Figure 20 – mountain and valley breezes

Local winds that are hot are caused by the advection of hot air from a warm source region. They may also be produced by dynamic heating of air as it descends from an elevated area to lowland. Few famous hot winds are:

♤ ‘ Loo’ is a hot and dry wind, which blows very strongly over the northern plains of India and Pakistan in the months of May and June. Their direction is from west to east and they are usually experienced in the afternoons. Their temperature varies between 45°C to 50°C.

♤ ‘ Foehn’ is strong, dusty, dry and warm local wind which develops on the leeward side of the Alps mountain ranges. Regional pressure gradient forces the air to ascend and cross the barrier. Ascending air sometimes causes precipitation on the windward side of the mountains. After crossing the mountain crest, the Foehn winds starts descending on the leeward side or northern slopes of the mountain as warm and dry wind. The temperature of the winds varies from 15°C to 20°C which help in melting snow. Thus making pasture land ready for animal grazing and help the grapes to ripe early.

♤ ‘Chinook’ is the name of hot and dry local wind, which moves down the eastern slopes of the Rockies in U.S.A. and Canada. The literal meaning of chinook is ‘snow eater’ as they help in melting the snow earlier. They keep the grasslands clear of snow. Hence, they are very helpful to ranchers.

♤ ‘Sirocco’ is a hot, dry dusty wind, which originates in the Sahara desert. It is most frequent in spring and normally lasts for only a few days. After crossing the Mediterranean sea, the Sirocco is slightly cooled by the moisture from the sea. Still it is harmful for vegetation, crops in that region. Its other local names are Leveche in Spain, Khamsin in Egypt, Gharbi in Aegean Sea area.

♤ Harmattan is a strong dry wind that blows over northwest Africa from the northeast. Blowing directly from the Sahara desert, it is a hot, dry and dusty wind. It provides a welcome relief from the moist heat and is beneficial to health of people hence also known as ‘the doctor’. It is full of fine desert dust which makes the atmosphere hazy and causes problems to the caravan traders. It may cause severe damage to the crops.