GEOG 1114 1st Edition Exam 2 Study Guide Lectures 7 10 Atmospheric Disturbances Air Masses and Fronts Air Mass Distinct parcel of air builds up temp moisture Front Boundary between two different air masses In Mid Latitudes Types of Air Masses Source Regions Polar P cold capitals refer to temp characteristics Tropical T warm Continental c dry Maritime m moist Arctic A very cold Equatorial E very warm lower case refers to moisture characteristics General Classes of Air masses A Arctic air mass typically builds at the poles mP Maritime Polar air masses towards the poles that develop over the oceanwet and cold cP Continental Polar dry and cold cT Continental tropical Dry south west New Mexico area mT Maritime Tropical moist wet warm E Equatorial FRONTS The boundary or interface between two unlike air masses Four Types Warm Front When war air moves into an area of cooler air the forward edge of the arm air is called a warm front When it comes into contact with the colder air the warm air pushes up over the cold air Convergent frontal uplift brings condensation and precipitation Usually move slowly and bring steady rains Cold Front When cold air moves into an area occupied by warm air the forward edge of the cold air is a called a cold front The cold air pushes under the warm air forcing the warm air t rise The frontal slop is much steeper as there is rapid development of cumulonimbus clouds with precipitation occurring just ahead of the front This cause a great drop in temperature and a line of strong short storms in spring and summer What causes thunderstorms to develop An extremely cold front meets a warm front and pushes it up rather quickly The frontal activity produces energy from the latent heat instability uplift adiabatic cooling Stationary Front same energy butting up against each other The boundaries between two air masses that are not moving displace each other PPTN and weather are not predictable along such fronts Often associated with gently rising warm air which can produce limited pptn Occluded Front Formed when a cold front overtakes a warm front Cyclones Low pressure at the surface air coming in and rising clockwise 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 precipitation When a front passes over temperature decreases sharply winds sift pressure falls clear skies are replacing by cloudiness and precipitation Anticyclones High pressure descends and spirals outward Anticyclones 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 US Minor Tropical Disturbances In Low Latitudes Weather 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 0 to 3 latitude There are as many as 100 year but only a few have the energy wind speeds and circulation to develop into hurricanes Localized Severe Weather Thunderstorms 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 hurricanes Tornadoes 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 from the 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 Oklahoma Air masses Secondary circulation patterns in mid latitudes characterized by distinct air masses Identified by their source regions A P T E c m Latitude Location Length of day Intensity of solar radiation affects temperature and rates of evaporation Seasons Ocean Currents Warm and cold tied to latitude and insolation Currents result of winds tides Coriolis force Proximity to Oceans Land near oceans less temperature range Topography Local elevation