The document provides an overview of essential weather and climate concepts, defining terms such as weather, climate, meteorology, and key elements including temperature, humidity, and precipitation. It explains the differences between weather and climate, the factors influencing atmospheric pressure, and the various types of precipitation and winds. Furthermore, it details the instruments used to measure weather-related conditions, enhancing the understanding of meteorological phenomena.

1. WEATHER AND CLIMATE
CHAPTER - 2
A Presentation by Deepu Hemish

2. Learning Terms
• Weather: The state of atmosphere at a given place and at a given time
• Climate: Average weather conditions along with vanations and extremes which characterise a place.
• Daily mean temperature: The average of maximum and minimum temperature values recorded in a day.
• Diurnal range of temperature: The difference between the maximum and minimum temperature in a day.
• Annual range of temperature: Difference between the mean temperatures of the hottest and the coldest
months.
• Meteorology: The study of weather and its elements is known as meteorology.
• Temperature: Temperature of a particular place denotes the degree of hotness or coldness of air at that
place.
• Specific heat: Amount of energy required to raise the temperature of one gramme matter of a substance by
one degree celsius is called the specific heat of that substance.
• Atmospheric pressure: The force exerted by a vertical column of air per unit of area on the earth’s surface is
called atmospheric pressure.

3. Weather is an ever changing phenomenon of our environment. Human life on
earth is influenced more by weather than any other phenomenon of the
physical environment. Today the newspapers, radio and television report a
wide range of weather events regularly. They also provide information about
the weather conditions likely to occur during the coming days. This shows the
great importance that weather conditions assume in our lives. For thousands
of years scientists have tried to predict the weather. The study of weather
and its elements is known as meteorology.

4. Weather and Climate
Weather keeps changing from hour to hour and from day to day.
Weather can be defined as the atmospheric conditions at a given
place and at a given time. The climate on the other hand, can be
defined as the sum of the weather conditions of a large area over a
long period. It is thus the average weather as well as the variations
and extremes of an area. The basic elements of both weather and
climate are the same.

5. Difference between Weather and Climate
1. It refers to short-term
atmospheric conditions that exist
for a given time in a specific area.
2. Weather refers to a 2 particular
station.
3. Weather may change at a very
short interval of time.
4. Weather is influenced by any one
of its predominant elements, i.e.,
temperature, humidity, etc.
Weather Climate
1. It refers to short-term
atmospheric conditions that exist
for a given time in a specific area.
2. Weather refers to a 2 particular
station.
3. Weather may change at a very
short interval of time.
4. Weather is influenced by any one
of its predominant elements, i.e.,
temperature,

6. Elements of Weather and Climate
The atmosphere is a complex medium and its mechanisms and
processes are sometimes very complicated. Its nature, however, is
generally expressed in terms of only a few variables which are
measurable. Temperature, atmosphere pressure, humidity,
precipitation, winds, clouds etc. are some of the important
elements of weather.

7. Temperature
Temperature affects all the major elements of weather including air
pressure, cloud formation, humidity and precipitation. The difference in
temperature is associated with the formation of heat zones and pressure
belts.
-> How the Earth and its Atmosphere get Heated?
The only permanent and continuous source of heat on the planet of earth is
the sun. The sun constantly radiates heat and light in all directions. This
process of giving out energy by the sun is called as the solar radiation.

8. How the Earth and its Atmosphere get Heated?
1. Insolation: Incoming solar radiation received on the surface of
the earth.
The amount of solar radiation received on the earth’s surface is
called insolation. The sun’s energy travels to the earth as
electromagnetic radiation. The incoming solar radiation is received
in the form of short waves. These waves reach the earth’s surface
without heating the atmosphere.

9. 2. Terrestrial Radiation
Solar radiation is in the form of short waves and it reaches. The
earth’s surface without heating the atmosphere. Most of this heat
energy is reflected back by the earth’s surface in the form of long-
wave radiations known as the terrestrial radiation. The atmosphere
is thus heated indirectly through the earth.
The amount of Insolation received on various parts of the earth is
not equal. It varies from place to place and depends on
How the Earth and its Atmosphere get Heated?

10. Latitude
The latitude at which a place is located affects the temperature of
the place. The spherical shape of the Earth causes the different
parts of the Earth to be heated to different degrees. The region
near the Equator gets more direct rays from the Sun. The direct
rays are concentrated over a smaller area and so they heat the
Earth more. As we move away from the Equator, due to the
curvature, the Sun’s rays strike the Earth at an angle. The slanting
rays of the Sun spread the heat over a larger area and so do not
heat to the same extent as the direct rays.

11. Latitude
Thus, the temperature decreases as the distance increases from the
Equator. The amount of rainfall also decreases from the Equator to
the poles since the rate of evaporation is related to temperature.
The angle at which the Sun's rays strike the Earth also varies
between seasons. In June the Sun’s rays are more direct in the
Northern Hemisphere than in the Southern Hemisphere.

13. Thickness of the atmosphere
The intensity of insolation at the earth’s surface also depends on
the thickness of the atmosphere. The insolation received per unit
area at the polar region is minimum because of the thickness
atmosphere.

14. Length of the day
The length of the day determines the duration for which the sun’s
rays and energy are received at a place.

15. Distribution of land and water
Land absorbs and reflects more heat than water because specific
heat of land is less than that of water. So land is heated and cooled
in a much short time than water.

16. Atmospheric Pressure
The force exerted by the vertical column of air per unit of area is
called atmospheric pressure.
Atmosphere surrounding the earth is held to it to gravity. Therefore,
the air has weight and it exerts a force on the earth’s surface.
Although the air has very little weight, yet due to its great height of
several hundred kilometres the column of air above the surface
exerts considerable pressure.

17. Factors affecting atmospheric pressure
1. Altitude
The pressure exerted by the atmosphere decreases with height or
altitude. The decrease in pressure is about 1 cm of mercury for
every 110 m of ascent. The atmospheric pressure is highest at sea
level. This is because at great heights the air is thinner or less dense
than the air at the sea level.

18. Factors affecting atmospheric pressure
2. Temperature
Atmospheric pressure decreases with increase in temperature. This
is because when the temperature rises, air expands. The molecules
of air move far apart (become less dense) and hence exert less
pressure.

19. World’s Pressure Belts
The unequal heating of the earth and its atmosphere, and the rotation of the earth are
the two main factors which are responsible for the formation of pressure belts of the
world.
The regions with high temperature have low pressure belts whereas regions with low
temperature have high pressure belts. There are following permanent pressure belts:
1. Equatorial Low Pressure Belt (Doldrums)
2. Sub-Tropical High Pressure Belt.
3. Sub-Polar Low Pressure Belt.
4. Polar High Pressure Belt.

20. Humidity
The amount of water vapours present in the air is called humidity.
Amount of moisture in the atmosphere is closely related to the
temperature of the air is said to be unsaturated air.
Humidity is measured and expressed in two ways:
(a) Absolute humidity, and
(b) Relative humidity

21. Humidity
(a) Absolute humidity
Absolute humidity is the amount of water vapour in grams per cubic
metre of air. Absolute humidity is normally expressed in grams of
vapour per cubic metre of air. For example, if the absolute humidity
is 20 gms/cu. M, it means that in a sample of one cubic metre of air,
the amount of water vapour present is 20 gms.

22. Humidity
(b) Relative humidity
Relative humidity is the ratio between the amount of water vapour
present in the air and the maximum amount that can be held by the
air at a given temperature. It is expressed in percentage. Suppose
the air can hold a maximum of 50 grams of water vapour at a given
temperature and only 25 grams of water vapour are present in it.
The relative humidity will be 50%. The relative humidity of
saturated air is 100% and that of absolutely dry air is zero per cent.

23. Precipitation
The process through which water from the atmosphere falls down
on the Earth is called precipitation.
In this process, no change of state of water is involved. There is
only change of geographical location – from the atmosphere to the
hydrosphere and the lithosphere.
Precipitation occurs when tiny cloud droplets join together into
larger rain-droplets, become heavier and fall to the Earth’s surface
through the atmosphere.

24. Types of Precipitation
Precipitation is classified according to its form in which it reaches the
ground. The temperature of the air, both inside and outside the cloud,
determines whether precipitation is rain, snow, sleet or hail.
1. Rain: Precipitation that reaches the ground in liquid form is called rain.
2. Dew: These are tiny drops of water that form when water vapour
condenses on the ground or cool surfaces. It occurs only on calm, cold and
clear nights.
3. Hail: Hailstones are frozen lumps of ice produced by thunderstorms.
They form inside tall cumulonimbus clouds which are much warmer at the
bottom than at the top where the temperature is freezing.

25. Types of Precipitation
4. Snow: This form of precipitation is common in the high latitude
areas and the mountains regions. Snow is precipitation composed of
ice crystals.

26. Winds
Air moves from high pressure areas to low pressure areas. Such a
horizontal movement of air is called the wind. Wind direction and
velocity are two characteristics of wind which are important to the
meteorologists. The winds are named on the basis of the direction
from which they blow. Wind blowing from the east is called an
easterly wind and wind blowing from the west is called westerly
wind.

27. Types of Wind
Planetary winds: Winds that blow all the time in the same areas of
the world are called permanent winds or prevailing winds.
Periodic Winds: Periodic winds are those which blow during a
particular period of the day or season of the year.
Small scale winds occur as a result of localized differences in
pressure and temperature. Therefore, periodic winds are also called
Local and Regional Winds.
Land and sea breezes and the Monsoon winds are typical examples
of periodic winds.

28. Clouds
A cloud is a large collection of very tiny droplets of water or ice
crystals. The droplets are so small and light that they can float in
the air. Clouds are formed through evaporation and condensation.
Classification of clouds: Clouds are classified on the basis of their
shape and the height at which they are formed. Basically there are
three types of clouds i.e. High clouds, middle clouds and low
clouds.

30. Weather Instruments
A weather instrument is any device that measures weather related
conditions.
Meteorologists use a wide variety of different instruments to
measure weather conditions. These instruments allow the
meteorologists to make predictions on weather conditions.

31. 1. Thermometer
Temperature is measured with the help of a thermometer. A thermometer
is made up of a glass tube which is filled with mercury. Mercury expands
more than the glass when it is heated and when cooled it contracts more
than the glass. Due to this fact the liquid in the glass tube rises when the
temperature rises and falls when the temperature falls. Temperature is
recorded in degrees celsius or fahrenheit. The most commonly used scale
of temperature is the Celsius scale. This is a decimal scale with values of
temperature ranging from 0° to 100°. 0° is the freezing point of water and
100° on this scale is the boiling point of water. In Fahrenheit scale the
freezing point and the boiling points are 32° and 212° respectively.

32. 1. Thermometer
A special type of thermometer known as Six’s Maximum and
Minimum Thermometer provides information provides
information about the maximum temperature and minimum
temperature over a particular period.

33. 2. Rain Gauge
Precipitation occurs in the form of rain, snow or hail. Rainfall is the
most common form of precipitation in tropical countries like India.
Rainfall is measured with the help of rain gauge. A vessel is put in
the cylinder to collect rain water. Rainwater is collected through
the funnel for a period of 24 hours and the collected water is
measured with the help of the measuring glass. The amount of
rainfall is measured in millimetres.

34. 2. Rain Gauge
A rainfall of 100 millimetres means that if the water of the rain is
allowed to collect over a level area without any evaporation of
percolation in the soil, the depth of the accumulated water will be
100 millimetres. An instrument providing a continuous record of
rainfall is called hyetograph.
Snowfall or hail is measured by melting it and measuring the
amount of water thus produced.
Rain gauge is kept in an open level area away from trees or
buildings which might obstruct the raindrops. Generally, it is kept
slightly above (30 centimetres) the ground.

35. Difference Between Precipitation and Rainfall
1. Precipitation may take place in
liquid or solid form.
2. Precipitation has different forms
such as snowfall, rainfall, hail, etc.
3. Precipitation is measured by
different methods because it has
different forms.
Precipitation
1. Rainfall has only one form, i.e.,
liquid form.
2. Rainfall is most common form of
precipitation.
3. Rainfall is measured by a
raingauge in millimetres.
Rainfall

37. 3. Hygrometer
Humidity means moisture in air. Moisture in air is in the form of
water vapour. Humidity can be expressed as absolute humidity or
relative humidity. Relative humidity is a most commonly used
method in meteorology.It is expressed as percentage. Saturated air
has a relative humidity of 100 per cent and dry air has a relative
humidity of zero per cent.Humidity varies from place to place and
from time to time. It can be measured with the help of an
instrument called hygrometer.

38. 3. Hygrometer
A simple hygrometer is a wet and dry bulb thermometer. Such a
thermometer consists of two thermometers. The bulb of one of the
thermometer is kept in the air which measures the temperature of the dry
air. The bulb of the other thermometer is kept humid by covering it with
threads which are kept dipped in water and thus it measures the
temperature of the humid air. If the temperature of the wet bulb
thermometer drops sharply, the humidity is very low and if the
temperature of this thermometer does not drop much it means humidity is
very high.

40. 4. Anemometer and Wind Vane
Direction and velocity are two characteristics of wind which are
important to the meteorologists. The winds are named on the basis
of the direction from which they blow. Wind blowing from the east
is called an easterly wind and wind blowing from the west is called
westerly wind. The direction of the winds is found with the help of
wind vane. The arrow of the wind vane points towards the direction
of the wind and the direction is shown on a dial connected to the
wind vane.

41. 4. Anemometer and Wind Vane
Velocity or the speed of the wind is measured with the help of an
instrument called anemometer. Wind velocity is measured in
kilometres per hour. Nowadays instruments recording wind
velocities continuously are used at weather stations. These
instruments are called anemograph. One can get some idea about
wind velocities without actual measurement also. When you find
smoke rising almost vertically, the wind velocity is less than one
kilometre When wind velocity is per more hour.

42. 4. Anemometer and Wind Vane
Than 40 kilometres per hour, one finds it difficult to hold an
umbrella. High wind velocity of more than 100 kilometres per hour
produces storm conditions in which trees are uprooted.

43. 5. Barometer
Atmospheric pressure is measured with the help of a barometer.
Different types of barometers are used for this purpose. Pressure is
read in centimetres or inches of mercury a true measure of the
height of the mercury column. Another pressure unit is millibars. In
a simple type of barometer mercury is used for measuring the
pressure. But such a barometer is difficult to carry.

44. Nowadays Aneroid Barometer is used for measuring atmospheric
pressure. It is easy to carry because it has no mercury column in it.
An altimeter tells the height of the plane during its flight. Another
instrument using an aneroid barometer is the barograph which
provides a continuous record of pressure.
5. Barometer

47. Isohytes and Isotherm
Isohyet or isohyetal is a line on a map which connects points that
have the same amounts of precipitation in a given period or for a
particular storm.
Isotherms are lines of constant or equal temperature. They are
often used on weather maps by meteorologists to give a large scale
view of temperatures across a region.

48. The spacing of isotherms depict the
temperature gradient across a portion of the
Earth's surface. Widely spaced isotherms (line
A-B in Figure) indicate a change in
temperature over a distance and closely
spaced isotherms (line C-D in Figure) indicate
large changes in temperature.

49. Difference between Isohyte and Isotherm
(i) A line on a map connecting
points that receive equal
amount of rainfall.
(ii) The unit of measure ment is
centimeters.
(iii) Closely spaced isohyets
means steep rise / fall in
precipitation.
(1) A line on a map
connecting points that have
same temperature.
(ii) The unit of measurement
is degree celsius.
(iii) Closely spaced isotherms
indicate great range of
temperature.
Isohyet Isotherm