Diurnal and seasonal changes

The budget is complicated still further by the Earth's rotation and by its tilted axis. Obviously, the surface absorbs no solar energy at night, when it is dark. There is a very large variation in energy gain and loss over the 24hour cycle. In the tropics this can amount to a net gain of about 1,000 W m-2 at noon and a net loss of about 70 W m-2 at midnight.

As the illustration shows, the Earth's axial tilt produces the seasons by turning first one hemisphere and then the other to face the Sun. The

How axial tilt produces the seasons. Because the rotation axis of the Earth is tilted in respect to the plane of its solar orbit, in June the Northern Hemisphere receives more solar radiation than the Southern Hemisphere and in D ecember the situation is reversed. This produces the seasons.

Seasonal Changes Weather

effect is to increase the number of hours of daylight in summer and decrease them in winter. During the summer, therefore, the surface gains heat for longer than it loses it and in winter it loses heat for longer than it gains it. That is why summers are warmer than winters. At the North and South Poles, where the Sun remains below the horizon for six months of the year, the surface continues to lose heat at about 70 W m-2. In Antarctica, however, the temperature falls by about 1°F (0.5°C) per day during the autumn, but reaches its lowest value at the March equinox, after which it falls very little. Antarctica is the only part of the world where this happens. The continent is said to have a coreless winter. It is the large difference in the amount of energy being gained at each latitude that produces the vigorous weather systems that are characteristic of climates in middle and high latitudes.

Despite the complications and regional variations, the total amount of energy falling onto the surface of the Earth can be measured. The movement of that energy, as it is reflected, absorbed, and scattered can be traced. The energy leaving the Earth, by reflection and infrared radiation, can also be measured. Not surprisingly, the two sides of the balance sheet produce the same total. The Earth's energy budget is in balance.

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  • nora
    What are diurnal and seasonal changes?
    4 years ago

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