Friday, November 25, 2005

Maximum rains spell minimum temperatures

B'lore chill factor: Maximum rains spell minimum temperatures
New Indian Express

BANGALORE: Feeling cold lately? Bangaloreans, pull out your heavy-duty pullovers, mittens, caps, coats and blankets.

For the weatherman has promised that the recent spell of chilly weather is likely to turn chillier with the mercury plunging to below 10 degree Celsius.

Being muffled up is half the story. Who would have thought that chill factors include a complex interplay of October's record monsoon downpours, icy winds sweeping in from the Himalayas, the City's high altitude and cloud cover that dissipates surface radiation?

Translation to plainspeak: Maximum rains spell minimum temperatures. Scientists at the Gandhi Krishi Vignana Kendra here have predicted below-10 degree Celsius temperatures based on similar weather conditions recorded in 1991: a record 530 mm of rainfall in October followed by temperatures that fell to 10.5 degree Celsius.

“Heavy October rains lower the minimum temperature during winter. The heavy rains in October (this year) sufficiently cooled the earth's surface,'' Dr Raje Gowda, the GKVK Professor who heads a team of agrometeorologists at its Agrometrology Department, told this website’s newspaper.

“From November to December, winds from the Himalayan region blow towards the South India Peninsula. But high altitude places like Bangalore slow down these winds”.

“These cold winds, coupled with the lowering in minimum temperature, increase the chill effect from December to February,'' he explained.

During these months, the minimum temperature drops to 10 degree Celsius. And moderate to high-speed winds and light showers literally chills the atmosphere.

What's more, grey overcast skies reinforce the rapid cooling down effect in Bangalore.

“On cloudy days, there is a considerable reduction in solar radiation reaching the earth's surface. But there is continuous outgoing long-wave radiation from the earth's surface”.

“This long-wave radiation, in the form of heat, will be collected below the clouds, and warms up the atmosphere because the clouds acts as a thermostat. A clear sky in winter increases the outgoing terrestrial long-wave radiation”.

“But the amount of solar short-wave radiation received at the surface does not compensate for the outgoing radiation. Hence the surface keeps on cooling till February,'' said Dr Gowda.

Once the clouds clear, the accumulated heat energy dissipates, cooling the atmosphere rapidly.

Evacuation of the cloud cover also creates low pressure that sucks in cold winds passing by and leads to even lower temperatures.

This chill effect may be reduced only if there stronger depressions in the vicinity, such as a cyclone in the Bay of Bengal.

Cold Hard Facts

* Heavy October rains herald severe winter

* Coldest week recorded: Second week of January 1992: 10.5 degree Celsius

* No units to measure chill effect. High-speed winds coupled with low temperatures cause severe chill

* Cold winds blowing from the Himalayan region towards the Indian Ocean pass through South India.


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