Linda Brown, age 12, of Taylorsville, Ky

What causes a ground fog?

On a misty morning, the world is shrouded in pearly film and you caw see for perhaps half a mile  This is classified as light fog, In a moderate fog, you can see for about athird 6f a mile and the thick fog hides the landscape beyond a fifth of a mile, Over London and other cities, a fog is sometimes mixed with soot and dust and we get a thick pea soup fog which, at high noon, can be darker than a starless midnight,

Whether it is filmy haze or a thick, midnight mixture, a fog is no more than a cloud sitting on the ground, All are made from fine droplets of moisture which measure anywhere from ten to one hundred to the millimeter, When condensed, a cubic yard of foggy mist is hardly enough to cover the bottom of a drinking glass with liquid water

The basic causes of clouds and fogs are the came, However, the weather conditions which produce fogs are different from those which cause most of the high‑flying clouds, The beaming suns the atmosphere and the solid earth with its wet areas of ocean and lakes, rivers and puddles interact with each other to form both clouds and fogs 

The radiant energy of the sun passes through the atmosphere without giving up much of its heat  It warms the ground and the ocean surface and they in turn warm the lowest layer of air, which is directly above them  This warm air soaks up moisture„ turning it to vapor which mixes with the other invisible gases of the air: Warm air tends to expand and, in so doing, it cools itself  And cool air can hold less moisture than warm air  It gives up its surplus moisture in the form of the fine droplets which form clouds and fog 

Moat clouds form adiabatically, that is when warm moist air is forced aloft and cools to below its saturation point 

Ground fogs are usually caused by  the temperature on the surface of the ground, During the night, the solid earth loses its daytime heat, This lowers the temperature of the air directly above it  and this air may have gathered up a load of vapors from tea previous warm day, The chilly night time temperature forces the air to yield up its surplus moisture in the form of a fuzzy fog  This may be called a radiation fog because it is caused by the loss of the earth’s heat by radiation 

There era other weather conditions which can force the layer of air near the ground to yield up its moisture in the form of misty droplets, One occurs when warm, wet ocean air blows over a cooler land surface, This may be called an advection fog and often occurs along the California coast when the warm, moist air from over the Pacific ocean meats the cooler land surface  Another type of fog may be caused when cold air blows over warm water  Enough moisture may evaporate to make the air reach saturation point and produce misty droplets  This is called an evaporation fog  Another type of fog is caused when warm, moist air is forced up a cooler mountain slope