GEOLOGY 1350 Exam # 4 Study Guide Lectures: 15-18Lecture 15 (October 30) Cyclone- area of intense low pressure around which the winds blow counterclockwise in the northern hemisphere and clockwise in the southern hemisphereMid lat cyclones- warmer on equator and cooler on poles, cyclones begins with a stationary front (usually a segment of the polar front)Nascent stage- of cyclone or incipient cyclone frontal wave developedMature stage- fully development open wave with cold and warm front, (more isobars stronger winds)Partially occluded stage begins- begins when the cold front starts to overrun the warm front Occluded stage- more warm air being pushed aloft and the size of the warm air wedge at the surface decreases significantlyRelationship b/n occluded fronts and midlats cyclone- warm air has stratus clouds, cold air acts like a wall and pushes warm then occlusion occurs and warm air pushes cold upwardsDissipation stage or death- final decay stage of the cyclone the warm air is isolated aloft with cold air beneath Winter is strongest storms and e systems because temp gradient is steeper can be as strong as hurricanesSummary- 1.starts with temp gradient 2. Something triggers evolution of frontal systems What else strengthens frontal systems and low pressure? 3rd dimension- when upper air divergence is stronger than surface convergence (more air is taken out from the top than is brought in at the bottom) surface pressure drop and the low intensifies or deepensConvergence and divergenceDeepening of cyclones into explosive cyclogenesis is prohibited when low pressure aloft is directly above the surface low, If we go up 500mb layer(50 above and below at 5.5 %)- what initiates cyclogenesis-when upper level divergence (air is going out) is stronger than lower level convergence(air coming in ) more air is going out at the top than is brought in at the bottom. Surface pressure drops and the low intensifies or deepensDivergence aloft will open up space (if lots of people go out the door people go left and right which is divergence and space opens up)Storm vertical structure- divergne of air aloft occurs as isobars intervals widen, low pressure systems deepen and intensify become strongerLecture 16 (November 4) The relationship b/n upper level ridge trough and surface high and lowUpper level waves- northern hemisphere earths poles are encircled by 3 to 6 longwaves (rossby waves) directing upper level winds around lows at the 500 mb surface (north), can trigger stormsShortwwave disturbance- 2 conditions barotropic- stationary front,isobars and isotherms are parallel then degenerate into baroclinic- high and low pressure systems large differences in temp. then into barotropic- occluded frontJet convergence and divergence- planetary waves, polar jet forces air convergence aloft upstream of the deepening open wave cyclone and then divergence downstream,when winds are gone cyclone degradesWave cyclone development- family of cyclones can move northCyclone and anticyclone paths-Cyclogenesis strengthens the cyclones and moves them to northLecture 17 (November 6) T-storms- warm moist air rises, unstable environment, near weather fronts, advance of upper level troughs, over mountain slopes, mature> updrafts may stop at the troposphere where the cloud ice crystals are pushed horizontally by winds and form an anvil top, or they may overshoot further into the tropopause. Dissipating>Once downdrafts dominate updrafts, the storm ends as precipitation leaves the cloud faster than it is replenished by rising, condensing air, lower level cloud particles will evaporate leaving an isolate cirrus anvil top section.Basic building block to t-storms- cells: compact region of clouds having strong updrafts; ordinary cell: a few km in diameter exists less than an hour; Super cell: larger than a few kilometer last for several hoursOrdinary t storms(air mass t-storms)- short lived, rarely produce strong winds or large hails,cumulus> cumulonimbus-unstable atmosphere, vertical updrifts keep precipitation suspended,mature>intense phase-dry air comes in causes cold air from evaporation triggeringdowndrafts (side by side with updrafts) and falling rain and small hail, dissipatiion> dominated by downdrafts and evaporation, dissipate themselves because downdrafts cut off the storm’s fuel supply, estimated 100,000 t-storms that occur annually in US, about 10% become severe storm. Ordinary into severe T-storms? In addition to the conditions favor T-storm, Key factor for severe storm is the existence of strong vertical wind shear, changes in wind direction and/or speed between different heightsSevere t-storms- wind gusts is greater than 50 knots or hail diameter greater than ¾ inches or a tornado, In ordinary storms the downdraft and falling precipitation cut off the updraft. In severe storms, winds aloft push the rain ahead and the updraft is not weakened and the storm can continue maturing.Multicell Storms- Cool downdrafts leaving a mature and dissipating storm, may relief summer heat, but they may also force surrounding, low-level moist air upward, therefore, dying storms often trigger new storms, and the successive stages may be viewed in the sky.Mesoscale Convective Complex-An organized mass, or collection, of thunderstorms that extends across a large region is called a mesoscale convective complex (MCC), With weak upper level winds (i.e, slow horizontal movements), such MCC's can regenerate new storms and last for upwards of 12 hours and may bring hail, tornadoes, and flash floods.Thunderstorm Movement- Middle troposphere winds often direct individual cells of a thunderstorm movement, but b/c dying storm downdrafts create new storms, the storm system tends to be right-moving relative to the upper level winds. In a figure upper level winds move storms to the northeast, but downdrafts generate new cells to the south, which eventually cuts off moisture to the old cell.Vertical wind shear- causes the strong updrafts to not remain vertical, but become tilted. The precipitation does not fall into updraft, allowing updrafts to maintain its strengths and storm to continue to manure.Squall Line-A Line of T-Storms,Squall lines identify major storms triggered by a cold front that may contain several severe thunderstorms, some possibly supercells, extending for more than1000 kilometers.Dryline Thunderstorms-Abrupt geographic changes from moist to dry dew-point temperature,called drylines, form in western TX, OK, and KS in