How does the water cycle interact with the atmosphere? Water and the Atmosphere

Water exists in three states on the Earth. Liquid when the temperature is above 0OC (32OF) Solid when the temperature is below 0OC (32OF) A gas when the temperature is above 100 OC (212OF)

Water never leaves the Earth Water never leaves the Earth. It is constantly being cycled through the atmosphere, ocean, and land. This process, known as the water cycle, is driven by energy from the sun. The water cycle is crucial to the existence of life on our planet.

The Water Cycle

During part of the water cycle, the sun heats up liquid water and changes it to a gas by the process of evaporation. Water that evaporates from Earth’s oceans, lakes, rivers, and moist soil rises up into the atmosphere.

The process of evaporation from plants is called transpiration The process of evaporation from plants is called transpiration. (In other words, it’s like plants sweating.)

As water (in the form of gas) rises higher in the atmosphere, it starts to cool and become a liquid again. This process is called condensation. When a large amount of water vapor condenses, it results in the formation of clouds.

Evaporation and condensation are occurring all the time Evaporation and condensation are occurring all the time. If the number of molecules leaving the liquid state exceeds the number returning, the water is evaporating. If the number of molecules returning to the liquid state exceeds the number leaving, the water vapor is condensing. If both rates are equal, the air is saturated; that is, the relative humidity is 100 percent.

When the water in the clouds gets too heavy, the water falls back to the earth. This is called precipitation.

When rain falls on the land, some of the water is absorbed into the ground forming pockets of water called groundwater. Most groundwater eventually returns to the ocean. Other precipitation runs directly into streams or rivers. Water that collects in rivers, streams, and oceans is called runoff.

Dew point temperature Temperature at which the relative humidity and the absolute humidity are the same (saturated air) Dew begins to accumulate on surfaces. Form on C nights: Clear Calm Cool

Condensation nuclei Gives condensing moisture in the atmosphere something to condense on. Necessary for the production of moisture in the atmosphere (rain, snow). As condensation continues, eventually there will be a point where enough water molecules have condensed on the nuclei that it can no longer remain air borne. It will then fall in the form of rain, snow, etc…

This figure compares the size of the condensation nuclei to the size of typical condensation droplets. Note that 1 micron is 1/1,000 mm.

Fog and Clouds Both of these are water droplets which have been condensed from the atmosphere. An upward movement of air keeps them from falling Clouds are identified according to whether they are: Cirrus – curly, thin, wispy Cumulus – piled up and fluffy Stratus – spread out like a blanket Watercycle

Credits By Christine Ward Chapter 24 McGraw Hill