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3 zones of Upward motion: ITCZ polar fronts and windward side of a mountain air rises, cools, and may condense 4 zones of Downward motion: poles 30ºN and S and leeward side of a mountain warms, so lower RH and dry conditions Winds blow because of differences in atmospheric pressure. Wind DIRECTION depends on: PRESSURE GRADIENT FORCE force derived from the difference in the pressure winds “want” to blow from high pressure to low pressure the steeper the pressure gradient, the stronger the wind isobars (lines of equal barometric pressure) close together and CORIOLIS EFFECT acts to deflect the wind greatest at the poles stronger wind, greater effect Winds are named by where they are FROM. A NORTH wind in Jacksonville is likely to be a COLD wind. A SOUTH wind is likely to be a WARM wind. N Low SW SE Low High Low NW NE Low Coriolis Effect deflects winds to the right in the northern hemisphere N Low SE SW Low High Low NE Low NW Coriolis Effect deflects winds to the left in the southern hemisphere Wind speed depends on: pressure gradient force greater the difference in pressure, the stronger the wind friction friction occurs from interference with the earth’s surface friction acts to slow down the wind GEOSTROPHIC WINDS H high altitude winds have little effect from friction geostrophic winds blow parallel to the isobars JET STREAM center of fast moving winds in the upper troposphere center of the geostrophic winds L Northern Hemisphere s u r f a c e w i n d s coriolis deflects to the right H L H L cw, out ccw, in cw ccw H L H L cw, in ccw cw ccw, out Southern Hemisphere coriolis deflects to the left g e o s t r o p h i c w i n d s HIGH PRESSURE anti-cyclone LOW PRESSURE cyclone other winds foehn or chinook--those warm, dry winds that blow down the leeward sides of mountains katabatic winds--cold winds that sink down off of a mountain because the cold air is very dense and heavy MONSOONS seasonal shift in the prevailing wind directions noted for bringing seasonal precipitation H L January July Valley Breeze warms warms during the day, the valley air warms, becomes less dense, and rises Mountain Breeze cools at night, the top of the mountain cools faster because of the thinner air, and the colder, denser air sinks down the mountain along a coastline SEA BREEZE H water COLD L HOT land During the day, the land heats faster than the water, the warm air rises, and low pressure develops. The air over the water becomes cold and heavy, sinking, creating high pressure. Air moves from highs toward lows, so a SEA BREEZE develops coming from the water. LAND BREEZE H L water HOT COLD land At night, the land cools faster than the water, the cold air sinks, and high pressure develops. The air over the water becomes warm and light, rising, creating low pressure. Air moves from highs toward lows, so a LAND BREEZE develops coming from the land.
