Meteorology

Today’s Weather

Aim: What is weather and the variables that affect it?

I. Weather – is the short term condition of the atmosphere at any location.

A. Factors that affect the weather:

1. Temperature – specific degree of hotness or coldness.

Freezing Point Boiling Point

32oF 212oF

0oC 100oC

273oK 373oK

a. Temperature is affected by amount of sunlight (intensity and duration), different surface materials (land or water), altitude, cloud cover, and air mass movements.

2. Humidity – dampness of the air.

a. Dew Point – temperature at which air is holding maximum amount of water vapor (gas form of water). The air is said to be saturated with water vapor at this temperature.

b. The ability of the air to hold water is directly related to the temperature of the air.

c. The higher the temperature, the greater the amount of water vapor the air can hold.

d. Relative Humidity – is the percent of saturation of the air. The ratio between the actual amount of water vapor in the atmosphere and the air’s capacity at that temperature. Ex: 50% relative humidity is when the air is holding half the water vapor that it is capable of holding.

e. Psychrometer – an instrument with two thermometers (wet and dry bulb) that can measure both the dew point and the relative humidity of the air.

Psychrometer

3. Air PressureAir Pressure – is caused by the weight of the air.

a. BarometerBarometer – instrument used to measure the air pressure in units of mercury or millibars.

b. Standard pressure at sea level is equal to one atmosphere (1013.2 millibars or 29.92 inches of mercury)

c. IsobarsIsobars – lines of equal pressure on a weather map.

Barometer

4. WindWind – the horizontal movement of air.

a. Winds are described in terms of both speed and direction. They are named for the direction from which they blow. Ex: A north wind comes from the north and blows towards the south.

b. Wind vaneWind vane – is used to indicate the direction the wind is blowing.

c. Anemometer Anemometer – indicates the speed of the wind.