CUNY PGEOG 130 - Weather Patterns (30 pages)

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Weather Patterns



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Weather Patterns

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Pages:
30
School:
The City University of New York
Course:
Pgeog 130 - Weather and Climate
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Chapter 9 Weather Patterns Mid Latitude Cyclones extratropical cyclones Nor easters Region southern FL to Alaska Lifecycle and associated weather Regional Influence Polar Front Theory Norwegian Cyclone Model WWI describes birth growth and decay of cyclones Generates cyclone at the surface 1 Midlatitude Cyclone primary weather producers low pressure systems 1000 km dia counterclockwise circulation toward center warm and cold fronts upward flow initiates precipitation Fronts boundary surfaces that separate air masses of different densities temperature moisture 15 200km wide line on the weather map 2 Fronts surface slope is gradual warm air overlies cold air air masses move at different speeds one air mass will advance clashing produces weather Fronts warm air is always forced aloft overrunning warm air gliding on top of cold air 3 5 Types of Fronts warm Cold Stationary Occluded Dryline Warm Front warm air mass is advancing displaces colder air at the surface red line with half circles gradual slope 1 200 speed 25 35 km hr 1 200 4 Warm Front adiabatic cooling cloud sequence gradual slope slow advance widespread light precip long duration precipitation precedes front E to SW wind shift 1 200 Warm Front precipitation and temperature profile 5 Cold Front cold air mass is advancing displaces warmer air at the surface cold air more dense forces warm air aloft blue line with triangles steeper frontal boundary 1 100 speed 35 50 km hr 1 100 Cold Front precipitation follows the passage of the front steeper frontal boundary speed more violent weather altocumulus and cumulonimbus 1 100 6 Cold Front same lifting of warm air only quicker over a shorter distance heavy downpours short duration narrow band of precipitation passage of front temperature drops polar air clear skies SW to NW wind shift 1 100 Stationary Front little to no horizontal movement across the front by either air mass lateral motion overrunning light precipitation 7 Occluded Front rapid moving cold front overtakes a warm front warm air driven aloft precipitation from wedging strong temperature gradients intense weather Occluded Front cold type occluded front advancing air is colder than air mass it is overtaking common east of the Rockies cP overtakes mP 8 Occluded Front warm type occluded front advancing air is warmer than air mass it is overtaking Pacific coast mP overtakes cP Drylines fronts based on moisture content not necessarily a difference in temperature dry air forces moist air aloft cT southwest US displaces mT Gulf spring and summer severe T storms from Texas to Nebraska 9 Life of a Midlatitiude Cyclone 2 10 days 6 basic stages Front develops Wave develops Cyclonic circulation established Occlusion begins Occluded front developed Cyclone dissipates Cyclogenesis cyclone formation Front develops Stationary front cP on the North easterlies mT on the South westerlies 10 Life of a Midlatitiude Cyclone Wave develops wavelength O 100 km wave steepens Cyclonic circulation established Warm air invades north warm front Cold air advances south cold front Low pressure at the crest 11 Life of a Midlatitiude Cyclone Occlusion beginning of the end Cold front advances past the warm front Strong temperature gradients storm intensifies Life of a Midlatitiude Cyclone Occluded front developed blizzards strong winds energy is being exhausted within a few days warm front driven aloft 12 Life of a Midlatitiude Cyclone Cyclone dissipates cold air mass surrounds the low at the surface horizontal temperature gradient eliminated 13 Idealized Weather of a Midlatitiude Cyclone Cyclone generally move from west to east Steered by the general westerly circulation Right side of the storm passes first Idealized Weather of a Midlatitiude Cyclone A Cirrus clouds Front 1200 km away Warm front advances cloud base lowers cirrostratus altostratus stratus 14 Idealized Weather of a Midlatitiude Cyclone B Nibostratus clouds Light precipitation gets heavier as front advances Temperatures increase Winds shift from an easterly direction to a southerly direction Idealized Weather of a Midlatitiude Cyclone C mT Air mass Warm moist Clear skies Southerly winds 15 Idealized Weather of a Midlatitiude Cyclone D Cumulonimbus Clouds Heavy rains Violent weather as cold front approaches Idealized Weather of a Midlatitiude Cyclone E Temperatures Drop cP Air mass Descending air Clear skies Low precipitation Wind shifts from southerly to westerly 16 Idealized Weather of a Midlatitiude Cyclone F G Occluded front region Temperature remains cool Precipitation beneath the front Type of precipitation depends on the lower temperature profile OF moves slower than the warm or cold fronts System rotates Veering winds rotate shift in a clockwise direction South of the storm Skies will clear as you move into the mT region or cP region 17 Backing winds rotate shift in a counterclockwise direction North of the storm pass through the occlusion Cold with precipitation 18 Polar Front Theory developed from surface observations Wave develops 1 Topographic irregularities Mnts 2 Temperature contrasts land sea 3 Ocean current influence hurricanes 19 Conditions aloft Surface cyclones are preceded by intensification of airflow aloft Zonal airflow W E little cyclonic activity Longitudinal airflow N S increase cyclonic activity Surface cyclone centered below the jet stream downwind of a upper level trough 20 Cyclonic Anticyclonic Circulation Cyclones and anticyclones are typically found together Surface divergence under an anticyclones feeds surface convergence under the cyclone Divergence aloft must be greater than convergence at the surface under a cyclone Regions of Cyclogenesis Topographic irregularities Mnts Temperature contrasts land sea Ocean current influence hurricanes 21 Storm Tracks Patterns of Movement In general east to northeast track Most of the north Pacific storms that influence the west coast do not make it over the Rockies in tact redevelop Storm Tracks Patterns of Movement 22 Modern View The Conveyor Belt Model 3 intersecting air streams belts 2 belts originate at the surface and ascend 1 belt originates aloft and descends Warm Conveyor Belt mT air moves toward the middle of cylone north over mP or cP air Ascends to middle troposphere JS joins the general westerly flow Primary producer of precipitation Troposphere 12km avg thickness 16km tropics 09km poles 23 Cold Conveyor Belt Originates at surface ahead of the warm front Flows westerly around the center and ascends


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