Dew Point, Air Temperature and Precipitation

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RESPONSE:

Your question was this: "In areas of precipitation, the dew point and air temperature are higher than in the surrounding areas not receiving rain. In areas of precipitation the dew point and air temperature are also the same or close to being the same. What can you say about the relationship between air temperature and the air's dew point for stations within areas of precipitation?"

Background and Definitions:

Air Temperature is defined as the measure of the average speed of atoms and molecules. The higher the temperature the faster they move. Dew point is the temperature at which water vapor saturates from an air mass into liquid or solid usually forming rain, snow, frost or dew. Dew point normally occurs when a mass of air has a relative humidity of 100 % (and air temperature and dew point are the same). If the dew point is below freezing, it is referred to as the frost point.

Precipitation occurs if there:(1) is any aqueous deposit, in liquid or solid form--that develops in a saturated atmosphere (relative humidity equals 100 %) and falls to the ground generally from clouds. Most clouds, however, do not produce precipitation. In many clouds, water droplets and ice crystals are too small to overcome natural updrafts found in the atmosphere. As a result, the tiny water droplets and ice crystals remain suspended in the atmosphere as clouds. (2) The state of being precipitated from a solution. (3) Precipitation is water in liquid, or solid phase falling through the atmosphere toward the surface of the earth the condensation and sublimation from which precipitation is derived are associated with the release of a significant amount of heat energy to the atmosphere. Causes of Precipitation-clouds and precipitation are the result of rising and adiabatic cooling of air. Precipitation Formation Processes--precipitation is usually produced in clouds that have been uplifted far enough for the air to have cooled adiabatically to well below the original dew point, thus forcing the condensation or sublimation of large quantities of precipitation collisions between smaller water droplets in clouds cause them to coalesce into larger water droplets which eventually fall to the ground (http://io.uwinnipeg.ca/~wbuhay/nov10.htm).

a. What, then, can you say about the relationship between air temperature and the dew point for stations within areas of precipitation?

Dew points indicate the amount moisture in the air: the higher the dew points, the higher the moisture content of the air at a given temperature. Dew point temperature is defined as the temperature to which the air would have to cool (at constant pressure and constant water vapor content -see below for unstable conditions) in order to reach saturation. A state of saturation exists when the air is holding the maximum amount of water vapor possible at the existing temperature and pressure.

When the dew point temperature and air temperature are equal, the air is said to be saturated. Dew point temperature is NEVER GREATER than the air temperature. In other words, dew point temperature is always less than air temperature (in fact, the air is said to be unsaturated when the air temperature is greater than the dew point temperature). Therefore, when the air cools (decrease in air temperature, moving closer to dew point temperature), moisture must be removed from the air and this is accomplished through ...