The Cycle of Rain Water plays a major role in weather, despite
making up such a small fraction of the atmosphere. In some
areas, the local atmosphere may contain as much as 4 percent
water, while other regions have no atmospheric water at all. As
water can exist as a solid, liquid or gas under normal
atmospheric conditions, it participates in the hydrologic cycle.
In this cycle, water evaporates from the ocean in the form of
water vapor and eventually returns to land and sea in the form
of precipitation. You can't see water vapor, but it quickly
becomes visible when it cools and condenses against something.
If you've ever noticed moisture beads on the windows of a warm
car on a cold day, you've seen condensation in action. Warm air
vapor touches the cold window and the vapor turns back to a
liquid. Clouds form along similar lines. The atmosphere is full
of tiny dust particles called condensation nuclei, which come
from volcanic eruptions, dust storms, fires and pollution. When
water vapor condenses, it clings