UW-Madison ATMOCN 100 - Tropical Cyclones (8 pages)

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Tropical Cyclones

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Tropical Cyclones


A lecture about tropical cyclones. It describes what we call them, the intensity of them, the parts, etc.

Lecture number:
Lecture Note
University of Wisconsin, Madison
Atmocn 100 - Weather and Climate
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Atm Ocn 100 Edition 1nd Lecture 30 Outline of Last Lecture I Reminders II Current Weather III El Nino Outline of Current Lecture II Reminders III Weather of the day IV Tropical Cyclone vs Midlatitude or Frontal Cyclone V Hurricane Tracks VI Parts and Weather of a Hurricane VII Wind and Storm Movement VIII Initiation of Tropical Cyclones IX Easterly Waves Current Lecture Reminders Homework Due Wednesday November 26 2014 TYU Ch 5 1 2 3 8 9 13 TYU Ch 23 1 2 3 4 5 6 7 8 10 13 19 TYPSS Ch 5 3 TYPSS Ch 23 none TYU Ch 24 1 5 7 9 10 14 18 19 22 23 25 TYPSS Ch 24 4 Plan Issue new homework set on Friday November 21 to be due Friday December 5 2014 Weather of the day The past few weeks Wisconsin has been in the purple and dark blue which is freezing But this weekend it looks like it will be a little warmer above freezing This weekend will be warmer but then it is supposed to get cold again next week Tropical Cyclones Chapter 24 Tropical cyclone forms over tropical Oceans Basic differences with mid latitude cyclone Tropical Cyclone Warm core Intensity increases downward strong surface winds Energy from warm ocean underlying relatively cool atmosphere Energy input by surface fluxes of latent and thermal heat that flow upward in deep precipitating eyewall clouds Midlatitude or Frontal Cyclone Cold core Intensity increases upward jet stream at upper reaches of cyclone Energy from north south temperature differences across a front Energy input by overturning air of contrasting densities i e warm light weight air rising over cold heavy weight air that is sliding underneath the warm air Main Differences between extratropical cyclones and tropical cyclones The extratropical cyclones have cold air in the middle whereas tropical cyclones have warm air in the middle The strongest winds are different between these two as well Extratropical cyclones have strongest winds high in the atmosphere And tropical cyclones tend to have the strongest winds low in the atmosphere Tropical cyclones are known as hurricanes as well Each of these get energy from is important too Extratropical cyclones are based on temperature differences from north to south For tropical cyclone its warm water causing convection and that convection leads to the development of the tropical cyclone and that is where it gets its energy What We Call Them A mature tropical cyclone can become extremely intense We call a mature tropical cyclone greater than approximately 65 knot winds We call them hurricanes in the North Atlantic Ocean They call them typhoons to the Northwest of the Pacific Ocean Some areas call them a severe cyclonic storm or tropical cyclone All of them have winds that are greater then 65 knots This is just calling them different things based on where they are Hurricane Tracks Hurricanes are steered by the mean lower tropospheric flow When the flow pattern moves the storm can be forced to curve or even do loops There is a subtropical high in the Atlantic Typical storms often come off Africa and Southern Atlantic and go west then they curve North curving into the Gulf or Atlantic Coast or off to sea and then once they curve they curve off towards Europe Sometimes subtropical high doesn t exist or it is very weak So then you can have a storm that starts off normally and then goes north and zigzags Main thing is that a typical track goes to the West to the North and then curves back to the East Tracks and Intensity of All Tropical Storms All storms have done this typical path go to the West North and then off toward Europe This map has been since the 50 s The bottom is called the Saffir Simpson Hurricane Intensity Scale A Category 1 is the weakest They go all the way down to Category 5 hurricanes Category 5 hurricanes are by far the most destructive They have at least 135 knots which is 249 mph Hurricane Katarina was a Category 5 at one point A tropical disturbance is an organized thunderstorm cluster and no closed circulation A tropical depression is it there is winds above 34 knots And then a tropical storm is if winds are above 34 knots up to 64 knots It is considered a hurricane if the winds are above 64 knots Some Hurricanes Pressure was insanely high for Hurricane Wilma and then Hurricane Gilbert There is even greater central pressure for Hurricane Rita Parts of the Hurricane There is the eye the eye wall and the spiral bands The eye is the calmest weather at the center of strong tropical cyclones The eye wall in the center is where the strongest winds and strongest rains are The spiral bands are weaker weather then the eye wall Weather of the Hurricane In the center is the eye and than the eye wall to the outside And then there are the spiral bands The strongest wind speeds tend to be near the surface There is wind speed verse height Weaker winds at the top stronger winds near the surface This means weaker winds aloft and strong winds at the surface The lowest pressure is right in the middle There is strong pressure going from the outer edges towards the middle We have a strong pressure gradient in the eye wall where there are strong winds Winds are the weakest in the eye and strongest in the eye wall Rainfall doesn t fall in the eye maybe a little but very light rain is heavy in the eye wall And there is heavy rain in the spiral bands as well Tropical cyclones are warm core systems so the center is actually warmer then what it is towards the outside Based on their location the area that is called cool is still quite warm It is because the tropical ocean Storm surge is the water driven by the wind Where the strongest wind is is where the most storm surge The storm surge isn t right center because it has to do with how the storm moves Wind and Storm Movement The storms movement and the wind are going in the same direction which is considered the right front quadrant To the right of the storms motion the wind is going the same direction The strongest winds are in that location The strongest winds can push the most water so if you have especially strong winds moving with the storm you can push a lot of water with it If you go to the other side the left side of the motion the wind is going against how the storm is moving Then there is weaker winds on the left side so they can t push as much water in the direction that the storms going So there tends to be weaker winds and less storm surge on the left side of the motion There is a diagram that describes what Stephen is talking about There is wind circulation around the

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