Water Vapor And Weather Change

By Clinton N. Maxwell

In a very basic way, the water vapor that makes up clouds is a major catalyst of weather change. Though we may not be able to see it, water vapor is there, throughout the earth's atmosphere. Almost all of it comes from evaporating water rising from the oceans. Ocean water is heated by the sun and when the liquid is changed to the lighter form, gas, it rises. This evaporation is one of the keys to starting climate changes.

Scientists recognized three basic processes in which an air mass may rise. There is the process of convection, as simply described above. But this process can also happen above soil and pavement surfaces, which gather heat rapidly. Moisture from these surfaces can also rise into the atmosphere and eventually form clouds.

A second process that may cause an air mass to rise involves the collision of warm and cold fronts. Clouds can form if there is sufficient moisture in warm air that is forced over a cold front.
Air can also be lifted if it comes into contact with a large geographic feature such as a mountain range. Scientists term this type of rising air mass "orographic lifting." If the air contains enough water vapor, clouds form (often in unusual shapes).

It is widely understood that an air mass will continue to rise if it is warmer than the air that surrounds. Conditions are unstable if the air mass continues to rise. It is also true that cold air at higher levels, above warmer air, means unstable conditions. Stable conditions would generally exist if the opposite were true, warm over cold.

Since the atmosphere enveloping the earth can't hold an infinite amount of vapor, the air becomes saturated. At this time (called the dewpoint), the water vapor begins to condense, changing back to its original state, liquid. Overall air temperature has a significant effect on this process, since air that is warmer can hold more vapor.

Clouds are born when this condensation process occurs well above the ground. But there is another key to the "proper" formation of clouds through condensation. The surrounding air must be dirty, containing dust particles and pollutants that are suspended in the air. These small particles act as the core or nuclei for water molecules to cling to. (Many laymen consider fog to be completely different from clouds, but the major difference is the altitude at which the "cloud" forms. (The condensation process is the same.)

There is one more key element to the formation of various types of clouds and to the type of precipitation experience on the ground. Temperature changes have a major effect on how water vapor acts in the atmosphere as well. If the temperature at a higher level in the atmosphere is below the freezing point, vapor may turn to ice directly. It stands to reason that higher-level clouds generally contain ice crystals, while lower level cloud formation features droplets of water. A particular combination of any of these factors leads to weather conditions beneficial or harmful to life on earth.

Clinton Maxwell's reports can be encountered on different web pages linked to climate changes. His articles on alicante temperatures can be found on http://www.alicante-spain.com in addition to many different web publications.

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