Climate & Monsoon — PPSC previous year questions

Winter rain over Punjab, Haryana and the rest of north-western India comes from western disturbances — extra-tropical cyclones that originate over the Mediterranean and travel east on the westerly jet stream. This rain is vital for the rabi wheat crop. The north-east (retreating) monsoon brings winter rain to Tamil Nadu and the Coromandel coast, not the north-west, and there is no 'north-west monsoon' in India.

Rainfall in Rajasthan increases from west to east: Jaisalmer and the western desert districts get under 20 cm a year, while the eastern districts of Jhalawar, Kota and Banswara get 60–100 cm, so eastern Rajasthan is wetter than western Rajasthan and (b) is true. Cotton grows best on black soil but is also grown widely on the alluvial soils of Punjab and Haryana and on red soils in the south, so (a) is wrong. Tamil Nadu gets its winter rain from the retreating north-east monsoon; western disturbances affect north-west India, not Tamil Nadu, so (c) is wrong. The Thar is not wholly sandy — it also has rocky hill outcrops, gravelly plains and salt lakes such as Sambhar — so (d) is wrong.

Fresh snow has the highest albedo of the surfaces listed, reflecting 80-90 per cent of incoming sunlight. Grassland and crops reflect about 20-25 per cent, tropical forest around 10-15 per cent, and a dark roof absorbs most radiation.

Western Disturbances are low-pressure systems that form over the Mediterranean Sea, travel east on the westerly jet stream and give winter rain and snow to Punjab, Haryana and the western Himalaya, which helps the wheat crop.

The daily (diurnal) range of temperature is greatest in continental interiors. Dry air and clear skies let the land heat fast by day. At night it loses heat fast by radiation. No sea is near to moderate it. As in the Thar or Sahara deserts. Coastal areas and small islands have small ranges. Sea breezes and water's high specific heat keep them steady. High summits stay cold all day.

Both statements have the deflection direction backwards. In the Ferrel cell, surface winds moving poleward are deflected eastward by the Coriolis force, which is why the mid-latitude westerlies blow from west to east. In the Hadley cell, surface winds moving towards the equator are deflected westward, producing the north-east and south-east trade winds.

Both statements are correct. Earth's axis is tilted about 23.5° to the plane of its orbit. So the angle at which the Sun's rays strike a place changes through the year as Earth goes round the Sun. Their intensity changes too. This gives us the seasons. Earth's orbit is only slightly elliptical, with perihelion in early January and aphelion in early July. The effect of this small change in distance is far smaller than the effect of the axial tilt. That is why the Northern Hemisphere has summer when Earth is farthest from the Sun.

The lapse rate is the rate at which temperature falls with increasing altitude in the troposphere — about 6.5 °C per 1,000 m (the normal lapse rate). It is why hill stations are cooler than the plains. Latitude, seasonality and vegetation also influence temperature but are not described by the lapse rate.

Earth reflects about 30% of incoming sunlight straight back to space (this share is called the planetary albedo). The remaining 70% is absorbed by the atmosphere, land and oceans and drives the water cycle, weather and photosynthesis.

All four are standard clues to past climate, called proxy records. Tree-ring widths show good and bad growing years, pollen and micro-organisms in lake and sea mud show what grew there, fossils and rock types reveal ancient conditions, and air bubbles trapped in ice cores preserve samples of the old atmosphere.