Instruments
for Measuring Weather Elements
Weather varies with the changes in
weather elements such as temperature, pressure, wind, humidity, cloudiness,
precipitation, sunshine and visibility. The weather is measured employing
particular instruments and recorded in weather stations. The weather elements are
listed below.
Temperature is the hotness or
coldness of a substance. The temperature of a particular place changes based on
the factors like latitude, altitude, season, time of day, cloud cover, wind,
location of the sea etc. Temperature is measured utilizing thermometers. There
are Centigrade, Fahrenheit, Wet Bulb, Dry Bulb and Tele thermometers.
In Centigrade thermometer, the
temperature of melting ice is taken as 00 C and the temperature of boiling water as 1000C. In Fahrenheit thermometer, 320F represents the freezing point and 2120F represents the boiling point of water. Wet Bulb
and Dry Bulb thermometers are used to measure humidity in temperature. Tele
thermometer is used to record temperature continuously within and outside the
building. Thermograph produces a continuous trace of the changing temperature
of a place.
Pressure is defined as the weight of
a unit column of air at any place. The barometer is an instrument to measure
atmospheric pressure. While both Barometer and Aneroid Barometer measures
atmospheric pressure above and below sea level, Altimeter measures air pressure
at a height above sea level. Barograph provides a continuous record of air
pressure. The unit of pressure is measured in millibars (mb). Globally, the pressure
determines the wind and weather pattern. High pressure and low pressure are
highly related with the increase or decrease in temperature.
The wind is moving air over the
earth’s surface. The air moves from high pressure to low pressure either vertically
or horizontally. Wind vane records the direction of the wind and points out
from which direction it blows. Cup Anemometer measures wind velocity, which is
expressed in knots. Wind Sock is a device that indicates the origin of wind
direction and speed.
The amount of water vapour present in
the atmosphere is termed as Humidity. It concentrates in the lower layer of the
atmosphere. It varies from place to place and time to time. It may be
classified as absolute, specific and relative humidity. Hygrometer is the
instrument that measures the relative humidity. Hygrograph is an automatic
instrument showing the change in relative humidity. Hygrothermograph records
both humidity and temperature.
Cloudiness indicates the amount of
sky covered by clouds. Clouds are present in the lower atmosphere at varying
altitude. Thay are varying in size and shape. The clouds are classified as
high, middle and low clouds. Ceilometer is an instrument that uses a laser to
determine the height of the cloud base. Ceiling projectors measure the height
of the base of clouds above the ground. Cloud mirror measures the percentage of
cloud cover. An Okta is a unit of measurement to describe the amount of cloud
cover. The measurement of 0 Okta indicates clear sky and 8 Okta denotes
completely overcast sky.
The water or ice particles reaching
the ground surface from the atmosphere is known as precipitation. The various
forms of precipitation are dew, mist, fog, sleet, drizzle, rain and hail.
Conventionally, the amount of rain has been recorded by the instrument called
Rain gauge. The amount of rain will be recorded in mm or cm or inches at a
given time. The automated weather station (AWS) instrument records the rainfall
with the help of sensors.
Sunshine means that the sun’s rays
lie within the visible spectrum that reaches the earth’s surface. The amount or
duration of sunshine in hours per day at a given region is measured using a
sunshine recorder. The sunshine of a place depends on various seasons.
Visibility means the transparency of
the air in the particular place. It depends on the presence of water, ice, dust
and smoke particles in the atmosphere. Visibility is measured by the distance
at which prominent objects can be seen and the details discerned. The scale of
visibility varies from zero, when objects cannot be easily seen beyond 25
metres, to visibility 9, when objects can be easily seen at a distance of 50
kilometres. Scale 0 to 3 indicate Fog, scale 4 represents Haze or Mist, scale 5
to 9 represents poor to Excellent visibility.
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