GEOG 111 1st Edition Lecture 15 Outline of Last Lecture I Temperature cont d a Apparent temperature b Vertical temperature patterns c Horizontal temperature patterns Outline of Current Lecture I Air Pressure II Wind a Wind systems Current Lecture I Air Pressure the pressure exerted by wind a P FORCE AREA b Gases moving about randomly create collisions when they run into a surface The collective force of all of those collisions is the air s force or atmospheric pressure c By adding more air to a concealed room the collisions and the pressure increases d Basically air pressure is proportional to density of the air e Barometer instrument used to measure air pressure i Ex Hurricanes are low pressure systems so as it comes closer there is less air and the mercury in a barometer goes down ii A bar b is a unit of pressure f Pressure changes with altitude i Decreases most rapid at low elevations and gradually tapers off to 0 bar a greater altitudes g Air pressure is identified on a map by plotting isobars i Isobar a line connecting points with equal atmospheric pressure at a given time ii Pressures are standardized to sea level 1 Therefore they can see real patterns and identify where weather systems are located iii Moving perpendicular with isobars indicates changing pressure iv Winds blow parallel to isobar lines 1 Pressure determines winds which determine weather h Vertical air pressure patterns i Distribution of air molecules in the atmospheric column ii Atmosphere is extremely compressible and expandable 1 Warming causes the column to expand a Molecules on the bottom of the column that are heated will convect upward to a higher place These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute b Pressure drops at the bottom of the column and pressure increases at the top 2 Conversely cooling causes the column to compress 3 Halfway up is the 500 mb level a A warm column will have a higher 500 mb level while a cool column will have a lower 500 mb level b Isobars tell how high you have to go up c Trough in the Eastern U S is coolest because the 500 mb levels are lower than the ridges in the Western U S d Trough elongated region of relatively low atmospheric pressure e Ridge elongated region of relatively high atmospheric pressure the opposite of a trough iii Examples of the negative relationship between surface temperature and pressure 1 Thermal low atmospheric pressure is lowest because temperature is highest a Why is it so hot in the southwestern U S Absence of clouds and vegetation in the desert incoming shortwave radiation is extremely high virtually no evapotranspiration so all radiation goes into the sensible heat flux 2 Arctic high cold area of high pressure 3 Temperature isn t the only factor of pressure a The Bermuda High area of high pressure in a warm ocean II Wind generated by pressure differences a Common wind systems i Monsoon in India seasonal reversal of winds 1 Winds blow in opposite direction at the changing of the seasons 2 Land warms much quicker than water so we have higher pressures over water and lower pressure over land in the summer a Air wants to move from higher to lower pressure 3 Summer hot land low pressure onshore flow of air starting at the end of May moisture lift rain a Warmest month is May because a lot of energy is going into the sensible heat flux very dry 4 Winter cooler land higher pressure offshore flow of air dry air from inland areas
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