Friday, February 1, 2013

What are cyclones?

A cyclone is a huge system of rotating wind around a large scale low pressure area called “eye”.

The rotation of wind is anti-clockwise in the Northern Hemisphere and clockwise in the South. This is due to Coriolis force which acts on a moving body (Wind) in a rotating reference frame (Earth).

Tropical Cyclones are known by different names in different areas:
• Hurricanes in the North Atlantic & Eastern Pacific• Typhoons in Western Pacific

Tropical Cyclones arise over ocean in the tropical latitudes (5°N - 15°N) where Coriolis force is substantial enough to stabilize its low pressure eye.

There are two factors that fuel its growth:

1. Evaporation - When the temperature of the ocean surface (up to the depth of 50m) exceeds 28°C, it intensifies evaporation. The warm and moist air above the ocean rises to create low pressure region. The cooler air swirls around to take its place.

2. Condensation - As the warm air rises, the water vapour condenses to form clouds and droplets of rain. This releases latent heat. This heat combined with heat from the ocean triggers more evaporation which in turn leads to greater condensation (chain of events)!

If Tropospheric Vertical Shear (change of wind velocity with height) is low, the storm builds into a cyclone within two to three days. Otherwise, frequently changing speed and direction of wind in upper atmosphere would halt the progress of storm in the upward direction.

When formed, a cyclone is roughly 600km across and 15km high. The winds in it can speed over 100kmph.

The eye of a cyclone is the region of lowest pressure and highest temperature (as compared to surrounding region). It experiences relatively calm wind and fair weather. It is usually about 50km across.

After the cyclone is formed, it is steered by Trade Winds (Global Winds that blow predominantly from east to west in the Northern Hemisphere) which is responsible for Hurricane Landfalls in North America.

After reaching the land, the break in chain of evaporation and condensation diminishes the energy of the cyclone. Hence, it dies within few days after landfall.

The fancy names of Tropical Cyclones are basically to facilitate easy communication. A list of 21 names (beginning with alphabets excluding Q, U, X, Y and Z) is prepared for each year. The first tropical storm in that year is given the name with A; the second storm is given the name with B and so on.

This was definitely a tough week for Caribbeans and Northeast Americans after being badly hit by Hurricane Sandy. These are the times when we realize how puny we are in front of the mighty forces of nature.

Tough times do not last, tough people do!

Wishing everyone a speedy recovery.

(Photo Source: NASA

Article References:
1. NOAA -
3. Earth Science -

For further study:

No comments: