ATMO 336 1st Edition Lecture 3 Outline of Last Lecture II. Wind direction and speed at 500mba. Closed lows= air turns counter clockwiseb. Closed highs= air turns clockwise III. Estimating likely areas for precipitation from 500mb height patternsa. Precipitation and clouds= air risingb. Fair weather=air sinkingc. Precipitation around “wrap around” closed lowsIV. Tucson January 2013 exampleV. Forecast mapsOutline of Current Lecture VI. Longwaves and the temperature patternVII. 500mb height pattern and precipitationVIII. lifting of aira. divergenceb. convergenceIX. common weather terminology; indicators of trough strengtha. zonal patternb. amplified (meridional)X. shortwavesXI. closed lows and cutoff lowsCurrent Lecture- Longwaves and the temperature patterno Recall that the 500mb surface is related to the (density averaged) temperature of the atmosphere below 500mb Higher the temp, the higher the height of 500mb levelo Warmer than average temperatures can be expected underneath ridges and colder than average temps can be expected underneath.o Longwaves: define the large-scale weather pattern. Wavelength of a long wave typically a few thousand meters (west to east dimension of the continental US) 2-7 long waves encircle northern hemisphere at any given time- 500mb height pattern and 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.o recall storms and precipitation occur over areas of downstream of troughs (trough ridge)o rising air means surface air is forced to move upward into tropopause= precipitationo precipitation does not occur where air is sinking (ie downstream ridges troughs)- Lifting of airo convergence= horizontal inflow of air into regiono divergence= horizontal outflow of air way from a regiono convergence and divergence force air to either rise or sink  rise= precipitation and clouds sink= fair weather, no chance for precipitation o both occur in the upper troposphere- Common weather terminology; indicators of trough strengtho zonal pattern= average temps are found everywhere and that strong areas of precipitation are unlikelyo amplified (or meridional)= more extreme weather expected (cold under deep troughs, warm under large ridges, strong areas of precipitation possible just beyond the positionsof troughso the amount or precipitation that occurs with winter-type storm depends on 2 things: atmospheric dynamics (how strongly air is forced to rise) availability of water vaporo things to look for in 500mb pattern that act to increase divergence (rising motion) stronger winds increase divergence (closely spaced height lines) more amplified pattern (amplitude of ridge/ trough pattern) sharper curvature of a trough, the stronger the divergence downwind of the trough (shortwaves) orientation of trough axis with respect to a north-south line- troughs along northwest to southeast line= negative tilt (stronger weather system)- troughs along northeast to southwest axis=positive tilt- shortwaveso smaller wiggles or waves that are superimposed on the longwave pattern.o Indicate smaller regions of warm/cold temp contrasts and forced rising and sinking in vertical air motionso Have much sharper curvature than longwaves= stronger divergence and forced rising motion= stronger weather systemso Flow through longwave pattern but at a slower speed (1/2 the speed of the 500mb winds)- Closed lows and cutoff lowso Closed low= region surrounded by one or more circular height contours (lowest heights at the middle)o Cutoff low= when a closed low becomes completely detached from the main westerly wind currents at 500mb Remain detached for days with little forward (eastward) progress Difficult to predict movement and evolution of cutoff lows Common off coastal pacific waters off southern California Can produce significant rain and high elevation snow in Arizona when positionedproperly Form when 500mb trough “pinches off”= clouds and precipitation wrapped around low by counterclockwise