Insolation and factors affecting it

Winter insolation is generally lower because a location receives sunlight for fewer hours and the Sun appears lower in the sky. The lower angle makes the rays more oblique, so the same energy is spread over a larger surface area. Oblique rays also travel through a greater thickness of atmosphere, where some energy can be scattered or absorbed. These effects reduce the energy received per unit area.

Option C is correct because it combines the two important seasonal factors: shorter days and slanting rays. Earth does not cover the Sun, and the Sun’s total energy does not suddenly end in winter. Option A describes the opposite of the usual winter condition. The exact amount of insolation also depends on latitude, season, and local atmospheric conditions, but the basic school-level reason is given by C.

The direct answer is A: more insolation reaches the surface. Insolation means incoming solar energy received by Earth. Atmospheric transparency tells us how easily sunlight passes through the atmosphere. Step by step: sunlight enters the atmosphere; gases, dust, smoke, clouds, and water vapour may absorb, scatter, or reflect some energy; when the air is clear and transparent, less sunlight is stopped; therefore more solar radiation reaches the ground and can heat it. Option A is correct because it states this direct result. Option B is wrong because transparency does not make insolation zero; it usually allows more energy through. Option C is wrong because sunlight does not become reversed. Option D is wrong because atmospheric transparency cannot end the day. Memory cue: clear sky means more sunlight at the surface.

Insolation means the solar radiation received by Earth’s surface. Dense fog contains many tiny water droplets. These droplets scatter and absorb part of the incoming sunlight, so less direct radiation may reach the ground. As a result, the surface can receive less solar energy and may remain cooler than it would under a clear sky. Fog does not change Earth’s axis or the size of the Sun; its main effect here is on the passage of radiation through the atmosphere.

Option B is correct because dense fog can reduce the insolation reaching the surface. The word “can” is important: the exact effect depends on fog thickness, duration, and the type of radiation considered, but dense fog generally limits direct sunlight at ground level. The other options describe impossible effects that are not atmospheric consequences of fog.

Air molecules and dust particles scatter solar radiation in different directions. Scattering can reduce energy reaching the surface.

Insolation is related to received solar energy. Therefore its amount is understood with reference to area and time.

The zone of vertical sun rays changes throughout the year. This changes insolation at different latitudes.

Around the June solstice, vertical sun rays fall on the Tropic of Cancer. This increases summer conditions in the Northern Hemisphere.

Around the December solstice, vertical sun rays fall on the Tropic of Capricorn. This gives more insolation to the Southern Hemisphere.

At equinox, vertical sun rays fall on the Equator. At this time, day and night are nearly equal.

The direct answer is option C: dark asphalt. Insolation means incoming solar radiation received by Earth’s surface. A surface’s albedo is its ability to reflect sunlight. Light surfaces generally have high albedo and reflect more energy; dark surfaces generally have low albedo and absorb more energy. Step by step: sunlight reaches each surface; white snow reflects a large part of it; light sand reflects more than a dark surface; dark asphalt reflects less and absorbs more; the absorbed energy changes into heat, so asphalt becomes warmer. Option A, white snow, is wrong because its high albedo causes strong reflection. Option B, light sand, generally reflects more solar energy than dark asphalt. Option C is correct because dark asphalt has low albedo and usually absorbs much insolation. Option D, shiny metal, reflects a considerable amount of radiation, so it is less suitable here. Memory cue: “Dark and dull absorbs; light and shiny reflects,” while remembering that exact absorption can vary with material and conditions.

Water heats and cools more slowly than land. Therefore land and sea temperatures change differently.

A slope facing the Sun can receive more insolation. Link slope aspect with local temperature differences.

In a shaded area, direct solar rays are blocked or greatly reduced before reaching the surface. Some diffuse radiation may still arrive, so insolation is generally lower than in an open sunlit area. Option C is incorrect because even when the Sun is overhead, an obstruction can still block direct rays in the shade. Exam tip: shade, cloud cover, and a longer atmospheric path all reduce insolation.

The direct answer is B: insolation is generally high when the Sun’s altitude is high. Solar altitude is the angle of the Sun above the horizon. Step by step: at a high altitude, rays arrive more nearly vertically; the same solar energy is concentrated over a smaller surface area; the rays also travel through a shorter thickness of atmosphere; less energy is scattered or absorbed before reaching the ground; therefore surface insolation is generally greater. Option B is correct. Option A, low, is usually associated with a lower Sun, when rays are more slanting and spread over a larger area. Option C, zero, is not correct during daylight merely because the Sun’s altitude is high; zero insolation occurs when no sunlight reaches the surface, such as at night or under special conditions. Option D, negative, is not the normal meaning of incoming solar energy; incoming insolation is measured as a positive amount. The statement is general, so clouds and dust can still reduce actual heating. Memory cue: high Sun, straight rays, smaller spread, stronger insolation.

The direct answer is B: the rate of energy received from the Sun. The solar constant is the average amount of solar energy received per unit area per unit time at the outer edge of Earth’s atmosphere, when the surface is held perpendicular to the Sun’s rays. The word rate is important because energy is measured over time, not simply as a total amount. Step by step: the Sun emits radiation; Earth receives part of it; scientists measure the incoming energy rate outside the atmosphere; this standard value is called the solar constant. Option A, rainfall, is weather and is not the definition. Option B is correct because it describes incoming solar-energy rate. Option C, ocean salinity, concerns dissolved salts. Option D, mountain height, concerns relief. Memory cue: solar constant means Sun’s energy flow, not rain, salt, or height.

Water vapour can absorb some radiation in the atmosphere. This affects the energy reaching the surface.

At high latitudes, sun rays are more oblique. Therefore less energy is received per unit area.

The direct answer is B: Earth’s rotation. Daily variation means the change that occurs during one day. Step by step: Earth rotates on its axis; as a place rotates toward the Sun, it experiences sunrise and increasing solar altitude; around daytime the incoming radiation changes; as the place rotates away, the Sun lowers and then sets; at night, direct insolation becomes zero. Thus Earth’s rotation produces the day–night cycle and the changing angle of sunlight, making it the main cause of daily insolation variation. Option B is correct. Option A, sea salinity, can influence local water properties but does not create day and night. Option C, the number of rivers, has no direct role in the daily position of the Sun. Option D, only the colour of rocks, may affect how much ground absorbs or reflects energy, but it cannot explain the daily rise and fall of incoming sunlight, and the word “only” makes it especially unsuitable. Do not confuse daily variation with seasonal variation, which is strongly related to Earth’s revolution and axial tilt. Memory cue: rotation makes a day; revolution plus tilt helps make seasons.

Insolation changes from season to season mainly because Earth is tilted on its axis and revolves around the Sun. Earth’s axis remains tilted by about \(23.5^\circ\), so different hemispheres receive more direct sunlight at different times of the year. The hemisphere tilted toward the Sun has longer days and a higher Sun angle, while the other hemisphere receives less direct energy. This produces annual changes in heating and insolation.

Option A is correct because axial tilt and revolution together create the seasonal pattern. River direction, cloud colour, and soil smell cannot explain the regular yearly change in the Sun’s apparent height and day length. Clouds may affect the amount of insolation on particular days, but they are not the basic cause of its annual seasonal variation. The combined action of tilt and revolution is the key idea.

Vertical sun rays can fall between the Tropic of Cancer and Tropic of Capricorn. Link this with the tropics.

On a rainy, cloudy day, dense clouds reflect, absorb, and scatter part of the incoming short-wave solar radiation. Hence, less insolation reaches the Earth’s surface. “Moderate” may apply with light cloud cover, but low insolation is generally expected under dense rain clouds. Exam tip: greater cloud cover usually means lower surface insolation.

Deserts may have fewer clouds and less moisture, allowing more solar energy to reach the surface. Hence daytime heating can be strong.

Dense tree canopy allows fewer sun rays to reach the ground. Therefore forest ground can remain cooler.

Dense cloud cover allows less solar radiation to reach the surface. Therefore it is a factor reducing insolation.

Vertical sun rays concentrate energy over a smaller area. Therefore insolation is higher in such a condition.