GEOG 1114 1st Edition Lecture 15Outline of Last Lecture Atmospheric Disturbances-Air masses and Fronts: definitions/ characteristics -Types of Air Masses -Types of Fronts Outline of Current Lecture Atmospheric Disturbances continued: -Cyclones-Anticyclones -Low-Latitudes -Minor Atmospheric Disturbances Current Lecture Cyclones: Characteristics/Development-Consist of convergent surface air that ascends and diverges in the upper atmosphere-Large migrating or traveling low-pressure systems (up to 1000 miles)-Called depressions in Europe-Develop in mid-latitude zones as a result of converging counterclockwise air flow (in N.H) that attracts cool air from the north and warm air from the south-Carried by the westerlies-Dominate day-to-day weather and bring precipitationThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.-When a front passes over: temperature decreases sharply, winds sift , pressure falls, clear skies are replace by cloudiness and precipitationLife Cycle of a Mid-Latitude Cyclone Front developsWaves appearCyclonic circulation is well developedOcclusion beginsOccluded front fully developedCyclone dissipatesOccurrence and Distribution of Mid-Latitude Cyclones-At any given time, there can be from 6 to 15 mid-latitude cyclones in the Northern Hemisphere. (Same for Southern)-Occur in westerlies - move generally from west to east-More numerous and faster moving in winter than in summerAnticyclones:-Consists of subsiding air from aloft and diverging at surface.-Descending air is warmed adiabatically thus reducing the moisture content and produce clear skies and fair weather-Develop over arctic regions during the winter. They bring cold dry fair weather when they descend-In summer, high-pressure systems are associated with subtropical highs that form in the Caribbean. These descend into the eastern third of the US bringing moist maritime tropical air into the USIn Low-LatitudesWeather in the Low Latitudes is characterized by Monotony: -Any changes in weather in the continental tropics results from the daily cycle of heating and cooling of moist air.*Many regions have strong seasonal contrasts and exhibit weather phenomena found nowhere else in the world.Tropical Hurricanes-Intensive low-pressure centers develop in late summer.-Characterized by steep pressure gradients, high wind speeds, and circulation-If wind speeds > 75 mph, these cyclonic disturbances are classified as tropical hurricanes-Develop when oceans reach their maximum temperature-In NA and Caribbean - Hurricane-In W. pacific -Typhoons-In Indian Ocean & Australia - Cyclones-Have non-stormy eye-Start as tropical disturbance (form in 0º to 3º latitude)-There are as many as 100 / year - but only a few have the energy, wind speeds, and circulation to develop into hurricanesMinor Atmospheric DisturbancesThunderstorms-Violent convective storms accompanied by thunder and lightning-Associated with vertical air motion, high humidity, and instability which are conditions that produce towering cumulonimbus clouds and pptn in response to frontal uplift-Sometimes produced by individual clouds formed by convective heating and uplift (summer).-Often produced with orographic and convergent uplift as well and can be associated and can accompany hurricanesTornadoes: an intense vortex: as deep low-pressure cell surrounded by a violently whirling cylinder of wind.-Small and localized, but can be very destructive-Associated with severe thunderstorms activity.-Tornadoes break out most commonly along thunderstorm or squall lines ahead of the cold fronts where temperature contrasts are large and instability great. -Vortex develops in the cumulonimbus clouds associated with these fronts in association with a vertical wind shear (a significant change in wind direction fromthe bottom to tope - updraft characterized by circulation)-These storms have the most extreme pressure gradients known (as much as 100 milibar difference from the center of the tornado to the air just outside the funnel.)-This pressure gradient produces rotating winds of extraordinary speeds, called a mesocyclone.-The tornado extends down from the wall cloud and as it approaches the surface it is retarded by friction and may take a course of its own.-They occur at random and become visible when water vapor condenses, producing the familiar funnel could. Dust and debris swept up form the ground create a much darker and more ominous-looking funnel. -Typically advance at a speed of 20-30 mph. Its track can be about 3-6 miles wide but a few are much longer.-They often appear in late afternoon, but many occur during night.*90 % of all tornadoes occur in US, most of which occur in