India's high-powered monsoon engines

MR. ALEXANDER FRATER, a British writer who was on a visit to India a few years ago to study the South-West monsoon was so much overwhelmed by the force, sometimes rising to a destructive fury, of its arrival on the coast of Kerala and subsequent long journey almost all over India right upto Assam that he called it the nature's engine which no human invention could match. Much to the despair of the Indian Meteorological Department (IMD), the manifestations of the monsoon are still unpredictable ranging from cool to roaring cyclonic winds accompanied by disastrous downpours to heartbreaking drizzles which takes the country to a dry, parched and sizzling summer after it makes its exit.

The IMD anticipates that there will be a normal south west monsoon this year with the rainfall amounting to 98 per cent with a plus or minus 4 per cent error for Kerala while for the peninsula region it will be 98 per cent. The anticipated rainfall in Kerala is expected to range around 215 cm upto the end of September as against 176 cm last year.

It should have taken sometime for the meteorologists to realise that India's two monsoons - the south-west and the north-east - are a scientific phenomenon making exacting demands for a proper grasp of their anatomy. The origin of the powerful winds and the accompanying winds of the south=-west monsoon in the Indian Ocean and Arabian sea just above the equator perhaps still remains very much unknown and buried in the clouds waiting to be ripped open by their heavy tonnages of rain. Over the years of study and unrelenting research, the meteorologists have arrived at two models of the monsoon, the parametric and power-regression. The first lists 16 land-ocean parameters of the monsoon.

They are:

- 50 hecta-pascal (hP) East-West Ridge rough pattern of January and February

- Eurasian Snow (December) of a million sq.kms.

- 500 hP Ridge along 75 Degrees East in April

- Central India minimum temperature (May)

- 10 hPa Zonal Wind at Balboa (January)

- East Coast minimum temperature (March)

- Nil pressure anomaly (January to April)

- Argentina pressure (April)

- Northern Hemisphere temperature anomaly (January+February)

- Northern oscillation index) (South of India, Tahiti and Darwin)

- El Nino (Previous year)

- Northern India minimum temperature (March)

- Equatorial Indian Ocean pressure (March to May)

- El Nino

- Himalayan Snow Cover (January to March)

- Darwin pressure (March to May)

The second Power Regression model is for quantitative analysis of the monsoon relating to the force at which the monsoon hits the major part of the Indian sub-continent before it fully discharges itself at the end of September when it recedes prior to the advent of the North East monsoon on the Coromandel Coast. The parameters listed above are under constant revision on the basis of knowledge obtained from continuing research. It is believed that four more have recently been added but the IMD has not stated what they are. Out of the stated sixteen parameters of the monsoon, as many as 10 are said to be favourable for ensuring a good monsoon every year. The listed parameters ranging from the 50hPa East-West ridge to the Darwin pressure seem to cover the atmospheric conditions on the route taken by the monsoon or its vicinity and which could influence its behaviour before its withdrawal at the end of September. The range of the parameters which cover the very negative El Nino factor as well as the atmospheric situation in places as far apart as Argentina and Darwin should give an idea of the far ranging influences on the monsoon.

While the showers of the south west monsoon discharge themselves all over the country, the northern parts of Tamil Nadu on the Coromandel Coast do not benefit from the heavy downpours it brings with it. This is attributed to east coast being on the rain-shadow region of the towering Western Ghats. However, there have been years when Tamil Nadu has also benefited substantially from the South West monsoon. This welcome departure from its normal behaviour by the monsoon is attributed to two reasons. The first is that the wind pressure of the monsoon originating from the sprawling Indian Ocean extending right upto the east coast of southern Africa lifts the rain laden clouds well above the barricading Western Ghats and include Tamil Nadu in its itinerary of India. The far more interesting feature which sometimes makes the Tamil Nadu a beneficiary of the monsoon is that the winds in the seas of the southern hemisphere influenced by what is described as the Corealli force could turn their direction towards Sri Lanka and then to the Bay of Bengal right upto Andamans before it gives a further turn around to the Coromandel Coast. This should explain why the eastern Coromandel Coast particularly of northern Tamil Nadu often benefits from the south west monsoon. It is stated that during this year there has been such a turn which has resulted in good downpours. If, as it appears, this has happened this year and brought heavy rains on the east coast of Tamil Nadu, it might well have advanced the onset of the south west monsoon from the east coast instead of making it oft-predicted beginning from Kerala and the west coast. The cyclone in the Bay of Bengal which had hit Assam and Meghalaya last year is attributed to the Corealli effect which had given a turn to the direction of the south west monsoon to the eastern course and filled it with such a force to hurl it to the north-eastern region. The other aspect of the south west monsoon is that its withdrawal by the end of September or early October is actually returns it the north-east monsoon from early or the middle of October.

The cyclone which had inflicted a heavy damage on the Gujarat coast is also said to have advanced the onset of the south west monsoon in Kerala this year. But there had been occasions when the monsoon had arrived in Kerala even earlier without any cyclone having advanced it. Apart from the misery which it causes, the cyclone is also part of the phenomena which still remains very poorly understood though it could now be meteorologically foreseen. Weather experts still have a long way to go before they could fully understand how they originate and could move with a deadly velocity and destructive force.

C. V. Gopalakrishnan

in Thiruvananthapuram

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