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UIUC ATMS 100 - Uooer Level Maps and Forces

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Lecture 9Outline of Last Lecture I. ClimateII. Climate Changes with TimeIII. Climate of Past 130 Years (Instrumental Record)IV. Global Warming-- Possible CausesV. Continental DriftVI. Milankovitch CyclesSolar VariabilityVII. VolcanismVIII. Past Climate: Natural Climate Forcing Agents OnlyIX. Anthropogenic AerosolsX. Greenhouse Gases: Selective IR AbsorbersXI. Past Climate: Natural and Anthropogenic Forcing AgentsXII. Global Warming RecapXIII. CO2 Emissions ScenariosXIV. Why Uncertainty?XV. Where will warming happen?XVI. Melting Glaciers on LandXVII. Sea Level RiseATMS 100 1st EditionXVIII. Perceiving Climate ChangeXIX. Climate Change and Extreme WeatherXX. What You Can Do: Energy ConservationOutline of Current Lecture XXI. Weather MapsXXII. Constant Height MapsXXIII. Constant Pressure SurfaceXXIV. Constant Pressure Surface- Heating and CoolingXXV. Analogy: Topographic MapsXXVI. Constant Pressure MapsXXVII. Forces in the AtmosphereXXVIII. Review of PressureXXIX. Pressure GradientXXX. Pressure Gradient ForceXXXI. Rotation of the Earth: Coriolis ForceXXXII. Merry-Go-Round ExampleXXXIII. The Coriolis ForceXXXIV. Coriolis Force and LatitudeXXXV. Coriolis ForceCurrent LectureXXXVI. Weather Mapsa. Constant height maps:i. example: surface mapsii. map has same elevation everywhereiii. pressure variesThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is bestb. Constant Pressure Maps:i. upper-air mapsii. map has same pressureXXXVII. Constant Pressure Surfacea. assume uniform surface pressure and temperatureb. this means that constant pressure surfaces are parallel to constant heigh surfaces (flat)c. high heights are indicative of warm air below that pressure leveli. warm air is less dense than cold aird. low heights are indicative of cold airi. as you heat air,it expandse. high heights on a constant pressure surface are analogous to high pressures on a constant height surfacef. low heights on a constant pressure surface are analogous to low pres-sures ona constant height surfaceg. if you only think about this in terms of “pressure always decreases withheight” you will get it h. in the troposphere, pressure surfaces generally slope downward from the Tropics toward the polar regionsi. waves are superposedXXXVIII. Constant Pressure Surface- Heating and Coolinga. now heat left side, cool right sidei. warm air expands-- pushes pressure surface upwardsii. cool air contracts-- pressure surface moves downwardiii. constant pressure surface no longerXXXIX. Analogy: Topographic Mapsa. contour eleveations on constant pressure surfaces just like on topo-graphic mapsb. hikers: what do closely spaced elevation contours mean?XL. Constant Pressure Mapsa. trough: valley; low heights (pressures)b. ridge: high heights (pressures)c. do not just look at shape of contour linesd. **high heights are indicative of warm air below that pressure level**i. analogous to high pressures on constant height surfaceii. remember: a high is a highe. **low heights are indicative of cold air below that pressure level**i. analogous to low pressures on a constant height surfaceii. remember: a low is a lowXLI. Forces in the Atmospherea. Newtwon’s Second Law Says:i. that a net force is required to accelerate any object, including airii. pressure gradient force (PGF)iii. Coriolis Force1. apparent force due to rotation of earthiv. Friction1. near-surface flow onlyv. Gravity 1. veritcal motions onlyXLII. Review of Pressurea. pressure= force/areab. related to the weight of the atmosphere above youiii. greater mass of air above a high pressure system than above a lowXLIII. Pressure Gradienta. air molecules want to flow from where there is greater pressure to where there is less pressureiii. extreme case: a vacuumb. increasing the pressure gradient yields greater acceleration and faster flow XLIV. Pressure Gradient Forcea. pressure gradient = change in pressure/distanceb. units= mb/kmc. tightly packed isobards- strong pressure gradientiii. big change over small distanced. widely spaced isobars-weak pressure gradientiii. small change over big distancee. PGF directed from higher to lower pressure (or higher heights to lower heights on constant pressure surface)iii. acts perpendicular to isobars (or height contours)f. PGF causes wind to blow iii. strong PGF= strong windsXLV. Rotation of the Earth: Coriolis Forcea. viewed from above the North Pole, the earth rotates counter-clockwiseb. wind blowing on the earth is analogous to throwing the ballc. viewed from over North Pole, earth rotates counter-clockwised. surface rotates at faster speed near equator, slower near polese. as air from equateor moves northword (inward) it moves faster than theair/ground around it and appears to be deflected eastwardf. view from earth over noth pole, earth rotates counter clockwiseg. surface rotates at faster speed near equator, slower near polesh. as air from Pole moves southward (outward) it moves slower than the air/ground around it and appears to be deflected westwardXLVI. Merry-Go-Round Examplea. if merry-go-round is not moving, ball will not appear to be deflectedb. if merry-go-round is moving, ball will still travel straight path as seen from abovec. ball will appear to be deflected to its from rotating platformiii. thrower sees ball move to his right-- appears to be due to exter-nal forceiv. catcher actually rotates to his right (thrower’s left) out of the wayof balld. same effect occurs on rotating earthXLVII. The Coriolis Forcea. if you take a turn too fast in your ca, you will be deflected outward fromthe axis of rotationb. for eastward moving air, this corresponds to a southwardc. the opposite scenario occurs for a westward accelerationd. air deflected inward toward axis of rotationiii. corresponds to a northward deflectione. Northward (south winds) moving objects-rotate faster than ground be-neath themiii. appear to be deflected eastwardf. southward (north winds) moving objects-rotate slower than ground be-neath themiii. appear to be deflected westwardg. eastward (west winds) moving objects- deflected outward from axis of rotation (southward in NH)h. westward (east winds) moving objects- deflected inward toward axis of rotation (northward in NH)XLVIII. Coriolis Force and Latitudea. change in distance from axis of rotation with north-south greatest near poles, zero at equatorb. coriolis force maximum at Poles, minimum at equatorXLIX. Coriolis Forcea. deflects objects


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