Тематический сборник текстов для чтения (английский язык). Соснина Е.П - 107 стр.

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winds, though persistent, are not deep. However, they are cool and strong, and can combine

with warm, moist Gulf Stream air transported northward by weather systems to produce

violent thunderstorms and tornadoes as far as 60°N on the North American continent.

The jet streams are rapidly moving upper-level currents. Travelling generally eastward

in the tropopaus e, the polar jets res ide at the juncture of the Ferrel cell and the Polar cell and

mark the location of the polar cold front. During winter, a second jet stream forms at about

the 30th parallel, at the interface of the Hadley and Ferrel cells, as a result of the contrast in

temperature between tropical air and continental polar air.

The jet streams are not continuous, and fade in and out along their paths as they speed

up and slow down. Though they move generally eastward, they may range significantly

north and south. The polar jet stream also marks the presence of Rossby waves, long-scale

(4000 - 6000 km in wavelength) harmonic waves which perpetuate around the globe.