UW-Madison ATMOCN 100 - More on Tropical Cyclones (5 pages)

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More on Tropical Cyclones



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More on Tropical Cyclones

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A lecture continuing information about tropical cyclones.


Lecture number:
32
Pages:
5
Type:
Lecture Note
School:
University of Wisconsin, Madison
Course:
Atmocn 100 - Weather and Climate
Edition:
1
Documents in this Packet
Unformatted text preview:

Atm Ocn 100 Edition 1nd Lecture 32 Outline of Last Lecture I Reminder II Current Weather III Basic reasons why Extratropical cyclones and Tropical cyclones exist IV Extratropical and Tropical Cyclone Configurations V Main Summary Points Outline of Current Lecture II Weather of the day III Some Review IV Hurricane Structure Current Lecture Wednesday class is optional it is a review session Today we will be finishing tropical cyclones Weather of the day There is a strong pressure system over Southern Canada We can see that there is a lot of precipitation here today Based on the fact that that there is a yellow line or the 540 thickness line is off to the east but is affecting us a lot It is going to keep snowing pretty much all day today This snow will not end till 3 am tomorrow morning We should expect about 2 3 inches of snow but could be more This morning said we could get up to 5 inches of snow Extratropical cyclones derive energy from a thermal contrast The low is made up of two air currents one going over the top and curving and another one from the north curving underneath As the cold air sinks downward it forms a vacuum above As it falls it lowers the pressure above which sucks in warm air When cold air is next to warm air the cold air falls and then produces pressure that sucks warm air The warm fluid is drawn over the top there is a sucking upward to bring in more air from behind As warm air over the cold air it is drawing air up from the south to fill void The low pressure is really an illustration of the sucking or low pressure The low pressure sucks warm air so it can rise Looking at warm air rising over the top of a falling cold air wedge A question about this is why does this occur in a small low pressure system that s rotating Some Review Why doesn t cold air everywhere slide to the south and then warm air go to the top of it What prevents that It has to do this in the form of extratropical cyclones because coriolis on the large scale holds that cold air up So on a large scale the cold air is propped up and it won t sink because it is in a balance with the coriolis effect But as you get to smaller scales of circulation the coriolis effect becomes less important We don t care about the earth spinning on smaller scales On a global scale it matters On finer scales this can happen which is why we have extratropical cyclones There is a big difference between extratropical cyclones and tropical cyclones There will be questions about this on the final A cyclone is not a cyclone A cyclone is there for a reason what is the reason for the extratropical cyclone Why do we have extratropical cyclone What is it doing In the big scheme of things it is allowing the cold air that is propped up that is kept in equilibrium of earth to advance to the south and the warm air to slide over the top of it and advance to the north And release energy that is built by that cold air sitting there The relationship of cold air and warm air next to each other the energy is there but it can t be released It is being propped up by the coriolis or spinning of the earth To spin the earth it holds the cold air there But it can still advance southward on a finer scale Meaning an extratropical cyclone The cyclones are there to advance the cold air to the south The cold air will be now in the middle of the US where before it was up in Canada The warm air at high levels will be way up in Canada rather then stopped somewhere The whole thing is released Tropical Cyclones some Review Hurricane Structure Again the tropical cyclone is there for an entirely different reason It is another cyclone across a wave The reason this is here is warm water and cooler temperatures aloft and the tendency to overturn Extratropical cyclone is a polar cell and a feral cell The feral cell is being pushed aside it is the average of the all the middle latitudes The tropical cyclone is localized overturning of deep convection in the tropics which is transporting high energy The Hadley Cell is powered by the convergence of the trade winds The trade winds move over the water and when they do that they pick up a lot of energy forming vapor and the vapor goes to the ITCZ and picks up as clouds This can lead to hurricanes Hurricane has low pressure in the middle And the pressure in the middle can be low because the vortex rotates so rapidly that the winds become in equilibrium with pressure gradient field The warming aloft can balance that pressure gradient The warming aloft comes from the energy released by the convection in the form of latent heat this raises the tropopause In the core of the tropical cyclone the warmth comes from sustenance from the stratosphere It takes energy to push that down In either case latent heat energy released is coming from the vapor which is coming from the surface from the water which is coming from the sun The circulation around the tropical cyclones looks like air spirals into the base is lifted up around the eyewall with a hole in the middle and the then spirals outward In the middle it rises cyclonically but then as it goes out it turns into anticyclonically More Structure and Crosssection information Strongest low pressure in the middle The maximum winds are in the eyewall This is because air coming in converges in the eyewall and rises in the eyewall The air in the middle moves with the storm The whole middle part does not have much air coming in from the outside instead it just is there At the upper levels of the eyewall there is some sinking but not a lot of motion at all Most winds are in the eyewall and rising The converging line is at the eyewall The air is converging and rising it is like the ITCZ spun around As you get to smaller radius the air is spinning up faster until it hits the eyewall where wind speed is the strongest At the ground the wind speed is made to slow down because of friction Rainfall occurs in bands The heaviest rainfall is under the eyewall itself But there can be multiple spiral bands that have heavy rain As the storm moves in one direction it will have stronger winds on one side than the other These winds can move water with them This can have the effect of a tidal wave effect If the storm moved on the Gulf shore it could create a huge tidal surge on one side The winds can move the water and make strong flooding The flooding associated with the tidal …


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