Figure 1 – Winter Monsoon: Surface Winds

♤ Jet stream and Upper Air Circulation – a different pattern of air circulation is observed at a height of about 3 km above the surface. Direction and velocity of winds at this height are different from those of the surface winds. All of Western and Central Asia remains under the influence of westerly winds along the altitude of 9-13 km from west to east (Figure 2). These winds blow across the Asian continent at latitudes north of the Himalayas roughly parallel to the Tibetan highlands. These are known as Jet Streams3. Tibetan highlands act as a barrier in the path of these jet streams. As a result, jet streams gets bifurcate – one to the south and other to the north of this mountain chain along 25° N latitude. This jet stream is

3 For more details about jet stream, See document “INSOLATION, EARTH’S HEAT BALANCE, DIFFERENT ATMOSPHERIC…”

responsible for bringing western disturbances4 from the Mediterranean region into Indian sub-continent. Winter rain and hail storms in northwestern plains and occasional heavy snowfall in hilly regions are caused by these disturbances.