Chapter Climate and microclimate

Summary

This chapter includes the following topics:

The sun's energy

Effect of latitude

Weather systems

Weather and climate

Climate of British Isles

Growing seasons

World climate

Local climate

Microclimate

Weather instruments

Types Waves Radiated Into Space
Figure 2.1 Agrometerological station showing rain gauge (left), Stevenson's screen (centre) and anemometer (right)

The Sun's energy

The energy that drives our weather systems comes from the sun in the form of solar radiation. The sun radiates waves of electro-magnetic energy and high-energy particles into space. This type of energy can pass through a vacuum and through gases. The Earth intercepts the radiation energy and, as these energy waves pass through the atmosphere, they are absorbed, scattered and reflected by gases, air molecules, small particles and cloud masses (see Figure 2.2).

Types Waves Radiated Into Space

Figure 2.2 Radiation energy reaching the Earth's surface showing the proportions that are reflected back and absorbed as it passes through the atmosphere and that which reaches plants indirectly. About 5 per cent of the radiation strikes the Earth's surface but is reflected back (this is considerably more if the surface is light coloured, e.g. snow, and as the angle of incidence is increased).

Figure 2.2 Radiation energy reaching the Earth's surface showing the proportions that are reflected back and absorbed as it passes through the atmosphere and that which reaches plants indirectly. About 5 per cent of the radiation strikes the Earth's surface but is reflected back (this is considerably more if the surface is light coloured, e.g. snow, and as the angle of incidence is increased).

About a quarter of the total radiation entering the atmosphere reaches the Earth's surface directly. Another 18 per cent arrives indirectly after being scattered (diffused). The surface is warmed as the molecules of rock, soil, and water at the surface become excited by the incoming radiation; the energy in the electro-magnetic waves is converted to heat energy as the surface material absorbs the radiation. A reasonable estimate of energy can be calculated from the relationship between radiation and sunshine levels. The amounts received in the British Isles are shown in Figure 2.3 where the differences between winter and summer are illustrated.

However, the nature of the surface has a significant effect on the proportion of the incoming radiation that is absorbed. The sea can

British Isles Sea Level

Figure 2.3 Radiation received in the British Isles; mean daily radiation given in megajoules per metre square. (a) January (b) July.

Land Areas The British Isles
17 17 19

Figure 2.3 Radiation received in the British Isles; mean daily radiation given in megajoules per metre square. (a) January (b) July.

absorb over 90 per cent of radiation when the sun is overhead, whereas for land it is generally between 60 and 90 per cent. Across the Earth darker areas tend to absorb more energy than lighter ones; dark soils warm up more quickly than light ones; afforested areas more than lighter, bare areas with grass are between these values. Where the surface is white (ice or snow) nearly all the radiation is reflected.

Was this article helpful?

0 0
Building Your Own Greenhouse

Building Your Own Greenhouse

You Might Just End Up Spending More Time In Planning Your Greenhouse Than Your Home Don’t Blame Us If Your Wife Gets Mad. Don't Be A Conventional Greenhouse Dreamer! Come Out Of The Mould, Build Your Own And Let Your Greenhouse Give A Better Yield Than Any Other In Town! Discover How You Can Start Your Own Greenhouse With Healthier Plants… Anytime Of The Year!

Get My Free Ebook


Post a comment