Chionosphere

(in Russian, khionosfera), a term used in Soviet scientific literature to denote the part of the troposphere in which snowfields and glaciers may form and exist on the land surface under favorable topographic conditions. The chionosphere envelops the earth in a continuous shell to a height of up to 10 km; the upper boundary reaches the maximum height in the equatorial belt and at low latitudes in the temperate belts.

The chionosphere is characterized by a combination of heat and moisture such that the annual amount of solid precipitation falling on a horizontal and unshaded surface exceeds the loss of such precipitation. The upper boundary of the chionosphere usually lies above the highest mountains and corresponds to a zero balance of solid atmospheric precipitation; in the mountains, the annual amount of solid precipitation usually increases to a certain elevation and then again decreases. The lower boundary forms the snow line when it intersects mountain ranges and rises with increasing distance from the sources of moisture. It is higher above the interior regions of upland plains than on the windward slopes of mountains.

At high latitudes in the southern hemisphere, the snow line descends to sea level. The tongues of many mountain glaciers descend below the chionosphere. Individual small glaciers sometimes lie entirely below the chionosphere when the snow density is high.