Lab IV: PV Diagnostics

Due: Friday 5 March

Problem 1:

Using GEMPAK, plot the 400 mb relative humidity from the MM5 simulation of the 1993 Inauguration Day Cyclone at 1500 UTC 20 Jan (see /home/charney/u/class/synoptic/ids/mm5_d1_ids.gem). Identify the position of the dryslot. Plot also the potential vorticity at this level. Compare the potential vorticity analysis to the relative humidity analysis. What is the relationship of the high PV air to the low RH air? Explain this relationship. Using your knowledge of the distribution of potential vorticity in the troposphere and stratosphere, explain the source of high potential vorticity air at this level.

Problem 2:

Plot the potential vorticity analysis for this time at 900 mb. What is the relationship of the high values of PV to the primary frontal features of the cyclone? Are these values typically associated with stratospheric or tropospheric air? Explain how this region of high potential vorticity was created.

Problem 3:

Describe the development of the Inauguration Day Cyclone using "PV-thinking." What were the main building blocks (or PV anomalies) for the cyclone event. What were the sources of these building blocks and, based on you understanding of potential vorticity, how did they interact to produce a major cyclone?

References of interest:
Bluestein, H. B., 1993: Synoptic-Dynamic Meteorology in Midlatitudes, Vol II: Observations and Theory of Weather Systems. Oxford University Press, pp. 181-207.

Davis, C. A., and K. A. Emanuel, 1991: Potential vorticity diagnostics of cyclogenesis. Mon. Wea. Rev., 119, 1929-1953.

Reed, R. J., M. T. Stoelinga, and Y.-H. Kuo, 1992: A model-aided study of the origin and evolution of the anomalously high potential vorticity in the inner region of a rapidly deepening marine cyclone. Mon. Wea. Rev., 120, 893-913.

Davis, C. A.,M. T. Stoelinga, and Y.-H. Kuo, 1993: The integrated effect of condensation in numerical simulations of extratropical cyclogenesis. Mon. Wea. Rev., 2309-2330.