Severe Weather COnditions:
Hurricanes:
The scientific term for these storms is tropical cyclone. Only ones that form over the Atlantic Ocean or eastern Pacific Ocean are called hurricanes. Tropical Cyclones use warm, moist air as fuel which is why they form in warm water and near the equator. The ocean water is usually 80 degrees or warmer. Warm air rises and causes an area of lower air pressure. Then, air from surrounding areas that have a higher air pressure pushes into the lower pressure areas causing the "new" air to become warm and moist and rise too. As that warm air rises, the surrounding air swirls in to take its place. The Coriolis Force is needed to create the spin in the hurricane and it becomes too weak near the equator which is why hurricanes never form there. As the warmed, moist air rises and cools off, the water in the air forms clouds. The whole system of clouds and wind spins and grows, fed by the ocean's heat and water evaporating from the surface. As the system rotates faster and faster, an eye forms in the center. The eye has a very low air pressure and the higher pressure from above flows down into the eye.
Storms formed north of the equator spin counterclockwise. Storms south of the equator spin clockwise. The difference is because of Earth's rotation of its axis.
Storms formed north of the equator spin counterclockwise. Storms south of the equator spin clockwise. The difference is because of Earth's rotation of its axis.
Tornadoes:
Several conditions need to be present in the atmosphere at the same time in order for a tornado to form. These are abundant low-level moisture, atmospheric instability, and a "trigger" such as a cold front or other low-level zone of converging winds that lifts moist air. When all of these are present, air will rise and become saturated with moisture. As the air continues to rise, it will produce a thunderstorm cloud if the atmosphere is unstable- a situation that happens when the temperature of the air drops rapidly as it rises, or when dry air overlays most air near the ground. Tornadoes usually form in ares where winds are strong and turn with height in a clockwise, or veering, direction. They can take many forms: Super cell tornadoes, dust devils, fire whirls, gustnado, land spout, and waterspout.
Thunderstorms:
There must be sufficient water vapor in order for a thunderstorm to form. This is the fuel for the storm. When an air mass becomes so unstable, meaning that the air in the lowest layers is unusually warm or humid or that the upper layers are unusually cool, that it convects (overturns) violently. Rising air in an unstable air mass expands and cools and as some water vapor condenses into a cloud that releases heat that makes the air even warmer, forcing it to rise even more in the atmosphere. This continues until a tall convective cloud, a thunderstorm, is formed. The upper portions of the storm are made of ice" ice crystals, graupel, snow, and sometimes hail. Around 50% of the rain reaching the surface in a thunderstorm was ice in the upper regions of the storm. Thunderstorms are most common over land in the afternoons due to the heating of the land by the sun that causes the lower part of the troposphere to become unstable from higher temperature and water vapor in the air. They can also form as a result of the upper atmosphere becoming too cool because of the approach of an upper air disturbance. Eventually, the storm stabilizes the atmosphere by using up the excess water vapor and cooling the lower atmosphere and warming the upper atmosphere.
For more information visit:
- "Tornado: How Tornadoes Form." The Weather Channel. N.p., 2013. Web. 6 Apr. 2014. http://www.weather.com/outlook/weather-news/severe-weather/articles/tornado-how-form_2010-03-30 .
- Leon, Nancy. "How do hurricanes form? :: NASA's The Space Place." NASA's Space Place :: Home :: NASA's The Space Place. N.p., 8 Mar. 2012. Web. 6 Apr. 2014. http://spaceplace.nasa.gov/hurricanes/en/ .
- "What causes thunderstorms?" Weather Questions. WeatherStreet.com, 2013. Web. 13 Apr. 2014. <http://www.weatherquestions.com/What_causes_thunderstorms.htm>.
Pictures:
- http://geology.com/hurricanes/hurricane-names.shtmlhttp://www.wired.com/2007/08/nasa-climate-ch/
- http://www.regency-group.com/blog/be-prepared-michigan-tornado-season
- http://spaceplace.nasa.gov/hurricanes/en/
- http://cliffmass.blogspot.com/2011_04_01_archive.html
- http://www.wired.com/2007/08/nasa-climate-ch/
- http://www.weather.com/outlook/weather-news/severe-weather/articles/tornado-how-form_2010-03-30