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GEOG 2110L
David Stanley

AIR PRESSURE & WIND *** Air Pressure: the weight of the air pushing down on a surface ** can vary both spatially and temporally ** avg. surface pressure = 1013 mb, 29.92 inches of Hg (mercury) ** shown on a map as lines of equal pressure or isobars * high or “heavy” pressure cells ----- H * low or “light” pressure ----- L ** Pressure Gradient Force (PGF): difference in air pressure between two places, horizontally ** initiates horizontal air flow or advection = WIND *** air pressure & the PGF determine wind direction & wind strength or speed. ** Steep gradient == strong PGF == strong (fast) winds ** Gentle gradient == weak PGF == light (slow) winds * WINDS flow from areas of HIGH pressures to areas of LOW pressure *** These diferences in pressure are set-up by differences in Temperature created by differential heating. energy imbalance ▯T° difference ▯ Pressure difference ▯ wind *** Coriolis Force: apparent deflection in path or movement of an object due to the earth’s rotation What causes this? * Earth is a sphere * objects move independent of the earth's rotation * the whole earth's surface does not spin at the same rotational velocity * deflection is: (with your back to the wind) * to the right of original path in Northern Hemisphere * to the left of original path in Southern Hemisphere ** Characteristics of Coriolis Force (CF): * it is strongest at the poles & zero at the equator * an objects speed will alter the amount of deflection increase speed = increase deflection * CE alters direction, but NOT speed of an object * affects not only wind, but ocean currents, flight paths of planes and missiles *** TYPES OF WIND: Geostrophic winds: upper level winds, >1-2 kms above surface * affected by Pressure Gradient Force & Coriolis Force * net effect is that geostrophic winds blow parallel to isobars with little to no friction ** 2 main patterns: Zonal flow: a more ‘flattened air flow with primarily an east-west orientation Meridional flow: a more curved flow/orientation with distinct ridges and valleys (troughs) (Read in your textbook and know about Rossby Waves and the Jet Stream.) Surface winds: winds below 1000m altitude * influenced by: Pressure Gradient Force, Coriolis Force & Friction * effect: Low pressure cells: have Cyclonic or counterclockwise flow or circulation, in the NH * Clockwise flow in
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