Atmosphere and Winds: Layers, Pressure Belts and Jet Streams

The correct answer is B, the stratosphere. Ozone is concentrated in the lower and middle stratosphere, and because it absorbs ultraviolet radiation the temperature of this layer rises with height instead of falling. The same absorption shields life at the surface from harmful radiation, and the stability of the layer makes it free of cloud and turbulence, so aircraft fly in its lower part.

Option A, the troposphere, is the layer of weather, where temperature falls with height and where all cloud and rain occur. Option C, the mesosphere, lies above the stratosphere; it holds very little gas, has the lowest temperatures in the atmosphere and is where meteors burn up. Option D, the thermosphere, is much higher still and is known for its ionised layers that reflect radio waves, not for ozone.

The correct answer is A, about 6.5 degrees Celsius per kilometre. This is the average rate at which air temperature falls as one rises through the troposphere, and it explains why hill stations are cooler than the plains and why high peaks carry snow even in the tropics.

Option B is far too small and would leave the top of the troposphere warmer than it is. Option C is close to the dry adiabatic rate at which a parcel of rising air cools by expansion, which is a different idea from the lapse rate of the still atmosphere and is the commonest trap here. Option D is the same figure as the correct one with the decimal point moved, a deliberate distractor; note also that the lapse rate is an average, and on a cold clear night an inversion can make temperature rise with height near the ground.

The correct answer is B, the mesosphere. Although the air there is thin, it is dense enough to heat a body moving at cosmic speed by friction, so most meteors glow and are destroyed in this layer and are seen from the ground as shooting stars. The mesosphere also contains the coldest point of the atmosphere, the mesopause, at its top.

Option A, the stratosphere, lies below the mesosphere; by the time a meteor reaches that height it has usually burnt out. Option C, the thermosphere, lies above it and is so thin that although individual molecules are very energetic, there is not enough air to destroy an incoming body. Option D, the exosphere, is the outermost fringe where the atmosphere merges into space and where satellites orbit with almost no resistance.

The correct answer is B, nitrogen, which makes up about 78 per cent of dry air by volume. It is comparatively inert, so it dilutes oxygen and slows combustion, and it enters living things mainly through the nitrogen cycle in which bacteria fix it in a usable form.

Option A, oxygen, is second with about 21 per cent; it is essential for respiration and combustion, but a candidate who answers from importance rather than from quantity gets the question wrong. Option C, argon, is the most abundant of the inert gases in air at a little under one per cent. Option D, carbon dioxide, is only about four hundredths of one per cent, yet it matters out of all proportion to its quantity because it absorbs outgoing heat and drives the greenhouse effect, and its share is rising.

The correct answer is A, the eastern slopes of the Rockies. The wind is the Chinook. It descends the leeward slope, is compressed and warmed as it sinks, and can raise the temperature sharply in a few hours; it melts or evaporates the snow cover, which is why herders call it the snow eater and why it is valued for exposing the grass for cattle.

Option B is the home of the Foehn, a wind of exactly the same type and origin, but the name asked for here is the Chinook, and mixing the two is the standard trap. Option C is where the Zonda blows down from the Andes. Option D is the source region of the Sirocco, a hot and dusty wind that crosses the Mediterranean from the Sahara, which is not a descending mountain wind of this kind.

The correct answer is A, the Loo. It is a strong, hot and dry wind that blows during the day over the plains of north India and Pakistan in the peak of summer, raising temperatures sharply and causing heat stroke, and it dies down after sunset. It is a local wind of the hot weather season, and the arrival of the monsoon ends it.

Option B, the Foehn, is a warm dry wind of the Alps caused by air descending a mountain slope. Option C, the Mistral, is a cold and dry wind that blows down the Rhone valley of France towards the Mediterranean. Option D, the Bora, is another cold wind, blowing from the north-east over the Adriatic coast. The last two are examples of cold local winds and are used as distractors because students memorise the names without the temperature.

The correct answer is A, Ferrel's law. It states the deflection produced by the rotation of the earth, the Coriolis effect, which turns every freely moving body to the right of its path in the northern hemisphere and to the left in the southern. The deflection is zero at the equator and increases towards the poles, which is why cyclones do not form very close to the equator.

Option B, Buys Ballot's law, is related but different: it says that if you stand with your back to the wind in the northern hemisphere, low pressure lies to your left and high pressure to your right. Option C is not a law of this kind; Hadley is remembered instead for the Hadley cell of tropical circulation. Option D, Charles's law, belongs to physics and relates the volume of a gas to its temperature at constant pressure.

The correct answer is A, the Mistral. It is a cold, dry and often violent wind that blows from the north down the Rhone valley of southern France to the Gulf of Lion, chilling the coast and damaging crops, which is why orchards there are protected by lines of trees and walls.

Option B, the Sirocco, is hot and dusty and blows from the Sahara northwards across the Mediterranean, arriving in Italy as a sultry, dust laden wind. Option C, the Harmattan, is a dry wind that blows from the Sahara over West Africa and is welcomed there as the doctor because it brings relief from damp heat. Option D, the Khamsin, is a hot southerly wind of Egypt. Only the Mistral in this list is a cold wind, and the region named in the question settles it.

The correct answer is B, the doldrums. Strong heating at the equator makes the air expand and rise, so surface pressure is low and horizontal winds are weak; sailing ships were often becalmed there. The rising air cools, condenses and gives the heavy convectional rainfall of the equatorial belt, and the zone where the trade winds of the two hemispheres meet here is the inter-tropical convergence zone.

Option A, the horse latitudes, is also a belt of calms but it lies near thirty degrees in the sub-tropical high pressure belt, where air sinks and the weather is dry. Option C, the roaring forties, names the strong westerlies of the southern ocean, the opposite of calm. Option D, the polar high, is the belt of cold heavy air over the poles from which the polar easterlies blow out.

The correct answer is C, the tropical easterly jet. In summer, as the subtropical westerly jet withdraws to the north of the plateau of Tibet, an easterly jet stream forms in the upper air over peninsular India and blows from east to west. Its appearance goes with the burst of the south-west monsoon, and its strength is linked by meteorologists to the performance of the monsoon.

Option A, the polar front jet, blows in the upper air above the meeting of polar and tropical air in the middle latitudes and is not a feature of the Indian peninsula. Option B, the subtropical westerly jet, lies south of the Himalaya in winter and brings the western disturbances; it is present in the Indian region, but in the cold weather season, not in the monsoon. Option D, the polar night jet, forms in the winter stratosphere over the polar regions.