INSOLATION
What is insolation?
Solar energy reaches earth in the form of short
waves is called insolation.
Heat transfer in the atmosphere
Processes of heat transfer in the atmosphere
Heat is transferred in the atmosphere by conduction,
convection, advection and terrestrial radiation.
¢ Conduction – Heat is transferred to the lower part of the atmosphere
through conduction.
¢ Convection – Heated air expands and rises up the cold air comes down
and gets heated up. This method of heat transference is known as convection.
¢ Advection – Horizontal transfer of heat by wind is known as
advection.
¢ Terrestrial radiation – Heat is transferred from the surface of earth
to the outer space in the form of long waves. This is known as terrestrial
radiation. The atmosphere is heated mainly by terrestrial radiation.
Which are the gases those absorb terrestrial
radiation? What is the consequences of such absorbtion?
Ans;
The gases like carbon dioxide and methane absorb
terrestrial radiation. Terrestrial radiation maintains the atmospheric
temperature at an optimum level even during night. But the presence of excess
carbon dioxide and methane in the atmosphere will lead to over absorption of
terrestrial radiation and the result will be global warming.
Terrestrial radiation occurs mostly at night. Why?
Ans:
At night the earth surface is warmer than the
atmosphere. So heat transference takes place from the surface of earth
to atmosphere mostly at night.
What is the difference between insolation and
terrestrial radiation?
Ans:
Solar energy reaches earth in the form of short
waves is called insolation. Heat is transferred from the surface of earth to
the outer space in the form of long waves is known as terrestrial radiation.
Give a brief note about heat budget
Ans:
About 35% of the amount of insolation reaching the
outer surface of the atmosphere is reflected back by the atmosphere. The
remaining 65% of the solar energy is distributed as follows.
Temperature is the degree of hotness of the
atmosphere.
¢ It is from the weather condition at 2pm that the
meteorologists measure the maximum temperature of a day.
¢ The minimum temperature is taken just before the
sunrise.
Which is the instrument used to measure
temperature?
Ans: Thermometer
Diurnal range of temperature
The difference between the maximum and the minimum
temperatures of a day is called diurnal range of temperature.
Daily mean temperature
The average temperature of a day is termed 'daily
mean temperature'.
It can be calculated as follows.
Daily mean temperature
= (Max.
temperature of the day + Min. temperature of the day)/ 2
Calculate diurnal range and daily mean temperature of the places shown in the weather report.
Maximum minimum
thermometer
This is the instrument for
measuring the maximum and minimum temperature in a day. Here the two
thermometers are connected using a U-shaped glass tube. The mercury filled in
the maximum thermometer expands with rise in temperature and pushes up the
metal indicator. The indicator remains at the position showing the maximum
temperature of the day. Thus the maximum temperature can be read at any time
during a day. The minimum thermometer has alcohol filled above the indicator.
When the temperature falls, the indicator is pushed up as the alcohol
contracts. The minimum temperature can be read from the position of the
indicator at any time.
Isotherms
The imaginary lines connecting places having equal atmospheric temperature
are called isotherms.
What are the
factors influencing the distribution of temperature? Explain.
Latitude
Altitude
Nearness to ocean
Winds
Latitude
Temperature will be higher at
equator and nearby latitudes. As go away from equator the temperature decreases
and at poles the temperature is very low. The angle of incidence of the
sun's rays becomes more inclined on approaching the poles. There occurs more
energy loss as the sun's rays have to travel more through the atmosphere owing
to the inclination
Nearness of
ocean
Temperature remains moderate at
places close to the sea. This is because the heating of land causes wind to
blow from sea to land and cooling of land causes wind to blow from land to sea.
Altitude
The temperature in the troposphere decreases at the rate of 1° C per 165 m of altitude. This process is known as normal lapse rate. The temperature is comparatively low at places situated much above the sea level.
Wind
The warm and
the cold winds can respectively raise or lower the temperature of the places
through which they pass.
The
temperature experienced in places like Idukki and Wayanad is lower than that of
the neighbouring districts Ernakulum and Kozhikode respectively. Why?
Ans:
Altitude of
places like Idukki and Wayanad is higher than that of places like Ernakulam and
Kozhikode. As altitude increases the temperature decreases. Therefore Wayanad
and Idukki experience lower temperature.
The diurnal
range of temperature is very high for Delhi and Bengaluru where as it is very
low for Thiruvananthapuram and Goa. Why?
Ans: The
difference between the maximum temperature of a day and the minimum temperature
of the day is diurnal range of temperature. Thiruvananthapuram and Goa are the
places located near the sea. Temperature remains moderate at places close to
the sea. The range of temperature will be high at places away from the sea and
hence the range of temperature will be high for places like Delhi and Bengaluru
which are located far away from sea.
Isotherms in
the southern hemisphere are almost parallel to the Equator compared to those in
the northern hemisphere. Why?
Ans: Due to
the differential heating of land and water, isotherms are curved at areas
including land and water. In southern hemisphere the land area is less and
there is vast area of oceans. So same temperature is experienced throughout a
latitude. Therefore Isotherms in the southern hemisphere are almost parallel to
the Equator compared to those in the northern hemisphere.
In the
weather maps for summer and winter seasons, the isotherms behave differently.
Why?
Ans: During summer, high
temperature prevails over the land compared to the sea and during winter, the
condition is reversed. The bending of isotherms is due to the differential
heating of land and water. In land areas during summer the isotherms bend
facing the poles, and in the oceanic region, isotherms bend facing the equator.
During winter the condition is reversed.
Water in the
atmosphere
Humidity
Water content in the atmosphere is called humidity.
Factors influencing the amount of moisture in the atmosphere.
— Temperature
— Rainfall
— Speed and
direction of wind
The actual
amount of water present in the atmosphere is called absolute humidity.
It is measured as the amount of water vapour present per cubic metre volume of
air (g/m³).
The stage at
which the atmosphere is fully saturated with water is termed as saturation
level. When the atmosphere becomes saturated, condensation begins. The
critical temperature at which condensation begins is called dew point.
The ratio between the amount of
water vapour present in the atmosphere and the total water holding capacity of
the atmosphere at a given temperature is called relative humidity. It is
usually expressed in percentage. Relative humidity is measured using the instrument
called wet and dry thermometer.
What will be the relative humidity at saturation level?
Ans: 100%
Sublimation
In some
instances, due to rapid fall in atmospheric
temperature, water vapour directly condenses to solid state
(snowflakes). This is called sublimation
When will
the condensation start?
Atmosphere
should reach the saturation level for condensation to begin. With further
addition of water vapour or due to a considerable fall in temperature, the
water vapour in the atmosphere begins to condense
Forms of condensation
What are the
different forms of condensation? Explain each.
Different forms
of condensation are dew, frost, fog or mist, and clouds.
Dew
The surface
of the earth gets cooled during the night and it cools the near atmosphere.
This causes the water vapour to condense and the condensed droplets cling on to
the cold surfaces on earth.
Frost
In the
places on the earth where the night temperature falls below 0𝑜 C,tiny ice crystals are formed.
This form of condensation is called frost.
Fog or Mist
The condensed tiny droplets of water
formed by the cooling of air remains suspended in the atmosphere itself. They
can very well be described as clouds close to the earth's surface. Fog or mist
is the result of condensation around the minute dust particles in the lower
atmosphere. This may obstruct visibility. If the range of visibility is less
than one kilometre, it is termed fog.If the range of visibility is more than
one kilometre, it is called mist.
Clouds
Clouds are formed by the condensation of
water vapour around the fine dust particles in the atmosphere. The water
droplets so formed are less than 0.001 cm in dimension. That is why they remain
suspended in the atmosphere.
Types of
clouds
Clouds can
be classified according to their form and height. Based on form there are
mainly 4 types of clouds.
Cirrus
clouds : These are feather-like clouds in the upper atmosphere in clear weather
conditions.
Stratus
clouds : These appear in thick layers in the lower part of the sky.
Cumulus
clouds : These clouds resemble huge cotton bundles and are formed due to strong
convection currents. They have large vertical extent.
Nimbus
clouds : These are dark rain clouds in the lower atmosphere. These clouds appear
dark as it does not allow sunlight to pass through due to thick concentration of water droplets.
Based on
height clouds are classified as follows
¢ High clouds
(20000 to 40000 ft)
¢ Medium
clouds (7000 to 20000 ft)
¢ Low clouds (< 7000 ft)
¢ Clouds with great vertical extent (2000 to 30000ft)
What is
precipitation?
Continuous
condensation causes the droplets in the clouds to grow in size. Being unable to
resist the gravitational force of the earth, the water droplets get released
from the clouds and fall on the earth in different forms. This process is
called precipitation.
What is
rainfall?
Rainfall is
the common form of precipitation in the form of water drops.
When does
snowfall occur?
When the
temperature falls below 0° Celsius, precipitation reaches the earth in the form
of tiny crystals of ice. This is snowfall.
What kind of
precipitation is called hailstones?
If the water droplets released
from the clouds happen to pass through colder layers of the atmosphere, they
may reach the earth in the form of ice pellets. This form of precipitation is
called hailstones.
Different types of rainfall
Orographic
rainfall
The moisture-laden wind from the sea enters the land and moves upwards along the mountain slopes where it gets cooled and condensed to form clouds. When the windward sides of the mountain receive heavy rainfall, the leeward sides do not receive rainfall due to the descending dry air. This type of rainfall is known as orographic rainfall or relief rainfall.
Convectional
rainfall
Due to high temperature, air gets
heated and rises up.Cumulus clouds
are formed by the cooling and
condensation of rising warm air. Rainfall occurs with thunder and lightning. This rain, mostly occurring in
the afternoon, does not last long. This type of rainfall is called convectional
rainfall. This is a common phenomenon in the tropical regions during summer.
Border rain
There is
always a difference in the atmospheric temperature over land and sea. If the
air over the sea comes in contact with the air over the land in the coastal
regions, the warm air will be pushed upwards causing cloud formation and
rainfall. This type of rainfall is called border rain.
What do you
mean by rain shadow region?
The windward
sides of the mountain receive heavy rainfall due to the moisture –laiden wind
from the sea. But the leeward side of the mountain do not receive any rainfall.
So the regions situated at the leeward side of mountains is known as rain
shadow regions.
When Kerala receives southwest monsoon
rainfall, the western parts of Tamil Nadu remain dry. Why?
Kerala is on
the windward side of sahya mountains. But the western parts of Tamilnadu is on
the leeward side of these mountains.so Kerala receives southwest monsoon
rainfall and at the same time the western parts of Tamilnadu remains dry.
The sun is
inevitable for sustaining life on earth. Do you agree with this statement?
Explain.
All the
functions of our living planet, the earth, are regulated by the sun. The very
existence of the biosphere is by direct or indirect dependence on the solar
energy. Even the distribution of plants and animals on earth is in accordance
with the availability of sunshine. The case of human beings also is not
different. All the atmospheric phenomena inevitable for sustaining life on
earth are controlled by solar energy.
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