A tropical cyclone or a hurricane is like a heat engine that is energised by the latent heat of condensation. Total amount of energy released in a hurricane is estimated to be equal to the total amount of electricity consumed in the United States over a 6-month period.

According to William L. Donn, the power equivalent of the energy liberated within a hurricane in one day is about ten thousand times the daily power consumption in the entire United States.

According to him, the daily energy release within a hurricane is equal to about one hundred thousand bombs of megaton strength.”

The exact mechanism that brings about the formation of tropical cyclones is not well- understood as yet. However, there are certain basic requirements as given below that must be fulfilled for the development of a hurricane.

ADVERTISEMENTS:

(1) Large and continuous supply of warm and moist air:

Tropical cyclones of the hurricane intensity originate over the warm tropical oceans where the surface temperature is about 27°C, so that the lower layers of air adjoining the ocean surface are full of water vapour.

Latent heat is transported into the storms and released in the process of cloud and rain formation. Tropical cyclones originate in the western part of the oceans where temperatures are relatively higher than their eastern parts.

The cold currents lower the surface temperatures of the eastern parts of the tropical oceans making them unfit for the breeding of such storms. Besides, warmer part of the year offers ideal conditions for the development of tropical storms.

ADVERTISEMENTS:

(2) Larger value of Coriolis force:

The very fact that tropical storms seldom originate in a belt 5°-8° wide on both sides of the equator proves that Coriolis force is an important factor in causing, the cyclonic circulation of air.

Most of these cyclones are limited to a belt extending from 5° to 20° latitudes with their maximum frequency in between latitudes 10° and 15°.

(3) Existence of weak tropical disturbances:

ADVERTISEMENTS:

It is the pre-existing mild tropical disturbances which, under favourable conditions, intensify and develop as hurricanes or violent tropical cyclones. Small local differences in the temperature of water and of air produce various low pressure centres of small size.

A weak cyclonic circulation develops around these areas. Then, because of the warm humid air and the latent instability of the air column, a true hurricane vortex may develop very rapidly. However, it may be pointed out that only a few of these disturbances develop into hurricanes.

(4) Upper-level outflow:

At a height of 9000 to 15000 meters above the surface disturbance, there must be an anticyclonic circulation, so that the ascending air currents within the cyclone may continue to be pumped out in order to maintain the low pressure at the centre of the cyclone.

ADVERTISEMENTS:

A tropical disturbance intensifies because of special dynamic conditions in the airflow near 200 millibar level.

(5) Weak vertical wind shear in the basic current:

Because of weak vertical wind shear, hurricane formation processes are limited to latitudes equator-ward of the subtropical jet stream.

(6) Small atmospheric vortices in the inter-tropical convergence zone:

ADVERTISEMENTS:

These atmospheric vortices initiate the hurricane forming processes. It may be pointed out that the trade winds from both the hemispheres meet along a line called the inter-tropical front.

Temperature contrasts between these air masses must exist when the inter-tropical convergence zone is farthest from the equator. Thus, the convergence of these winds of different temperatures and the resulting instability are the prerequisites for the origin and growth of violent tropical storms.

The tropical cyclones develop over tropical oceans, where there is an acute paucity of weather observing stations.

Naturally, therefore, the required data about atmospheric conditions are missing, and this unfortunate situation makes the task of investigating the factors responsible for the development of tropical cyclones all the more difficult.

ADVERTISEMENTS:

If additional observing stations on the surface are made available, and if they can supplement aircraft and satellite surveillance, then the unanswered questions concerning tropical cyclones may be solved.