GEOG 1114 1st Edition Lecture 10 Outline 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 responsible for air movement 2 of 4 weather climate elements pressure wind temperature moisture Atmospheric pressure indirectly affects the landscape Pressure 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 altitudes These 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 dense KNOW THIS Pressure and Temperature The 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 low Strongly 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 high Strongly descending air often produces high pressure at the surface a dynamic high Measurement and Mapping of Pressure Weather stations record pressure in units of millibars with a barometer 1 bar 1000 millibars 14 7 pounds per sq inch Isobars lines of equal pressure Ridge 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 Movement Originated of wind uneven heating of earths surface creates temp and pressure gradients Pressure 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 left in southern hemisphere Turns 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 FF Anticyclones 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 centers Northern 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 flow Southern Hemisphere converging clockwise flow Vertical Component of Air Movement in Pressure Center Cyclone air converges and rises Anticyclone air descends and diverges Wind Speed Wind speed is determined primarily by the pressure gradient Steeper gradients cause faster winds slower gradients cause gentle wind General Circulation Model of the Atmosphere Atmosphere is in constant motion Major semi permanent conditions of wind and pressuregeneral 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 circulation Atmospheric 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 climates