Loo (wind)

The Loo (Hindi: लू, Urdu: لُو‎, Punjabi Gurmukhi: ਲੂ) is a strong, hot and dry summer wind from the west which blows over the western Indo-Gangetic Plain region of North India and Pakistan. It is especially strong in the months of May and June. Due to its very high temperatures (45 °C–50 °C or 115 °F–120 °F), exposure to it often leads to fatal heatstrokes.

Since it causes extremely low humidity and high temperatures, the Loo also has a severe drying effect on vegetation leading to widespread browning in the areas affected by it during the months of May and June.

The Loo mainly originates in the large desert regions of the northwestern Indian subcontinent: the Great Indian Desert, the Cholistan Desert and the desert areas of Southern Balochistan.

The Loo ends in late summer, with the arrival of the Indian monsoon. In some areas of North India and Pakistan, there are brief, but violent, dust storms known as Kali Andhi (or black storms) before the monsoon sets in. The arrival of monsoon clouds in any location is frequently accompanied with cloudbursts, and the sudden transformation of the landscape from brown to green can seem "astonishing" as a result of the ongoing deluge and the abrupt cessation of the Loo.

Since the plains of North India and Pakistan are both very hot and extremely dry during this season, water evaporates quite readily. Although this leads to the drying out of many ponds and lakes, the extreme dryness of the air is also easily exploited to create evaporation-based cooling systems. Windows shielded with fiber-screens of the fragrant khas (ख़स/خس or vetiver) dry-grass that are kept damp with a simple water-pumping mechanism are quite effective as an inexpensive form of air conditioning, and have been in common use throughout the plain portions of the northern Indian subcontinent for centuries. Because evaporation proceeds at a very rapid rate in the extreme dryness, the cooling effect can be quite dramatic and result in dwellings where the interior feels chilly. The water in the screens evaporates very rapidly, however, so it must constantly be replenished from raised tanks or with pumps (that can sometimes be driven by the Loo itself). Any water reservoir used must also be shielded from the Loo and the sun, or it can rapidly be depleted.

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Wikipedia