Meteorology and Atmospheric Energy s-katy/vweather_zoom/pressure_lg.htm

What is Weather? The short term condition of the atmosphere at any location. –Due to the interrelationship of temperature, humidity, air pressure, and winds.

Temperature Varies in a daily cycle: –Depends on intensity and duration of sunlight. –Over land or water. –Altitude, cloud cover, movement of air masses.

Humidity The amount of water vapor in the air. Dew point temperature- air is holding the maximum amount of water vapor (water holding capacity of air related to temperature {Saturated}. Relative humidity is the % of saturation of the air measured of the ratio: = Actual amount of water vapor in the atmosphere Air capacity at that temperature

How do you measure dew point or relative humidity? You use a psychrometer which has two thermometers, one has a wick around the bulb and is wet, the other does not. This instrument is whirled in the air. The wet bulb will have a drop in temperature due to evaporation. The difference between the two with the help of a chart will determine the dew point and relative humidity.

Air Pressure Caused by the weight of the air (measured by a barometer in milibars of mercury (or in inches)

Isobars On a map they represent lines of equal air pressure. Usually there is 4 milibars between lines

Wind Horizontal movement of air. –Described by both speed and direction. –A north wind blows from the north to the south. –Or ocean winds blow from the ocean to land. –Measured with a anemometer- rotating cups. eclipse99.ksc.nasa.gov

Weather Variables Fact: warm air can hold more water than cold air. Fact: warm air is less dense (more spaces between molecules) than cold air. Fact: 10 degrees C rise will result in doubling the amount of water vapor the air can hold. Fact: as air cools the dew point temperature and the relative humidity nears 100%. –Space between molecules is reduced, increase the possibility of condensation or precipitation forming.

Warm Air not as many molecules Cold Air more molecules

Condensation Change of water vapor to liquid water.

Weather Variables Continued Variation of air pressure may be caused by temperature, altitude, and moisture content. –If the temperature changes the pressure will change. Lower temperatures cause and increase in density, higher temperatures result in decrease in density. –If the pressure changes then the temperature will also change accordingly.

Temperature changes the pressure will change

Con’t Fact: If there is an increase in altitude then the pressure will be reduced. Fact: Moisture or humid air exerts less pressure than dry air (since air molecules are replaced by smaller lighter water molecules). Fact: The surface of the earth heats unevenly- temperature changes cause pressure changes. Winds always blow from areas of High Pressure (H) to areas of Low Pressure (L).

Monsoons Seasonal winds (dry or wet weather) Winter monsoons=dry Summer monsoons=wet

Which way does the wind blow? Coastal lands: during the summer the land becomes warmer than the oceans or lakes. –Air over the land warms, rises, expands, becomes less dense, (L) low pressure.

Which way does the wind blow? During the day: Warm air over land rises Sea Breeze moves inland Cumuli develop aloft and move seaward Upper level return land breeze Cool air aloft sinks over water Sea Breeze (meso-cold) Front

Which way does the wind blow? Cool air over land sinks Land Breeze moves out over water Relatively warmer water heats air which then rises Upper level return sea breeze Cool air over land sinks

Winds Rotation of the earth prevents the wind from going in a straight line (Coriolis Effect). –In the northern hemisphere the winds move towards the right. –In the southern hemisphere the winds move towards the left.

Cited katy/vweather_zoom/pressure_lg.htmhttp://curriculum.calstatela.edu/courses/builders/worlds/planets_03/vesta/images- katy/vweather_zoom/pressure_lg.htm nt.jpghttp://geography.sierra.cc.ca.us/booth/Physical/chp5_atm_pressure/pressure_gradie nt.jpg eclipse99.ksc.nasa.gov Garnsey, Wayne and Virginia Page, Physical Setting: Earth Science, N&N Printing Co.,Inc., 2006