Hurricanes Essay Research Paper How a Hurricane

Hurricanes Essay, Research Paper

How a Hurricane Begins

The Equatorial trough is the area in the ocean in which the trade winds converge. It moves north and south with the seasons. This phenomena can not be explained by scientists. Hurricanes always form along or be the Equatoral trough but, never in it.

In the Tropics warm air rises, cools, sinks and then returns to the equator with the trade winds. Once this air starts sinking it warms adiabatically. This produces and layer of high level air that is warmer than the air below it. This is called a high level temperature inversion. In this rising warm air is usually trapped. This cause storms to develop closer to the surface of the Earth. If a storm is growing vigorously, and is being pushed up by unusually strong winds, then there is a possibility of it breaking through the low lying air. This causes a Tropical depression, that can be up to 40,000 feet tall.

For a tropical depression to grow further into a hurricane, there must be low pressure at the surface accompanied by high pressure at an altitude of about 56,000 feet. This forms an anticyclone Constant vertical moving air feeds the anticyclone. This causes the air to circulate around the high and low pressure areas. In the northern hemisphere the air turns clockwise around the high pressure, and counterclockwise around the low pressure areas. the directions are reversed in the Southern hemisphere. This event is called cyclone circulation.

The wind continues to strengthen until the pressure between the high and the low pressure areas can accelerate no further. It then rises until it meets the anticyclone. The anticyclone (turning clockwise) pushes the rising air outwards away from the center. By removing the rising air more air is drawn upwards. This forces the surface.s atmospheric pressure fall. This fall in pressure need not be great. The average sea-level pressure is 1,016mb. In the center of a hurricane it is 920mb-980mb. This means that the pressure only falls about 4-10%.

Now there is an area, 400m or more across, in which a storm has developed. The air in the center circulates upward towards the top and then disperses outwards. This draws more air upwards. If the air in the center becomes warmer then the air around it the sky in this area will clear, leaving a sunny area surrounded by what appears to be a wall of cloud. This is the eye, and what once was a tropical depression is now a hurricane.

Where Hurricanes Occur

Hurricanes begin as tropical depressions. These are areas where the atmospheric pressure

is just a little lower than the air around it. Hurricanes only start in the tropics, it is impossible for

them to start in places such as Minnesota. Hurricanes have different names in different places. In

the Western Hemisphere they are called hurricanes. In the Bay of Bengal they are called cyclones. Over most of the Pacific they are called typhoons. Near Indonesia they are called baguios. Also some people in Australia call them willy-nillies. Meteorologists use one common name for all of these things. They call them Tropical cyclones. Tropical cyclones are always more intense in the tropics. The opposite of tropical cyclones are anticyclones. These areas of high atmospheric pressure.

In order for a tropical cyclone to form their must be a fall of atmospheric pressure over a large area. This fall in pressure need not be great, only 20mb over a period of two days. This fall in atmospheric pressure is common in temperate latitudes, but is very unusual in the tropics where the air pressure is fairly constant over very large areas. Under certain circumstances this fall in pressure can be enough to trigger a tropical storm.

There are two main scenarios in which tropical storms turn in to hurricanes. It may be that a pocket of low pressure air becomes detached from the edge of a mid latitude weather system and spills over into the tropics as a tongue of low pressure (called a trough) extending the equator at high altitudes. On the other hand, a low pressure system on land may drift out over the sea, or wave develop along the equatoral trough. This will produce a depression that detaches itself from the equatoral trough, which reforms behind it. No matter what the causes it the depression moves westward in an easterly wave.

Minor depressions can start anywhere but will only turn into a hurricane if it crosses over an expanse of very warm sea. This confines the birth place of hurricanes to the tropics. In latitudes higher than 20 degrees the sea surface temperature is usually to low. In areas close to the equator the sea is often warm enough to start a hurricane but hurricanes never start in latitudes lower than 5 degrees. This is because of the Coriolis Effect. The Coriolis effect is needed to swing the air moving towards the low pressure area into a circular path. The effect is not strong enough to cause the swing within 5 degrees of the equator.

Vorticity will cause the air to move in a curved path and eventually cause it to rotate. After it.s momentum accelerates it forms into an even smaller radius. In order for a hurricane to form within 5 degrees of the equator air would need to converge on the low pressure region from such a vast area that there is simply not enough air available.

Taking into account the need for high sea s