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CLIMATE OBSERVATIONS, STATIONS

AND NETWORKS

by

PROF. A. BALASUBRAMANIAN

DEPARTMENT OF STUDIES IN EARTH SCIENCE

UNIVERSITY OF MYSORE, MYSORE

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Weather monitoring Stations :

Weather monitoring Stations should be located

to give representative climatic characteristics

that are consistent with all types of terrain, such

as plains, mountains, plateaus, coasts and

islands, and surface cover such as forests, urban

areas, farming areas and deserts within the area

concerned.

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Station density should be dependent upon the

purposes for making the observations and the

uses of the data.

The density and distribution of climatological

stations to be established in a land network

within a given area depend on the

meteorological elements to be observed, the

topography and land use in the area, and the

requirements for information about the specific

climatic elements concerned.

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The rate of variation of climatic elements across

an area will differ from element to element.

CLIMATIC ELEMENTS:

Surface and subsurface elements:

A principal climatological station usually

provides a broader range of observations of

weather, wind, cloud characteristics, humidity,

temperature, atmospheric pressure,

precipitation, snow cover, sunshine and solar

radiation.

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In order to define the climatology of

precipitation, wind, or any other specific

element, it is sometimes necessary to operate a

station to observe one or a subset of these

elements, especially where the topography is

varied. It is desirable to have a network of these

stations in each country, representing key

climate zones and areas of vulnerability.

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The observations from these networks and

stations are required for the timely preparation

of weather and climate analyses, forecasts,

warnings, climate services, and research.

In addition to surface elements, subsurface

elements such as soil temperature and moisture

are particularly important for application to

agriculture, forestry, land-use planning and

land-use management.

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Other elements that should be measured to

characterize the physical environment for

agricultural applications include evaporation

from soil and water surfaces, sunshine, short-

and long-wave radiation, plant transpiration,

runoff and water table, and weather

observations (especially hail, lightning, dew and

fog).

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Upper-air elements:

Upper-air observations are an integral

component of the Global Observing System.

Climatic Elements measured by remote sensing.

INSTRUMENTATION:

Climatological stations that are part of a

national network should be equipped with

standard approved instruments.

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Calibration of instruments:

It is of paramount importance, for determining

the spatial and temporal variations of climate,

that the relative accuracy of measurement of

individual sensors in use in a network at one

time be measured and periodically checked, and

similarly, that the performance of replacement

sensors and systems can be related to that of

those replaced.

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The Siting of Climatological Stations:

The representativeness and homogeneity of

climatological records are closely related to the

location of the observing site. A station sited on

or near a steep slope, ridge, cliff, hollow,

building, wall or other obstruction is likely to

provide data that are more representative of the

site alone and not of a wider area.

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A station that is or will be affected by the

growth of vegetation, including even limited

tree growth near the sensor, growth of tall crops

or woodland nearby, erection of buildings on

adjacent land, or increases (or decreases) in

road or air traffic (including those due to

changes in the use of runways or taxiways) will

provide neither broadly representative nor

homogeneous data.

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A climatological observing station should be

sited at a location that permits the correct

exposure of the instrumentation and allows for

the widest possible view of the sky and

surrounding country if visual data are required.

Prevention of unauthorized entry is a very

important consideration, and may require

enclosure by a fence. Security is needed.

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1. Synoptic stations reports are complied every

three hours in an international numerical code

by staff of the Fiji Meteorological Service. The

weather stations are vastly networked, and are

distributed over the main islands of the Fiji

group as well as, other remote islands.

2. Climatological Stations provide more

detailed information on elements like,

temperatures (air/soil), humidity, rainfall,

radiation, sunshine hour and wind.

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3. The Automatic Weather Station (AWS) is

defined a station which automatically transmits

or records observations obtained by measuring

instruments. The data derived from AWS

include the dates, time of observation, station

indicators, wind speed, direction, temperature,

relative humidity, MSL pressure and rainfall

data.

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4. Rainfall Stations provide rainfall data that

are measured every day at 9.00am. These

stations are manned by workers of either

corporate organizations, or other government

departments and are normally called voluntary

observers.

5. Radar observations : Weather and wind-

profiling radars are proving to be extremely

valuable in providing data of high-resolution in

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both space and time, especially in the lower

layers of the atmosphere.

Weather radars are used extensively as part of

national, and increasingly of regional networks,

mainly for short-range forecasting of severe

weather phenomena.

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Weather radars are particularly useful for

estimation of rainfall amounts and, when

Doppler capable, wind measurements. Wind

profiler radars are especially useful in making

observations between balloon-borne soundings,

and have great potential as a part of integrated

observing networks.

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6. Observing stations at sea :

Over the oceans, the GOS relies on ships,

moored and drifting buoys, and stationary

platforms.

Observations made by about 7 000 ships

recruited under the WMO Voluntary Observing

Ship Programme, collect the same variables as

land stations with the important additions of sea

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surface temperature and wave height and

period.

The operational drifting buoy programme

comprises about 900 drifting buoys providing

12 000 sea surface temperature and surface air

pressure reports per day.

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7. Observations from aircraft :

Over 3 000 aircraft provide reports of pressure,

winds, and temperature during flight. The

Aircraft Meteorological Data Relay (AMDAR)

system makes high-quality observations of

winds and temperatures at cruising level, as

well as at selected levels in ascent and descent.

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The amount of data from aircraft has increased

dramatically in recent years to an estimated 300

000 reports per day.

8. Observations from satellites

The environmental and meteorological space-

based Global Observing System includes

constellations of operational Geostationary and

Low Earth Orbit (near-polar-orbiting)

observation satellites.

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Meteorological observations of Variables

- temperature (at various heights above the

ground or sea surface),

- atmospheric pressure or air pressure

- humidity or relative humidity, dew point

temperature

- wind speed and direction

- precipitation (amount and duration), snow

cover

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- solar radiation (short wavelength, UV-a, UV-

b, sunshine duration),

- horizontal visibility

- evaporation,

- soil moisture content, soil temperature

(various depths),

- upper air pressure, temperature, humidity

- upper air wind ,

- weather state (present weather, past weather) ,

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- clouds (type, sort and height) and degree of

coverage ,

- ozone

- composition of the atmosphere

- sea water temperature;

- waves and swell (height, direction, period);

- lightning.

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The observations are generally “ground based”,

i.e. that they are measured on or at the surface

level of the ground or sea.

A number of meteorological variables

(temperature, relative humidity, wind, pressure,

etc.) are also measured at greater altitudes:

- by releasing balloons with radio sondes (up to

altitudes of more than 15 km);

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- at various levels on the Cabauw measuring

mast (up to a height of 200 m).

Meteorological observations are carried out in

principle as a continuous process, in which the

frequency of observation can vary from a

fraction of a second up to periods of 24 hours.

Observations are made using instruments,

manually, visually or by ear.

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A value is not directly determined for a number

of meteorological variables, but is rather

derived from other variables that have been

directly observed or measured.

Examples are evaporation (calculated from

temperature and global solar radiation), dew

point temperature (calculated from temperature

and relative humidity) and sunshine duration

(calculated from global shortwave radiation).

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Important weather information is acquired

using remote sensing techniques (e.g. radar

systems for detecting showers), satellite

observations, observations made on board ships,

measuring buoys at sea and observations made

from aircraft (AMDARs).

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Type of observing station:

The observational network shall include

comprise the following types of

meteorological stations:

a) Manned weather station: visual and

instrumental observations;

b) Automatic weather station (AWS):

exclusively instrumental observations;

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c) Wind measuring mast: instrumental

observations of wind direction and speed only;

d) measuring mast: instrumental observations at

heights from 20 m to 200 m;

e) precipitation stations: (manual) observations

of precipitation amount and snow cover;

f) lightning detection masts: observations of

lightning discharges.

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Times of observations & Regularity:

The distinguishing feature of a meteorological

station is that the variables concerned are

measured or are observed there regularly in

order to provide a (real-time) picture of the

actual weather situation in that region.

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The observational data collected from a

weather station is to be validated (using pre-

determined objective procedures) and

systematically archived for later analysis of

specific events and for climatological purposes.

A selection of the data is also used for the

analysis and verification of operational weather

models.

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Conditions relating to the layout of the

measurement site of a weather station:

A measurement site is surrounded by a fence to

prevent unauthorized access. The measuring

instruments are positioned on the site in such a

way as not to interfere with each other. The

neighbourhood of the measurement site must be

free of objects that could affect the

measurements.

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Spatial distribution of the measuring stations

and the representativeness of the

observations

Diagram of an automatic weather station

Observations at ordinary climatological and

precipitation stations should be made at least

once (and preferably twice) each day at fixed

hours that remain unchanged throughout the

year.

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At principal climatological stations,

observations must be made at least three times

daily in addition to an hourly tabulation from

autographic records, but non-autographic

observations are usually taken hourly.

If changes are made to the times of observations

across a network, simultaneous observations

should be carried out at a basic network of

representative stations for a period covering the

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major climatic seasons in the area at the old and

new times of observation.

Logging and reporting of observations

On-site quality control

Report monitoring at collection centres

Station documentation and metadata

Basic station metadata should include station

name and station index number (or numbers);

geographical coordinates;

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elevation above mean sea level;

administrator or owner;

types of soil, physical constants and profile of

soil;

types of vegetation and condition;

local topography description;

description of surrounding land use;

photographs and diagrams of the

instrumentation,

site and surrounding area;

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type of AWS, manufacturer, model and serial

number;

observing programme of the station (elements

measured, reference time, times at which

observations and measurements are made and

reported, and the datum level to which

atmospheric pressure data of the station refer);

and contact information, such as name and

mailing address, electronic mail address, and

telephone numbers.

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Instrument metadata should include sensor

type, manufacturer, model and serial number;

principle of operation; method of measurement

and observation; type of detection system;

performance characteristics; unit of

measurement and measuring range; resolution,

accuracy (uncertainty), time constant, time

resolution and output averaging time; siting and

exposure (location, shielding and height above

or below ground); date of installation; data

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acquisition (sampling interval and averaging

interval and type); correction procedures;

calibration data and time of calibration;

preventive and corrective maintenance

(recommended and scheduled maintenance and

calibration procedures, including frequency, and

a description of procedures); and results of

comparison with travelling standards.

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The Design of Climatological Networks

A network of stations is several stations of the

same type (such as a set of precipitation

stations, radiation measuring stations or

climatological stations), which are administered

as a group.

Each network should be optimized to provide

the data and perform as required at an

acceptable cost.

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It has been common practice to assume that at

least ten years of daily observations are

necessary to produce the relevant base statistical

parameters for most elements, and at least thirty

years for precipitation.

The identification of redundant stations

allows network managers to explore options for

optimizing the network, for example, by

eliminating the redundant stations to reduce

costs or by using the resources to establish

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stations at locations where observations are

needed for a more effective realization of the

network objectives.

A sparse network is sufficient for the study of

surface pressure, a fairly dense network for the

study of maximum and minimum temperature,

and very dense networks for examining the

climatology of precipitation, wind, frost and

fog, especially in regions of significant

topography.

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The measurement network comprises of

various equipment. The measurement network

consists of a substantial number of weather

stations on land and in the Sea. Observations

and (automatic) measurements of

meteorological variables should be carried out

at these stations.

The observing stations and the instrumentation

used meet the requirements set by the World

Meteorological Organization (WMO):

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There should be a team of station inspectors

monitor the quality of the observations by

regularly checking the measuring equipment

and the environment at the measurement site.

The observational data is carefully verified,

validated, stored and processed for a large

number of applications.