factors that affect the temperature of a place
TRANSCRIPT
FACTORS THAT AFFECT THE TEMPERATURE OF A PLACE
LATITUDE
You have heard that land near Equator is always hotter while round the Poles
it is terribly cold and is never warm. Why is it so? Sun shines all the year
round for 12 hours out of 24 hours at the Equator. It adds up to 6 months in a
year. The period for which Sun shines at the Poles is also 6 months. Then
why the difference? The answer lies elsewhere. It is the difference between
the heating power slanting rays by morning or the evening and the more
direct rays falling at the midday. Now the noontime Sun at poles is never
more than 23 1/2° above horizon. So, its rays are always slanting and have
little heating power despite the long summer days. On the other hand at
equator, Sun is never less than 66 1/2° above the horizon. The heating
power of ever directly falling rays is great. Thus, when the Sun's ray are
vertical over the Equator, they fall at an angle of 40° at 50° N and S latitudes
and at 0° at the poles. As Earth has a spherical shape, the angle of Sun's
rays on surface of the Earth differs from one place to another and
temperature changes at every latitude. We should also remember that the
angle of Sun's rays and the length of day and night during different seasons
change all the year round due to the tilt of Earth's axis. Had it not been so,
we would have no seasons and the climate in each belt would remain the
same throughout the year. Hence the temperature of a particular place at a
particular time of the year depends, on angle of Sun's rays and the length of
day and night. Both in turn depend on the latitude. On the basis of
differences in latitudes, the temperatures are high in the torrid or the tropical
zone and seasonal contrasts are lesser. In the North and South temperate
zones, Sun's rays are always slanting and seasonal variations in
temperatures are large. In the North and South Polar Regions i.e., in Frigid
Zone, Sun's rays are at a very low angle during summer and during winter
these are always below the horizon. So the temperatures in this zone are
very low. As the rays of the Sun fall vertically on the Equator, the
temperature is always high there. Places within the tropics have the mid-day
Sun almost overhead, and the temperatures remain high. Outside the
tropics, the Sun's rays reach the earth's surface obliquely, and the
temperatures are correspondingly lower. There are two similar bands of rays
coming from the Sun to two different latitudes on the earth's surface. The
band of rays falling vertically over the equatorial latitudes heats up a smaller
surface, and there the temperature is high. The band of rays falling obliquely
over the temperate latitudes heats a larger area (this is due to the curvature
of the earth), and there the temperature is low. Thus, we conclude that the
temperature of places away from the Equator (on higher latitudes) goes on
decreasing according to their distances from the Equator. Hence, the
temperature of a place depends on its latitude.
ALTITUDE OR HEIGHT ABOVE SEA LEVEL
Yet the temperature does not depend on latitude alone. Mt. Kenya in East
Africa is on the Equator. Yet its peak is always covered under snow, because
it is over 5000 meters above sea level. Bermuda islands are situated at 30°
N latitude in the Atlantic Ocean, over 3200 km from the Equator. These
islands never have snowfall. Bangalore and Chennai as well as Ludhiana and
Shimla respectively in South and North India are situated on two different but
same latitudes. Yet both Bangalore and Shimla remain cooler than Chennai
and Ludhiana respectively because of their higher altitude. It is because the
atmosphere is not directly heated by the Sun's rays. First, the Sun's rays
heat the earth's surface then, the lower atmosphere is heated by conduction
from the earth. Close to the earth's surface, the layers of air are denser than
at higher altitudes. So the temperature nearer the earth's surface is more
than that higher up. Thus, as we go to higher altitudes, the temperature goes
on decreasing. In general, on climbing every 166 meters, there is fall of 1°C
in temperature (or a fall of 1°F for every 300’. This is known as normal lapse
rate. Hence, if the temperature at a place at sea-level is 26°C, then at the
top of a mountain of 1,660 meters height the temperature will be 16°C
approximately). We can draw a conclusion that temperature of an object or
of a place does not depend only on the amount of heat which it receives but
also upon the amount of heat it loses. If an object loses more heat than the
heat received from the Sun, it gets colder and its temperature falls and the
vice-versa. An elevated plateau received more heat than a piece of low
ground because Sun's rays have crossed a lesser thickness of atmosphere to
reach it. But loss of heat is rapid from the clearer, dust-free rarefied air of the
plateau than from the low ground. In the low area the air is dense and dust
particles as well as water vapors are more helping greater retention of heat.
The result is that elevated areas remain colder of the two. However, in
mountain regions, at times, the temperature is less in valleys than at greater
heights. It occurs particularly on calm, cold winter nights, when the sky is
clear and the air very dry. Because of these conditions, the heat from the
earth's surface and the lower layer of the atmosphere escapes rapidly back
into space, making the upper slopes warmer. The cold is further increased by
the sinking of the cool air from the mountain sides. Thus, there is a reversal
in the vertical distribution of temperature. This is known as the Inversion of
Temperature. This phenomenon is very common in the mid-latitude regions.
Due to this, the fruit-growers have their orchards on the upper slopes of the
hills.
DISTANCE FROM THE SEA
At seaside in summer, water is cool and the sand nearby is hot though each
is receiving the same amount of heat from the Sun. Why? Land and water
differ in their behavior when heated. Sun's rays pass through water to a
great depth as water is transparent. Water is also mobile and so the warm
water mixes easily with the cold water. Because of these reasons, the water
is neither heated not cooled quickly. Its temperature rises very slowly. In
contrast to this, the Sun's rays heat a piece of land more rapidly because the
heat obtained by the piece does not mix with other pieces or layers of land.
Therefore the land gets heated or cooled more quickly than water. So during
the day, the land is hotter than the sea. The heated air over the land
becomes lighter and rises. This creates a low pressure area over the land. At
this time, the air above the sea is cooler. When this air blows towards the low
pressure area over the land, it lowers the temperature of the air on land. This
is known as Sea Breeze. This sea breeze has a moderating influence on
coastal regions. During the night, conditions are just the reverse. At this
time, the sea remains warmer than the land. So the land breeze blows from
the land to the sea, and relieves the cold of the land. The areas, close to the
sea have lower daily and annual ranges of temperatures.
OCEAN CURRENTS
Ocean currents also affect the temperature of a place. These ocean currents
may be warm or cold. When the winds blow over them, they get their
warmth or cold and affect the temperatures of coastal areas. The warm
North Atlantic Drift raises the winter temperature of North-West Europe,
especially those of the British Isles and Norway. Because of the influence of
the Warm Drift, the port of Bergen (about 60°N) in Norway remains open
during the winter season, whereas ports on the north-east coast of Canada,
located in the same latitudes, remain frozen for several months because of
the influence of the cold Labrador Current. But it should be noted that cold
currents have less effect upon temperature, because they usually lie under
off-shore winds. However, there are exceptions like the on-shore wind
blowing over the cold Labrador Current, and the cold Beguile Current. But
the cool Canaries has little cooling effect in summer on the coast of Iberian
Peninsula (Portugal and Spain), because at that time that region comes
under the influence of off-shore north-east trade winds. In those areas,
where the warm and cold current meet, the temperature falls below the dew-
point, giving rise to foggy conditions. The mixing of warm moist air over
Labrador Current causes dense fogs in the neighborhood at the Grand Bank
of New Found land and at the mouth of the St. Lawrence. The fogs extend
several kilometers in land, reduce visibility and hinder communication.
WINDS
Prevailing Winds: Winds indirectly change the temperature of a place in the
neighborhood of sea or according to the areas from which they blow. The
prevailing winds, in temperate latitudes, coming from the land area lower the
temperature in winter and raise it in summer. In contrast, the prevailing
winds coming from the sea areas raise the winter temperatures, but lower
the summer temperatures. In winter, central and northern parts of China get
winds from cold Central Asia, and, therefore, their temperatures are
sufficiently lower than those of other places lying in the same latitudes
elsewhere. The high Himalaya does not allow the cold central Asian winds to
cross towards the northern plains of India. Calcutta and Guangzhou (South
China) are both on the same latitude. But the January temperature of
Calcutta to the south of Himalaya is about 20°C while that of Guangzhou to
its north is 14°C.
Local Winds: Several local winds bring a marked change in the temperature.
During the day the land is hotter than the sea. The heated air over the land
becomes lighter and rises. This creates a low pressure area over the land. At
this time, the air above the sea is cooler. When this air blows towards the low
pressure area over the land, it lowers the temperature of the air on land. This
is known as Sea Breeze. This sea breeze has a moderating influence on
coastal regions. During the night, conditions are just the reverse. At this
time, the sea remains warmer than the land. So the land breeze blows from
the land to the sea, and relieves the cold of the land. The areas, close to the
sea have lower daily and annual ranges of temperatures.
In the plains of northern India, the hot wind, called Loo, blowing from
Rajasthan makes western U.P. very hot. Every year, in the summer season, it
is the cause of sun-stroke to thousands of people. The warm dry Chinook
wind, blowing across the Rocky Mountains from the west, causes a
considerable rise in temperatures in the Central Plains of the U.S.A. This wind
gets warmed up, when it descends along the eastern or leeward slopes of
the Rocky Mountains. Like the Chinook, the Cohen also is a warm dry
descending wind. It blows across the Alps down the northern or leeward
slopes in winter. When it descends down the mountain slopes, it warms up.
The Hamates, a dry wind that blows over North-West Africa from north-east
areas, brings relief to those areas from the damp heat of the tropics.
Although full of dust, it is welcomed by the people. It is known as the
'Doctor'. The Sirocco, hot dry wind blowing from the Sahara to the
Mediterranean, is most unpleasant. When this wind crosses the
Mediterranean Sea, it picks up sufficient moisture. This makes it an
oppressively hot moist wind. Its scorching nature brings a great loss to
vegetation and crops. The Mistral and the Bora are the cold winds which blow
from the north of Europe. The Mistral is taken as the violent wind in the lower
Rhone Valley and across the Mediterranean coast up to Genoa. It often
causes the winter temperature to fall below freezing point. The Bora occurs
in winter, when the atmospheric pressure over continental Europe is more
than that over the Mediterranean Sea. This is a dry and very cold wind. It is
more violent than the Mistral.
CLOUDS
Clouds in the sky also affect the temperature of a place. The presence of
clouds in the sky prevents the amount of solar radiation coming to the
earth's surface. It also prevents the ground radiation, leaving the earth's
surface. Because of this, the places, where clouds are less, experience a high
day temperature (more than 38°C) and a much lower night temperature
(less than 21°C). Such is the condition in deserts. In the equatorial areas,
because of the abundance of cloud cover, day temperatures are not so high
and night temperatures not so low.
SLOPE OF THE LAND
The effect of slope of the land is not so much noticed in the tropical areas,
because in those latitudes the mid-day Sun is always high in the sky, and its
rays fall more or less vertically over the whole land. But in temperate
latitudes its effect is noticed significantly. In these latitudes, the Sun facing
slope of mountains that are more or less parallel to the equator gets warmer
than the land sloping away from the Sun or towards the Poles. This is
because the slope facing the Sun will get more or less vertical rays, whereas
the slope away from the Sun will get slanting rays. In the Northern
Hemisphere, the land, having its slope towards the south, is warmer than the
land having its slope towards the north. In the Southern Hemisphere the
position is just the reverse. In mountain regions, as for example, of the
Himalaya, as soon as the Sun rises, it starts warming the south facing slopes.
It favors the creation of human settlements and orchards or croplands along
these slopes.