Nature Bulletin No. 478-A   January 27, 1973
Forest Preserve District of Cook County
George W. Dunne, President
Roland F. Eisenbeis, Supt. of Conservation

****:LITTLE CLIMATES --  Part One: Weather in the Soil

Climate vitally affects our lives. Wherever we live, climate has largely 
determined the plant and animal life in that region, the development of 
civilization there and what people do. The climate of any region 
represents its overall weather picture: the sum of its weather today, 
tomorrow, and during past centuries. We are accustomed to think of 
climate as a set of conditions occurring entirely in the atmosphere 
above the earth's surface, and it may sound silly when we say that there 
are climates underground -- little climates just as real as those above -- 
but it's true, There are special kinds of weather in the soil.

Land is not a solid wall. It is like a sponge. There are pores or channels 
in it. It is a complex mixture of soil particles and air spaces. The spaces, 
or pores and channels, vary with the type of soil. In sand they are tiny 
pockets between the grains. In clays they are narrow or threadlike 
spaces frequently occurring as deep twisting tubes that taper downward. 
Weather from aloft can invade such pores or real air currents, fogs, 
drizzles and snows.

Air currents in the soil move generally up and down. Air sinks into the 
soil because it has weight and is pulled downward by gravity. It rises 
underground when it is energized by heat and expands; it also rises 
when it is shoved upward by other air or by water. It may escape above 
the surface or, if the "push" is weak, into another part of the soil.

Weather conditions underground, such as fogs, drizzles and snows, are 
created by air currents there and three forms of water. We are all 
familiar with liquid water and with ice, the solid form, but there is a 
third: vapor, which is the gaseous form. The latter occurs when liquid 
water or ice are heated to the point where their tiny particles, filled with 
energy, are expelled and streak away on separate courses. Widely 
separated and invisible, they form vapor. If vapor is chilled -- its store 
of heat energy is taken away -- the particles are brought together and 
become visible as liquid water or ice.

Drizzles and moist fogs are two kinds of liquid water that result from 
the cooling of water vapor, but a drizzle contains much larger particles 
which we call "drops ll. Both occur and travel underground. They are 
shoved around by subsurface air currents and are valuable sources of 
moisture for plant roots. At night, sometimes, it is possible to shine a 
strong flashlight into the cracks or large pores in a soil and glimpse an 
underground fog or drizzle.

Ice fogs and snow also occur underground. Sometimes, during winter 
months, they develop from moist fogs and drizzles chilled to or beyond 
the freezing point by cold air currents in the soil, and may be moved 
about by such currents. Ice fogs are composed of minute particles; snow 
particles are much larger and more visible but both may be seen 
occasionally by exploring with a flashlight at night. Eventually they are 
melted by warmer air currents, or by contact with deeper warmer layers 
of soil, and provide moisture for plants.

Underground moisture, from whatever source, is never "pure" water. It 
always contains dissolved gases and minerals of various kinds: some 
gathered by rainwater as it falls from the sky; some absorbed by 
subsurface fogs, drizzles and snows. Rainwater, for example, gathers 
dust particles and carbon dioxide gas. Plant roots suck in such moisture 
and then the dissolved gases and minerals are changed into foods that 
sustain plant and animal life.

Little climates, underground, are real and vital.