Heating and cooling of the atmosphere

Evaporation on moist surfaces causes cooling. Exam tip: link soil moisture with surface temperature control.

Strong wind mixes cold air near the surface. Exam tip: remember clear calm night for frost formation.

The direct answer is A: heating of slopes makes the nearby air lighter, so it rises upslope. During daytime, sunlight warms mountain slopes. The air touching the warm slope is heated, expands, becomes less dense, and moves upward. Cooler air then moves in to replace it, producing a local upslope breeze called a valley breeze. A is correct because it gives both the heating and the rising-air process. B is wrong because the Moon’s gravity does not create this regular daytime slope wind. C is wrong because sea waves do not travel up mountain slopes to produce the wind. D is wrong because permanent snow would generally cool a surface rather than explain daytime upward airflow. Remember: daytime heating makes valley air rise; nighttime cooling produces the opposite downslope flow.

At night, the ground and mountain slopes lose heat by terrestrial radiation. The air touching these cooled slopes also becomes colder. Cold air is denser and heavier than warm air, so gravity makes it move downward along the slope and collect in lower areas. This local downslope flow is called a mountain or drainage breeze. Therefore, the main reason is the radiational cooling of the slopes, as stated in option A. The other choices do not describe a physical process: sunlight is absent at night, the sea cannot become a mountain, and air density never becomes zero in this situation.

The important chain is cooling, increased density, and downward movement. It is not simply that air chooses to move downhill; cooling makes the air heavier and creates the condition for the flow. During the day, the reverse pattern may occur because sunlit slopes warm the adjacent air, making it lighter and encouraging upslope movement. Thus option A correctly explains the night-time wind.

Rising air cools by expansion and descending air warms by compression. Exam tip: use it in mountain weather.

The surface absorbs solar energy and terrestrial radiation heats the atmosphere. Exam tip: remember energy flow in order.

Wind is produced when air pressure is unequal from one place to another. Unequal heating and cooling create differences in temperature, and these differences lead to differences in air density and pressure. Air then moves from a region of relatively higher pressure toward a region of relatively lower pressure. This movement of air is wind. The size and direction of the resulting wind depend on how strong the heating contrast is and how the surrounding land, water, and relief influence the air. Therefore, option A correctly links unequal heating and cooling with wind systems.

The reasoning should be remembered as heat difference, pressure difference, and air movement. For example, land and water may warm or cool at different rates, producing local breezes. The options about lunar eclipses, renaming rivers, or removing the atmosphere are unrelated to atmospheric circulation. They do not explain why air moves. Hence option A is the only choice that gives the correct physical relationship.

Melting snow takes heat from surroundings and can cause cooling. Exam tip: connect change of state with latent heat.

The correct answer is A. Earth's surface loses energy at night partly by emitting longwave radiation. Water vapour absorbs some of this radiation and re-emits energy, including back toward the surface, which can slow nighttime cooling.

The correct answer is A. With little water vapour and often few clouds, the surface can receive strong solar heating by day, while less longwave radiation is absorbed and re-emitted back toward the surface at night. The result can be a large day–night temperature range.

The correct answer is A. At night the surface continues to emit longwave radiation. With little water vapour or cloud, less of this outgoing energy is absorbed and sent back downward, so the surface loses heat more rapidly.

The correct answer is A. Materials such as asphalt and concrete absorb and store heat during the day, then release some of it after sunset. This helps keep urban areas warmer at night, although it is not the only factor in the urban heat island effect.

The correct answer is A. With few clouds, much solar radiation can reach the ground during the day. Desert air is usually dry, so there is less water vapour to absorb and re-emit outgoing terrestrial radiation at night; the ground therefore loses heat readily and cools.

A is correct. Water takes in substantial energy with a relatively small temperature change because of its high heat capacity. Mixing also distributes heat through a larger volume of water. The sea warms and cools more slowly than land, moderating nearby temperatures and reducing the day-to-night temperature range.

The correct answer is A. After sunset, incoming solar radiation is absent, but the surface continues to emit longwave radiation. Longwave radiation emitted downward by the atmosphere partly offsets that surface cooling, so it must be considered when explaining nighttime temperature.

The correct answer is A. Increased surface emission does not pass directly and completely into space if the atmosphere absorbs more of it. The atmosphere can re-emit absorbed longwave energy both upward and downward, so the change in energy reaching space need not match the change in surface emission.

Water vapour is an important greenhouse gas. After the surface cools, it emits infrared radiation upward, but water vapour absorbs part of this outgoing radiation and re-emits energy in different directions, including back toward the surface. Consequently, the loss of heat is reduced and the temperature may fall more slowly, especially during humid nights. The effect does not mean that water vapour creates heat; it mainly reduces the rate of radiative cooling.

During daylight, clouds can reflect a portion of incoming short-wave solar radiation back toward space. This reduces the solar energy reaching the ground and may produce a cooling influence at the surface. Clouds can also absorb infrared radiation and affect rainfall, but they do not remove all water vapour or eliminate every chance of precipitation.

Atmospheric scattering occurs when gases and small particles such as dust, smoke, aerosols, or droplets redirect radiation from its original path. Increased scattering can therefore change the direction and distribution of sunlight, often reducing direct radiation at the surface while increasing diffuse light. It cannot remove the atmosphere, eliminate ocean salinity, or suddenly change mountain height.