GPH 212, Week 3 Notes
GPH 212, Week 3 Notes GPH 212
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This 4 page Class Notes was uploaded by Sheridan Smede on Thursday September 8, 2016. The Class Notes belongs to GPH 212 at Arizona State University taught by Matei Georgescu in Fall 2016. Since its upload, it has received 12 views. For similar materials see Introduction to Meteorology in Physical Geography at Arizona State University.
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Date Created: 09/08/16
Important: ● Exam 1 September 21st Continued Lecture ● Density ○ Defined as mass (kg) per unit volume (m^3) ○ Due to compressibility, near surface air is more dense than that above ○ As you move upwards, atmosphere becomes less dense ○ At sea level, air density is ~1.2 kg m^3 ○ Mean free path ■ Average distance a molecule travels before colliding with another molecule ■ A lot less when close to surface; a lot more farther away ○ Temperature decreases as we move through troposphere ■ Temperature stops decreasing with height in tropopause ■ As we continue to rise in the stratosphere, temperatures rise ■ Atmospheric mass thins out with height ■ Atmosphere is most dense closest to earth’s surface ○ Less density means less resistance a football can be kicked farther in a place with less density (example: Colorado) Pressure ● Closely related to density ● Pressure is a result of the atmosphere’s mass ● Value of pressure reflects the mass of atmosphere above a given point (P = F/a) ○ A = area ○ F = force ● Pressure decreases vertically but not at a constant rate Why doesn’t weight of atmosphere crush us? ● Because we have air inside of our bodies not allowing us to be crushed, it we did not have air in our bodies we would in fact be crushed ● For example: if you remove all air from inside a bottle, it will collapse into itself Why do our ears pop? ● Pressure is changing instantly ● Body is trying to reach equilibrium with surrounding atmosphere Weather Basics ● Humidity ○ Term used to describe amount of water vapor present under the current conditions in the atmosphere (temperature) ○ Relative humidity: amount of water vapor present in relation to the max temperature. Reported as a percentage ○ Dew point: the higher the dew point, the greater amount of water vapor in the air. It is an absolute metric (not a percentage) with units of temperature Atmospheric pressure and wind ● Gas molecules are constantly in motion (and exert a pressure [force per unit area] when they strike a surface) ● Air tends to: ○ Blow away from regions of high pressure to low pressure (wind) ○ Rise in areas of low surface pressure and sink in areas of high pressure ■ Rising motions favor cloud formation, while sinking promotes clear skies ○ The atmosphere is always moving ○ Low pressure causes poor weather (inclement weather) ○ Air rises = low pressure ○ As air continues to rise, condensation begins ■ Condensation change in state from gas to liquid (clouds) ○ Air subsides = high pressure Mapping air pressure ● Atmospheric pressure is plotted correction applied based on elevation above sea level) on maps using lines called isobars ● Sea level correction reveals difference in pressure reflective of air motion (important for forecasting, climate, etc.) ● Pressure is measured using millibars (U.S.) and kilopascals (Canada) ○ [PA > kg m^1s^2; 1mb = 100 Pa] ● Isobar: contours of equal pressure Surface weather map ● Top number temperature ● Bottom number dew point ● Oval cloud coverage ● Wind bar wind direction Temperature ● Varies in time and location ● Drastic temperature differences are caused by fronts ○ Cold fronts ■ Boundary separating cold air moving towards warm air ○ Warm fronts ■ Boundary separating warm air moving towards cold air ○ Occluded fronts ■ Combination of warm and cold front ○ Stationary fronts ■ Not moving ○ Fronts move at different speeds ○ Precipitation is common along fronts, so when a front approaches it is not unusual to have rain or snow in addition to a change in temperature ■ Intensity of precipitation varies ○ When fronts meet, one air mass dominates (for example, if the warm air becomes dominant, it is a warm front) ○ After a cold front departs, there is often very sunny and clear weather
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