Topics Covered in this Lecture
Two conditions are necessary-
Example- Mumbai – Pune
Mangalore – Bangalore
Example 1 – A narrow strip running parallel to western Ghats on its leeward side is drought prove due to the Rainshadow effect of Western Ghats.
2 – Leh- Ladakh is deserts due to rain shadow effect of Himalayas.
3 – Patagonia desert due to rain shadow effect of Andes.
Note- Cyclonic Rain is covered under the topic “Cyclone”.
Topics Covered in this Lecture
Air pressure is the height of the column of air on a substance. It is also known as barometric pressure. Air pressure is maximum at the sea level (0km). In climate, pressure is inversely related to temperature.
There are two warm air rises causing low pressure while cold types of pressure conditions:-
Warm air rises causing low pressure while cold denser air decent causing high pressure.
Winds always flow from high pressure to low pressure. The greater the difference between high pressure and low pressure greater is the speed of wind.
It is the zone of mixing of two different winds that is cold polar easterlies and warm westerlies and hence, it is known as zone of fronts. The low pressure is created as the winds are forced to rise from these latitudes.
There are three types of winds are as follows:
Wind always flow from high pressure to low pressure. Greater the difference between high pressure and low pressure is greater is the speed of wind.
As per the coriolis effect, the objects , winds, ocean currents are deflected to the right in northern hemisphere and they are deflected to the left in southern hemisphere Coriolis force is inversely proportional to the rotational speed of the earth.
As the rotational speed of earth is maximum at the equator therefore Coriolis force is 0 at the equator and it is maximum at the poles.
Reduces the wind speed. Since there is no friction in the upper air, they move with great speeds. example: jet streams.
It is the fourth factor and it is permanent winds or planetary. “The control release from the dams would have release the gravity of the calamity” sugar an industry>loss>no new investment because demand is constant and production sugarcane mills>loss.
They flow from subtropical high pressure to the equatorial low-pressure belt. The coverage at the equatorial low-pressure belt and therefore this belt is ITCZ (Inter Tropical Convergence Zone).
Note: why deserts are located in the western side of the continent?
The trade winds are onshore on the eastern sides of the continent and therefore they give rainfall mostly throughout the year. Depending upon the rainfall the trade wind zone is divided into-
example: madagascar, brazil, carribian etc.
roaring 40s @40-degree South
furious fifties @50- degree South
shrieking sixties @60-degree South
Extremely cold, dusty(show) winds which are lethal are polar easterlies.
(It refers in Indian geography)- see the topic in Indian geography
The word monsoon means a complete reversal in wind direction. Monsoon type of climate is present In south Asia, mainland Southeast Asia which includes- Myanmar, Thailand, and French East India-
When the sun is in the northern hemisphere, the sun is vertically overhead over the tropic of cancer. This results in heating of south and southeast Asia, developing low pressure over this region. After 21st June, ITCZ shifts and becomes parallel to the foothills of the Himalayas because low pressure or heating is intensified. On the other hand, in the southern hemisphere, there is winter season and high pressure. This causes the winds to originate over the Australian region. These winds after crossing the equator are deflected to the right due to Coriolis force and approach India as the southwest monsoon as these winds are onshore they give rainfall.
With the shifting of the
Sun to the southern hemisphere, ITCZ shifts to the south, and hence the southern hemisphere starts experiencing the summer season. on the other hand, due to extremely cold temperatures or climate, high pressure develops over India. This causes the winds to originate over the high-pressure center as the northeast monsoon. Since these originate except some winds which pick up moisture from the Bay of Bengal and give rainfall to the Coromandel coast (TN COAST).
These are diurnal or daily winds. During the day sea breeze as the land is more heated compared to the sea. During the night time, land losses the heat more quickly develops high pressure and therefore land breeze flows from land to the sea.
During the day the upper slopes of mountains are heated, developing low pressure hence winds flow from valley to mountains top as valley breeze. On other hand during the might time, winds flows from the slopes into the valley, because the mountains slopes will loose the heat quickly. While the valley floors are comparatively warmer. Mountain breeze responsible for temperature.
Hot/warm local winds
cold local winds
It is a local wind which flows along the eastern slopes of the rockees, while descending it gets heated and raises the temperature so during the winter season arrival of chinook causes melting of snow and hence the name is snow eater. Similar mind which blows on the northern slopes of the alps is known as fohn.
Agriculture is possible throughout the year in the narrow slopes along the foothills of rockees.
Because of fohn Switzerland is climatic oasis of Europe.
Extremely hot and hyper arid winds which originates in Sahara desert and flow towards the western coast of Africa is known as harmattan. With the arrival of harmattan excessive humidity is removed from this region making life easier and hence they are doctor winds.
Warm and dusty winds that originates from the Sahara Desert and flow toward the Mediterranean Sea are known as Sirocco. These winds pick up moisture from the Mediterranean Sea and give rainfall to the southern part of Spain, France, and
Italy. Along with the rain, red-colored sands fall and hence people call it blood rain. Sirocco has also various names:
Khasmin in Egypt
Ghibil in Libya
Chilli in Tunasia
Laventer in Spain
Simoon in Arabia
Sirocco us harmful for agriculture.
Very high velocity winds which originate from the Alps and flows toward the Mediterranean Sea is Mistral. Mistral after entering a narrow valley of River Rhone attains a strong force causing disruptions in the communication network in Southern Europe. Hence, North facing houses are avoided in Europe.
A cold wind which blows along the Adriatic Sea. It picks up moisture from Adriatic Sea and give precipitation in Italy.
Extremely cold, dusty (full of snow), lethal wind which is an extension of polar easterlies during the winter season is known as Blizzard. It is known as Norther in USA and Canada. Burran in Siberia.
Monsoon shower along the western coast of India due to localised pressure differences is either known as Mango shower because they help in early ripening of mangoes or blossom showers because they help in blossoming of coffee plantation in Karnataka and Kerala.
Kal Baisakhi are local thunderstorms associated with violent winds, torrential downpours, often accompanied by hail. Loo These are strong, gusty, hot, dry winds blowing during the day over the North and North-Western India. Sometimes they even continue until late in the evening.
The pressure belts occupy their original position only during the equinox while they shift with the northward and southward movement of the sun. Mediterranean type of climate is an outcome of the shifting of pressure belts. The climate is located in-
This region comes under the influence of offshore trade winds during the summers and hence experiences dry climatic conditions. But, during the winters, as all the pressure belts move to the South, this area comes under the influence of onshore westerlies giving rainfall. Hence, Mediterranean type of climate is famous for dry summers, but moist winters.
Here, Sclerophyll vegetation dominates. In this, plants have natural insulating layer which doesn’t allow air to penetrate.