Capt A. Ranganathan

The Meteorological Department has declared that the monsoon has set in and is advancing rapidly. They seem to have jumped the gun based purely on the heavy rainfall that lashed the western coast and ignored the most important factor - "The winds". For the monsoon to be active, the upper level winds from the easterly direction have to be very strong (80 to 100 kmph) and the lower level winds have to be moderately strong from the southwest to west (60 to 80 kmph).

To quote from the meteorological texts, ``the periodical reversal of winds is known as the monsoon". The monsoon is generated on account of thermal conditions, which produce a typical wind circulation, which in turn causes enormous amount of rainfall, due to complex land-sea interaction in association with Orography.

The Indian monsoon is caused due to the influx of the winter - southern hemispheric air into the summer - northern hemispheric as a warm maritime current constituting "southwest monsoon".

Having operated flights over the country during the last 10 days, I would say the wind speeds in the upper levels are practically calm and the lower level winds are too feeble to be called monsoon currents.

CYCLONIC CIRCULATION

The torrential rains that we have witnessed are only due to a cyclonic circulation near the Arabian Sea area and this is a condition never witnessed during the southwest monsoon season. Once the circulation and the trough line disappear, the weather conditions are going to clear up. Moreover, the rain bearing cumulonimbus clouds are rarely over 30,000 feet high but the clouds that we have encountered all over India are towering above 45,000 feet. This is more like the pre-monsoon weather and the declaration of an early monsoon leaves many of us in aviation a bit perplexed!

(The author, an airline pilot with 19,000 hours of flying experience, specialises in accident prevention studies)

(This article was published in the Business Line print edition dated June 2, 2006)
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