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Lab05 - AOS 311 Lab 5 Leeside Troughs Objective Apply...

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AOS 311 Lab 5 – Leeside Troughs Objective: Apply theory of potential vorticity (PV) conservation to mid-latitude cyclones. Understand the importance of topography on weather in the Midwest. Motivation: Leeside troughs are one of the most important phenomena for the genesis of cyclones in the Midwest. The process by which leeside troughs form can be easily understood from the perspective of PV conservation. The presence of the Rocky Mountains creates a unique environment whereby two of the most important characteristics of mid-latitude cyclones – low pressure and strong horizontal temperature contrasts – can be created through this one process. Assignment: We will be making use of two GEMPAK programs today. As before, we will use GDPLOT to make horizontal plots of useful variables for identifying leeside troughs and the synoptic environments that cause them. In addition, we will use a new program, GDCROSS, to look at vertical cross-sections through a leeside trough to develop a 3- dimensional understanding of the event. Part 1: Observing a Leeside Trough Run the program by typing gdplot and hitting ENTER in the terminal. Then input the following parameters: GDFILE = /labdata/data/gemdata/hds/08012700_eta104.gem GDATTIM = f00 GLEVEL = 850!0 GVCORD = pres!none PANEL = 0 SKIP = SCALE = 0 GFUNC = sub([email protected],[email protected])!pmsl CTYPE = c CONTUR = 3/1 CINT = 50!4 LINE = 3/1/1!1/1/3 FINT = FLINE = HILO = HLSYM = CLRBAR = GVECT = WIND = REFVEC = TITLE = 1/-2/ <TITLE> TEXT = 0.75 CLEAR = yes GAREA = top-- IJSKIP =
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PROJ = utm MAP = 5/1/1 MSCALE = LATLON = 23/10 DEVICE = xw STNPLT = Where <TITLE> is a description of your plot (don’t include angle brackets). Type SAVE PLOT1 and hit ENTER to save your current settings. Then type run and hit ENTER to create the plot: What you should see are 1000-500 hPa thickness contours in green, with sea level pressure in white. The plot is at analysis time (GDATTIM = f00). QUESTION: How do thicknesses relate to column-average temperature? Look at the thickness contours on your plot. A leeside trough event occurs when air is forced to sink as it passes over an obstacle, like the Rocky Mountains. Is there any evidence of subsidence warming on the lee-side of the Rockies? Explain. Now save the plot to a postscript file and print. First, make the following change: *********************************************************************** * DEVICE = ps |filename.ps Where “filename” is whatever you want to call the file ( CAUTION: do not include spaces or special characters in the file name). Type run and hit ENTER to create the postscript file.
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