Insolation and factors affecting it

At lower solar altitude rays are oblique and spread over a larger area while passing through a longer atmospheric path. In exams treat solar altitude as a key control of insolation.

In summer the day is longer and the Sun rays are more direct. In exams consider both duration and angle together.

At the June solstice vertical Sun rays are near the Tropic of Cancer, giving more energy per unit area. Remember the link between solstice and vertical rays.

At poles rays remain very oblique and ice surfaces reflect much energy despite long daylight. Do not treat day length alone as the cause in exams.

Clouds reflect and scatter solar radiation, reducing direct insolation. In exams treat clouds as a short-term control.

Daily insolation depends not only on solar angle but also on day length. For total daily energy in exams always include time.

At higher altitude the atmosphere is thinner, so absorption and scattering can be lower. Link altitude with atmospheric path in exams.

Dust and aerosols scatter and reflect solar radiation. Remember them as factors reducing atmospheric transparency.

Near the equator the Sun stays high throughout the year and day length varies little. In exams separate annual average from seasonal contrast.

For seasons axial tilt is more important than Earth Sun distance. Do not confuse aphelion with Northern Hemisphere summer in exams.

A dark dry surface can heat more because of lower reflection and lower evaporation. Link surface nature with heating effect in exams.

Vertical rays deliver energy over a smaller area, increasing energy per unit area. Compare vertical and oblique rays in exams.

In winter rays are oblique and day length is short, reducing total energy. In exams mention both reasons together.

In deserts clear skies and low water vapour block less solar radiation. Link desert clarity with direct insolation in exams.

A more reflective surface sends back a larger part of energy, so absorption decreases. Treat reflection and absorption as inversely related in exams.

During daytime clouds block and reflect incoming solar radiation, so the surface heats less. Distinguish day and night cloud effects in exams.

At higher latitudes rays are more oblique and pass through more atmosphere. Link latitude with angle and path in exams.

Scattering distributes solar energy in many directions, weakening the direct beam. Keep direct and diffuse radiation separate in exams.

Fresh snow has very high reflectivity, so it absorbs little energy. Remember snow with high albedo in exams.

A long day can increase total energy, but thick clouds strongly reduce incoming energy. In exams understand combined effects of factors.

Solar constant is measured at the outer limit of the atmosphere. In exams distinguish it from surface insolation.

With same latitude and day length, differences can arise from transparency factors like cloud, dust and humidity. Identify local factors in exams.

In January Earth is near perihelion and the Southern Hemisphere has summer. In exams treat the distance effect as small but real.

A sun-facing slope can receive more direct rays, increasing energy received. Treat aspect of slope as a local control in exams.

Vegetation provides shade and uses part of energy in transpiration. Distinguish insolation from actual heating effect in exams.