UW-Madison ATMOCN 100 - Extratropical Cyclones Conclusion (6 pages)

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Extratropical Cyclones Conclusion

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Extratropical Cyclones Conclusion


A lecture about troughs and how they lead to cyclones

Lecture number:
Lecture Note
University of Wisconsin, Madison
Atmocn 100 - Weather and Climate
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Atm Ocn 100 Edition 1nd Lecture 35 Outline of Last Lecture I Reminders II Weather of the day III Air Masses and Fronts a Illustration of different fronts IV Extratropical Cyclones Outline of Current Lecture II Announcements III Weather of the day IV Some Review V Troughs Cyclones VI Summary For Cyclone East of Rockies VII Cyclones Forming Along Gulf and East Coasts Current Lecture Announcements Homework due today There is a new homework that only half will be due next week The other half will be optional if turned in we get extra credit Homework Due Friday December 12 2014 TYU Ch 13 2 4 6 7 18 TYPSS 3 TYU Ch 16 1 2 3 7 11 TYPSS 2 Extra Credit Not to be covered in Class TYU Ch 17 1 3 5 13 TYU Ch 15 1 2 3 4 5 6 7 Weather of the day Yesterday we can see a storm that started off as a category 5 tropical cyclone It is supposed to hit the Philippines The eye dissipates as it weakens The clouds around it how they look make it seem like there is something from the west causing the storm to weaken Another map is the sheer map it shows the difference of wind speed there is from upper levels to low levels The streamlines are the direction the wind is coming from The wind is weakening but the Philippines will still be hit with a category 3 tropical cyclone This was one of the strongest recorded super typhoons but now it is dissipating a little bit so it will be more like a category 3 instead of a category 5 The sea surface temperatures are warm but they aren t a lot warmer then normal So it is interesting we are getting these really strong typhoons so late in the season Typhoons take warm water and turn that warm water into vapor The sun warms the water and then it evaporates that evaporation turns into vapor and then it condenses and turns it back into heat This warms the air and transmits back to the atmosphere The water cycle warms the atmosphere Hurricanes suck energy right out of the water and then go into the atmosphere Where does the energy go after that The air has warm and gone upward the only way to get rid of that is transfer it to space It gets transferred around the tropics the energy will then be transmitted and make a strong subtropical jet This will get into the Westerly s and create waves that will affect us What is going to happen here If a big amount of energy is expelled it could produce a strong jet surge into the polar regions that would push a very strong ridge up over the Gulf of Alaska Eastern Siberia Last winter attributes in part because of typhoon that hit the Philippines This winter is different because we have an El Nino The forecast for the next couple weeks is a very zonal type flow But this typhoon may change this We aren t sure what is going to happen yet This is a complex situation of how this will interact Last year the typhoon didn t get down to a category 3 The week before Xmas is when we may feel the effects of this typhoon Back to lecture Some Review Cold Front Clouds Steep frontal slope 50 1 or about 1 km up in about 50 km horizontal distance Warm Frontal Clouds Slope less than a cold front 100 1 or about 1 km up in 100 km horizontal distance Special Setup for Cyclones East of Rockies When things go over the mountains they stretch and spin up and see low form They often go into Gulf of Alaska Often there is a trough over North America and the upper air is compressed Tend to have low pressure at upper elevation like at 500 mb and above And lower pressure over North America a trough and the lows would come across the mountains and get caught in northwestern flow and go southward circle through planes The jet stream steers this whole process Troughs Cyclones There are troughs of different scales North America would typically have a trough at 500 mb The trough would usually come down to the right of the mountains When the low comes in there is a trough within a trough There is a little trough where a low would in the trough Between the beginning and the end of the trough is called a long wave trough And the space between the middle of the trough is called the short wave trough The individual storm is associated with the short wave trough it moves faster and moves through the long wave trough and circles around through the bottom of it and then goes to the right The long wave trough would normally be associated with a high amplitude low index pattern There are about 5 of these throughout the world A clipper moves so quickly something can be in Alberta and move to New York in like 3 days There is a cold front from the Artic air to the north When it goes to the other side of the mountains there is a front and a dry line As the cold front crosses the Rockies it then drives cold air down south Another place that this happens frequently is in Colorado In many places there is a trough over the great basin and then it will span like Alberta to the eastern side of Colorado These then span cyclones The Colorado low when it goes south it goes near the Gulf of Mexico This is a completely different situation When the Alberta clipper goes south it has downward motion How much rainfall snowfall will it produce coming from the north It starts really far from oceans No moisture gets across the Rockies that can precipitate on the other side Most snow comes from the plains if there is any water in the air and it is lifted Not much water from the west A foot of snow for us will come from a Colorado low that takes a drink from the Gulf Need moisture for that to happen Precipitation shield forms on dry line not cold front Creates conveyor belt of moisture and drops a huge snow band on the north and west side of the storm which is where we would lie To the east of this would be mostly rain Rain itself will be 20 degrees like the air temperature it would freeze immediately when it hits the ground That is known as freezing rain Summary For Cyclone East of Rockies Special conditions present alteration to Norwegian cyclone model Lower portion of cold front unable to move across from Pacific i e cut off by Rockies Dry line forms on west side of Rockies Arctic Pulse of cold Canadian air mass plunges south on lee of Rockies Movement of air over mountains causes lee cyclogenesis or stretching of vorticity downward causing initial spin up of cyclonic flow Chapter 11 Cyclones Forming Along Gulf and East Coasts They …

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