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Atmospheric and Oceanic Circula4on • • • • Wind Essen)als Driving Forces Within the Atmosphere Atmospheric Pa9erns of Mo)on Oceanic Currents Wind Essen4als • Air Pressure and Its Measurement • Wind: Descrip4on and Measurement • Global Winds AIR PRESSURE IS THE PRESSURE PRODUCED BY THE MOTION, SIZE, AND NUMBER OF GAS MOLECULES IN THE AIR AND EXERTED ON SURFACES IN CONTACT WITH THE AIR THE WEIGHT OF THE ATMOSPHERE, THE AIR PRESSURE, EXERTS AN AVERAGE FORCE OF 14.7 POUNDS PER SQUARE INCH AS SEA LEVEL AIR IS COMPRESSED AND IS DENSER NEAR EARTH’S SURFACE . . . AND RAPIDLY THINS OUT WITH INCREASED ALTITUDE 1 ANY INSTRUMENT THAT MEASURES AIR PRESSURE IS CALLED A BAROMETER THE BAROMETER WAS DEVELOPED BY GALILEO’S STUDENT EVANGELISTA TORRICELLI IN 1643 WIND WIND IS THE HORIZONTAL MOTION OF AIR RELATIVE TO THE EARTH’S SURFACE . . . IT IS PRODUCED BY DIFFERENCES IN AIR PRESSURE FROM LOCATION TO ANOTHER . . . AND THE TWO PRINCIPLE VARIABLES ARE SPEED AND DIRECTION WINDS ARE NAMED FOR THE DIRECTION FROM WHICH THEY ORIGINATE Driving Forces Within the Atmosphere • • • • Gravity: Pressure Gradient Force Coriolis Force Fric4on Force 2 GRAVITY EQUALLY COMPRESSES THE ATMOSPHERE WORLDWIDE WITH DENSITY DECREASING AS ALTITUDE INCREASES PRESSURE GRADIENT FORCE THE FORCE THAT CAUSES AIR TO MOVE FROM AN AREA OF HIGHER BAROMETRIC PRESSURE . . . TO AN AREA OF LOWER BAROMETRIC PRESSURE DUE TO THE PRESSURE DIFFERENCE THEREBY CAUSING WINDS COLD, DENSE AIR AT THE POLES EXERTS GREATER PRESSURE THAN WARM, LESS DENSE AIR AT THE EQUATOR THE EFFECT OF DRAG BY THE WIND . . . AS IT MOVES ACROSS A SURFACE . . . IS THE FRICTION FORCE SURFACE FRICTION SLOWS THE WIND . . . 3 Atmospheric PaBerns of Mo4on • Primary High‐Pressure and Low‐Pressure Areas • Upper Atmospheric Circula4on – Jet Streams • Local Winds – Monsoonal Winds Primary High‐Pressure and Low‐ Pressure Areas • • • • Equatorial low‐pressure trough Polar high‐pressure cells Subtropical high‐pressure cells Subpolar low‐pressure cells Equatorial low‐pressure trough • Intertropical convergence zone (ITCZ) • Trade winds 4 THE EQUATORIAL LOW-PRESSURE TROUGH ALSO KNOWN AS THE ITCZ . . . OR THE INTERTROPICAL CONVERGENCE ZONE THE EQUATORIAL LOW-PRESSURE TROUGH IS AN ELONGATED . . . AND NARROW BAND OF LOW PRESSURE THAT CIRCLES THE EARTH Subpolar low‐pressure cells • Aleu4an low • Icelandic low • Polar front SUMMARY HERE ARE OUR PRIMARY HIGHPRESSURE AND LOW-PRESSURE AREAS: TWO HIGH-PRESSURE AREAS: 1. SUBTROPICAL HIGH-PRESSURE (dry, hot)) 20* - 35* DYNAMIC BERMUDA/AZORES HIGH HAWAIIAN/PACIFIC HIGH 2. POLAR HIGH-PRESSURE CELLS (DRY, FRIGID) AROUND 90* THERMAL AND VERY WEAK 5 TWO LOW-PRESSURE AREAS: 1. THE EQUATORIAL LOW-PRESSURE TROUGH THERMAL 10* N AND S OF EQUATOR FORMS THE ITCZ WARM, MOIST 2. THE SUBPOLAR LOW-PRESSURE CELLS DYNAMIC, COOL AND MOIST 60*N ALEUTIAN AND ICELANDIC LOWS Local Winds • Land‐sea breezes • Mountain‐valley breezes • Kataba4c winds LAND-SEA BREEZES CAUSED BY DIFFERENT HEATING CHARACTERISTICS OF LAND AND WATER SURFACES DURING THE DAY LAND HEATS FASTER THAN WATER OFFSHORE BECAUSE WARM AIR IS LESS DENSE IT RISES . . . TRIGGERING AN ONSHORE FLOW OF COOLER MARINE AIR WHICH IS USUALLY STRONGER IN THE AFTERNOON 6