Air masses, fronts, and cyclones

An air mass is classified as maritime when it develops over an ocean or sea. Because water surfaces supply moisture through evaporation, maritime air masses are generally more humid than continental air masses formed over land. The terms tropical or polar describe temperature zones, not the surface of origin. Therefore, option C is correct.

An air mass that forms over a large land area is called continental. Since land generally supplies less moisture than an ocean, continental air masses are often relatively dry, although their temperature may be tropical, polar, or arctic depending on latitude. Maritime refers to ocean origin. Hence, option D is the correct answer.

Low latitudes lie closer to the Equator and receive more direct solar radiation throughout the year. Surfaces in these regions generally warm the overlying air, so air masses formed there are usually warm or tropical. Their humidity can vary according to whether the source region is land or sea. Thus, option A is correct.

High latitudes receive oblique solar rays and have lower average temperatures, especially during the long winter season. Air that remains over these cold surfaces acquires low-temperature characteristics and is therefore generally cold or polar. Its moisture content may differ according to the source surface, so temperature alone does not determine whether it is moist or dry. Option B is correct.

A front is a transition zone or boundary where two air masses with different temperatures, humidity, and density meet. The contrasting air does not immediately mix, so the boundary can produce clouds, precipitation, and changes in wind or temperature. A cyclone and an anticyclone are pressure systems, not the boundary itself. Therefore, option C is correct.

A front separates air masses that have different physical properties. The most important contrasts are temperature and humidity, and these differences create variations in density and stability. When the air masses interact, the front may bring cloud formation, rainfall, wind shifts, or a noticeable temperature change. Therefore, option D correctly identifies the usual differences.

A stationary front forms when two contrasting air masses meet but neither one advances enough to replace the other. The boundary therefore remains nearly fixed for some time. Clouds, precipitation, and changing weather may still occur along it, but the defining feature is the absence of clear forward movement by either air mass.

An occluded front develops in a mature mid-latitude cyclone when a faster-moving cold front catches up with a warm front. The warm air is lifted above the surface because the advancing cold air undercuts it. This produces a combined frontal zone and often brings cloud, rain, or other unsettled weather.

A cold front is the leading edge of a colder, denser air mass advancing into a region occupied by warmer air. Consequently, after the front passes, the air behind it is generally colder and denser. This change may also bring a drop in temperature, a wind shift, clouds, and sometimes heavy showers.

At a warm front, lighter warm air rises gradually over a retreating or denser cold air mass. The gentle, widespread ascent allows clouds to develop across a broad area ahead of the front. The cloud sequence may include high clouds followed by thicker layered clouds and prolonged, generally steady precipitation.

At a cold front, the advancing cold air is dense and wedges beneath the warmer air, forcing the warm air to rise relatively steeply and rapidly. Rapid uplift promotes quick cooling, condensation, cumuliform cloud development, and sometimes short-duration heavy showers or thunderstorms near the frontal boundary.

At a front, warmer or less dense air is forced to rise over colder, denser air. As the rising air expands and cools, it may reach saturation; water vapour then condenses into cloud droplets or ice crystals. When these particles grow sufficiently, they fall as rain or other precipitation.

A cyclone is a large-scale rotating weather system centred on a region of relatively low atmospheric pressure. Air at the surface moves inward toward this centre and rises, often producing clouds, rain, and strong winds. Thus, low pressure is the defining pressure association of a cyclone.

Because a cyclone is a low-pressure system, the pressure-gradient force directs surface air toward its centre. Friction and the Coriolis effect modify the exact path, so the winds spiral inward rather than moving in a perfectly straight line. Near the centre, converging air rises and supports cloud formation and unsettled weather.

In the Northern Hemisphere, the Coriolis effect deflects moving air to the right. Around a low-pressure centre, this deflection produces inward-spiralling winds that rotate anticlockwise. The answer describes horizontal circulation around the cyclone, not the separate upward movement of air at its centre.

In the Southern Hemisphere, the Coriolis effect deflects moving air to the left. Around a low-pressure centre, this produces inward-spiralling winds with clockwise circulation. This is opposite to the anticlockwise circulation of Northern Hemisphere cyclones, although both systems involve convergence and rising air near the centre.

Tropical cyclones generally develop and strengthen over warm ocean water, usually with a sea-surface temperature of about 26.5°C or higher. Warm water increases evaporation, and the rising moist air releases latent heat when it condenses. This heat provides energy that sustains the cyclone. Therefore, warm ocean water is the essential condition among the given options.

The main fuel of a tropical cyclone is the combination of heat and moisture supplied by warm ocean water. Strong evaporation loads the lower atmosphere with water vapour. As this moist air rises and condenses, latent heat is released, lowering pressure and strengthening the circulation. Thus, warm moist ocean air is the correct answer.

After landfall, a tropical cyclone is cut off from the warm ocean that supplies heat and moisture. Friction over land also increases, while mountains and irregular terrain disrupt the circulation. Evaporation and latent-heat release decline, so the central pressure rises and the winds usually weaken. Therefore, D is correct.

The eye is the central region of a mature tropical cyclone. Air often descends there, producing relatively light winds, fewer clouds, and comparatively calm conditions, although the pressure is very low. The violent winds and heaviest rain usually occur in the surrounding eyewall. Hence, the eye is relatively calm, making A correct.

The eyewall is the ring of deep convective clouds immediately surrounding the eye. It contains the cyclone’s strongest sustained winds, intense upward motion, and often the heaviest rainfall. The eye itself is comparatively calm, so the eyewall is the most active part around it. Therefore, option B is correct.

A storm surge is an abnormal rise of sea level produced mainly by the strong onshore winds of a cyclone, with low atmospheric pressure adding to the effect. It can push seawater inland, flood coastal settlements, damage infrastructure, and contaminate freshwater. Thus, storm surge is the relevant coastal hazard and C is correct.

Cyclones contain abundant moisture, especially when they develop over warm seas. Convergence near the low-pressure centre forces moist air to rise. Rising air expands and cools; water vapour then condenses into clouds and rain, releasing latent heat that can further support the system. Therefore, rising moist air makes D correct.

Temperate, or extratropical, cyclones generally develop in the middle latitudes where contrasting warm and cold air masses meet along the polar front. The strong temperature gradient and upper-air westerlies help generate and intensify these systems. They are not restricted to the equator, the South Pole, or desert dunes. Hence, A is correct.

Temperate cyclones form where contrasting air masses meet, so they commonly include warm and cold fronts. A warm front develops when warmer air advances over cooler air, while a cold front forms when colder air advances and lifts warmer air. These fronts produce characteristic clouds and precipitation. Therefore, B is correct.