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WBCHSE HS Geography study materials
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WBCHSE HS Geography practice questions

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Question 1Geomorphology and lithosphere

Which seismic discontinuity separates the Earth's crust from the mantle?

  1. Lehmann discontinuity
  2. Repetti discontinuity
  3. Mohorovičić discontinuity Correct answer.
  4. Gutenberg discontinuity

Explanation

The Mohorovičić discontinuity, usually called the Moho, is the boundary where P-wave velocity jumps from about 7 km/s in the crust to about 8 km/s in the mantle. The Gutenberg discontinuity separates the mantle from the core, and the Lehmann discontinuity lies between the outer and inner core.

Question 2Geomorphology and lithosphere

Which characteristic is typical of intrusive igneous rocks such as granite?

  1. They form by compaction of plant remains under swamps
  2. They cool slowly at depth and develop coarse crystals Correct answer.
  3. They are produced by regional metamorphism of limestone
  4. They solidify rapidly at the surface and are always glassy

Explanation

Intrusive igneous rocks crystallise from magma below the surface, where slow cooling allows large mineral crystals to grow, as in granite. Extrusive rocks cool quickly at the surface and are fine-grained or glassy; coal is organic sedimentary and marble is metamorphic.

Question 3Geomorphology and lithosphere

Which landform is produced where a river loses velocity on entering a standing body of water?

  1. Levee
  2. Alluvial fan
  3. Oxbow lake
  4. Delta Correct answer.

Explanation

When a river enters a sea or lake, its velocity falls abruptly and the sediment load is deposited at the mouth, building a delta. Alluvial fans form on land where a steep stream debouches onto a plain, while oxbow lakes and levees are floodplain features.

Question 4Geomorphology and lithosphere

The matching of glacial till deposits and striation directions across southern continents is best explained by which concept?

  1. Sea-floor spreading at the Mid-Atlantic Ridge
  2. Convection currents in the outer core
  3. Isostatic rebound following deglaciation
  4. Continental drift of Gondwana fragments Correct answer.

Explanation

Similar late Palaeozoic glacial deposits and striation directions occur in South America, Africa, India, Australia and Antarctica, which are now widely separated. Alfred Wegener used this and other evidence to argue that these landmasses once formed the supercontinent Gondwana and later drifted apart.

Question 5Geomorphology and lithosphere

In a cold highland region, repeated freeze-thaw cycles break granite into angular blocks. This process is best described as which type of weathering?

  1. Exfoliation caused by unloading
  2. Chemical weathering by carbonation
  3. Biological weathering by root wedging
  4. Mechanical weathering by frost shattering Correct answer.

Explanation

Water expands on freezing and exerts pressure within joints; repeated freeze-thaw cycles prise the rock apart into angular blocks, a process called frost shattering or block disintegration. Carbonation is a chemical process on limestone, root wedging is biological, and exfoliation is pressure-release sheeting.

Question 6Geomorphology and lithosphere

In limestone regions, surface drainage is often sparse and sinkholes are common. Which process best accounts for this?

  1. Chemical solution of calcium carbonate by carbonic acid Correct answer.
  2. Hydraulic action of waves along the coast
  3. Mechanical abrasion by wind-blown sand
  4. Plucking of bedrock by glacier ice

Explanation

Rainwater absorbs carbon dioxide to form weak carbonic acid, which dissolves calcium carbonate along joints and bedding planes in limestone. This solution weathering enlarges fissures into sinkholes and underground caverns, so surface streams often disappear underground.

Question 7Geomorphology and lithosphere

A glacial trough with a tributary valley entering high above the main floor indicates which feature?

  1. A misfit stream cut by later river action
  2. A hanging valley formed by unequal glacial erosion Correct answer.
  3. A kame terrace built at the ice margin
  4. An esker deposited by a subglacial stream

Explanation

The trunk glacier deepens its floor more than the smaller tributary glacier, so after ice retreat the tributary floor stands above the main trough as a hanging valley, often with a waterfall. Misfit streams are underfit rivers, eskers are ridges of stratified sand and gravel, and kames are mounds of meltwater deposits.

Question 8Geomorphology and lithosphere

P-waves from an earthquake are recorded first at a distant seismograph because they have which property?

  1. They consist of transverse vibrations that travel fastest
  2. They are surface waves that follow the ground surface
  3. They cannot pass through the liquid outer core
  4. They travel as compressional waves with the highest velocity Correct answer.

Explanation

P-waves are compressional (longitudinal) body waves and have the highest velocity of all seismic waves, so they reach a distant station before S-waves and surface waves. S-waves are transverse and cannot pass through the liquid outer core, while surface waves travel most slowly.

Question 9Geomorphology and lithosphere

A shield volcano is built from fluid basaltic lava, whereas a composite cone has steep slopes and explosive eruptions. Which pair of factors best explains this contrast?

  1. Age of the volcano and its latitude
  2. Grain size of the surrounding rock and rainfall
  3. Silica content of the magma and its gas content Correct answer.
  4. Rate of isostatic uplift and coastal erosion

Explanation

Basaltic magma is low in silica, so it is fluid and allows gas to escape quietly, producing broad shield volcanoes with gentle slopes. High-silica magma is viscous and traps gas until pressure builds up, giving explosive eruptions and steep composite cones.

Question 10Geomorphology and lithosphere

According to the concept of isostasy, which situation would cause regional uplift of a continental block?

  1. Erosion and removal of mass from the block Correct answer.
  2. Addition of a thick ice sheet over the block
  3. Cooling and contraction of the block
  4. Deposition of sediment on the block

Explanation

Isostasy is the gravitational balance of lithospheric blocks floating on the denser mantle. Removing mass by erosion lightens a continental block and causes it to rise, whereas loading by ice or sediment causes subsidence.

Question 11Geomorphology and lithosphere

The asthenosphere is important in plate tectonics mainly because it

  1. forms the root of continental mountain belts
  2. is a rigid layer that snaps during shallow earthquakes
  3. is a weak, plastic layer beneath the plates Correct answer.
  4. is composed mainly of liquid iron and nickel

Explanation

The asthenosphere lies within the upper mantle and is weak enough to deform plastically over long periods. This allows the rigid lithospheric plates above it to move. It is not the liquid outer core, nor is it the rigid crust.

Question 12Geomorphology and lithosphere

Which metamorphic rock forms when limestone is subjected to heat and pressure?

  1. marble Correct answer.
  2. gneiss
  3. quartzite
  4. slate

Explanation

Limestone is composed mainly of calcium carbonate; under heat and pressure it recrystallises into marble. The other rocks listed have different parents: slate comes from shale, quartzite from sandstone and gneiss from granite or other high-grade precursors.

Question 13Geomorphology and lithosphere

On a meander bend, the fastest current and maximum erosion occur along which part of the channel?

  1. the concave outer bank, where flow is fastest Correct answer.
  2. the convex inner bank, where flow is slow
  3. the point bar, where sediment accumulates
  4. the centre of the channel, where turbulence is least

Explanation

On a meander bend, centrifugal force pushes the fastest flow towards the concave outer bank, where undercutting is strongest. The convex inner bank receives slower flow and accumulates a point bar. The thalweg therefore lies near the outer curve.

Question 14Geomorphology and lithosphere

In a barchan dune, the crescent-shaped horns point in which direction relative to the prevailing wind?

  1. across the prevailing wind, owing to helical flow
  2. downwind, past the steep slip face Correct answer.
  3. straight upward, because of strong vertical eddies
  4. upwind, where sand piles against the windward toe

Explanation

A barchan is a crescent-shaped dune with a gentle windward slope and a steep leeward slip face. The horns are the trailing arms of the crescent and extend downwind beyond the slip face. They do not point upwind or across the wind.

Question 15Geomorphology and lithosphere

A cirque is best described as which glacial landform?

  1. a deep, narrow inlet formed by a drowned glacial trough
  2. an armchair-shaped hollow at the head of a glacial valley Correct answer.
  3. a long ridge of till along the side of a glacier
  4. a mound of stratified sand and gravel deposited by meltwater

Explanation

A cirque is a steep-backed, armchair-shaped hollow carved at the head of a glacier by plucking and abrasion. A lateral moraine is a ridge of till at the valley side, a fjord is a drowned glacial trough, and an esker is a meltwater ridge.

Question 16Geomorphology and lithosphere

A spit forms where longshore drift

  1. carries sediment across a bay where the coast bends Correct answer.
  2. moves sediment offshore during a storm surge
  3. deposits material at a river mouth, building a delta
  4. erodes a cliff base and leaves a wave-cut notch

Explanation

Longshore drift moves sediment along the shore in the direction of the dominant waves. Where the coastline bends or a bay opens out, the drift continues across the gap and deposits a ridge of sand and shingle: a spit. A delta forms at a river mouth, and a wave-cut notch is erosional.

Question 17Geomorphology and lithosphere

An artesian well flows without pumping when which condition is met?

  1. the well is drilled into an unconfined sandy aquifer
  2. the aquifer lies between impermeable beds and is dry
  3. a confined aquifer is recharged above the well head Correct answer.
  4. the well reaches a shallow water table that rises after rain

Explanation

In a confined aquifer, water is held under pressure between impermeable layers. If the recharge area is higher than the well head, the piezometric surface stands above ground and water flows out without pumping. An unconfined aquifer is drained by the water table and normally needs a pump.

Question 18Geomorphology and lithosphere

At an ocean-continent convergent boundary, such as the Andes margin, which pair of features is typically produced?

  1. a mid-ocean ridge and a rift valley
  2. a broad continental shelf and a barrier island
  3. a deep ocean trench and an inland volcanic chain Correct answer.
  4. a transform fault and a linear island chain

Explanation

Where oceanic lithosphere subducts beneath continental lithosphere, a deep trench marks the down-going plate and a volcanic mountain chain rises inland above the magma source. This is the Andes-type margin. Mid-ocean ridges and rift valleys form at divergent boundaries, not convergent ones.

Question 19Geomorphology and lithosphere

Horizontal sedimentary layers rest on tilted, eroded older strata. Which sequence of events does this relationship indicate?

  1. tilting, deposition, folding, then igneous intrusion
  2. deposition, tilting, erosion, then renewed deposition Correct answer.
  3. erosion, deposition, metamorphism, then folding
  4. deposition, metamorphism, erosion, then tilting

Explanation

An angular unconformity records older strata that were tilted, uplifted and eroded before younger horizontal layers were laid down on the erosion surface. The sequence is therefore deposition, tilting, erosion, then renewed deposition. Intrusion or metamorphism would leave additional cross-cutting or foliation evidence.

Question 20Geomorphology and lithosphere

A river's long profile shows a sharp break in slope, called a knickpoint. Which interpretation is most reasonable?

  1. the river is building a delta at its mouth
  2. the river has reached a graded profile and stopped eroding
  3. the river is carrying only suspended load after velocity falls
  4. the river is rejuvenated after base level falls or land rises Correct answer.

Explanation

A knickpoint is a break in the river's long profile that commonly marks rejuvenation after a fall in base level or uplift of the land. The new, steeper gradient migrates headward, eroding the older profile. A graded river would have a smooth, concave-up profile without such a sharp break.

Question 21Geomorphology and lithosphere

New oceanic lithosphere is continuously generated along which type of plate boundary?

  1. Transform boundary
  2. Convergent boundary
  3. Divergent boundary Correct answer.
  4. Passive continental margin

Explanation

At a divergent boundary, such as a mid-ocean ridge, hot asthenospheric mantle rises, decompresses and partially melts. The melt cools to form new basaltic oceanic crust, and the two plates move apart in a process called sea-floor spreading. Convergent boundaries consume lithosphere, transform boundaries produce horizontal slip, and passive margins are not active plate boundaries.

Question 22Geomorphology and lithosphere

In a hot, humid tropical region, granite weathers to a clay-rich saprolite. Which chemical weathering process chiefly converts feldspar into clay minerals?

  1. Oxidation
  2. Salt crystallisation
  3. Hydrolysis Correct answer.
  4. Carbonation

Explanation

Hydrolysis is the reaction of silicate minerals such as feldspar with water and hydrogen ions, which breaks down the crystal framework and produces clay minerals together with soluble ions. Oxidation mainly attacks iron-bearing minerals, carbonation acts on carbonate rocks such as limestone, and salt crystallisation is a physical weathering process.

Question 23Geomorphology and lithosphere

A waterfall commonly develops where a river flows across which arrangement of rock?

  1. A uniform bed of resistant rock
  2. A broad, flat floodplain of alluvium
  3. A single thick band of impermeable clay
  4. Alternating bands of resistant and weak rock Correct answer.

Explanation

A waterfall typically forms where a river crosses from a resistant rock band onto a weaker one. The weaker rock is eroded more rapidly, creating a steep step and a plunge pool, and the fall retreats upstream as the resistant caprock is undermined. Uniform resistant rock tends to favour rapids or gorges, while alluvium is an unconsolidated depositional material.

Question 24Geomorphology and lithosphere

A chain of volcanic seamounts in the Pacific shows progressively older rocks to the northwest. Which interpretation best explains this pattern?

  1. Alternating slip along a major transform fault
  2. Plate passage over a fixed mantle plume Correct answer.
  3. Rifting of a continent that then drifted northwest
  4. Eruption along a stationary mid-ocean ridge

Explanation

A fixed mantle plume or hotspot produces volcanism at one place while the lithospheric plate moves over it. Each volcano is carried away from the plume and becomes extinct, and a new volcano forms above the plume, giving an age progression in the direction opposite to plate motion. Transform faults, continental rifting and mid-ocean ridges do not produce this fixed-source age pattern.

Question 25Climatology and atmosphere

Which gas accounts for the largest share of the atmosphere by volume in its dry state?

  1. Oxygen
  2. Carbon dioxide
  3. Nitrogen Correct answer.
  4. Argon

Explanation

Dry air is about 78% nitrogen and 21% oxygen by volume. Argon is close to 0.93% and carbon dioxide roughly 0.04%, so nitrogen is clearly the dominant gas.

Question 26Climatology and atmosphere

In which layer of the atmosphere is the ozone layer mainly concentrated?

  1. Thermosphere
  2. Stratosphere Correct answer.
  3. Troposphere
  4. Mesosphere

Explanation

Most atmospheric ozone lies in the stratosphere, roughly 15 to 35 km above the surface. There it absorbs harmful ultraviolet radiation and warms the stratosphere.

Question 27Climatology and atmosphere

Why does a sea breeze blow from the sea towards the land during the day?

  1. The land heats faster, creating lower pressure over the land Correct answer.
  2. Both land and sea heat at the same rate, so pressure stays equal
  3. The land cools faster, creating higher pressure over the land
  4. The sea heats faster, creating lower pressure over the sea

Explanation

Land has a lower specific heat than water and warms more quickly under daytime sunshine. The warm air over land rises, lowering surface pressure, so cooler air flows in from the higher-pressure sea.

Question 28Climatology and atmosphere

The subtropical high-pressure belts near 30° latitude are produced mainly by which process?

  1. Convergence of trade winds at the surface
  2. Deflection of winds by the Coriolis force
  3. Strong surface heating that expands air upward
  4. Subsidence of air descending from the upper troposphere Correct answer.

Explanation

Air rising near the equator moves poleward aloft, cools, and sinks around 30° latitude. This subsidence compresses and warms the air, producing the semi-permanent subtropical highs.

Question 29Climatology and atmosphere

How does the Coriolis force on a moving air parcel change with latitude?

  1. It is strongest at the equator and zero at the poles
  2. It is the same at all latitudes
  3. It increases from the equator towards the poles Correct answer.
  4. It decreases steadily from the equator towards the poles

Explanation

The Coriolis force is proportional to the sine of latitude, so it is zero at the equator and greatest at the poles. This is why deflections are small in the tropics and large in mid-latitudes.

Question 30Climatology and atmosphere

A parcel of air keeps a constant mixing ratio while its temperature falls from 30°C to 20°C. What happens to its relative humidity?

  1. It decreases
  2. It increases Correct answer.
  3. It remains unchanged
  4. It becomes zero

Explanation

Relative humidity is the actual vapour content compared with the saturation capacity at that temperature. Cooling lowers saturation capacity, so with the same vapour present, relative humidity rises.

Question 31Climatology and atmosphere

At the surface, winds in a Northern Hemisphere tropical cyclone blow in which pattern?

  1. Anticlockwise and outward
  2. Anticlockwise and inward Correct answer.
  3. Clockwise and outward
  4. Clockwise and inward

Explanation

A cyclone is a low-pressure system, so surface air converges inward. In the Northern Hemisphere the Coriolis force deflects this inflow to the right, giving an anticlockwise spiral.

Question 32Climatology and atmosphere

A radiation temperature inversion is most likely to develop under which conditions?

  1. An overcast, rainy day
  2. A clear, calm winter night Correct answer.
  3. A cloudy, windy night
  4. A hot summer afternoon

Explanation

On a clear, calm night the ground radiates heat rapidly to space and cools the air in contact with it. With little wind to mix the layers, a shallow inversion forms near the surface.

Question 33Climatology and atmosphere

How does the northward shift of the subtropical westerly jet stream relate to the Indian summer monsoon?

  1. It shifts north of the Tibetan Plateau and helps establish the Tibetan high and monsoon onset Correct answer.
  2. It strengthens the trade winds over the Arabian Sea and delays the monsoon
  3. It pushes the ITCZ south of the equator and weakens monsoon rainfall
  4. It increases salinity in the Arabian Sea and blocks moisture inflow

Explanation

In summer the subtropical jet migrates northward over the Tibetan Plateau. The resulting upper-level anticyclone, or Tibetan high, supports rising motion and helps trigger the onset of the southwest monsoon.

Question 34Climatology and atmosphere

Why is descending air on the leeward side of a mountain range warm and dry?

  1. It absorbs large amounts of solar radiation during descent
  2. It is heated by friction with the ground during descent
  3. It released latent heat while rising on the windward side and warms further by dry adiabatic compression Correct answer.
  4. It mixes with warm tropical air masses at the mountain top

Explanation

Air rising on the windward side cools at the saturated adiabatic rate and loses moisture as rain. Descending leeward, it warms at the higher dry adiabatic rate, so it arrives warmer and drier than at the same altitude on the windward side.

Question 35Climatology and atmosphere

Within the troposphere, temperature normally falls with increasing height at an average rate of about:

  1. 1 °C per kilometre
  2. 16 °C per kilometre
  3. 0.6 °C per kilometre
  4. 6.5 °C per kilometre Correct answer.

Explanation

The average environmental lapse rate of the troposphere is about 6.5 °C per kilometre, which is why high mountains stay cold even at tropical latitudes. The actual rate varies from day to day and place to place with humidity, cloud and season, so 6.5 °C per kilometre is only a mean value.

Question 36Climatology and atmosphere

Lines drawn on a weather chart joining places that have equal mean sea-level pressure are known as:

  1. isohels
  2. isotherms
  3. isohyets
  4. isobars Correct answer.

Explanation

Isobars join stations of equal pressure reduced to mean sea-level, and the spacing of these lines shows the strength of the pressure gradient. Closely packed isobars mean a steep gradient and strong winds, while widely spaced isobars indicate gentle winds.

Question 37Climatology and atmosphere

The equatorial belt of light, variable winds with frequent convectional cloud, where the trade winds of the two hemispheres meet, is called the:

  1. polar front
  2. roaring forties
  3. horse latitudes
  4. doldrums Correct answer.

Explanation

This belt is the Intertropical Convergence Zone, traditionally called the doldrums because sailing ships were often becalmed there. Surface convergence forces air to rise, giving low pressure, towering cumulus and heavy convectional rain.

Question 38Climatology and atmosphere

Fog that forms when warm, moist air drifts over a colder sea surface is best described as:

  1. radiation fog
  2. upslope fog
  3. frontal fog
  4. advection fog Correct answer.

Explanation

Advection fog forms when air moves horizontally over a colder surface and is chilled from below until it reaches its dew point. Warm, humid air over a cold sea is the classic setting, and the resulting fog may be thick and persistent over shipping routes.

Question 39Climatology and atmosphere

Temperature rises with height through the stratosphere mainly because:

  1. the air there is denser than in the troposphere
  2. ozone absorbs ultraviolet radiation from the sun Correct answer.
  3. convection currents carry heat upwards from below
  4. water vapour absorbs outgoing long-wave radiation

Explanation

Ozone concentrated in the stratosphere absorbs short-wave ultraviolet radiation, converting it into heat and warming the upper part of the layer. The resulting temperature inversion makes the stratosphere very stable, so vertical convection and weather are largely confined to the troposphere beneath it.

Question 40Climatology and atmosphere

At the surface in the Southern Hemisphere, the trade winds of the tropical belt generally blow from the:

  1. north-west
  2. south-east Correct answer.
  3. south-west
  4. north-east

Explanation

Air flows outward from the subtropical high near 30°S toward the equatorial low, and the Coriolis force deflects it to the left in the Southern Hemisphere. The result is a south-east trade wind, which is why these winds reach the equator from that direction.

Question 41Climatology and atmosphere

Above the friction layer, a steady wind blowing parallel to straight isobars is maintained by the balance between:

  1. pressure gradient force and Coriolis force Correct answer.
  2. gravity and pressure gradient force
  3. pressure gradient force and frictional drag
  4. Coriolis force and centrifugal force

Explanation

This is the geostrophic wind, in which the pressure gradient force pushing air from high to low pressure is exactly opposed by the Coriolis force. Because the two forces cancel, the air has no net acceleration and flows along the isobars rather than across them.

Question 42Climatology and atmosphere

Hot deserts such as the Thar experience a very large diurnal range of temperature mainly because:

  1. the subtropical high-pressure belt suppresses vertical mixing throughout the day and night
  2. clear skies and dry air allow rapid daytime heating and rapid night-time cooling Correct answer.
  3. the high albedo of the sandy surface reflects most of the incoming solar radiation back to space
  4. the weak Coriolis force at low latitudes allows the surface to lose heat quickly after sunset

Explanation

With little water vapour and almost no cloud, incoming solar radiation heats the ground strongly by day, while at night outgoing long-wave radiation escapes freely to space. The absence of a blanketing moist atmosphere therefore produces very hot afternoons and markedly cool nights.

Question 43Climatology and atmosphere

The environmental lapse rate at a place is 5 °C per kilometre, and a saturated air parcel with a saturated adiabatic lapse rate of 6 °C per kilometre is pushed upwards. The atmosphere at that level is:

  1. neutral
  2. absolutely stable Correct answer.
  3. conditionally unstable
  4. absolutely unstable

Explanation

The ascending parcel cools at 6 °C per kilometre while the surrounding air cools at only 5 °C per kilometre, so the parcel soon becomes colder and denser than its environment. It therefore tends to sink back to its original level, which is the definition of absolute stability, since the environmental rate is below the saturated adiabatic rate.

Question 44Climatology and atmosphere

A surface air parcel has a temperature of 20 °C and a dew point of 12 °C. Taking the dry adiabatic lapse rate as 10 °C per kilometre and the dew-point lapse rate as 2 °C per kilometre, its lifting condensation level is about:

  1. 800 metres
  2. 1000 metres Correct answer.
  3. 400 metres
  4. 1600 metres

Explanation

The temperature is 8 °C above the dew point, and lifting closes this gap at 10 − 2 = 8 °C per kilometre. The parcel therefore becomes saturated after about one kilometre of lifting, so the lifting condensation level is roughly 1000 metres.

Question 45Climatology and atmosphere

Which instrument is used at a weather station to measure the relative humidity of the air?

  1. Anemometer
  2. Hair hygrometer Correct answer.
  3. Barograph
  4. Campbell-Stokes sunshine recorder

Explanation

Relative humidity is the ratio of actual water vapour in the air to the maximum it can hold at that temperature. A hair hygrometer uses a bundle of human hairs whose length changes as humidity rises and falls, giving a direct humidity reading. The other instruments measure pressure, wind speed and sunshine duration, not moisture.

Question 46Climatology and atmosphere

An air parcel at the surface has a temperature of 25°C and a dew point of 15°C. If it is lifted, its temperature falls at 10°C per km while its dew point falls at 2°C per km. At approximately what height will condensation begin?

  1. 0.5 km
  2. 2.0 km
  3. 5.0 km
  4. 1.25 km Correct answer.

Explanation

Condensation begins when the falling temperature equals the falling dew point, that is, when the initial gap of 10°C has closed. The temperature and dew point approach each other at 10 − 2 = 8°C per km, so the gap closes in 10 ÷ 8 = 1.25 km. This level is the lifting condensation level, where cloud base forms.

Question 47Climatology and atmosphere

A station has mean monthly temperatures above 18°C throughout the year and receives about 220 cm of rainfall, almost all of it in a pronounced summer wet season followed by a short dry season. In the Köppen classification, which climate type does this station represent?

  1. BWh - hot desert
  2. Af - tropical rainforest
  3. Csa - Mediterranean
  4. Am - tropical monsoon Correct answer.

Explanation

Every month above 18°C places the station in the tropical group, and the very heavy summer rainfall with a short dry season is the signature of the tropical monsoon type, Am. The Af type has rain spread through the year, while BWh and Csa are too dry and have cooler winters respectively.

Question 48Climatology and atmosphere

Tropical cyclones very rarely develop within about 5° of the equator mainly because

  1. sea surface temperatures there are too low to supply enough latent heat
  2. upper-level divergence is absent over the equatorial belt
  3. the Coriolis force is too weak there to give the converging air a cyclonic rotation Correct answer.
  4. the trade wind inversion completely suppresses convection near the equator

Explanation

A tropical cyclone needs a spinning circulation, and that spin comes from the Coriolis force acting on air flowing towards low pressure. The Coriolis force is nearly zero at the equator and only becomes appreciable several degrees away, so within about 5° latitude convergence cannot organise into a rotating storm. Warm water and strong convection are in fact abundant near the equator.

Question 49Oceanography and hydrosphere

Spring tides occur when the Sun, Moon and Earth are aligned, because

  1. solar and lunar gravitational forces act at right angles and cancel each other
  2. the Moon is at its farthest point from Earth and its pull is weakest
  3. the Earth's rotation slows and the tidal bulge has more time to develop
  4. solar and lunar gravitational forces act along the same line and reinforce each other Correct answer.

Explanation

Spring tides occur around new moon and full moon, when the Sun, Moon and Earth lie nearly in a straight line. The solar and lunar tidal forces then reinforce each other, producing the greatest tidal range. At quadrature the forces oppose each other and neap tides result.

Question 50Oceanography and hydrosphere

Surface salinity in equatorial seas is usually slightly lower than in the subtropical high-pressure belts mainly because

  1. evaporation is much greater near the equator than in the subtropics
  2. seawater freezes more frequently near the equator
  3. equatorial waters receive less solar radiation than subtropical waters
  4. heavy rainfall and large river discharge dilute the equatorial surface water Correct answer.

Explanation

The equatorial belt receives heavy convectional rainfall and huge river discharge, especially from the Amazon and Congo. This fresh water dilutes the surface layer, so salinity is slightly lower than in the subtropical belts. In the subtropics, clear skies and strong evaporation concentrate salts.