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Frost Tube Protocol

PurposeTo monitor the timing and depth of freezing in soil at a Frost Tube Site or a designated GLOBE Study Site.

OverviewStudents will construct a Frost Tube that is inserted into a hole in undisturbed and uncompacted soil. During the cold months, students measure the depth at which water in the Frost Tube has frozen, indicating that the surrounding soil has also frozen.

Student OutcomesStudents will be able to,

Observe when water in the Frost Tube freezes

Collect and analyze data related to freezing of soil to understand how soil temperature and moisture coincide with changes in seasons across different biomes.

Examine relationships among air, soil and permafrost

Communicate project results with other GLOBE schools

Collaborate with other GLOBE schools (within your country or other countries)

Share observations by submitting data to the GLOBE archive

Compare the timing and depth of freezing in soils in different regions around the world

Predict the timing and depth of freezing for upcoming seasons (advanced)

Science Concepts Earth and Space Sciences

Some regions of the world have freeze/thaw cycles and these occur seasonally. Other regions do not have these cycles as the soil never freezes or thaws.

Water infiltrates into the soil and freezes at certain depths during the seasonal cycles.

Depending on the geographical location of the soil being tested, some water in soil may never thaw or freeze.

Water circulates through soil changing the properties of both the soil and the water.

The depth of snow and/ or organic material (moss, leaf litter, etc) can impact how deep soil freezes.

Life SciencesThe temperature of the soil will

impact the type of life growing on and in it and how it grows. (Organisms’ functions relate to their environment.)

The type of vegetation growing on soil can influence how deep soil freezes and thaws as well as the rate at which it freezes and thaws. (Organisms change the environment in which they live.)

Scientific Inquiry AbilitiesUse appropriate tools and techniques

including mathematics to gather, analyze, and interpret data.

Develop descriptions and predictions using evidence.

Recognize and analyze alternative explanations.

Communicate procedures and explanations.

Time Construction of Frost Tube: 1 - 2 hoursSelection of site, set up and installation of Frost Tube: 1 - 2 hours

LevelAll

FrequencyDepth of frozen ground is measured at the same time of day (preferably within one hour of solar noon) once a

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IntroductionWhy Study Frozen Ground?

The temperature of the soil is an important measurement to understand because it affects microclimate, plant growth, the timing of budburst or leaf fall, the rate of decomposition of organic material, and other chemical, physical, and biological processes that take place in the soil. In general, the pattern of soil temperature over the course of a year tends to stay about the same (e.g., the mean (average) summer soil temperature, mean winter soil temperature, and mean annual soil temperature stays relatively constant from year to year). However, if a change in mean summer, winter, or annual soil temperature occurs from one year to the next, it could be due to some significant change in the surrounding environment such as an increase in air temperature due to global warming or some type of disturbance such as deforestation, removal of the insulating soil surface, or urbanization (see the GLOBE Soil Temperature Protocol for more information

about soil temperature). Monitoring the timing and depth of soil freezing and thawing helps scientists to understand how the temperature of the soil is changing over time so that they can identify the effect of climate change such as warming or other disturbances on the ecosystem.

At mid-latitudes and mid-elevations on the Earth, parts of the soil near the surface freeze in the winter. In northern and southern latitudes and at high elevations, some soil layers/earth materials that remain at or below 0 C for at least two consecutive years are known as permafrost (http://www.uspermafrost.org/glossary.php). The soil Frost Tube Protocol allows GLOBE students and scientists to see what part of the soil freezes and when the freezing starts and ends in different parts of the world. If, after some disturbance or because of climate change, the soil temperature over the year may be warmer, the depth of soil freezing may decrease, and the time of freezing may be delayed. Other parts of the environment will also be affected. In cold climates, large

qFrost Tube (see Instrument Construction and Installation for instructions on how to construct and install a Frost Tube)

Preparation Select a site for installing your frost tube. Ideally, the site should be in relatively undisturbed and uncompacted soil in native vegetation and within 30 meters of your Atmosphere study site if you have one. Check with appropriate authorities for safety in digging in soil at the selected site. Obtain a GPS reading of the Frost Tube Protocol study site.

PrerequisitesGLOBE GPS Protocol

RecommendedGLOBE Soil Temperature ProtocolGLOBE Soil Characterization Protocol GLOBE Atmosphere Protocol (Air and Soil Temperature; Precipitation)

week beginning when air temperatures approach freezing (0°C).

Materials and Toolsq Frost Tube Site Definition Field Guide

q Frost Tube Site Definition Sheet

q Frost Tube Field Guide at Air Temperatures Warmer Than -20 C

q Frost Tube Field Guide at Air Temperatures Colder Than -20 C

q Frost Tube Data Sheet

q GPS Protocol Field Guide (if using a new site)

q GPS Protocol Data Sheet (if using a new site)

q GPS receiver (if using a new site)

q Soil auger (needed once for installation)

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amounts of organic matter (dead plants and animals) are present in the soil and become locked up in the permafrost. As the permafrost thaws, the organic matter starts to decompose and greenhouse gases such as carbon dioxide and methane are released. An increase in greenhouse gases in the atmosphere leads to higher air temperatures, which leads to even warmer soil temperatures, more thawing of permafrost, and the release of even more greenhouse gases as more organic material decomposes. This positive feedback cycle continues to add to global warming once it starts. The surface layers over the soil become thinner and have less insulating ability, and trees that were growing over the frozen soil layers with high ice content fall over and look like a “drunken forest”. The types of vegetation will be affected by the changing hydrologic regimes.

What is Permafrost?Permafrost is a layer of soil or rock, at some depth beneath the surface, in which the temperature has been continuously below 0°C for at least two years or more; it exists where summer heating fails to reach the base of the layer of frozen ground (National Snow and Ice Data Center http://nsidc.org/cgi-bin/

words/word.pl?permafrost). In areas where air temperatures rise above freezing for a few months of the year, the ground surface may temporarily thaw before freezing again after the arrival of cooler weather. The layer of soil above permafrost that seasonally freezes and thaws is called the active layer. The thickness of permafrost and the active layer depend on local climate conditions, vegetation cover and soil properties as well as from heat within the Earth.

As air temperatures cool (e.g. fall going into winter) the layer of freezing in the soil should increase but other variables such as snow depth and the thickness of the vegetative layer will impact how much and how quickly freezing occurs. If the layer of snow and or vegetation is very thick, it will insulate the soil and prevent it from freezing until later in the winter. When there is heavy snowfall early in the year and it persists, it will delay ground freezing. The maximum freeze in undisturbed soil generally occurs in late winter or early spring when air temperatures are starting to warm up. In the same way, the depth of thawing in permafrost areas is usually deepest at the end of the summer or even after the first few frosts in early autumn.

Figure 1. Permafrost extent in the Northern Hemisphere

(Map from Brown et al., 1997 modified by UNEP/GRID)

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Permafrost zones occupy up to 24 per cent of the exposed land area of the Northern Hemisphere (Figure 1). Permafrost is also common within the vast continental shelves of the Arctic Ocean. This subsea permafrost formed during the last glacial period when global sea levels were more than 100 m lower than at present and the shelves were exposed to very harsh climate conditions. Subsea permafrost is slowly thawing at many locations. Permafrost of various temperatures and continuity also exists in mountainous areas, due to the cold climate at high elevations.

The Big PictureThe temperature of soil is directly linked to the temperature of the atmosphere because soil is an insulator for heat flowing between the solid earth and the atmosphere. For example, on a sunny day, soil will absorb energy from the sun and its temperature will rise. At night, the soil will release the heat to the air having a direct and observable effect on air temperature. The amount of heat that will be absorbed or released by the soil from and to the atmosphere depends on a number of factors including topography, vegetation cover, organic matter content, soil texture, soil bulk density, and soil moisture. A north facing slope will be colder and more likely to freeze than a south facing slope in northern latitudes. The type of trees or other vegetation growing on the soil determines how much heat and light reach the soil below the vegetation canopy. A more open canopy will let more heat and light in than a closed canopy. A moss layer or organic matter in the soil acts as an insulator that slows the transfer of heat to and from the mineral parts of the soil. Wet soils heat more slowly than dry soils because the water in the pore spaces between the soil particles absorbs more heat than air. The denser the soil, the more heat is conducted through it so that a sandy soil or a soil with a high bulk density will conduct heat faster than a clay or loamy soil with good structure and low bulk density.

As the soil surface is impacted from disturbances such as changes in hydrology,

building roads, urbanization, cutting trees, or mining peat moss, the insulating properties of the soil surface are removed and more heat and light move into the soil, increasing it’s temperature and causing frozen layers to melt. As heat leaves the soil surface, the water and minerals in the soil freeze from the top down. However, as the air temperature warms and the ice in the upper soil horizons melts, the melted water moves through the soil and freezes again as it reaches the permafrost layer so that the soil begins to freeze from the bottom up.

One of the indications of permafrost presence is the presence of “patterned ground”. These include polygon shaped features across the landscape and large features called “pingos”, which form when the soil freezes and thaws over many seasons pingos have an ice core that is being pushed up by groundwater.

What is a Frost Tube?The instrument used to measure the depth and timing of the freezing of the ground is called a Frost Tube. This instrument is easily made and installed in undisturbed soil near your school. The Frost Tube consists of a piece of 6-8 mm clear plastic tubing (inner tube) marked in 5 cm increments holding colored water that sits inside a 10 mm (outer diameter) radiant heat tube (middle tube) sealed on the bottom. This is placed inside a 12 mm CPVC pipe (outer tube), open on both ends.

Figure 2. Patterned Ground (http://www.uspermafrost.org/glossary.php)

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Figure 4. Another view of the Frost Tube showing inner, middle and outer tubes

Figure 3. Components of a Frost Tube

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Instrument Construction and InstallationInstructions for Making and Installing a Frost Tube to Measure Depth of Frozen Ground

Materials□ 6 – 9 mm (1/4 – 3/8”) outside diameter

clear tubing, about 3 m (10’) long (inner tube)

□ 10 mm (7/16”) outside diameter radiant heat tube, about 3 m (10’) long (middle tube)

□ 12 mm (1/2”) inside diameter CPVC Pipe about 3 m (10’) long (outer tube)

□ 1 CPVC cap, to fit over 12 mm pipe□ Epoxy putty

□ Latex or vinyl gloves (for handling epoxy putty)

□ Food coloring and water□ Gas burner□ Black waterproof marker□ Meter stick with cm markings□ Soil auger□ Frost Tube Site Definition Data Sheet

Directions for Construction The Frost Tube consists of three layers:

• The innermost tube is a piece of clear tubing sealed on both ends, which holds colored water.

• The middle tube is a piece of radiant heat tubing sealed on the bottom. • The outermost tube is a piece CPVC pipe, open on both ends with a removable

cap on top.

1. Determine the length of the Frost Tube.In areas of permafrost: The length of the Frost Tube depends on the depth of the ac-tive layer.

• Check the thickness of the active layer using a steel stick (thaw probe) at the end of the summer.

• Pound the probe into the ground until you hit permafrost. It will feel like you have

Figure 1a. Parts of Frost Tube Figure 1b. Assembled Frost Tube

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hit rock or something very hard. Your Frost Tube should extend to this depth.In areas of seasonally frozen ground: The length of the Frost Tube should be a little longer than the depth to which the ground freezes in winter. A length of 2 m below the ground should be long enough.

2. Add 1 m to the estimated frost tube length so it will stick up above the winter snow cover. Drill using a soil auger into the ground. A height of 1m above ground should keep the top of the pipe above snow for most areas so that it is accessible to students.

3. Cut all three tubes (inner, middle and outer tubes) to the estimated final length.

4. Use the epoxy putty to seal the bottom end of the radiant heat (middle) tube. Following the manufacturer’s instructions and wearing protective gloves, make a small ball out of the epoxy putty and affix it on one end of the radiant (middle) tube being careful to keep it from building up on the outside so that it will not prevent the bottom end of this middle tube from going down into the bottom of the open-ended CPVC pipe (outer tube).

5. In a large bowl mix water and enough food coloring to make deep/bright/strong color. Fill the clear tube with the colored water up to 15 cm from the top being careful to keep it from pouring out of the other end. (Eventually you will seal both ends of the inner tube but for now leave both ends unsealed. If you seal one end the water will not go into the tube since it will not displace the air present.)

6. Seal one end of the clear tubing by heating it with the burner and press the ends together. Be careful not to burn yourself. Make sure that the seal does not distort the bottom of the tubing so it slides easily down into the radiant heat ( middle) tube and make sure that you do not stretch the tube so that it is still the same length as the radiant heat tube and CPVC pipe (outer tube). Figure 2 (see above).

Instrument Construction and Installation Field Guide – Page 2

Figure 2. Frost Tube assembly showing liquid-filled inner tube (both ends sealed), middle and outer tubes as well as the as-sembled frost tube placed in the ground.

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7. Seal the top end of the clear (inner) tubing by heating it with the burner. Be careful not to burn yourself. Flatten this end so that it is just wider than the diameter of the radiant heat pipe (middle tube). This way the top of the clear (in-ner) tube will rest on top of the middle tube and can be easily retrieved for measuring depth of freezing.

8. Hold the inner tube against the outer tubing buried in the soil. Mark the inner tubing starting at 0 to mark ground level

9. Slip the clear inner tube, now filled with the colored water, into the radiant heat middle tube so that it extends to the sealed bottom of the middle tube.

10. Insert both into the outer CPVC pipe and place the cap on top of the outer tube.

Instrument Construction and Installation Field Guide – Page 3

Figure 3. Top of inner tube resting on top of middle tube with cover in gloved hand

Figure 5. Assembled frost tube on left with a meter stick on the right

Figure 4. Ground surface/level marked on inner tube

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Directions for Installation

1. Complete the Frost Tube Site Definition Data Sheet.

2. Dig a hole for the Frost Tube with the soil auger. The hole should be just deep enough to accommodate the “in ground” portion of the outer tube.

3. Save the removed soil. Maintain the order in which the different soil layers were re-moved. If possible, perform the Soil Characterization Protocol on the soil that is removed (see GLOBE Soil Characterization Protocol using an auger).

4. Place the entire Frost Tube assembly into the hole. It should fit snuggly in the hole.

5. If there is a large gap between the outside of the CPVC Pipe and the hole wall:

• Mix the removed soil with a little water. Mix each soil layer separately.• Fill the gap between the frost tube and the surrounding soil with this paste. Try to

place the different kinds of soil back into the gap in the reverse order in which they were removed, i.e., the last removed is the first replaced.

• Gently work the soil into the gap with a stick, trying to eliminate any air pockets.

6. Measure the distance between the soil surface and the top of the CPVC pipe (outer tube).

7. Pull the inner clear tubing out and put close to the outer tube, lining up the top of the inner tube with the top of the outer tube. Clearly mark where the soil surface occurs with a permanent marker on the outside of the inner tube. Label the soil surface as 0 cm.

8. ***Mark 5 cm increments from the 0 cm line to the bottom of the inner tubing using a meter stick and permanent marker. Write in the number next to every 10 cm interval (i.e., 10, 20, 30, 40, etc.). Place hatch marks 1 cm apart so there are 4 evenly placed hatch marks between each 5 cm mark.

9. Return the inner tubing to the installed middle and outer tubes of the Frost Tube as-sembly.

10. Cover the top of the Frost Tube with the CPVC cap (do not glue!) to minimize the chance of cold air, snow or water getting down inside.

Instrument Construction and Installation Field Guide – Page 4

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Figure 5. Progression of freezing

Teacher SupportDepth of soil freezing is related to the length of time it has been cold above ground. That is why measuring the depth of freezing indicates the type of climate where the study is. Monitoring the depth of soil freezing helps scientists and engineers understand how the temperature of the soil is changing over time so that they can identify the effect of climate change.

When winter comes the ground freezes and the frozen soil becomes thicker as winter progresses. How thick will it become?

The depth of ground freezing depends on many different parameters, such as freezing degree days, soil moisture content, bulk density, grain particles, etc. This can be simplified by the following formula:

D = aF

D = depth of freezinga = constantF = √t (square root of t) = freezing degree days

F is the number of freezing degree days at the ground surface. Freezing degree days (fdd) is a measure of how cold it has been and how long it has been cold; the cumulative fdd is usually calculated as a sum of average daily degrees below freezing for a specified time period (10 days, month, season, etc.). (National Snow and Ice Data Center http://nsidc.org/cgi-bin/words/word.pl?freezing%20degree-days).

a is a constant of the thermal property of the soil, soil moisture content and characteristics of frost heaving. Frost heaving is characterized by soil particle size. a varies between 1 to 5 and is usually around 2.7 but it strongly depends on location. For example, saturated sandy material is around 3. Dry silty material is about 2.3. Organic material would probably be around 2.

Using depth of soil freezing and freezing degree days we can figure out a. By knowing a and climactic conditions (#freezing degree days, F) we can calculate the depth of freezing, D. If we know the frost depth and a then we can calculate freezing degree days. In this way scientists can better understand how the climate may be changing by gathering more data about soil freezing depth.

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Who can do the Frost Tube Protocol?First, ask the following questions:

1. Do air temperatures reach freezing during some time of the year?

2. Does the soil freeze during part of the year?

3. Is there permafrost underlying soil in your area?

If you answer yes to any of these questions, then this protocol is a worthwhile investigation for your class. This protocol is a first step to helping students investigate relationships among air, soil, snow and permafrost (where it occurs).

Site SelectionIdeally, the Frost Tube Study Site should be in relatively undisturbed and uncompacted soil in an area of native vegetation. Since the results for this protocol could be combined with temperature and precipitation data from a GLOBE Atmosphere Investigation, try to choose a site close to the Atmosphere study site, if you have one. It would also be best to locate your Frost Tube within a 5 minute walk from your school so it is relatively easy to access in cold weather.

Because many soils in northern latitudes were formed from glacial parent material, soils in this region may contain many large rocks that may make it difficult to dig into. If possible, locate an area with a minimum of rocks or you may need to use more robust equipment for inserting the frost tube. Check with the appropriate authorities for permission to dig at your proposed site and to locate it safely away from any buried cables or pipes. Be aware that nearby buildings, roads and even lakes or rivers may influence soil temperatures and affect the data you collect so carefully document this information on the Frost Tube Site Definition Sheet. If you live in an area of permafrost, check the clear tube late in summer to measure the distance from the soil surface to the boundary between water and ice at the bottom of the tube. Enter this data in the Comments/ metadata section of the Frost Tube Data Sheet.

Measurement Procedure It is highly desirable that these observations be done by a minimum of two people per visit.

Students will measure the depth of freezing as the ground cools.

• Depth of Freezing = distance in the Frost Tube (inner tube) from the soil surface to the boundary between the ice layer and unfrozen water. This represents the depth of freezing between the soil surface and the underlying unfrozen soil.

Managing StudentsIt is very important that someone visits the Frost Tube site every week to take measurements once the air temperature drops below freezing. Students need to collect measurements quickly and efficiently to reduce the impact of the surrounding air temperature on the Frost Tube. When students are finished making their observations they must replace the top cap to keep snow, water and cold air out of the assembly.

Frequently Asked Questions1. Where is the deepest ice-water boundary in non-permafrost underlain areas?

The depth of where the colored water ends and clear water begins is used as an aid to read the ice-water boundary; however sometimes when the water in the inner tubing freezes and thaws, the color or dye is pushed out of the frozen portion, and even when it thaws and refreezes, the color does not go back. So bend the tube to detect or locate presence of ice.

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Frost Tube Protocol – Looking at the DataAre the data reasonable?The freezing front (boundary of ice and water interface) usually moves very slowly from the soil surface down (less than 1 cm per day). However if below freezing air temperatures persist and there is no snow cover, near surface soil depth freezing could happen quickly in the top 5-10 cm of soil early in the winter depending on soil water content and ambient air temperatures. This typically happens in permafrost underlain regions such as in Interior Alaska. In either case, freezing usually proceeds at increasing depths in most of the Alaska, but not southeast or Prince William Sound area.

What do scientists look for in the data?Frost tube (depth) can tell many things. The maximum depth of freezing would be one of the important measurements for this. Ground freezing mostly depends on air temperature, snow depth, and soil properties. Severe winter conditions in one area could result in deeper soil freezing than warmer winter conditions in another area. Delay in ground freezing could be captured by Frost Tube data. Delay in ground freezing directly affects degradation of the permafrost in northern latitudes.

Also snow thickness is an important factor in ground freezing because of snow’s insulating quality. Different freezing depths could result in areas with the same air temperature but with different snow depths

These differences in ground freezing depths can be simulated or modeled once soil conditions or characteristics (designated as “a” in the equation given earlier in the Teacher Support section), is calculated. Freezing degree days (accumulated daily average surface ground temperatures colder than 0 ˚C) increases until the end of the winter. Snow depth and air temperature affect freezing degree days (fdd) and ground-freezing depth. However “a” stays the same. Hence we can predict depth of freezing (D) using fdd. Depth of ground or soil freezing (“D” in equation) can be estimated from one year of frost tube data.

Estimating soil frost depth: Calculating freezing degree days (FDD):

The maximum depth of freezing depends on winter air temperature, snow thickness, soil moisture content, soil physical properties, such as grain size, pore space, mineral composition etc. Freezing degree days (fdd) at ground surface are a common measure of freezing depth estimation used by scientists. For this method, you will need the daily average ground surface temperature data for your school from September 1st (if you live in the Northern Hemisphere) or April 1st (if you live in the Southern Hemisphere) up to and including the date of when temperatures are above freezing (0°C).

To calculate freezing degree days:

1. First, for each day, calculate the daily average ground surface temperature (Tavg)

2. Starting with September 1 or April 1, check to see if Tavg is less than 0˚ C. If it is, record this temperature. If Tavg is greater than 0˚ C, ignore it. Go to the next day. Again, check to see if Tavg is less than 0˚ C; if it is, add it to the temperature you recorded for the first; if not, again ignore it. Repeat this process for each subsequent day up to the day of no freezing (e.g. until late spring). The sum of the daily average negative temperatures is your freezing degree days (fdd unit is “°C days”). But remove negative sign (-) from sum of the daily average of negative temperatures. Freezing degree days does not include minus (-) sign before number. Record values in the Table on your Data Sheet.

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dayFDD frost depth Tavg FDD by

dayFDD frost depth

Homer Homer Homer Homer Igiugig Igiugig Igiugig Igiugig10/1/08 2 0 0 nd nd nd10/2/08 1 0 0 0 nd nd nd 010/3/08 1 0 0 nd nd nd10/4/08 0 0 0 nd nd nd10/5/08 0 0 0 nd nd nd10/6/08 0 0 0 nd nd nd10/7/08 -1 1 1 nd nd nd10/8/08 -1 1 2 nd nd nd10/9/08 -1 1 3 nd nd nd

10/10/08 -1 1 4 nd nd nd10/11/08 4 0 4 nd nd nd10/12/08 2 0 4 nd nd nd10/13/08 0 0 4 nd nd nd10/14/08 0 0 4 nd nd nd10/15/08 0 0 4 2 0 010/16/08 0 0 4 -2 2 210/17/08 1 0 4 -4 4 610/18/08 1 0 4 2 0 610/19/08 0 0 4 -2 2 810/20/08 0 0 5 -4 4 1210/21/08 -1 1 5 -2 2 1410/22/08 -1 1 6 -6 6 2010/23/08 -1 1 8 -6 6 2610/24/08 -3 3 11 -6 6 3310/25/08 -4 4 15 0 0 3310/26/08 -2 2 17 -4 4 3710/27/08 4 21 -9 9 4610/28/08 -6 6 28 -13 -9 9 5510/29/08 -6 6 34 0 0 5510/30/08 -5 5 39 2 0 5510/31/08 -2 2 41 -4 4 59

11/1/08 -5 5 45 -3 3 6211/2/08 -6 6 52 -5 5 6711/3/08 -7 7 59 -10 10 7811/4/08 -7 7 66 -10 10 88 -2711/5/08 -5 5 70 -32 -7 7 9511/6/08 -3 3 74 -4 4 9911/7/08 -3 3 77 -7 7 10611/8/08 -5 5 82 -2 2 10811/9/08 -5 5 87 -37 2 0 108

11/10/08 -1 1 88 1 0 10811/11/08 0 0 88 -2 2 110 -3711/12/08 -1 1 89 -3 3 11311/13/08 -3 3 91 -5 5 11811/14/08 -4 4 96 -4 4 12211/15/08 -4 4 100 -2 2 12311/16/08 -5 5 104 -3 3 12711/17/08 -2 2 106 -7 7 13411/18/08 -5 5 111 -11 11 145 -3611/19/08 -7 7 118 -12 12 15711/20/08 -7 7 126 -15 15 17211/21/08 -5 5 131 -18 18 19011/22/08 -7 7 138 -14 14 20411/23/08 -8 8 146 -10 10 21411/24/08 -4 4 149 1 0 21411/25/08 -1 1 151 -11 11 22511/26/08 -3 3 154 -14 14 23911/27/08 -4 4 158 -12 12 25111/28/08 -2 2 160 -6 6 25711/29/08 -1 1 161 -40 -10 10 26711/30/08 -1 1 162 -21 21 28812/1/08 -3 3 164 -13 13 30112/2/08 -3 3 167 -3 3 30412/3/08 -2 2 169 1 0 30412/4/08 -1 1 170 2 0 30412/5/08 0 0 171 2 0 30412/6/08 0 0 171 1 0 30412/7/08 0 0 171 -1 1 30512/8/08 0 0 171 0 0 305

Excel Data Table of surface temperature, freezing degree days, and frost depth from 10/1/2008 until 5/1/2009 is provided as a separate document. Students can use these data to practice figuring out FDD based on ground surface temperatures.

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In order to calculate freezing degree days students first examined the temperature data to see if there were any dates with missing data during the freezing period. They found only one – 27 October, 2008, at Homer. For that missing temperature on that date, they looked at the mean temperature for the day before which is 26 October, and the day after which is 28 October. To esti-mate the mean temperature on 27 October,

Figure 6. Estimate of missing datum for surface temperature on 27 October, 2008, at Homer.

they performed a linear interpolation, which is a technique often used by scientists to es-timate the values of missing data. The graph below shows the mean temperature data for 26 October (-2°C) and 28 October (-6 °C). They drew a line connecting these two points and then estimated the mean temper-ature for 27 October as -4 °C. Then they cal-culated the freezing degree days at Homer.

Next they calculated the freezing degree days for Igiugig. They calculated the freez-ing degree days of 411 FDD at Homer and 1212 FDD at Igiugig. Data show that the site with greater number of freezing degree days, had deeper ground freezing, 155 cm depth at Igiugig; and the site with less number of

freezing degree days, Homer, had shallow ground freezing of 37cm depth. Also number of freezing degree days and frost depth indi-cated thicker (more) snow accumulated after November at Homer, that prevented further ground freezing, hence, ground temperature stayed near 0°C for the rest of the winter.

10/26/08 10/27/08 10/28/08

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Figure 7. Freezing degree days and frost depths at Homer and Iguigig, Alaska

Questions for Further InvestigationHow will frost depth differ in different regions across the globe?

What would cause the timing and depth of freezing in soils to change from one year to another?

How does the depth of freezing affect veg-etation phenology in a particular region?

Is there any relationship between the freez-ing of the ground and freshwater ice season-ality?

What other parts of the ecosystem are af-fected by the timing and depth of soil freez-ing?

ReferenceBrown, J., Ferrians, O.J.J., Heginbottom, J.A. and Melnikov, E.S. (1997). International Permafrost Association Circum-Arctic Map of Permafrost and Ground Ice Conditions, Scale 1:10,000,000. U.S. Geological Survey

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Frost Tube Site DefinitionField GuideTaskTo describe the site where the Frost Tube is located.

What You Need□ GPS receiver □ Meter stick□ GPS Field Guide □ Compass□ GPS Data Sheet □ Clinometer□ Frost Tube Site Definition Sheet □ Camera□ Pen or pencil

In the Field

1. Fill out the top part of the Frost Tube Site Definition Sheet (Coordinates, Source of Location Data, Site Type and Cover Type).

2. Use the GPS receiver and GPS Field Guide and GPS Data Sheet to identify the lati-tude, longitude and elevation.

3. Provide the date the Frost Tube was installed (this may be different than the date you define the site).

4. Record the height of the Frost Tube above ground, its depth below ground, and its total length.

5. If known, note whether or not permafrost is present and whether its distribution in the area is continuous, discontinuous or unknown in the metadata section. If present, mea-sure and record the depth to permafrost in the metadata.

6. Fill in the type of topography. If your site is located on a slope, use the clinometer, to calculate the slope angle and the compass to calculate slope aspect.

7. Describe the type of vegetation and, if forest is present, note the type of forest floor.

8. Note whether there are any water bodies within 100 m of the Frost Tube site and the distance to it.

9. Note whether there is human activity or structures within 100 m of the Frost Tube site and the distance to it in the atmosphere section of the data sheet.

10. Standing by the Frost Tube, take four photographs in the four cardinal directions, North, South, East, and West.

11. Describe any other information you think is important and enter as metadata.

GLOBE® 2017 Frost Tube Protocol - 17 Soil (Pedosphere)

Frost Tube Protocol at Air Temper-atures Warmer Than –20 CField GuideTaskObserve and record the depth of freezing in the ground’s active layer (where there is per-mafrost) when air temperatures are warmer than – 20° C (determined by a GLOBE Atmo-sphere site nearby or from another reliable source).orObserve and record the depth of freezing in the ground (where there is no permafrost) when air temperatures are warmer than – 20° C (determined by a GLOBE Atmosphere site nearby or from another reliable source).

What You Need□ A properly installed Frost Tube □ Pen or pencil □ Frost Tube Data Sheet □ Meter stick Students will measure the depth of freezing as the ground cools.

• Depth of Freezing = distance in the Frost Tube from the soil surface to the boundary between the ice layer and unfrozen water in the inner tube. This represents the depth of freezing between the soil surface and the underlying unfrozen soil.

In the FieldFirst time only/getting started1. Complete the upper portion of your data sheet.

Every visit1. Record the date on the Frost Tube Data Sheet.

2. If you have a GLOBE Atmosphere site nearby, record the current air temperature on the Frost Tube Data Sheet. Otherwise, consult a reliable source (e.g., local Weather Ser-vice station) for this information. If the air temperature is colder than -20° C then use the Frost Tube Protocol for Temperatures Colder than -20 C Field Guide. If the air tempera-ture is warmer than -20° C then continue with the following procedure.

3. Walk to the Frost Tube site using the same path to reduce impact on the snow condi-tions.

4. Working quickly to reduce impact on the Frost Tube reading, remove the CPVC cap and pull the inner tube (containing the colored water) out just far enough to note the depth of freezing or thawing. Be sure to hold the outer CPVC pipe (outer tube) and radiant heat (middle) tube to prevent them from lifting out of the hole as well.

GLOBE® 2017 Frost Tube Protocol - 18 Soil (Pedosphere)

5. Determine the depth of freezing:

• Locate the soil surface mark (0 cm) on the water-filled inner tubing. Hold the meter stick by the inner tube.

• Find the boundary between the ice at the top of the clear tubing and the water below it. The ice appears relatively clear while the water is colored. (Note: Sometimes the ice will be mottled with some color still left in it from the food coloring. This happens when the first freezing occurs so quickly that some of the dye crystals are trapped in the ice.) There should still be a distinct boundary evident between this partially colored ice and the unfrozen water, which will have a homogeneous color.

• Read off the depth of this boundary to the nearest centimeter (by holding meter stick by the inner tube.

6. Quickly return the clear tube to the structure and replace the CPVC cap.

7. Record the depth of freezing on the Frost Tube Data Sheet and the observer names.

8. Repeat the measurements once each week at the same time, ideally within one hour of solar noon.

9. If possible, for each time the Frost Tube is read, note the current air temperature and depth of snow (if present) at the Frost Tube site where there is minimal disturbance.

Frost Tube Protocol at Air Temperatures Warmer Than -20C Field Guide – Page 2

GLOBE® 2017 Frost Tube Protocol - 19 Soil (Pedosphere)

Frost Tube Protocol at Air Temper-atures Colder Than –20 CField GuideTaskObserve and record the depth of freezing in the ground’s active layer (where there is per-mafrost) when air temperatures are colder than – 20° C (determined by a GLOBE Atmo-sphere site nearby or from another reliable source).orObserve and record the depth of freezing in the ground (where there is no permafrost) when air temperatures are colder than – 20° C (determined by a GLOBE Atmosphere site nearby or from another reliable source).

What You Need□ A properly installed Frost Tube □ Pen or pencil □ Frost Tube Data Sheet □ Meter stick Students will measure the depth of freezing as the ground cools.

• Depth of Freezing = distance in the Frost Tube from the soil surface to the boundary between the ice layer and unfrozen water in the inner tube. This represents the depth of freezing between the soil surface and the underlying unfrozen soil.

In the Field

First time only/getting started1. Complete the upper portion of your data sheet.

Every visit

1. Record the date on the Frost Tube Data Sheet.

2. If you have a GLOBE Atmosphere site nearby, record the current air temperature on the Frost Tube Data Sheet. Otherwise, consult a reliable source (e.g., local Weather Ser-vice station) for this information. If the air temperature is warmer than -20° C then use the Frost Tube Protocol for Temperatures Warmer than -20 C Field Guide. If the air tempera-ture is colder than -20° C then continue with the following procedure.

3. Walk to the Frost Tube site using the same p ath to reduce impact on the snow condi-tions.

4. Use a meter stick to record the depth of snow in three undisturbed locations near the Frost Tube. Enter these data on the Frost Tube Data Sheet.

5. Working quickly to reduce impact of colder than -20° C temperatures, remove the CPVC cap and pull the inner tube (containing the colored water) out just far enough to note the depth of freezing or thawing. Be sure to hold the outer CPVC pipe and radiant

GLOBE® 2017 Frost Tube Protocol - 20 Soil (Pedosphere)

heat middle tube to prevent these tubes from lifting out of the hole as well.

6. Determine the depth of freezing:

• Locate the soil surface mark (0 cm) on the water-filled inner tubing. Hold the meter stick by this inner tube.

• Find the boundary between the ice at the top of the clear tubing and the water below it. The ice appears relatively clear while the water is colored. (Note: Sometimes the ice will be mottled with some color still left in it from the food coloring. This happens when the first freezing occurs so quickly that some of the dye crystals are trapped in the ice.) There should still be a distinct boundary evident between this partially colored ice and the unfrozen water, which will have a homogeneous color.

• Read off the depth of this boundary to the nearest centimeter (by holding the meter stick by the inner tube).

7. Record the depth of freezing on the Frost Tube Data Sheet and the observer names.

8. Because the extremely cold air temperature may cause some of the unfrozen water in the tube to freeze during the time it is pulled out of the assembly, you will need to remove the clear tubing from the Frost Tube and carry it inside to completely thaw it out for at least 24 hours. After removing the inner tubing, be sure to replace the cap on the outer CPVC pipe.

9. The following day replace the clear tubing in the Frost Tube:

• Carefully coil up the tubing and place it under your coat before you go outside. This will help to reduce the influence of the cold air.

• Walk to the Frost Tube site, remove the cap and quickly place the clear tubing back into the Frost Tube. Replace the cap immediately.

• Note the date that the Frost Tube was removed for thawing out and the date it was replaced on the Frost Tube Protocol Data Sheet in the Comments/ metadata section on the bottom of the page.

• Do not disturb the Frost Tube until it is time to take the next measurement.

10. Repeat the measurements once each week at the same time, ideally within one hour of solar noon. If the cold weather continues, you will need to repeat this procedure each time you read the Frost Tube (depth of freezing is observed and recorded).

11. If possible, for each time the Frost Tube is read, note the current air temperature and depth of snow (if present) at the Frost Tube site where there is minimal disturbance.

Frost Tube Protocol at Air Temperatures Colder Than -20C Field Guide – Page 2