Lecture Notes for September 23, 2008

Tuesday September 23, 2008 Global Temperature Patterns Annual temp range ? The difference in temp between the coldest and the warmest months ? Usually increases as latitude increases ? Day length changes very little by the equator ? As you go to the north and south the range of day length increases greatly ? Land masses ? Annual temp range is larger over land than over oceans Atmospheric Pressure and Wind ? Uneven distribution of atmosphere ? Redistribution of energy ? Causes weather Atmospheric Pressure ? Most of the atmosphere is compressed into the lowest level (closes to Earth) ? What is atmospheric pressure? ? The weight of the air that exerts pressure on the surface of the Earth ? If atmosphere were to be put in a column that was 1 inch by 1inch the weight would be roughly 14.7 lbs/square inch ? Lbs/square inch à millibar ? 14.7 lbs/square inch à 1013.25 mb ? With increasing altitude, pressure ALWAYS decreases, the air would weight less ? Density (kg/m^3) ? With increasing altitude, density ALWAYS decreases Map of Surface Pressure (isobar map) Areas of low pressure ? Cyclones ? an area of low pressure that is circular in shape ? Troughs ? An elongated area of low pressure Areas of high pressure ? Anticyclones ? An area of high pressure that is circular in shape ? Ridges ? An elongated area of high pressure Why Care About Atmospheric Pressure Systems? ? When you have areas of high and low pressure there is always going to be a tendency for the air to move from the areas of high and low pressure ? All of these things greatly affect our weather ? Wind determination ? Winds blow primarily because of differences in atmospheric pressure ? Air tens to move from areas of high pressure to areas of low pressure Why Does Air Tend to Move From High to Low Pressures? ? Force ? A gravitational push or pull that causes matter to speed up or slow down or to change direction Other Forces That Affect Winds ? Pressure Gradient Force ? a force that is pushing the air from high to low pressure ? Friction Force ? opposes air movement ? strength determined by surface roughness ? only affects winds near the surface (the friction layer or boundary layer) ? Coriolis Force ( or Effect) ? causes wind to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere ? Exists because the Earth is rotating ? Causes winds to change direction ? Strength determined by ? Latitude ? Zero at the equator ? Maxes out at the poles ? Wind speed ? Faster winds are deflected more than slower winds Pressure Systems and Wind Patterns ? At the surface ? Patterns of winds around anticyclones and cyclones ? Pg 131, Figure 6.14 ? Aloft ? Geostrophic wind ? Winds aloft that blow parallel to the isobar ? No friction Causes of Pressure Differences and Winds ? Uneven distribution of energy, or heating of the atmosphere, creates differences in pressure ? Air above land is warmer than air above water Convection upward