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. This module highlights all these aspects.

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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.