c When the polar jet is stalled or fixed for extended periods Weather extremes

C when the polar jet is stalled or fixed for extended

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c) When the polar jet is stalled or fixed for extended periods: Weather extremes may result . In other words, the weather over a period of time may be hotter, colder, drier, or wetter than normal. The westerlies help transfer heat from the Equator to the poles , because the jet stream meanders, producing large amplitude waves and a general north to south flow. (Cold air is allowed to advance southward .)
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Middle Latitude Cyclonic Storms They redistribute large quantities of heat across the midlatitudes . They move cold air southward and warmer air northward . Eventually the redistribution results in a weakened temperature gradient, and a return to a flatter flow aloft, and less intense weather at the surface.
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Jet Streams A jet stream may be best pictured as the fast core of the overall westerly flow – like the fastest part of a river . Jet streams follow wavy paths that have long wave lengths. The longest wave patterns are called Rossby Waves and have wavelengths of 2500 to 4000 miles (4000 to 6000 km). Therefore three to six Rossby Waves will fit around the globe . Rossby Waves tend to remain stationary or move slowly.
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Subtropical Jet Stream ` This is a semi-permanent jet stream that occurs over the subtropics. It flows at 30,900 feet – 45,000 feet near the tropopause (about 8 miles up). It exists only in the winter . It is not present in the summer, because of the lack of a strong temperature contrast at subtropical latitudes. It is centered at 25 0 latitude at an altitude of 8 miles (13 km) . The subtropical jet is slower than the polar jet. The subtropical jet meanders from 20 0 to 50 0 latitude.
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Warming of the Polar Regions As the polar regions warm, the Polar Vortex is opening up more often. The Polar Vortex is a center of very cold air and low pressure found at high altitudes over the Polar Regions. Normally there are three to five Rossby Waves circulating the Polar Vortex around the North and South Poles. As the Polar Regions warm, the waves are becoming larger and they shift more slowly from west to east. (This perturbs the movement of the jet streams.) Extreme weather events in the midlatitudes in winter stay in place longer. They pass more slowly.
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Monsoons (Summary) Winter Season Overall flow off the continents which is accompanied by dry conditions . Much drier than North American winters ; high pressure and subsiding air dominate the continent. Summer Season Winds flow from the sea toward the land, and this part of the monsoon is often associated with heavy rainfall . Low pressure and convergence dominate the circulation of Southern Asia. Heavy rains occur from the warm, moist air drawn from the oceans over the Asian land mass.
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One half the world’s population inhabits regions affected by monsoon circulation, and most depend upon subsistence agriculture for subsistence . Failure of the summer monsoons to bring normal high amounts of precipitation have historically led to the starvation of hundreds of thousands of people in one year.
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  • Fall '16
  • Mark Smith
  • weather, Tropical cyclone, Atmospheric dynamics

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