08 - Storms Are Variations in LargeLarge-Scale Atmospheric...

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Unformatted text preview: Storms Are Variations in LargeLarge-Scale Atmospheric Circulation Storms are regional atmospheric disturbances. Storms have high winds and most have precipitation. Tropical cyclones occur in tropical regions. These storms can cause millions of dollars worth of damage and endanger life. Cyclonic vs. Anticyclonic CYCLONIC NP LOW HIG H ANTI-CYCLONIC EQ Extratropical cyclones occur in Ferrel cells, and are mainly winter weather disturbances (though they can occur any time of year). These storms can also cause extensive damage. Both types of storms are cyclones, or rotating masses of lowlowpressure air. LOW SP HIG H Extratropical Cyclones Form between Two Air Masses (a) The genesis and early development of an extratropical cyclone in the Northern Hemisphere (b) How precipitation develops in an extratropical cyclone. These relationships between two contrasting air mases are responsible for nearly all the storms generated in the polar frontal zone and thus responsible for the high rainfall within these belts and the decreased salinities of surface waters below. Fig. 8-20, p. 218 Tropical Cyclones Form in One Air Mass The internal structure of a mature tropical cyclone, or hurricane. (The vertical dimension is exaggerated in this model of a hurricane.) Fig. 8-22, pp. 218-219 1 Tropical Cyclones Form in One Air Mass The dynamics of a tropical cyclone, showing the influence of the Coriolis effect. Note that the storm turns the "wrong" way (that is, counterclockwise) in the Northern Hemisphere, but for the "right" reasons. Fig. 8-22, pp. 218-219 Tropical Cyclone Classification -When wind speeds reach at least 119 km/hr called a hurricane - When wind speeds are between 63 km/hr to 118 km/hr the system is called a tropical storm -When wind speeds are 62 km/hr or less the system is called a tropical depression Hurricane Wilma Oct. 2005 Tropical Storm Karen Oct. 2007 Tropical Depression 6 July 2003 Tropical Cyclones Form in One Air Mass What is needed for Tropical Cyclone formation? 6 parameters are necessary for formation 1. Warm ocean surface (>26 (>26 C) 2. High humidity 3. Convection/convergence/instability in the lower atmosphere 4. Coriolis force (cannot be right on the equator, where the Coriolis force is zero!) 5. Low vertical wind shear 6. Existing disturbance with some component of rotation Without one of these, a tropical cyclone will NOT form! But having all six doesn't guarantee formation either... Fig. 8-24, p. 221 2 Water vapor in the atmosphere from the University of Wisconsin Wind streamlines (lines that follow a constant wind direction) from the UK Met Office Wind Shear Vertical wind shear is the change of wind speed and/or direction with height: Fastest Fast Slow Slowest Westerly Westerly Easterly Easterly What is needed for Tropical Cyclone formation? Remember the latent heat of vaporization? vaporization? That large amount of heat that is added to a water molecule to cause evaporation is released when water condenses! This allows a tropical cyclone to continually power itself once it forms: -Water vapor from above the ocean is blown upward into the storm, cooling as it goes, and eventually, it will condense -Upon condensation, that latent heat is release and is used to power the motion of the storm. -The water will then fall out as rain 3 Where do they form...and where do they go? 1985 2005 Global Tropical Cyclone Tracks The tracks of tropical cyclones. The breeding grounds of tropical cyclones are shown as orangeorange-shaded areas. The storms follow curving paths: First they move westward with the trade winds. Then they either die over land or turn eastward until they lose power over the cooler ocean of mid-latitudes. Cyclones are not spawned over the South Atlantic midor the southeast Pacific because their waters are too chilly; nor in the still air - the doldrums - within a few degrees of the equator. Note the lack of storms in the South Atlantic waters are usually too cold to promote storm development Only one storm in recorded history: March 25, 2004 at Category 1 storm formed off the coast of Brazil Consequences Strong Winds: -Saffir-Simpson scale used to Saffircategorize storms Heavy Rain: -rainfall rate can exceed 1 in/hr Storm Surge: -low pressure in the storm's center can lead to a dome of seawater - this mass of water is driven by the storm -can cause quick and deadly flooding when this reaches land -storm surge of 12m was reported in Bangladesh in 1970, and 8m from Hurricane Katrina! Tropical cyclones usually last about 5-10 days 5but could last up to 3 weeks! Hurricane Andrew (1992) upon Florida landfall Hurricane Dennis (2005) upon Cuba landfall Hurricane Katrina (2005) upon Louisiana landfall Hurricane Frances (2004) upon Florida landfall Hurricane Gaston (2004) upon South Carolina landfall Actual damage done depends a lot on the quality of construction of buildings along the coast (relates to building codes) Hurricane History Galveston, TX September 8, 1900 ~8,000 people killed by a Category 4 hurricane 1/3 of total tropical cyclone related U.S. total fatalities No warnings were available because of technology at the time Storm surge arrived at high tide causing massive flooding Galveston, TX, 1900 4 Hurricane History 2005 North Atlantic Hurricane Season 28 tropical cyclones! 15 hurricanes! 3 of the hurricanes reached Category 5 strength! 7 storms in July 2005 alone! First tropical cyclone to strike Europe in recorded history Hurricane Vince, October 11, 2005! US$100billion in damage! 1.5 million people displaced from their homes! Hurricane Katrina -Most costly U.S. natural disaster -Reached Category 5 strength over the Gulf of Mexico, after briefly making landfall in Miami as a Category 1 hurricane -Weakened before making landfall -Mississippi and Louisiana particularly hard hit flooding broke New Orleans levees massive flooding Hurricane Rita -Less than a month after Hurricane Katrina, Hurricane Rita made landfall at TX-LA border as Cat. 3 hurricane TX-Severe property damage, but low loss of life -Again broke New Orleans weakened levees Hurricane Wilma -Most intense storm ever recorded in the Atlantic -Wind speeds over 195 km/hr (that's 185 mph!!) -Caused heavy damage to Cancun and Cozumel, Mexico Global Warming and Tropical Cyclones -Global warming will lead to higher temperatures, including sea surface temperature -But we don't know if that is enough to give us more storms or stronger storms... -Remember the 6 necessary parameters for storm formation: 1. Warm ocean surface (>26 (>26 C) 2. High humidity 3. Convection/convergence/instability in the lower atmosphere 4. Coriolis force (cannot be right on the equator, where the Coriolis force is zero!) 5. Low vertical wind shear 6. Existing disturbance with some component of rotation 5 Global Warming and Tropical Cyclones -According to a 2006 study by Anthes et. al., sea surface temperatures have risen .6C since we began measuring -And as of 2003, approximately 41% of the world's populations live on coasts (Martinez et. al., 2007). -So, it is really important that we prepare for any changes in tropical cyclone frequency or intensity. There are two types of studies completed to answer the question of what will happen to tropical cyclones in a warming environment: 1. Historical data analysis 2. Computer model experiments Historical Data Analysis Historical record not reliable across the globe: -Different Meteorological agencies use different wind speed averaging methods (so what one nation may call a Category 3, another might call a Category 2) -Record isn't reliable until the mid 1980's, when infrared technology became available on satellites, and we could monitor storms day and night. -Prior to the satellite era, we only knew about a storm if it made landfall, or a ship came across it Historical Data Analysis -Scientists who study the historical record have to take all of these facts into account when they try to see if storm intensity and frequency are increasing -So far, scientists have not come to any solid conclusions: --separate studies don't agree on results --most scientists unwilling to attributes changes to sea surface temperature the other important parameters change with global warming too! -Additionally, atmospheric/oceanic oscillations, such as ENSO, affect tropical cyclones 6 Model Studies -Model studies can look into the future of tropical cyclones, and can use more of the important parameters necessary for storms to form -However, resolution of the model is really important and can greatly affect the results. --Some models look at area of 50km x 50km --Some --Other look at areas as large as 200km x 200km --Other -But details of tropical cyclones are REALLY small in comparison to the model resolution -Still, we can get a better an idea of what climate change will do to the nature of storms -The only result that seems to be robust: North Atlantic Hurricanes that are more intense...but not necessarily greater numbers of them. -Many of the models have shown that vertical wind shear will increase, and the atmosphere will become more stable in parts of the world, leading to a wide variety of results in other tropical cyclone basins. 7 ...
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