Uso de las redes sociales y pautas de consumo

Insolation may be described as the amount of solar radiation falling upon an environment per unit area. The amount of solar energy, that gets to the outer atmosphere of the earth is called the solar constant.

Less than 50% of the solar constant pass through the atmosphere and arrive at the earth's surface. The remainder is reflected back into space by dust and clouds or is scattered by air. molecules, water vapour and dust or is absorbed by the atmosphere.

The solar radiation that penetrates through to the surface of the earth may be:

1 Reflected back into the atmosphere and eventually into space

2. Absorbed by the earth's land mass and water bodies, which is eventually lost through convention, conduction and long wavelength infrared radiation to the atmosphere.

The quantity of insolation experienced by an area hinges on solar constant, latitudinal position, season of year and the transparency of the atmosphere.

Insolation patterns are essential factor in the development of natural environments and also influence human activities such as agriculture.

Figure 6.1 Sun provides Energy for the entire environment.

Source: Miller (1999)

It is the most significant climatic parameter because it provides energy for the entire environment. Solar energy on earth initiates energy balance, water balance for plant growth, light energy for photosynthesis, pressure systems and other associated weather characteristics (see figure 6.1 above).

Solar radiation is most often measured indirectly by using sunshine recorders.

However, studies have shown that sunshine and the amount of solar radiation have direct relationship. This means that as sunshine increases solar radiation also increases and vice versa.

The sun being the source of solar radiation has been described by some scientists as a gigantic fireball of hydrogen (72%) and helium (28%) gases (Miller, 1999). Temperature on the surface of the sun has been estimated to be over 6000°C. Temperature and pressure in the inner core is so high that hydrogen nuclei fuse to form helium nuclei to release very large amount of energy.

The solar energy is in all directions as electromagnetic radiation (see figure 6.2 below).

Solar energy in all directions in the electromagnetic spectrum differs in wavelength and energy content.

Figure 6.2

(Not to scale)

Source: Miller (1999)

This radiation moves at the speed of light and makes the 150 million km trip to the Earth in about 8 minutes. The earth is been compared to a grain of rice within the entire Milky Way.

The time space occupied by the earth gives the opportunity to receive only about one billion of this output of energy. About 28% of the solar energy reaching the troposphere is reflected back into space by clouds, chemicals, dust and the earth's land and water surface.

Figure 6.3 Incoming and Outgoing Radiation from the Sun

Source: Miller (1999)

Most of the remaining 72% of solar radiation warms the troposphere and land, energize the hydrologic cycle (see figure 2.5 in unit two) by way of evaporating water and cycles it through the biosphere, and generate wind. A

very small fraction of about 0.023% is captured by green plants, bacteria, and stimulates the process of photosynthesis.

In Nigeria the average animal sunshine hours has been reported to be 1,300 in the south (example Delta State) while 3,200 hours were reported in the North (example Yola).

The hour of sunshine is more dynamic as you move southwards of latitude 9°N. To the north of the altitude where the change is more stable. The latitude 9°N is the approximate surface location of the inter-tropical Discontinuity (ITD) that is, the region of penetration of moist maritime air mass.

Please note that the values presented above are not the same for all the months, but varies with time. For instance, January - March, the average sunshine hours in the south vary from 200, to a maximum of 325 at Maiduguri (by January). Considering the period when rainy season should have begun, April, May and June, the increase in cloud cover reduces sunshine intensity to less than 300 hours in the North-East. The lowest sunshine records for our country are found between July and September when the Niger Delta zone records 20 hours of sunshine.

The length of sunshine hours does not make significant impact on an environment or in our country rather it is the system of net radiation for heat and water balance (see figure 1). This is what influences the Nigerian ecosystems or any other environment.

Note: Net Radiation is the balance between in-coming and outgoing radiation. See figure 6.1 and 6.3 for graphic conceptualization.

Try and, imagine figure 6.1 buried within figure 6.3 specifically between in-coming and out-going radiation.

In Nigeria, it has been found that, the values of the net daylight radiation increase Northwards from the coast to around latitude 12°N. Then there is a fall towards the Northern boundary. At the surface, radiation follows the same format reaching about 60kg-calm 2yrl along the coast, to 80kgcalm2yrl in latitude 8⁰N and 90kg- calm2yri in the midst of Northern Nigeria (Ojo 1972).

Exercise 6.1:

Locate latitude 12°N on the Nigeria Map.

Note: kg- cal m2 yrl implies kilocalorie per meter square per year

The values indicate that the average net radiation is about 55 per cent of the total incoming radiation in Nigeria. However, in the dry season the skies are clear with few cloud cover with an average yearly value at 70% but declines to only 45% in the rainy season when more cloud exist.