For the past few days, Chandigarh and its neighbouring states have been experiencing unusually cold days although the night temperatures are normal.

Try this PYQ:

Consider the following statements:

1. The winds which blow between 30°N and 60°S latitudes throughout the year are known as westerlies.
2. The moist air masses that cause winter rains in the North-Western region of India are part of westerlies.

Which of the statements given above is/are correct?

(a) Only 1

(b) Only 2

(c) Both 1 and 2

(d) Neither 1 nor 2

Temperature anomaly in North

• Meteorological officials have attributed the trend to the cloud cover in the region which was absent until a few days ago.
• It is the result of a western disturbance, which has brought about a spell of precipitation in the northwest Himalaya.

Role of clouds

• During the day, clouds obstruct the heat from the sun from reaching the surface of the earth, reflecting some of it back into space.
• This lowers the temperature. Cold winds blowing down from snow-bound areas in the mountains also contribute to the cooling effect.
• At night, however, clouds act like blankets – they help retain some of the heat energy radiated back by the earth’s surface.
• Overcast weather at night, thus, increases greenhouse warming.

What are western disturbances?

• In northern India, winter rains and clouds are generally caused by moisture-bearing wind systems called western disturbances.
• They originate and gather moisture over the Mediterranean region and flow eastwards towards the Indian subcontinent.
• When some of these winds run into mountains of the northwest Himalaya, they are forced upward.
• At higher altitudes, the temperatures drop and water vapour gets condensed. This leads to cloud formation and eventually rain and snow.

Other factors for severe winters in North

• In north India, the huge temperature difference between summers and winters is due to its continentality (distance from seas and oceans).
• Air from oceans moderates the temperature as it moves onshore, but this effect is missing in continental interiors.
• As a result, north India has greater seasonal differences as compared to peninsular India.
• Temperature also reduces rapidly with altitude, and thus, the Himalayan region is colder still.

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