EAS328_Lect3_ExtratropicalCyclones_Part1 - EAS 328 Natural...

Info icon This preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: EAS 328: Natural Environmental Hazards Lecture Slides for Tuesday, Feb 9, 2016: PART 1 *Office hours tomorrow (Feb. 10) are canceled. For meeOng this week, send an email. I can also answer quesOons via email. Plan for today: 1.  IntroducOon to Extratropical Cyclones (ETCs) 2.  Extratropical Cyclone Physics 3.  BREAK 4.  Extratropical Cyclone Impacts OUTLINE FOR PART 1 -­‐  Review the basics for cyclones -­‐  Introduce the global characterisOcs of ETC -­‐  Examine the storm-­‐local characterisOcs -­‐  Learn some basic physical terminology of atmosphere dynamics -­‐  Understand what powers extratropical cyclones and how they develop Other goal of this lecture: Provide a set of websites for visualizing ETC behavior and impact Introduction to Cyclones (same slide as in Tropical Cyclone lecture) •  An area or center of low pressure with rotating winds –  Counter-clockwise in Northern Hemisphere –  Clockwise in Southern Hemisphere •  Characteristics: –  1) strong winds –  2) mobile –  3) vertical motion above the region of low pressure Circular moOon in the opposite direcOon of cyclonic moOon: anOcyclonic h\p://earth.nullschool.net/ Historical Understanding of the Storm paths A study from 1888, using observaOons from land and ships Extratropical Cyclone Tracks for Jan and Feb, 2010 (number of cyclone tracks shown in this figure: 302) General Characteristics of Extratropical Cyclones (ETCs) •  More ETCs pass over the oceans than over land. •  There are more ETCs in the southern hemisphere than in the northern hemisphere. •  ETCs can last from 18-­‐hours to 6-­‐days and can travel only 1110 km or travel half way a_er the globe. •  Can occur during all four seasons, at almost all longitudes. Loca&on •  There are some ETCs in the polar regions, but they are also rare. •  ETCs do not exist in the tropics and there are very few in the subtropics (hence their name). Strong Extratropical Cyclone Over the US Midwest, October 25-­‐27, 2010 SOURCE: NASAEarthObservatory (GOES Satellite) Storm Local Characteristics of Extratropical Cyclones (ETCs) The storms grow in size as they develop. Usually the storms move from southwest to northeast as they grow. Maximum Size: 2220 km (i.e. ~20 degrees of laOtude or 28 degrees of longitude) Clouds develop into a comma-­‐like structure. (The storm is not symmetric about about the low pressure center). WARM ABOVE COLD AIR COLD AIR SECTOR WARM AIR SECTOR Storm Local Characteristics of Extratropical Cyclones (ETCs) •  Storms include include a warm sector (also called the warm air mass) that is in the front of the storm (warm air going north), and cold sector (also called a cold air mass) in the back of the storm (cold air being moved north). •  The warm and cold sectors of the storm are separated by strong temperature gradients. The gradients are referred to as fronts. The warm front is located at leading edge of the warm sector. The cold front is located at the leading edge of the cold sector Cyclone Precipitation h\p://water.weather.gov/precip/ PrecipitaOon occurs mainly in the warm sector extending equatorward along the cold front. Weather Forecast Maps for Extratropical Cyclones (ETCs) The maps include: 1)  Low pressure center 2)  Surface temperature fronts 3)  LocaOons of the precipitaOon h\p://www.wpc.ncep.noaa.gov/ noaa/noaa_archive.php? month=10&day=26&year=2010&cycl e=00&lang=english&format=gif Slide le_ intenOonally blank. Clicker quesOons will go here. Physics of Extratropical Cyclones (ETCs) Surface Pressure The actual, measured pressure at the surface, regardless of the height of the surface Sea Level Pressure The pressure at any lat/lon point that would be experienced if the point was adjusted so that its height was the the height of sea level. This is very useful for studying atmospheric circulaOon, because it allows us to compare the pressure globally for a fixed height level. Physics of Extratropical Cyclones (ETCs) Background informa&on: Jet Stream: a strong west-­‐to-­‐east wind in the upper troposphere in the midlaOtudes (clearly visible only in the Ome mean). Mechanism: VerOcal wind shear in the east-­‐west direcOon is proporOonal to the strength of the south-­‐to-­‐north temperature gradient. MulO-­‐year average of east-­‐west winds at height of 10 km in the atmosphere Dec-­‐Feb average MulO-­‐year average of east-­‐west winds at height of 10 km in the atmosphere June-­‐Aug. average Physics of Extratropical Cyclones (ETCs) Surface pressure contours and circulaOon: Due to the coriolis force, winds flow parallel to the pressure contours. As an analog to pressure contours, one can use the heights lines of constant pressure as stream funcOons (i.e., the winds flow along the lines at which a fixed pressure is at a fixed temperature. h\p://ww2010.atmos.uiuc.edu/(Gh)/guides/ mtr/cyc/upa/jet.rxml Physics of Extratropical Cyclones (ETCs) KEY: These storms are primarily driven by the equator-­‐to-­‐pole temperature gradient warm in the low laOtudes VS. cold in the high laOtudes •  This temperature difference creates instability in the atmosphere (think of the atmosphere as a fluid). •  The response of the atmosphere is to transport heat in an effort to remove the temperature gradient (warm, moist air is moved north and cold, dry air is moved south). The net affect of both of these is a net transport of heat polewards Physics of Extratropical Cyclones (ETCs) Contours show the sea level pressure. Color shading shows the temperature. Contours show the height of a fixed pressure level (which is near the 5 km height level) (ignore color shading) Key: a surface the contours are closest together near the warm front, mean while, alo_, in the region of the warm front, the contours are more spaced apart compared to the upstream region. Physics of Extratropical Cyclones (ETCs) KEY: These storms are primarily driven by the equator-­‐to-­‐ pole temperature gradient The temperature gradient creates atmospheric circulaOon in which there is local convergence of air at the surface low and a local divergence of air in the upper troposphere, at the front edge of the warm sector. The creates rising moOon within the storm. Rising moOon creates clouds and precipitaOon (it can be rain, ice or snow. Physics of Extratropical Cyclones (ETCs) Physics of Extratropical Cyclones (ETCs) 3-­‐D view of the circulaOon, showing the air trajectories A large amount of condensaOon can occur in the air rising in the warm conveyor belt. h\p://www.meted.ucar.edu/mesoprim/bandedprecip/print.htm#3.3 Physics of Extratropical Cyclones (ETCs) These storms are primarily driven by the equator-­‐to-­‐ pole temperature gradient The secondary source of energy in the storms is condensaOon (i.e., latent heat release). Moisture in the warm sector of the storm strengthens the rising moOon in the storm. CondensaOon within the warm sector of the storm strengthens the overall circulaOon. CondensaOon at the cold front strengthens the winds at the cold front. Life Cycle of Extratropical Cyclones (ETCs) Sea level pressure contours and surface temperature fronts. Life Cycle of Extratropical Cyclones (ETCs) Summary for Extratropical Cyclone Physics From Personal Experience: WinterOme storms in the Northeast. CharacterisOcs: -­‐ low pressure center -­‐abundance of rain and/or snow From Theory: CirculaOon response to the Forecast for Dec. 26, 2010 Equator-­‐to-­‐Pole temperature difference. Nature is working to wipe out the gradient. http://www.hpc.ncep.noaa.gov/noaa/noaa_archive.php ...
View Full Document

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern