Climate scientists at the National Aeronautics and Space Administration (NASA) have developed a database available online that displays the extratropical storm tracks that occurred between 1961 and 1998, allowing visitors to find out what the weather was like on the day they were born or any other day in the featured time span.
The original purpose for the creation of the climate atlas was to look back and try to assess the impact of global warming on storms. The online atlas plots the paths of storms and records statistics by tracking the atmospheric low-pressure centers at sea level. The system records several pieces of information, such as storm frequency and intensity, along with the paths of individual storms. It also produces maps of average storm intensity of the most severe storms. The site provides data on individual monthly and seasonal averages for the years 1961 to 1998 as global maps in a variety of projections. Besides images, the hard data is also available for downloading, which contains information on length and location of storms, atmospheric pressure at the storm's center, day, month, year, and time. NASA is currently working to expand the years of coverage to go back to 1950 and extend through 2001.
A hurricane forms when the movement of warm, humid air and cold, unstable air between the upper and lower atmospheres meet. Strong, gusty winds and heavy rains fed by the warm ocean water enter the hurricane from the bottom.
A hurricane begins with the creation of a tight group of thunderstorms over the tropical oceans. Meteorologists refer to this condition as a tropical disturbance. These disturbances start when warm winds converge (collide). When the air collides, it forces it to move upward, starting a thunderstorm.
Often, when the trade winds of the Northern and Southern Hemispheres meet in the Intertropical Convergence Zone (ITCZ), they collide and rise. If a group of thunderstorms breaks away from the ITCZ, it can form an organized storm system. Storms can also form if warm and cold air collide. Once the storm gets organized, the surface air pressure falls in the area around the storm and winds begin to spin in a cyclonic circulation (counterclockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere). Latent heat gets released, which makes the air rise, while the surrounding air sinks. The sinking air gets compressed and warmed. At the surface, it is drawn back toward the center and rises. This process sets up a circular cell. Increasing winds spin around the center of the storm and draw heat and moisture from the warm ocean surface, which provides more fuel to keep the system
Tropical cyclones, such as this one off the coast of Brazil, are some of the most deadly storms on Earth. (NOAA)
going. This system becomes self-perpetuating. A cycle of evaporation and condensation brings the ocean's heat energy into the vortex (center) and fuels the storm.
The storm takes the easily recognized spiral shape because of the Coriolis force generated by the rotation of the Earth. Once a storm system starts and its winds reach 23 miles per hour (37 km/hr), its category moves from a tropical disturbance to a tropical depression. When winds increase to 39 miles per hour (63 km/hr), the cyclone is referred to as a tropical storm and receives an official name. As soon as the winds reach 74 miles per hour (119 km/hr), the storm system is classified as a hurricane. A hurricane can only persist if conditions in the upper atmosphere remain just right. If high pressure exists in the upper atmosphere, it keeps the air currents that are needed to fuel the hurricane from rising. Also, if strong upper level winds exist, they can keep a hurricane from forming by ripping the thunderstorms apart, which keep temperatures from warming and make it impossible for a low pressure system to form at the surface, effectively cutting off the energy to fuel the hurricane. A hurricane will also fall apart if it moves over cooler water with no supply of warm, moist air, or if it moves over land.
Protecting people and the environment from severe weather triggered by global warming currently has many research scientists at the National Hurricane Center at NOAA and elsewhere engaged in theoretical studies, computer modeling, and collection and analysis of field data in an effort to gain a better understanding of the mechanics of global warming and its interaction with the environment to improve forecasting, response, and safety.
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