the

board's budget, additional western North Dakota

counties dropped out of the program. This was likely a

contributing factor for the reduction in participation in

eastern North Dakota as well.

A resurgence of interest has recently developed

after several very positive evaluations of the NDCMP

(see Chapter Three) have been published. Williams

County joined the program on a full-time basis after a

four-year trial program was concluded in 2000. The

issue of whether to continue the program in WilliamsCounty passed by 80 to 20 percent in the November

2000 general election. Preliminary interest has also been

indicated by other western North Dakota counties,

although it is too early to tell if that interest will translate

to participation.

1.2 Research

In 1980, a federally funded research program

was undertaken to develop an understanding of the

physical processes involved in hail and precipitationformation and how such processes might be best

modified beneficially. That program, known as the

Federal-State Cooperative Program in Atmospheric

Modification Research, was funded through the National

Oceanic and Atmospheric Administration (NOAA), an

agency within the Department of Commerce.

Roughly half a million federal dollars per year

were pooled with the available state resources to collect

and analyze thunderstorm data. Major field efforts were

mounted every three to four years; analysis efforts filled

the years between field efforts. Numerous citations of

technical publications resulting from this researchprogram appear in latter chapters of this manual.

The ARB has gained national recognition

through the Atmospheric Modification Research

Program and in the process has built strong ties with the

John D. Odegard School for Aerospace Sciencesat the

University of North Dakota (UND), the Institute of

Atmospheric Sciences at the South Dakota School of

Mines and Technology (SDSMT), the National Center

for Atmospheric Research (NCAR), and several NOAA

research laboratories. Ties and interactions with the

National Weather Service have also been strengthened.

In 2001, another federal research program was

approved with the mission of advancing the science of

weather modification. The Weather Damage

Modification Program was a collaborative effort

involving a number of western states conducting cloud

seeding operations.

Beginning in 2006, a seeding experiment called

POLCAST, or Polarimetric Cloud Analysis and Seeding

Test, was conducted to study whether hygroscopic

seeding could increase rainfall and reduce hail formation

in North Dakota. POLCAST was a cooperative

experiment involving the ARB, UND, WMI, and Ice

Crystal Engineering. For additional experiment cases,another season of POLCAST was conducted in 2008 and

is planned for 2010.

REFERENCES

Butchbaker, A.F., 1973: Results of the Bowman-Slope

Hail Suppression Program. Journal of Weather

Modification, 5.


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2. PROJECT ORGANIZATION

2.1 Organizational Structure

The overall organizational structure of the

North Dakota Atmospheric Resource Board (ARB) is

shown in Fig. 1. The ARB is by law a division of the

North Dakota State Water Commission (SWC).

However, because it (the ARB) has its own law,

administrative rules, and regulations, it is different than

the other SWC divisions. While the Governor chairs the

SWC, the ARB chairperson is elected from the ARB

membership.

The Atmospheric Resource Board itself

consists of ten members. Seven of these are governor-

appointed representatives from multi-county districtsaround the state. The other three members are: the

Director of the Aeronautics Commission, the State

Engineer, and a representative from the State

Department of Health and Consolidated Laboratories.

Project personnel are provided with membership lists for

the ARB and each County Authority during the pre-project ground school each spring. County residents

have direct input to the ARB through their countys

Weather Modification Authority. County Weather

Modification Authority members are appointed by their

county commission after the Authority has been created

by popular election or petition.

Operations Advisory Committees (OAC) are

comprised of an Authority member and county

commissioner from each county in each target area and

may also include a county commissioner from each

adjacent non-target county.

OACs provide ARB with input regarding thestatus of cloud seeding operations during the program.

Figure 1: Organizational structure of the North Dakota Atmospheric Resource Board.


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Project Organization4

Note that the ARB Director also receives

counsel from a number of advisors in universities,

government and private industry.

2.2 Cloud Seeding Operations

During the NDCMP field season the County

Authorities and the OACs have a great deal of

interaction with the Director concerning operations (see

Fig. 2). Seeding may be suspended entirely if conditions

become too wet. Seeding may also be momentarily

suspended if weather conditions meet or exceed safety

criteria established by the ARB. Safety criteria are

periodically reviewed by a panel of experts, which

makes recommendations to the ARB through a thoroughoverview of NDCMP operations (Orville et. al, 2003).

2.3 Project Equipment Locations

Figure 3 illustrates typical locations of aircraft

and radars involved in the NDCMP. Each radar is

equipped with Global Positioning System (GPS) real-

time aircraft tracking which increases operations

effectiveness and safety. Radar sites are also providedwith Internet access and GR Analyst, allowing radar

meteorologists to monitor weather conditions in and

around the operations area. In the case of a radar outage

at either of the Bowman or Stanley sites, GR Analyst

allows for limited back-up radar coverage for direction

of seeding operations.

Support facilities at the Bismarck ARB office

also include Internet access for collecting weather

information from a vast array of Internet web sites.

Satellite and radar data, surface observations, upper-air

observations and numerical model data are collected for

the purpose of making daily, district specific, weatherforecasts. In addition to ASOS and AWOS Systems at

Bowman and Stanley Airports, both radar field sites

employ a basic weather station that displays and records

high and low temperatures, dew point, wind direction,

speed, gusts, rainfall and atmospheric pressure.

Figure 2: Infrastructure of NDCMP operations.


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2.4 NDCMP Operations Area

Participation in the NDCMP has always been a

local decision. Grass-roots support of the program has

been the base of support for the program since the earlydays of cloud seeding in North Dakota. Historically,

county taxes have been the primary funding mechanism

for the program, with the state providing assistance

through cost-sharing. Participation in the NDCMP has

ebbed and flowed over the last fifty-plus years.

Participation peaked in the mid-1970s when the state

first implemented 50 percent cost sharing with

participating counties. Shortly thereafter, when state

funding was pared back, many counties were unable to

bridge the funding gap and dropped out of the program.

In 2000, the program grew as Williams County joined

the NDCMP, more than offsetting the loss of part of

Slope County.

The NDCMP is currently split into two

districts; District I in the southwest, and District II in the

northwest. The total project area covers 10,425 square

miles, or nearly 6.7 million acres, almost 15% of thestates area.

2.5 Statement of Equal

Opportunity

The Atmospheric

Resource Board does not

discriminate on the basis of race,

color, national origin, gender,

religion, age or disability in

employment or the provision of

services.

REFERENCES

Orville, H.D., D.A. Banaszewski,

J.A. Heimbach, Jr., L. Osborne,

P.L. Smith, and W.L. Woodley,

2003: A Review of the North

Dakota Cloud Modification

Program. Report of a Review

Panel to the North Dakota

Atmospheric Resource Board,

March, 2003. 29p.

Figure 3:NDCMP operations districts, aircraft locations, and radar

coverage.


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Evaluation6

3. EVALUATION

Since the creation of the Atmospheric Resource

Board (originally the Weather Modification Board) in

1975, a number of evaluations have been made of theeffects of the program. These evaluations have been

based on a variety of different data sources. Among

them are: Atmospheric Resource Board Cooperative

Observer Network (ARBCON) growing season

precipitation data, National Weather Service (NWS)

rainfall data, crop hail insurance data compiled by the

National Crop Insurance Service (NCIS), and crop yield

and price data compiled by North Dakota State

University (NDSU).

Computer-based numerical models have also

played an important role. Economic models have

provided estimates of the economic benefits of theprogram, while cloud models have produced increased

insights into the complex processes within the clouds

that ultimately govern hail and rain production.

All of these evaluations have been independent,

as they've been conducted by agencies and universities

unaffiliated with the ARB. [It is here noted that one

might be subjected to severe criticism if one engaged in

self-evaluation.] In addition, the evaluation by outside

agencies allows the most qualified persons to do the

evaluations, improving the chances for an unbiased,

scientific approach.

As of this date, all evaluations of the programhave shown positive or neutral results. No suggestions

have been found of negative impacts, either within or

outside target areas. Overviews of the most significant

evaluations follow. For the more interested reader, the

reference to each is provided at the end of the chapter.

3.1 Rainfall

The first rainfall evaluation in North Dakota

was appropriately named the North Dakota Pilot Project

(NDPP). Conducted in McKenzie County from 1969-72(Mountrail and Ward Counties participated in 1972), the

NDPP was a randomized experiment, allowing for the

best possible statistical analysis of the results . As

explained by Dennis et al. (1975), experimental protocol

set up eight-day blocks in advance of each project

season where six days were randomly designated seed

days and two were no-seed days. Following the four-

year project, data from 67 rain gauges in McKenzie

County were subjected to a variety of statistical tests to

determine the seeding effects. Analysis of the data

revealed strong evidence that silver iodide seeding of

towering summertime clouds led to an increase in thefrequency of rainfall events, an increase in the average

rainfall per rainfall event, and an increase in the total

rainfall in the seeded area. Further, the total potential

rainfall increase for the area was estimated at one inch

per growing season.

Two recent rainfall evaluations have been

conducted on the NDCMP; one looking at ARBCON

rainfall data (Wise, 2005) and the other at NWS climatic

rain gauge data (Smith et al., 2004). The ARBCON

rainfall analysis, which takes advantage of hundreds of

rain gauge locations in western ND, indicated that

between the years 1977-2003, the seeded areas and

those areas slightly downwind received about 4.2% to

9.2% more rainfall than the upwind control areas where

1The significance level is an indicator of the degree of confidence, which

may be accorded the result of a statistical test of two populations

(seeded vs unseeded, for example). The lower the numericalsignificance, the greater the confidence. For example, a significance

level of 0.08 indicates a 92% chance that the two populations are reallydifferent, i.e, that the observed effect is real.

Figure 4: Target (counties), control (solid line),

and downwind (hatched) areas for the 1982 project

year (from Johnson, 1985).


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no seeding

occurred. Not only positive news for

the

seeded areas, but it also addresses the concern of some

that seeding upwind will reduce downwind precipitation,

or "steal someone's rain. Conversely, there is no

evidence that cloud seeding contributes to largeincreases in precipitation at long distances downwind of

seeded areas. Previous studies of the NDCMP and other

states' seeding programs indicate that downwind effects

diminish with increasing distance from the target area.

The Smith et al. (2004) study found no statistical

difference in rainfall between the NDCMP counties and

an upwind control area. The author concluded, however,

that the sparse coverage of NWS rain gauges in both

areas and the 0.1 confidence interval would not allow

the analysis to determine differences in precipitation

over the two areas at a level of ten percent or less, the

typical range of effect identified by several other rainfallstudies.

Other evaluations of rainfall in and near the

NDCMP include one by Eddy and Cooter (1979) and by

Johnson (1985), which examined NWS rainfall data for

seven years, 1976-82. Johnson defined three areas for

each storm event: the multi-county target areas (Target),

the regions downwind of the Targets (Downwind), and

the areas neither in the target nor downwind (Control)

(see Figure 4).

Figure 5 illustrates the rain gauge coverage

used in a typical season.

Some of the more interesting findings of this analysis

showed:

1. Evidence of an overall increase in precipitation

downwind of the target (relative to the control area),

especially notable in July (15% increase, significant at

the 0.08 level1).

2. Evidence of increase in the target areas on days

with heavier rains (14% increase significant at the 0.13

level).

Other findings showed additional increases both

in and downwind of the target areas, correlated at various

(generally lower) confidence levels with upper air

features. The report concluded that, "It appears that

seeding for hail suppression in the mode employed in

North Dakota likely increases rainfall."

3.2

Crop Hail Damage

Several evaluations have been completed which

help define the efficacy of the North Dakota hail

suppression efforts; one of the earliest by Miller et al.

(1975), which indicated positive impacts of seeding on

hail during the NDPP. Others employed years of crop

hail insurance data in an attempt to determine the degree

of effectiveness of the hail suppression effort (Smith et

al.,1987, 1997). Smith et al. (1987) defined a control

area comprised of upwind eastern Montana counties

adjacent to North Dakota. Hail insurance claims

recorded for a lengthy pre-project periodfrom this control area were compared to

those for the modern-day NDCMP target

to first establish the historical

relationship. Then the losses in both

areas accrued during the NDCMP were

compared to establish the magnitude of

the change. The loss ratiois the ratio of

the amount of claims paid to the amount

of insurance sold. Thus, a high loss ratio

indicates a high hail loss. When the loss

ratios for the target were plotted versus

those for the upwind (west) control areafor each year, a significant difference

emerged between the historical years and

those of the NDCMP (Fig. 6). Sixty-one

years are compared; ten for the NDCMP

years (circles), and 51 years for the

"historical" period which preceded the

NDCMP. In Fig. 6, a single (solid)

regression line is plotted for all years,

Figure 5: National Weather Service rain gauge locations used in a

typical seasons evaluation by Johnson (1985).


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Evaluation8

Figure 8: Economic impacts of the NDCMP and

potential statewide impacts in dollars.

seeded and unseeded. When separate lines are plotted

for the seeded and historical years however, a striking

difference is observed. The difference between the slopes

of the Historical and NDCMP regressions can be

interpreted as the change induced by seeding. In thisevaluation, the NDCMP averaged 43.5% less crop

hail damage when compared to the upwind control

area. The statistical confidence level for this test was

.002, indicating that "...the target area loss ratio values

during these [NDCMP] years were considerably lower

than would have been predicted by the historical and

control area regression lines". The authors of the report

conclude with the observation that, "Therefore, the

sponsors of the NDCMP would seem to be fully

justified in continuing their support of seeding

operations."

Since the completion of the original Smith et al.

report, an additional three years' data from the NDCMP

(1986-88) have been added to the original database. In

an identical analysis (Smith et al., 1997), the expanded

13-year NDCMP database showed a 45% decrease in

losses in the target area with a statistical significance of

.025. These findings were published in the Journal of

Applied Meteorology in 1997.

The findings of the 1987 Smith et al. study

were used to develop a detailed, county-by-county

economic assessment of the effects of crop-hail damage

mitigation efforts by cloud seeding (Johnson et al.

1989). Results put the ten-year average annual savings

for the target area at $3.75 million. However, that figure

did not include any forage crops (hay) or other less

common crops (at that time) such as sugar beets,

potatoes, beans, canola, lentils, and so on. Statewide, it

was estimated about $97 million could be saved each

year by hail suppression cloud seeding, according to

Johnson, et al.

Likewise, results from the 1997 Smith et al.

study were used, in addition to rainfall results from

Johnson (1985), to calculate the economic impacts the

program was having in the target counties and thepotential benefits to the rest of North Dakota. The report

was conducted by Sell and Leistritz (1998) and later

updated by Bangsund and Leistritz (2009) and used 5

and 10 percent increased rainfall scenarios. Results

indicated that the NDCMP has an annual direct

economic impact of $19.7 million in the target counties

(using the 10 percent rainfall scenario). Further, the

total business activity resulting from that increase was

estimated at $60.5 million annually. If applied

Figure 7: Direct impact and total business activity

increase per planted acre for NDCMP counties (10

percent rainfall scenario).


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statewide, the report estimated cloud seeding could yield

a direct impact of $134.5 million and an increase in total

business activity of $414.2 million annually! The $8.3

million increase in state tax revenues would be more

than the estimated annual cost of the project.Economic impacts for the NDCMP target

counties are shown in Figure 7. Based on those figures

and estimated project costs, the benefit to cost ratio for

total business activity is 78 to 1 for NDCMP counties!

Breakdowns of the five and ten percent scenarios for

increased rainfall benefits to the NDCMP and for a

potential statewide program are shown in Figures 8 and

9.

3.3 Other Studies

Though evaluations that attempt to statisticallyestablish and/or quantify precipitation or hailfall are

useful, the "bottom line" for the county-sponsored

NDCMP is really what is obtained in terms of increased

crop yields. When all is said and done, it doesn't really

matter how the crop production is increased, or how the

objective of less hail is achieved, it is only important that

benefits are realized and that they in fact are due to the

cloud seeding program-- not chance. In an attempt to

define this "bottom line", wheat yield data for western

North Dakota were analyzed for the growing seasons

from 1935 through 1988 (Smith et al.1992). Figures 10

and 11 best illustrate the findings of this study. Thehistorical target-control relationship is shown in Fig. 10,

while the NDCMP years are shown in Fig. 11. The

difference? While the historical period revealed no

significant differences in yields, about 6% more wheat

was harvested in the target areas during the NDCMP

years.

Note that during drought years (1980, 1988),

little difference is observed between the target and

control. This comes about because droughts in North

Dakota are generally characterized by a shortage of

clouds having sufficient lifetimes and/or liquid water

Figure 10: Historical relationship between

NDCMP target areas and adjacent control

areas.

Figure 11: Wheat yields during NDCMP project

years. Except for droughts, most years exhibit a

significant increase within the target areas.

Figure 9: Five and ten percent economic

benefit scenarios for the NDCMP.


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Evaluation10

contents to produce much rain-- and these factors also

significantly limit seedability. While the ultimate

conclusion is that present cloud seeding technology

cannot break a drought, the larger implication for the

wheat yield study by Smith et al.is that one would notexpect to observe a significant difference in yields

during dry years. If a difference between target and

control is consistently not observed during such years,

the conclusion that the 6% otherwise observed is

attributable to cloud seeding is reinforced.

Thus, the bottom line seems to be more

production in the target area, without any decrease being

observed in the control areas. This is important, for it

supports observations that suggest rainfall is not simply

being redistributed. It appears that more rain is falling

over a significant fraction of the state.

3.4 Urban Effects

To date, the effects of the seeding program on

urban areas have not been quantified. This is an area

that certainly deserves more attention from the

evaluation standpoint, but some statements may be made

in this regard.

First, the North Dakota economy remains

largely agriculture-based. When harvest is bountiful, the

rural dollars are spent in the cities. This translates into

sales of automobiles, trucks, farm implements,

appliances, and so forth. Considerable additional taxrevenue is also generated for the state and counties,

which eases pressure in the urban areas. Many have

noted that, "As goes agriculture, so goes North Dakota."

However, the above impacts are all secondary.

The primary impact on urban areas comes in the same

form as it does to rural areasless, or smaller hail and

therefore less hail damage. Less hail damage means

fewer roofs to be replaced, fewer dents to be repaired on

motor vehicles, and fewer gardens turned to mush. The

damage caused by a single severe hailstorm passing over

an automobile dealership can be on the order of many

millions of dollars.Increased rainfall also has a positive impact by

reducing the amount of water (from city water supplies)

that must be used on lawns and gardens.

REFERENCES

Bangsund, D., and F.L. Leistritz, 2009: Economic

Impacts of Cloud Seeding on Agricultural Crops in

North Dakota. February, 2009. 37p.

Dennis, A.S., J.R. Miller, Jr., D.E. Cain, and R.L.

Schwaller, 1975: Evaluation by Monte Carlo tests of

effects of cloud seeding on growing season rainfall in

North Dakota. Journal of Applied Meteorology, 14,

959-969.

Eddy, A., and E. Cooter, 1979: The Evaluation of

Operational Cloud Seeding in North Dakota: Some

Preliminary Findings. Final report to the North Dakota

Weather Modification Board. Amos Eddy, Inc.,Norman,

Oklahoma. 43p.

Johnson, H.L, 1985: An Evaluation of the North Dakota

Cloud Modification Project. A final report to the North

Dakota Weather Modification Board, June, 1985. 35p.

Johnson, J.E., R.C. Coon, and J.W. Enz, 1989:

Economic Benefits of Crop-Hail Reduction Efforts in

North Dakota. Agricultural Economics Report No. 247,

Department of Agricultural Economics, North Dakota

State University, Fargo. 26p.

Miller, J.R., Jr., Boyd, E.I., Schleusener, R.A., andDennis, A.S., 1975: Hail suppression data from western

North Dakota, 1969-1972. Journal of Applied

Meteorology, 14, 755-762.

Sell, R.S., and F.L. Leistritz, 1998: Economic Impact of

Reducing Hail and Enhancing Rainfall in North Dakota.

December, 1998. 29p.

Smith, P.L. Jr., J.R. Miller, Jr., and Paul W. Mielke, Jr.,

1987: An Exploratory Study of Crop-Hail Insurance

Data for Evidence of Seeding Effects in North Dakota.

Consortium for Atmospheric Resource Development,Rapid City, South Dakota. 21p.

Smith, P.L. Jr., L.R. Johnson, D.L. Priegnitz, and P.W.

Mielke, Jr., 1992: A Target-Control Analysis of Wheat

Yield Data for the North Dakota Cloud Modification

Project Region. Journal of Weather Modification, 24,

98-105.


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Smith, P.L. Jr., L.R. Johnson, D.L. Priegnitz, B.A. Boe,

and P.W. Mielke, Jr., 1997: An Exploratory Analysis of

Crop Hail Insurance Data for Evidence of Cloud Seeding

Effects in North Dakota. Journal of Applied

Meteorology, 36, 463-473.

Smith, P.L. Jr., P.W. Mielke Jr., and F.J. Kopp, 2004:

Exploratory Analysis of Climatic Raingage Data for

Evidence of Effects of the North Dakota Cloud

Modification Project on Rainfall in the Target Area.

Institute of Atmospheric Sciences, South Dakota School

of Mines and Technology, Rapid City, SD. 11p.

Wise, E.A., 2005: Precipitation Evaluation of the North

Dakota Cloud Modification Project (NDCMP). A thesis

submitted to the graduate faculty of the University ofNorth Dakota. 63p.


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4.3 Pilot-Meteorologist Joint Responsibilities

Note that radar meteorologists' responsibilities

listed in Table 1 include weather watch, handling

weather briefings, and pilot communications. Pilotcommunication is critical to overall program

performance. Meteorologists must be able to assimilate

information from a variety of sources to keep the pilots

well informed. Meteorologists must also understand the

aircraft requirements for safe and timely operations.

Periodic visual observations by all field staff, is

essential.

The basic seeding hypothesis of the NDCMP

depends upon seeding young clouds, which may noteven be producing a radar echo. Visual observations of

the sky are to be made often to detect clouds before they

become too mature to be effectively seeded.

The frequency of observations required will

TABLE 1

Radar Meteorologist Responsibilities

Direction of Operations

Launching seeding aircraft for seeding and reconnaissance.

Prescribing seeding methods and rates.

Recall of aircraft if weather conditions might present an aircraft safety concern.

Operation of Linux-based computer (IRIS/TITAN) for archival and display of radar echoes.

Radio communication with aircraft.

Tracking storms, monitoring of intensity (severe weather potential).

Start-up and shut-down of radar auxiliary power unit when power outages threaten/strike.

Flying with aircraft when severe weather is not imminent nor forecast.

Tracking aircraft (GPS-based system).Visual observations prior to and during aircraft operations.

Monitor aircraft fuel and chemical status, to ensure that storms are seeded continuously.

In short, the radar meteorologist must make the real-time observations and decisions that run

the show and must plan for and anticipate storm development.

Meteorological Record Keeping

Entries in Radar Log.Archiving weather data on a daily basis.

Logging of all hail and significant rainfall reports received from project personnel and local citizens.

Routine Field Site Administration

Assignment of aircraft status: standby or alert.

Pilot Briefings and updates.Visual observations prior to and during aircraft operations.

Supervision of intern meteorologists.

Informing the ARB office of district chemical status.

Weather Watch when no aircraft are on Alert Status.

Equipment maintenance, such as can be done by persons other than electronics technicians.

Assist technician with radar calibration.

Operation of radar when in surveillance mode (prior to operations).

Severe WeatherSuspension of seeding if tornado, funnel cloud, or flash flood potential is observed.

Notification of the National Weather Service when severe weather is observed.

Interaction with local weather modification authorities and law enforcement agencies (civil defense).

Administrative Record KeepingEntries in Radar Log.

Completion of Operations Summary reports.

Mailing of weekly forms, reports.

Verify that radar is operating at expected performance levels.


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Responsibilities14

vary. In some cases, it will be important to make a

visual observation every 5 to 10 minutes! Don't forget

to look directly overhead. The radar is seldom pointed

there, and a storm can quickly develop and go

undetected until it is well beyond the threshold of

seedability-- in the extreme case, already hailing.

Once operations are underway, the flight crew

must in a sense serve as the radar meteorologist's eyes,

conveying descriptions of cloud character, areas of

development, new growth, rainfall, and so forth. The

radar conveys a picture of what already is, not what is

to be, and therefore cannot readily depict nuances of

storm behavior apparent to the seasoned Pilot-In-

Command (PIC). In return, the radar meteorologist

must provide the flight crews current storm echo

information, including cloud tops, motion, position

relative to target, estimated time before exiting thetarget, and so on.

4.4 Pilots-In-Command

It is important that the PIC's and ICP's keep the

district meteorologist(s) well informed. Any problems

such as illness or potential aircraft problems should be

communicated to the district meteorologist(s) as soon as

possible so that schedule/staffing changes might be

considered.

The PIC's work for the contractor, but havedirect responsibilities to the ARB. In general, the PIC's

are responsible for ensuring their aircraft and seeding

equipment are in good working order. They should be

ready to launch within 15 minutes if on standby, and

immediately if on alert status. Each PIC and ICP is

required to be reachable by telephone or pager at all

times. Pilots are responsible for keeping accurate

records of their chemical inventory and flight data. The

intern may assist, but is not required to do inventory;

consequently the responsibility lies with the PIC. The

inventory is expected to be completed for each week by

noon on Monday.One means by which communication between

aircraft and radar is expedited is through the use of

"code" descriptors for precipitation. There are five

"codes" used to describe convective rainfall, all of which

are perfectly acceptable to use on flight forms, radar

logs, and other project documentation. They are:

Code Zero: No precipitation observed below the base of

the subject cloud.

Code One: Precipitation beginning from cloud base, but

not reaching the ground (also called virga).

Code Two: Precipitation just beginning to reach the

ground, but very easy to see through. No obscuration of

surface features beyond the precipitation is observed.

Code Three: Significant precipitation observed, partial

obscuration resulting. Features beyond precipitation

shaft may be difficult to discern.

Code Four: Heavy precipitation resulting in complete

obscuration beyond rain shaft, at least portions of it.

4.5 Intern Copilots

The first purpose for Intern Co-pilots (ICPs) is

to be trained on the principles of cloud modificationprocedures and become knowledgeable of safe aircraft

operations around thunderstorms. Interns will also be

extremely conscientious in their record keeping. All

NDCMP records are public information. The PIC is

responsible for seeing that this information is collected

in a manner that accurately portrays the events of each

flight. Please refer to the PARS Manual and Chapter 10

of this manual for further information.

It is understood that the PIC will provide the

ICP opportunities to fly the aircraft from the left seat and

gain seeding experience. The intern may become a PIC

in later years so this experience is important. Since thePIC has ultimate responsibility for the operation of the

aircraft, decisions about the intern having left seat time

must remain entirely at the PICs discretion. In the past,

the quality of the ICP's and the training they received at

the University of North Dakota has been consistently

very good.

Weather Watch is a responsibility of all

project personnel, including interns. At points distant

from the radar, pilots become the eyes of the

meteorologists. Again, many seeding opportunities,

including those for hail suppression, must be detected by

visual observation. Pilots should never assume themeteorologists know about a cloud or storm, but should

always call just to make sure.

4.6 Safety

The NDCMP has an excellent safety record.


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Safety comes first when making any decision. Stunt

flying with project aircraft is prohibited and will result in

termination from the program. The Director need only

write a letter to the contractor or the University

removing any PIC or ICP from the program. Whensafety becomes a concern during the NDCMP, it takes

precedence over all operations and activities. If any

NDCMP staff member feels that a situation or decision

would be unsafe, they should contact Bismarck ARB

Office personnel no matter what time of day it is. ARB

staff are on-call 24/7 during the project to assist with

questions or concerns.

4.7 General Responsibilities

All project personnel are considered to berepresentatives of the Board, the contractor, and the

County Authorities. As such, they are expected to be

courteous and helpful to people that visit field sites.

Keep in mind that even antagonistic people will often

calm down a great deal if you are patient and polite.

Most of the local people who contact you will just be

curious, or supporters of the program. Local people pay

for the program and should always be treated with

respect. Dont try to answer questions about

unfamiliar subjects. Refer those questions to the

radar meteorologists or the ARB office. If you need

materials describing the program, the ARB will

supply them on request.

A host of informational materials are availablewhich address natural precipitation processes as well as

the physics, effects, limitations, and benefits of cloud

seeding. Copies will be made available to field

personnel upon request.

Although flight hours may be limited based

upon the districts budgets, pilots and meteorologists

should not be hesitant to launch reconnaissance

missions if there is concern about severe weather

potential. In general, the best policy is better safe than

sorry.

Research conducted by the South Dakota

School of Mines and Technology (Smith et al., 1985)concludes that; of the storms treated for hail damage

reduction in 1981, only one-half to two-thirds were

seeded on-time (Fig. 12). A more strict definition of

on-time, (seeding feeders before or as a radar echo

forms) yields an even lower percentage.

Significant strides have been made since the

study was released in 1985. Upon re-evaluation using

2002 hail events and comparable criterion, ARB staff

found that 95 percent of hail flights fell between what

Figure 12: Reproduction of timeliness graph of initial seeding events for hail suppression in 1981

(from Smith et. al. 1985) using a 45dBz threshold (74 instances of hail suppression).


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Responsibilities16

was designated early and late in the Smith study (Fig.

13). Furthermore, a full 86 percent fall in the category

of being either early or on time (within the fifteen

minute standby time limit). An updated study of 2007-

09 seeded events (Fig. 14) shows an encouraging

timeliness trend. Although there were only 74 total

events evaluated for the three operational years, 88

percent of them were in either the early or on time

classification. When it comes to operations, however,

timeliness can always be improved on.

Timeliness issues stem from several factors.

Perhaps the single largest factor is the inability of field

personnel to consistently anticipate the transition of

subject clouds from cumulus humilis or cumulus

mediocris to cumulus congestusor cumulonimbus. A

second factor is the reluctance of radar meteorologists to

launch aircraft until they have a suitable target cloud in

hand. A third factor may be a perceived lack of funding,

which supports the use of numerous flight hours for

reconnaissance purposes. The final factor is that pilots

are sometimes less prepared than they should be, or are

not easily contacted by the radar meteorologists, so

ground delays contribute to the tardiness.

Consequently, reconnaissance time and adequate

attention to weather watch are vital to the success of

the project. Flight crews should note that

Figure 13: Timeliness graph of initial seeding events for hail suppression in 2002 (by ARB staff) using

a 45 dBZ threshold 5000 ft above O

C level (129 instances of hail suppression).

Figure 14: Timeliness graph of initial seeding events for hail suppression in years 2007-2009 (by ARB

staff) using 45 dBZ threshold 5000 ft above 0

C level.


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reconnaissance time does not include return flight time

aftera seeding mission, or chemical deliveries. Flight

hours not spent seeding or in reconnaissance should be

designated as other. An exception to this is

maintenance time which is billed to the contractor, notthe Board (see Chapter 10).

From time to time, difficulties may develop in

the field that cannot be resolved by the parties involved.

Examples of such problems include personality clashes,

recurrent equipment problems, and the failure of project

personnel to perform as expected. In all cases, it is

imperative that such problem be reported to the ARB

office so that corrective action can be taken. This allows

a recovery plan to be put in motion that enables the

situation to be corrected. Equipment can be modified or

replaced, personal differences can be resolved (perhaps

even through reassignment of person(s) involved), andpersonnel performing below expectations can be

contacted to determine the nature of the problem. It has

been found that in organizations and businesses as a

whole, 85% of all problems are related more to

processes than people. This means that a problem is far

more likely to arise as the result of a process that has

been poorly designed than because someone isnt doing

their job. Before corrective action can be taken,

however, the problem must be made known. Therefore,

it is the responsibility of all project personnel to identify

problems of any type so that the source of the problem

can be modified/corrected, and a recovery plan put intoaction.

REFERENCES

Smith, P.L., J.R. Miller, Jr., A.A. Doneaud, J.H. Hirsh,

D.L. Priegnitz, P.E. Price, K.J. Tyler and H.D. Orville,

1985: Research to Develop Evaluation Techniques for

Operational Convective Cloud Modification Projects.

Institute of Atmospheric Sciences, South Dakota School

of Mines and Technology, Rapid City, SD 57701,

Report SDSMT/IAS/R-85/02, 94p.


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Seeding Conceptual Model18

5. SEEDING CONCEPTUAL MODEL

The seeding conceptual model for the

NDCMP has been developed, reviewed, and refined

over a period of years. A number of respected

atmospheric scientists have been involved in the

process. The following subsection covers the seeding

conceptual model in its most up-to-date form and is

largely based upon previous work of the NDCMP

Hypothesis Description and Assessment Committee

(1984) and the NDCMP Operations and Safeguards

Committee (2003).

Seeding in the NDCMP is conducted in two

modes: within updrafts at cloud base and by direct

injection during aircraft penetration at or near cloud

top. All seeding is done by aircraft. The former mode

is most often used, as three out of every four projectaircraft are not equipped for repeated cloud

penetrations and do not possess the performance

required for cloud top work. Seeding agents are

largely glaciogenic (silver iodide complexes from

solution and flares also have some hygroscopic traits)

as observations of northern Great Plains cumuliform

clouds indicate that most precipitation results from

processes involving the formation of ice.

5.1. Seeding for Rainfall Increase

In cloud base seeding silver iodide complexes

are produced either by the combustion of

acetone-based solutions or by the burning of

silver-iodate flares (or recently, other formulas)

attached to racks on the trailing edges of the wings.

The nuclei thus produced are ingested by the target

clouds, transported upward to the regions containing

supercooled liquid water and mixed through a

significant portion of the cloud volume, where

nucleation occurs. If treatment is timely the seeding

agent should reach the supercooled portions of the

cloud at about the time the cloud top is growingthrough the -10C level. Nucleation in these seeded

clouds is believed to occur on average about 5 to 10C

warmer than most natural nucleation. Given typical

cloud growth rates this affords a "head start" in

precipitation development on the order of 3 to 5 min.

In direct-injection seeding either dry ice

pellets (frozen CO2) or ejectable silver iodate flares

are used. Again, clouds growing through the -10C

level are targeted. The seeding agents are placed into

the supercooled cloud where nucleation is desired, so

the updrafts in these cases are relied upon only to

provide a continuing source of condensate, not to

transport the seeding agent upward from cloud base.

This delivery technique thus requires less anticipation

on the part of those directing the seeding and may

have a more immediate effect.

In both cases, the intent is to glaciate portions

of the cloud, initiating ice development minutes earlier

than would naturally have been the case. For smaller

or more isolated convective towers, glaciogenic

seeding may accelerate hydrometeor growth

sufficiently to allow the cloud to produce

precipitation-sized hydrometeors during its short

lifetime (microphysical effects) while addingbuoyancy, which may stimulate updrafts and prolong

the cloud lifetime as well (dynamic effects). Both

effects contribute to increased precipitation

production.

5.2. Hail Suppression and the Conceptual Model

As previously noted, the NDCMP is

dual-purpose. However, hail suppression is the

primary goal of the project. The hail suppression

concepts employed in North Dakota are based uponthe following:

Natural Development:

! The main updraft of a mature thunderstorm,

which is responsible for a large fraction of the

storm's total mass flux, also supports the larger

hydrometeors (hailstones) as they grow. Primary

hailstorm updrafts are usually tilted and

frequently possess speeds between 30 and 40 m

s-1

, which greatly facilitate the production of

large hail (Nelson 1983).

! Feeder clouds, which flank mature thunderstorm

cells, develop significant quantities of

supercooled liquid water (SLW). Cloud droplet

spectra are usually continental in nature, and

precipitation development through

collision-coalescence processes is uncommon


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within these typically short-lived clouds.

Furthermore, significant ice development most

often does not occur until cloud top temperatures

of -15 to -20C are reached.

! Because of the slow development of natural

(ice-phase) precipitation in typical feeder clouds,

precipitation-sized hydrometeors usually have

only very recently developed at the time of

merger with the mature cell. Cloud bases of such

feeder clouds are typically still rain-free.

Significant concentrations of millimeter and

larger graupel (potential hail embryos) remain

aloft within the feeder cloud.

! Graupel particles generated within the feeder

clouds of the flanking line then become hailembryos after either a) being transported to or

ingested by the mature updraft, or b) remaining

within the feeder cloud updraft as it matures and

becomes dominant. In either case, the initially

small embryos are transported into the

supercooled upper reaches of the storm by the

updrafts. Ensuing hydrometeor growth is rapid;

hailstones become too large to have any chance

of melting completely during fallout, and

damaging hail reaches the ground.

Seeded Development:

! Treatment with glaciogenic nuclei of supercooled

clouds within the flanking line as they grow

through the -10C level will initiate significant

ice development minutes before it would

otherwise occur (see Dennis and Koscielski

1972).

! Significant glaciation of the treated feeder cloud

often results (see Stith et al.1990). The release

of the latent heat of fusion during glaciationresulting from seeding adds buoyancy to the

feeder cloud. Much of the supercooled liquid

cloud water is converted to ice by either riming

or deposition. Less supercooled liquid water

remains in treated clouds than in untreated

clouds. Precipitation mass within the feeder

cloud is greatly enhanced.

! Updrafts in the treated feeder clouds remain

significantly weaker than those of the mature

cell. The developing hydrometeors (graupel)

soon gain significant terminal velocities. (Fig.

15).

! Precipitation begins. A developing precipitation

shaft exists where there otherwise would have

been a rain-free cloud base [early rainout].

Because the hydrometeors are yet small

(millimeters in diameter), melting occurs well

before most particles reach the surface. In some

cases, especially in cooler spring and autumn

environments, unmelted particles do reach the

ground, but such particles are usually small.

!

Merger with mature cell occurs.

! Because less SLW remains in the feeder cloud1,

less freezing occurs within the main cell.

Seeding accelerates the glaciation of the feeder

cloud, releasing the latent heat outsidethe mature

cell, depriving the main updraft of a source of

energy. Thus, the buoyancy and strength of the

mature updraft are reduced1 [energy transfer].

See again Fig. 15.

! A significant population of precipitating

hydrometeors is transported into or ingested bythe mature cell as merger occurs. This results in

additional mass loading, further slowing the

mature updraft [updraft loading.]

! Hydrometeors produced by seeding continue to

grow in the moisture-rich environment and

compete with naturally occurring

hydrometeors. This increased competition for

supercooled liquid water necessitates natural

hydrometeors in the seeded cloud growing

smaller than they would naturally [beneficial

competition].

! The large populations of precipitating ice-phase

hydrometeors present in the feeder clouds at

merger continue to deplete the supercooled liquid

1when compared to similar natural clouds.


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Seeding Conceptual Model20

water resident within the mature updraft as

rainout continues [trajectory lowering].

! Many multicell thunderstorms feed on moist

boundary layer air being drawn in from the

southern or eastern quadrants. The precipitation

shaft [where the rain-free base previouslyexisted] may partially restrict or block such

inflow, reducing the "fuel supply" to the mature

updraft [fuel starvation].

! Total supercooled liquid water is diminished in

the mature updraft. The mature updraft is

weakened by mass loading, reduced latent heat

release within it, and possible fuel starvation.

The environment is less favorable for the growth

of hail.

!

The rain shaft of the storm is broadened by earlyrainout. Some areas that would otherwise not

have received measurable precipitation now do

as a result of seeding. Some areas that would

have received locally intense precipitation

receive less intense precipitation.

Ice particles originating in the primary

updraft (perhaps as a direct result of artificial

nucleation) dont generally grow sufficiently during

their brief residence within the main updraft to

develop appreciable terminal velocities. Such

particles remain resident within the primary updraft

for only a few minutes, remain small and ultimatelyexit the updraft as they are transported into the upper

reaches of the storm anvil (Ryan 1974). Thus, seeding

the primary updraft of a mature storm has little effect

on the storm, and will not effectively diminish hail

development.

Figure 15 illustrates most aspects of the

conceptual model. In natural clouds, nucleation of

first ice often does not begin until temperatures on the

order of -15C or lower are attained by the developing

clouds. In a seeded cloud nucleation often begins at

temperatures between -5C and -8C. Thus, the ice

initiated at colder temperatures is afforded less timeresident in the flanking line (compared to ice

originating at warmer temperatures) and is

significantly smaller when merger with the mature cell

occurs. Subsequently these ice hydrometeors are

easily supported by the stronger, SLW-rich updrafts of

the mature cell, and they rapidly grow into hailstones.

When earlier ice development occurs the latent heat of

Figure 15: The NDCMP hail suppression conceptual model, generalized. For detail, see text.


27/66


freezing is liberated, adding buoyancy (heat) to theyoung updraft, strengthening it. Because the latent

heat is released in the smaller turrets, rather than the

larger towers and the mature updraft, the latter are in

essence deprived of the energy. [Note: this assumes

that the total latent heat release is unchanged in the

course of the storms lifetime. This may not be the

case as additional heat release within smaller clouds

may or may not offset the decrease in latent heat

release in the mature updrafts. The conceptual model

is also supported by observations of Alberta hailstorms

(Krauss and Marwitz 1984).

All the factors discussed in the model areinteractive, that is each process affects another. For

example, the earlier release of latent heat will intensify

the updraft in the seeded flanking line cell, while

diminishing the mature "main" updraft. Large

hydrometeors already resident in the mature updraft

may then precipitate, resulting in increased

evaporative cooling, divergent outflow and subsequent

"cut-off" of the warm, moisture-laden air, which fuelsthe main updraft. Likewise, increased populations of

small ice-phase hydrometeors (as result from seeding)

might lead to increased hail production in an

environment without competition (among growing

hailstones) for available supercooled liquid water.

However, the processes that build the potential hail

embryos also deprive the mature updraft of some

energy and SLW, producing an environment less

favorable for the generation of hail. Because the

interactions are so numerous and variable the outcome

of a particular seeding action might seem to be very

much in doubt. However, the evaluations reviewed inChapter 3 suggest that the outcome on the whole is

very positive.

Presently, the full scale of these interactions

is being best addressed through numerical (computer)

cloud models (see Fig. 16, from Orville et al. 1991).

While such cloud models, until very recently,

suggested that increased rainfall must be accompanied

Figure 16: Various outcomes of glaciogenic (ice-phase) cloud seeding (Orville et al. 1991).


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6. IDENTIFICATION OF SEEDING

OPPORTUNITIES

Identifying seeding opportunities and properly

delivering seeding materials go hand-in-hand. Pilots andmeteorologists should carefully review this chapter as

well as Chapters 4 and 5. Differences between seeding

to achieve hail suppression and to gain increases in

rainfall are subtle. For the purposes of the NDCMP,

seeding for hail suppression shall be considered to be

the treatment of any cloud which possesses radar

signatures indicative of hail, or clouds which without

treatment, the radar meteorologist believes to be

capable of hail production. Under this definition, even

cumulus congestus would qualifyproviding the speed

and circumstances of their development (unstable

atmosphere, high surface dew points, significantdirectional wind shear, etc.) cause the radar

meteorologist to believe the cloud will, without

treatment, eventually produce hail. From this definition

it logically follows that seeding for rainfall increases

shall be considered to be the treatment of clouds not

considered to be hail threats, but believed capable of

producing additional precipitation if stimulated by the

addition of glaciogenic nuclei. In the completion of

flight documentation the statement of mission objectives

is required. Radar meteorologists will inform flight

crews, while missions are underway, of the seeding, i.e.,

hail suppression or rainfall increase.

The following sections discuss in some detail

the vigilance and cloud traits that together optimize

recognition of targets of opportunity and minimize

response times.

6.1 Targets Suitable for Rainfall Increase

Seeding

The primary candidates for rainfall

augmentation treatment are towering cumulus which are

either not making the transition to cumulonimbus, or are

very slow in doing so. Preliminary identification of dayssuitable for rainfall augmentation operations must come

from the strategy-planning portion of the day; the daily

forecast will detail the likelihood of suitable clouds

developing.

Rainfall enhancement seeding will generally

not be conducted at night due to safety considerations,

primarily limited visibility. [Since very few isolated

towering cumulus clouds develop at night, this is seldom

a limiting factor, but remember, target clouds are too

small to produce a radar echo, but must be clearly seen

to ensure that the seeding agent is properly targeted.]

Relatively isolated towers well illuminated by moonlightafford the only opportunity for nocturnal rainfall

augmentation seeding.

Forecast parameters are secondary in

recognizing any type of seeding opportunities. At best,

the forecast can only serve to alert field personnel to the

possibilities of seeding opportunities later in the day.

Regardless of the forecast, any time clouds are forming

which appear to be suitable, at least one nearby aircraft

should be placed on alert and if necessary, launched.

[Failure to recognize and respond to suitable

opportunities may result in telephone calls from

residents of the sponsoring counties, many of whom arewell acquainted with this aspect of the program.] Some

general characteristics of good rain enhancement

candidate clouds are crisp, cauliflower-like tops and

sides and firm, flat, rain-free bases. Some shear (as

evidenced by the cloud leaning with height) is

acceptable. Too much shear is present if the cloud tops

are being swept away from the base.

The reconnaissance aircraft should verify that

the cloud base is below 12,000 ft msl. The cloud top

must be colder than 0C and preferably around 5C. If

there is some doubt, it may be necessary for the

reconnaissance aircraft to climb to cloud top altitude.

[Note: the decision to launch seeding aircraft solely for

rain enhancement operations should be made prior to the

formation of a radar echo, when possible. If an echo has

formed, that cloud is too mature, however, there will

likely be many more clouds to grow through that stage in

the impending minutes and hours. The best rainfall

augmentation cases are generally characterized by

numerous suitable cumulus congestus scattered over the

target area. This being the case, a single echo should not

usually be sufficient to deter operations.]

Because rainfall increase operations work with

small non-precipitating clouds, it is not known at the

time of treatment whether rainfall will result or not.This uncertainty arises from the fact that the cloud

lifetimes are short (~30 min) and the target cloud must

be treated while it is only a few minutes old.

Treatment at cloud top by direct injection is

preferred for several reasons. Treatment at cloud base

requires greater time for the agent to reach the

supercooled cloud top. Penetration seeding at cloud top


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Opportunity Recognition24

affords the flight crew a taste of the cloud updraft and

SLW, while base seeding only allows the updraft to be

tested. And finally, any cloud base aircraft that circles a

prospective target cloud several times in search of

updraft is easily observed. If an updraft is found and thecloud treated, this is no problem. However, it has been

noted on numerous occasions that if the cloud base

seeder doesnt find an updraft and departs in search of

another cloud, uninformed persons on the ground may

misconstrue this as seeding. The impression left is a

devastating one, for the departure of the would-be cloud

base seeder is due to a lack of an updraft, which

guarantees that the cloud is no longer viabledying.

Observers on the ground have been known to attribute

the departure of the aircraft and subsequent cloud

collapse to seeding, which must be avoided. Thus,

operations to stimulate rainfall from non-precipitatingclouds are best conducted from cloud top. Cloud top

treatment is more rapid and the flight crew has a more

complete picture of the cloud character by virtue of

having flown through it.

Finally, rain enhancement seeding may be

temporarily suspended if a County Weather

Modification Authority or the Director indicates

conditions are too wet, or there is no immediate desire

for additional rainfall (e.g. during harvest). See Section

8 for additional details on seeding suspension criteria.

6.2 Hail Suppression Opportunities

As in rain enhancement cases, the morning

forecast provides initial clues that hail-bearing clouds

may form. The presence of abundant low-level moisture,

strong wind shear, a deep unstable layer, or a strong

trigger mechanism such as a short-wave trough, frontal

boundary, or dry line, all contribute to severe weather

situations.

This is especially true when these features are

present in combination. The decision trees shown in

Chapter 8 describe these parameters somewhat more

quantitatively. Again, the atmosphere may change

substantially during the day and so the morning forecastis only a planning tool.

Accurate and frequent visual observations

and quick reactions are vital to a well conducted hail

suppression mission in situations where clouds are

forming and growing. This is especially true in cases of

a very unstable atmosphere, where clouds can become

hail-bearing thunderstorms in a matter of minutes (Boe

and Johnson 1990). The visual appearance of a cloud

that will become a hail threat is initially similar to that of

a rain enhancement candidate. The only difference is

that the hailer-to-be will continue to grow, probably

rapidly, and soon extend above 30,000 ft msl or so.Ideally, seeding of the new growth should again begin

prior to the formation of the first 20 dBZ radar echo.

In situations where thunderstorms have

already formed and are moving into the district, the radar

must serve as the primary tool for identifying hail. The

height of radar-measured cloud top and reflectivity

structure of the storm are the main keys in detecting the

presence of hail.

The height of the 45 dBZ contour is a

criterion tested in the Swiss hail suppression program

(Waldvogel, et al. 1979). The Swiss research indicated

that all hailers had 45 dBZ contours that exceeded30,000 ft msl. There was a False Alarm Rate (FAR) of

50%, largely because some strong rain storms also met

the criterion. However, it is much preferable to make an

error and assume that a heavy rainstorm is going to

produce hail than to mistakenly believe that a hailer is

only going to produce heavy rain.

Although not proven for North Dakota,

experience suggests that the Swiss criterion is

reasonable. The physical reasoning behind it is simply

that high radar reflectivities suggest significant liquid

exists at temperatures cold enough for large hail growth.

Any cell having the 45 dBZ contour extending more

than 1.4 km (5 Kft) above the 0C level(as determined

by the most recent appropriate sounding), WILL BE

CONSIDERED A HAILER (i.e. the planes should

already be in the air).

REFERENCES

Boe, B.A., and H.L. Johnson, 1990: Destabilization

antecedent to a tornadic northern High Plains

mesoscale convective system. Preprints, Sixteenth

Conference on Severe Local Storms, American

Meteorological Society. Kananaskis Park, Alberta,Canada, 538-541

Waldvogel, A., B. Federer, and P. Grimm, 1979:

Criteria for the detection of hail cells. Journal of

Applied Meteorology, 25, 1521-1525.


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7. DELIVERY TECHNIQUES

One of the first things a student pilot is told

in ground school is that thunderstorms are dangerous,and that they should be avoided by at least 20 miles if

at all possible. This statement, examined in light of

what the average pilot knows about such storms, is

true. However, a little knowledge can go a long way

towards mitigating the hazard (Bertorelli 1993). As

far as operational cloud seeding goes, the early

identification of suitable clouds, the timely delivery

of the treatment material and SAFETY are the three

critically essential tasks. Since the cloud top aircraft

are used to measure temperature, supercooled liquid

water content, ice content and updrafts in potential

target clouds before seeding, they are ready to seed if adecision to do so is made. Thus, the identification of

suitable clouds and the initiation of seeding must be

considered as one continuous process.

Two modes may be used to deliver the

seeding material into the updraft of suitable target

clouds. These are:

! Nuclei can be released directly in the updraft

by flying through the top of the growing

turrets, or

! Nuclei can be released in the areas of updraft

(inflow) near the base of the cloud.

In both modes the pilot must be familiar with the rate

of climb, power settings and airspeed characteristics of

her/his aircraft.

For most seeding situations, cloud top

seeding is preferred. However, it is not always

possible to use this mode. Aircraft performance

limitations and/or the inability to identify the most

suitable seeding locations are the most common

problems. If cumuliform tops are higher than 25,000

feet, the cloud may be too turbulent for safe aircraft

penetration (clouds this size may be producing ice

naturally anyway). In night operations or when

intervening cloudiness hides the regions of new cloud

growth, it may not be possible to identify the desired

target areas.

Cloud base seeding is used in cases where

well-developed updrafts can be identified, or when in-

cloud seeding by penetration near cloud top is not

practical. This mode is generally the only mode used

at night unless unusual conditions (moonlight, for

example) provide the visibility required for cloud-top

seeding.

A disadvantage of below-base seeding is that

the pilot must infer the rate of cloud growth from the

strength of the updraft and the appearance of the cloud

base, and cannot know the degree of glaciation (if any)

at cloud top. Subcloud seeding does not permit

frequent visual observation of the cloud top.

Visual characteristics of cloud base provide

clues to the location of the inflowing (updraft) air.

Monitoring the evolution of radar echoes can also

provide hints about the updraft structure of the cloud.

In addition, knowledge of the environmental

conditions in which the cloud evolves is important in

locating updrafts. (Refer to other chapters of theOperations Manual for discussions of these topics).

Locating an updraft is generally not difficult.

However, in the case of large multi-cellular clouds,

multiple updrafts and multiple hail shafts are not

uncommon (Nelson 1987). It then becomes necessary

to ensure that the proper inflow area(s) are treated. It

is sometimes necessary to investigate the larger-scale

storm structure prior to initiating seeding.

Positioning of the aircraft with respect to the

target cloud must be done carefully, as a joint effort of

the meteorologist and the pilot. The meteorologist

must use the radar information and his/her knowledgeof cloud processes to assist the pilot in locating the

general area of seeding. The pilot then selects the

specific locations.

7.1 Rain Augmentation Seeding Procedures

Speed shear in the wind field may have a

significant effect on the results of seeding. Slightly

different techniques should be used for seeding under

different conditions of vertical (speed) shear. Any

possible variation of wind speed with altitude mayoccur and the pilot must be aware of the shear

conditions and be prepared to take advantage of them.

Cloud top seeding with CO2 pellets or

ejectable flares is used on clouds with top

temperatures between -5C and -15C, and is best used

on cauliflower cumulus whose tops are between -5C

and -10C. Dry ice is the preferred initial method of


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upwind of the cloud. Seeding is done in the upwind-

most turret that reaches or exceeds the height at which

the nucleant can be expected to function. Penetration

is from the side, across the shear; the seeding agent is

dropped in a recognizable updraft. The X marks the

seeding position relative to the cloud updraft. Again,

the seeding agent(s) is released in the edge of the

upwind-most turret that is between the -5C and -10C

levels. It is desirable to seed where total vertical cloud

depth is greatest. Penetration of isolated turrets can be

in any direction, but on larger clouds, prudence

dictates entry at right angles to the wind shear or

penetration in a turn into the upwind portion only. If

one studies the natural evolution of clouds in shear

environments, it will be observed that new turrets

appear and evolve progressively upwind, at intervals

of roughly ten minutes. If a given tower is seeded justas it reaches maturity, the next pass should be made,

not on the original tower, but on the next one upwind.

With ideal timing, each new tower is caught just as

it reaches seeding level (at temperature between -5C

and -10C). Successful seeding of leaning clouds

requires a slightly larger cloud than in the case of

vertical towers.

Seeding at base is also done upwind, toward

the rear portion of the storm, as shown in Fig. 18.

Inflow in the range of 500 fpm should be selected for

rain enhancement. If it is difficult to maintain less

than 500 fpm updrafts, this can be an indication thatthe system may become more than a rain storm.

Seeding rates may then be adjusted accordingly.

7.1.3 Reverse-Shear Seeding

When the wind speed decreases with

increasing height, the upper part of the cloud moves

downwind more slowly than the bottom of the cloud

and appears to lean into the wind. The occurrence of

reverse-shear clouds can be foreseen from pilot,

balloon or rawinsonde observations, forecasts orrecognized by noting smoke near the ground, waves

on water, or cloud drift. Seeding should be done on

the downwind side of the cloud so that coalescence of

old cloud and new growth is a maximum. As with

other cumulus congestus treated for rainfall increase,

seeding should be done by penetration (Fig. 19).

Seeding should be done on the downwind-most rising

tower that reaches the -5C temperature level at which

the nucleant becomes effective at generating ice.

Similarly, base seeding should be conducted

downwind (opposite of the shear) or in advance of the

cumulus.

7.1.4 Embedded Cumulus

Having determined that the embedded

cumulus clouds of interest are seedable (firm,

unglaciated tower tops, etc.) the pilot should seed thetower by penetration from the top using ejectable

flares or CO2 at a relatively low rate. Only one

ejectable should ever be released per tower. If the

tower grows following the first treatment, repeat

seeding at 20 min intervals until significant glaciation

is evident or growth stabilizes, then cease operations

on that tower. If no growth follows the initial

treatment the tower should not be seeded again.

When seeding embedded convection it is

imperative that the aircraft operate primarily in the

clear air above the stratus deck. Continuous

operations within a supercooled stratus deck may

lead to the rapid accumulation of airframe icing and

may pose a severe safety threat.

If the aircraft cannot climb above the stratus

deck seeding may be conducted be

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