Synoptic Meteorology Lab 9
1 April, 2010
Frontogenetic circulation
To start, please watch the meted modules by Jim Moore on
 frontogenetical circulations and stability (http://www.meted.ucar.edu/norlat/frontal_stability/)
 isentropic analysis (http://meted.ucar.edu/isen_ana/ )
This is useful background information.
You remember that you produced a map of the 1000 mb 2D frontogenesis at 0000 UTC 01 February 2002 in Lab 6.
We now look for evidence of a frontogenetic circulation in a vertical cross section across the front.
You will need to run gdcross. This program is similar to gdplot: it uses model output to generate a vertical transect.
There is no need to include the tropopause, so you can set the max height to 200 or 250 mb in the variable YAXIS.
Fig. A1  Plot isentropes [THTA], circulation vectors [CIRC(WND, OMEG), please use arrows, not barbs] and 2D
frontogenesis function [FRNT(THTA,WND)] in a cross section from 35.5N, 97.5W to 34.5N, 86.5W [CXSTNS=
35.5;-97.5>34.5;-86.5]. This is roughly from Oklahoma City to Huntsville in northern Alabama. Time/date is 0000
UTC on 01 February 2002. Draw the location of this cross section on the frontogenesis map you did in Lab 7 (please
hand in that map as part of the current lab assignment). Also, draw a curved line marking the location of the coldfrontal surface in the cross section.
Note 1: when you plot the circulation vectors, you will find that the flow is from the left (westerly) everywhere. In
Lab 1 you estimated the speed of the cold front to be about 15 m/s, moving from the WNW. You can
subtract 15 m/s from the wind to obtain “storm-relative” flow, and plot CIRC(VSUB(WND,(14,5)),OMEG). Note that in a storm-relative framework, there may well be easterly flow over the front, and a
closed circulation. At least, if you remove the cold-frontal motion, then you retain a more meaningful
circulation. Jim Moore emphasizes this in his METED module on isentropic analysis.
Note 2: I suggest that you use colors and submit this assignment electronically, but if you prefer to use paper, use
solid & dashed lines to distinguish the different fields. In either case, please type or write in a figure caption
to help you and me with the interpretation.
Fig. A2  As Fig. 1, but for a section further north across the front [CXSTNS= 40.8;-96.8> 39.8;-86.3], that is from
Lincoln NE to Indianapolis IN. Again, draw the location of this cross section on the frontogenesis map from Lab 7.
Questions:
1: Describe the 2D frontogenesis function in the two cross sections (sign, strength, depth …).
2: Explain the difference in 2D frontogenesis in the two cross sections. Hint: recall that gempak’s frontogenesis
function only captures 2D frontogenesis, i.e. due to horizontal wind.
3: Is the circulation in the cross section consistent with the frontogenesis; in other words, is there a secondary
circulation across the front that opposes the 2D frontogenesis, thermally direct if F2D>0 and thermally indirect
if F2D<0?