Hurricane, or typhoon, or tropical cyclone are different names of a similar weather phenomena. Hurricane is a region-specific term used for severe tropical storm with high speed wind occurring in North Atlantic Ocean including the Gulf of Mexico and the Caribbean Sea; the Northeast Pacific Ocean and the South Pacific Ocean. Hurricanes, generally, will have a minimum rotating speed of more than 74 miles per hour. The hurricane season in the Atlantic, Gulf of Mexico, Caribbean and Central Pacific Basin is usually between 1st of June to 30th November, whereas the hurricane season in the Eastern Pacific Basin is usually from 15th May to 30th November. This terrifying blast of the nature can cause great calamities.
Similarities with Tropical Cyclones
Tropical cyclone, or typhoon are just other names used for similar tropical storms such as a hurricane; with their locations being the only difference. Severe storms in the northwest side of the Pacific Ocean are called typhoons and the term tropical cyclone is applied for severe storms with strong wind and rain, characterized by a low-pressure center over the warm waters of the South West Indian Ocean.
Low-pressure center, strong winds and spiral bands of thunderstorms are common characters of tropical cyclones and hurricanes. The force of a hurricane or tropical cyclone decreases when they hit the land, as they are fueled by warm ocean water, but they can cause greater disasters when accompanied by heavy rain and stormy wind.
Origin of the Term Hurricane
The origin of the term Hurricane has an influence of mythology. It is believed that the word Hurricane is derived from the term "Hurican”, which is the Carib Indian’s 'God of Evil'. Even the term Hurican is further derived from Hurakan, the Mayan creator of God who is believed to have created dry land from chaotic water before destroying the men of wood with heavy storm and flood.
Physical Structure of a Hurricane
A hurricane has three main parts: An eye which is the center of the storm, an eye wall and the spiral rain bands in the outer region. A mature hurricane has winds blowing in roughly circular shape. The eye of a mature hurricane is usually 20-to-30 miles wide, with calmer air and light or no rain. The surface wind of a storm blows inward towards the center. The wind speed increases at the eye wall, which surrounds the eye.
The eye wall is characterized by strong rainfall and storm. The spiral rain bands, the third important part of the hurricane, are long bands of clouds spiraling inbound to the eye wall. The rain bands are also capable of producing heavy rain and wind.
Scientific Reasons Behind Hurricane Formations
The great temperature difference between the warm water and the overhead cloud triggers the formation of a thermodynamic engine of hurricane. The temperature of the warm water above 26 degree Celcius creates the energy for the hurricane. The heat of the warm water causes the water to evaporate and create moist air and overhead clouds.
The cloud above the warm water surface pulls up the moisture and air from the water surface and creates a low pressure area beneath, which further attracts cooler air from the surrounding high-pressure areas. The cooler air then becomes warm, coming in close proximity of the warm water surface and continues to rise above. The warm, moist air, after rising, cools off and forms clouds. The whole process of cloud formation and wind speed grows and the storm becomes faster creating a hurricane or a cyclone, depending on its location.
Hurricanes are formed mainly due to the presence of three prime factors: First, the warm ocean water which provides moisture and heat to the overhead air required to fuel the hurricane; second, moisture in the atmosphere from evaporation of the ocean water, combined with heat energy, to form powerful hurricane; third, a wind pattern is required near the surface of the ocean to spiral air inwards, which is required to form a hurricane. Besides, some preexisting weathering disturbances in the tropical circulation or even tropical depression can propel a hurricane.
Due to the rotation of the earth on its axis, the storm in the north of the equator rotates counterclockwise and that in the south rotates clockwise. Late summer is the time of increases in cyclone occurrence, as, at this time of the year the difference between sea water temperature and the overlying air is the greatest.
Types and Reasons of Movement
A hurricane has two kinds of circulations - primary and secondary. The primary circulation of the storm is purely circular in nature and is the rotational part of the flow. This circulation is influenced by Coriolis force, centrifugal force, pressure gradient and friction. The secondary circulation is the overturning part of the flow; it is in the radial and vertical directions.
The movement of a hurricane is navigated by the global winds and the “beta effect”. A hurricane moves along the path guided by its surrounding wind field. For example, trade winds or the easterly winds in the tropics direct the hurricane towards the west. The other factor influencing the hurricane movement is the beta effect that is the variation of Coriolis force with latitude. The beta effect drifts the hurricane North Westward.
Dissipation of a hurricane, in simple words, means disappearance of the storm. A hurricane would dissipate when it loses its strength due to natural causes; that is, when it hits the land it loses its energy that was propeled by the warm ocean water. Even when the storm moves over to the colder ocean water with less than 26.5 degree Celcius temperatures, the hurricane loses its strength. Besides, when a hurricane moves into the middle latitudes, it can transform into an extra tropical cyclone with weakening of warm center and transition to cold core center.
Effects of Hurricanes
Hurricanes have massive environmental as well as economic effects. Hurricanes create large waves and cause heavy rainfalls, which results in floods and resultant destruction and casualties. Hurricanes bring along strong gusty winds, which have the potential of destroying vehicles, buildings, bridges, uprooting trees and damaging other structures.
Millions of people have been affected by hurricanes and billions of dollars have been spent in hurricane preparedness and also in rebuilding those areas which are damaged by nature’s fury. Besides, when a hurricane touches the shore it carries salt from warm ocean water and increases the level of salinity of many freshwater areas, consequently affecting many freshwater habitats. Hurricanes also have some positive impact like it maintains global heat balance by taking the warm moist air to middle latitudes and polar areas.
Observation and Forecasting of Hurricanes
Satellites, land-based observation, ship-based observation, or hurricane-hunter aircrafts are tools for hurricane forecasters to predict the path of the storm. Satellites today are the best tools for getting information about the ocean-borne hurricanes, which are far from the land-based observation network.
Even aircraft-based observations have been successful before the advent of the satellites. Agencies like Tropical Cyclone Warning Center and National Hurricane Center define the future path of the storm by designing computer models from the data drawn from the observation platforms. When the surrounding wind field or the trade winds are stronger, forecasting of the storm path becomes easier for the forecasters.
Classification of Hurricanes
Hurricanes are classified on the basis of their intensity: Tropical disturbance, depression, storm, and tropical cyclone, or hurricane. In fact, tropical disturbance is the first stage of the beginning of a hurricane. It is a low pressure area in the atmosphere with converging wind, which results in the tropical disturbance. Once the system develops with organized circulation center of the wind, it becomes a depression. The depression then turns into tropical storm with increase in the wind speed to about 39 miles per hour. When the wind speed intensifies and grows above 74 miles per hour, the storm becomes a hurricane over the Atlantic and a typhoon in the west of Pacific.
Man-made Causes of Hurricanes
An in-depth analysis of the recent extreme natural disasters reveals that the over exploitation of environment and its resources by its people is the main factor behind such disasters. Scientists believe that the increase in the number of strong hurricanes is mainly due to the global warming and resultant increase of the sea surface temperature and rise in the sea water levels. Hurricane Katrina of 2005, in the US, for instance, caused immense damage and causalities not because of the strong hurricane that it was, but because of the destruction of wetlands, construction of houses, pipelines near the coast in hurricane-prone areas and other such human activities.
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Last Updated : February 21, 2017