The Effect on Climate of Seasonal Variation in Air Masses and Global Circulation Figures are from: Lutgens, F. (2007). The Atmosphere, 10ed. Upper Saddle.
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Presentation on theme: "The Effect on Climate of Seasonal Variation in Air Masses and Global Circulation Figures are from: Lutgens, F. (2007). The Atmosphere, 10ed. Upper Saddle."— Presentation transcript:
1 The Effect on Climate of Seasonal Variation in Air Masses and Global Circulation Figures are from:Lutgens, F. (2007). The Atmosphere, 10ed. Upper Saddle River, NJ: Pearson Education.
2 Air Mass Source Regions for North America Source regions are mostly confined to subtropical and subpolar locationsMiddle latitudes are the site where cold and warm air masses collideDue to converging winds of a traveling cycloneThis zone lacks the conditions needed to be a source region (stagnant air)Winter and Summer maps show that the extent and temperature characteristics fluctuate.
3 Semipermanent Pressure and Wind Systems Average Surface Pressure and Global Winds for January and JulyOn both maps, the pressure regimes are elongated, not zonal.Subtropical highs, centered between 20o and 35o over subtropical oceans, are the most prominent features.Some pressure cells, such as subtropical highs are year-round features.Others are seasonalLittle pressure variation occurs from midsummer to midwinter in the Southern Hemisphere due to the large amount of water in the hemisphere.
4 January Pressure and Wind Patterns Polar HighsProminent features of winter circulation over northern continentsSiberian High over frozen landscape of northern AsiaA weaker polar high is located over North AmericaAzores HighPositioned near the northwest coast of AfricaSemipermmanent lows (Aleutian and Icelandic lows)Not present in July and are not stationary. They are the composite of many cyclonic storms that move across the regions.Regions affected by these lows experience cloudy conditions with abundant winter precipitation.Aleutian low’s cyclonesProduced by frigid air and directed by the Siberian high (flows off the continent of Asia and overrun comparatively warm air over the PacificThis generates cyclonic storms and travel eastward, bringing abundant preicipitation to coastal areas of N. America.Note the position of the ITCZResults in cool, dry air over Asia due to a strong high that develops.Subtropical highs with subsiding drier air dominate Asia
5 July Pressure and Wind Patterns Increased insolation on North American landmassesCause high surface temperaturesLows replace winter highsThermal lows have warm ascending air that causes inward surface flow of airStrongest low is over southern AsiaWeakest is over SW United StatesTropical highs in the Northern HemisphereDominate summer circulation over oceansPump warm moist air onto the continents west of the highs resulting in increased precipitation over parts of eastern North America and Southeast Asia.The Bermuda High is positioned near Bermuda (hence, its name)A Subtropical high that migrates to the east during the winter and is then called the Azores high.ITCZ moves to the north and draws warm, moist air onto the Asian continentThe summer monsoon with heavy rainfall over the Indian subcontinentEastern Asia and Southeastern Asia experience high precipitation from frequent thunderstorms.