|HABYTIME MINI LECTURE 74:|
SURFACE SOLAR INTENSITY 2
METEOROLOGIST JEFF HABY
There are a variety of surfaces and mediums in which solar radiation absorbs, transits through or reflects off. The amount of each of these will
influence how much solar radiation is able to warm a surface. The diagram below shows several surfaces and mediums in which
solar radiation will strike.
Solar radiation must penetrate through the entire depth of the atmosphere before it can even get to the surface. With this distance to cover,
some of the radiation is reflected or absorbed within the air. About 23% of the solar radiation that enters the earth’s atmosphere is
absorbed by the air. This will result in a warming of the air but since the atmospheric depth is over a vast distance, this warming
is not noticed nearly as well as when warming of a thin surface such as the ground occurs. A thin region where all the absorption
takes place will produce a more localized warming as compared to when absorption occurs gradually over miles of atmosphere.
About 30% of the solar radiation that enters the earth’s atmosphere is reflected back into space. Thus, this energy is not able to warm the
earth’s surface and not able to warm the atmosphere. Thus, about 70% of the solar radiation that enters the atmosphere goes into warming
the ground and atmosphere. The solar radiation that is reflected back into space occurs to reflection off clouds, water, earth’s surface,
particulates in the air and the air itself. Particulates in the air that can reflect solar radiation back into space include dust, ash,
haze and pollen.
Surface reflectors have a powerful influence on how much surface warming can occur. Three surface covers that produce a strong reflection
of solar radiation include snow, ice and water (water is true when the sun angle is near the horizon). Since these three factors are more
prevalent at high latitudes, this contributes to the polar areas being very cold since these areas get so little solar radiation to
begin with and a large percentage of the solar radiation they do get is reflected right back into space.
Weather forecasting is influenced by solar energy reflection. Here is a list of several ways it is influenced:
1) Cloud cover increases solar reflection which helps keep the ground surface cooler
2) Snow cover (especially fresh snow cover) strongly reflects solar radiation which helps keep the ground surface cooler
3) Fog, dust and ash reflect solar radiation which helps keep the ground surface cooler