In
order for a tornado to form, it first needs a rotating body of air at the
ground called a vortex tube. It
requires vertical wind shear as strong westerly flows aloft travel opposite of
southeasterly surface winds at the surface.
The vortex tube is then lifted off the ground by a strong warm updraft
associated with thunderstorms. Once the
air mass is lifted near vertically it is referred to as a mesocyclone. The mesocyclone becomes fully developed in
the updraft of the thunderstorm, and it begins to spin faster as its diameter
decreases while being elongated due to the conservation of angular
momentum. Once the spiraling funnel
cloud touches the ground, it is officially a tornado.
In
the United States, tornadoes usually travel from west to east.
This
is the dominant direction for tornadoes to travel in the United States due to
the prevailing Westerlies that largely control the movement of the severe storm
systems associated with tornadoes. On average, 1,253 tornadoes are observed in the United States annually.
Tornadoes occur in eastern India as well. However the exact number of occurrences is unknown due to a lack of coverage and observation. Below is a map with the highlighted areas known hot spots for tornadoes around the world. Note that eastern India is covered in this map.
Even though the number of observed tornadoes has increased over the past 30 years, this may actually be due to
increased scientific observations and media coverage and not in an actual increase in the tornadoes themselves.
Hurricane Overview:
The
three main requirements for hurricane formation are warm ocean temperatures in
excess of 80 degrees F, a deep warm ocean layer at least 200 meters in depth,
and Coriolis to initiate the spinning.
The
main hurricane formation regions are as follows: 1) In the Atlantic and East Pacific they are
called hurricanes. 2) In the Indian
Ocean near Australia they are referred to as cyclones. 3) Off
the coast of China and Indonesia they are called Typhoons. Below is a map of the regions where hurricanes form:
In
the United States, hurricanes usually travel in a “C” pattern approaching from
the east through the Caribbean and then making a northern turn that takes it up
through the Gulf of Mexico or along the eastern seaboard. Once hurricanes travel to the higher
latitudes, they’re pushed west and back out into the Northern Atlantic.
This
is the dominant path for hurricanes in the Atlantic due to the Trade winds in
the lower latitudes that push the storm westward through the Caribbean. Then as the hurricane travels north, the
westerlies prevail and drive the system back towards the east and into the
Northern Atlantic.
11.3
named systems occur in the Atlantic on average each year
Hurricanes
occur in India, but they are referred to as cyclones.
On
average, 5.4 cyclones occur in the North India Ocean basin annually.
