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OU GEOG 1114 - Characteristics of Pressure
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GEOG 1114 1st Edition Lecture 10Outline of Last Lecture -Review of thermal concepts: Thermal capacity, inertia, heat, and conductivity Land and water heating characteristics Mechanisms of Heat Transfer – circulation patterns in the atmosphere Outline of Current Lecture -Characteristics of Pressure -Agents of Atmospheric Motion -Patterns/Speed of Surface Winds=General circulation of the Atmosphere Current Lecture Characteristics of Pressure is defined as the force exerted by gas molecules in the atmosphere about 14.7 pounds per square inch at sea level Unequal heating of the earth due to the tilt, rotation, revolution Role of Pressure and Wind in Atmospheric Circulation- Spatial variation in pressure responsiblefor air movement -2 of 4 weather/climate elements (pressure, wind, temperature, moisture) -Atmospheric pressure indirectly affects the landscapePressure is closely related to density.Air density-refers to mass of matter in a unit volume- varies from place to place because gas expands as far as environmental pressure will allow. -At lower altitudes air density is higher due to earth’s gravitational pull, which results in higher pressure at lower altitudesThese 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.As air rises it expands and it becomes less denseKNOW THIS: Pressure and TemperatureThe complex relationship between temperature, density, and pressure makes it difficult to predict how a change in one will affect another. With this complex relationship in mind, we can make the following generalizations, which help us understand surface pressure conditions:Very warm surface conditions often produce low pressure at the surface (a thermal low). Warm=lowStrongly rising air often produces low pressure at the surface (a dynamic low)Very cold surface conditions often produce high pressure at the surface (a thermal high). Cold=highStrongly descending air often produces high pressure at the surface (a dynamic high)Measurement and Mapping of PressureWeather stations record pressure in units of millibars with a barometer (1 bar = 1000 millibars = 14.7 pounds per sq. inch.)Isobars: lines of equal pressureRidge: of high pressure separates two isobars of low pressure Trough: of low pressure separates two isobars of high pressure Three Agents of Atmospheric Motion (Wind) – Control the Direction of MovementOriginated of wind – uneven heating of earths surface creates temp and pressure gradientsPressure Gradient Force (PGF)Refers to horizontal movement of all air parcels from areas of high pressure to areas of low pressure The greater the difference in pressure, the faster the air moves Wind blows at right angles to isobars Coriolis Force (CF)Deflection of air caused by the earth’s rotation: to the right in northern hemisphere; to the leftin southern hemisphereTurns wind to the right (clockwise) in the northern hemisphere, left in the southern hemisphere Only affects wind direction, not speed, though faster winds turn more Greatest at poles; decreases as you move toward the equator Geostrophic Winds: There is constant battle between pressure-gradient and Coriolis force. -When these 2 forces are in balance air flows parallel to the isobars geostrophic winds occur. -These winds tend to occur at higher altitudes where effects of CF are greater and friction is less.Frictional Force (FF): The frictional drag of the earths surface slows down wind speed and modifies direction - Frictional effect is greatest at low altitudes Patterns/Speed of Surface Winds in Response to PGF, CF, FFAnticyclones – High Pressure Circulation Pattern Surface divergence and high pressure indicate sinking motion, sinking motion results in sunny skies Air diverges away from areas high-pressure centersNorthern Hemisphere – air spirals out away from high pressure center in a clockwise direction. Southern Hemisphere - spiraling out occurs in counter-clockwise direction.Cyclones – Low Pressure Circulation Patterns Surface convergence and low pressure indicate rising motion, results in clouds and storms Air spirals into center of low pressure (converges)Northern Hemisphere – converging counter clockwise flowSouthern Hemisphere – converging clockwise flowVertical Component of Air Movement in Pressure Center Cyclone: air converges and risesAnticyclone: air descends and divergesWind SpeedWind speed is determined primarily by the pressure gradient. Steeper gradients cause faster winds; slower gradients cause gentle wind. General Circulation Model of the AtmosphereAtmosphere is in constant motion, Major semi permanent conditions of wind and pressure-general circulation -Strong solar heating at the equator-Little heating at poles-Thermal low pressure at the equator-Thermal high forms over poles-Earths rotation increases complexity of circulationAtmospheric circulation provides the mechanism for the transfer of heat from energy surplus areas at the equator to the energy deficient poles. Atmospheric circulations, combined with global insolation patterns are the two major determinants of world


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OU GEOG 1114 - Characteristics of Pressure

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