OVERVIEW Recognize how moisture affects the atmosphere.

OUTLINE

More than two-thirds of Earths surface is covered with water. Water from this extensive source is continually evaporating into the atmosphere, cooling by various processes, condensing, and then falling to the ground again as various forms of precipitation.

The remainder of Earths surface is composed of solid land of various and vastly different terrain features. Knowledge of terrain differences is very important in analyzing and forecasting weather.

The worlds terrain varies from large-scale mountain ranges and deserts to minor rolling hills and valleys. Each type of terrain significantly influences local wind flow, moisture availability, and the resulting weather.

Moisture in the atmosphere is found in three statessolid, liquid, and gaseous. As a solid, it takes the form of snow, hail, ice pellets, frost, ice-crystal clouds, and ice-crystal fog. As a liquid, it is found as rain, drizzle, dew, and as the minute water droplets composing clouds of the middle and low stages as well as fog. In the gaseous state, water forms as invisible vapor. Vapor is the most important single element in the production of clouds and other visible weather phenomena. The availability of water vapor for the production of precipitation largely determines the ability of a region to support life.

The oceans are the primary source of moisture for the atmosphere, but it is also furnished by lakes, rivers, swamps, moist soil, snow, ice fields, and vegetation. Moisture is introduced into the atmosphere in its gaseous state, and may then be carried great distances by the wind before it is discharged as liquid or solid precipitation.

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