The CSI Homepage: Calculating CSI

PROPER METHODOLOGY

In a follow-up manuscript (Schumacher and Schultz, in preparation), we will advocate a process to correctly assess conditional symmetric instability. This methodology can be applied either in an operational environment to forecast slantwise convection or in a research mode to assess whether slantwise convection may have occurred in a particular case study.

These seven steps are:
1. Construct a cross section of frontogenesis.
2. Generate a horizontal map of frontogenesis at the level determined from step 1 and MPVg* slightly above that level.
3. Construct a horizontal map of frontogenesis and an upper-level forcing mechanism.
4. Construct a cross section of MPVg* and theta-e*.
5. Choose a level(s) where MPVg* is negative and create a horizontal map of MPVg* and d theta-e*/dp on the same level(s).
6. Generate cross section and horizontal maps overlaying MPVG* and relative humidity.
7. Compare the characteristics associated with the band(s) with those predicted by moist symmetric instability theory.

There are better ways to do this in a single panel or two. See the COMET CSI Webcast for some easy diagnostic ideas.

AWIPS

Phil has created the ability to examine MPVg* (using the geostrophic wind and theta-es) in AWIPS. The code for AWIPS is available from Dan Baumgardt's Volume Browser homepage (http://www.crh.noaa.gov/arx/vb/index.htm). A comparison between the results in GEMPAK and in AWIPS is favorable. An exact match, however, is not possible because AWIPS uses the bell filter on the height field when computing the geostrophic wind whereas GEMPAK does not. But, the match was close enough that Phil has confidence in the results.

GEMPAK

Below we make available GEMPAK scripts that create figures similar to those in our manuscript that can be used to assess the susceptibility of the atmosphere to slantwise convection in the same manner as we do. The code is self-explanatory and well-documented.

Quick-look GEMPAK four-panel figure (written by Schumacher and Schultz), documented header should be self-explanatory.
Suite of GEMPAK programs for the NWS SAC workstation (written by Schumacher). Download this text file to your UNIX workstation. Then to uncompress, type "tar -xvf csiscr~1". Click here for more information. Note that while these files were written specifically for the SAC workstation, they can be easily configured to work on any UNIX platform running GEMPAK.

WordPerfect documentation for the above GEMPAK programs (written by Schumacher) Download this to your workstation or PC, running WordPerfect.
Hints on calculating MSI using GEMPAK version 5.2 (not 5.4, which is the most recent version, as of 10/20/98) (submitted by Scott Overpeck, Texas A&M)

PCGRIDDS

As far as we are aware, PCGRIDDS cannot calculate the fully three-dimensional form of MPVg*. Therefore, the formulas in the appendix of Wiesmueller and Zubrick (1998) are not the most accurate way of assessing MSI, particularly in regions of strong curvature or along-front variations.

If you have your own code or tips on how to assess moist symmetric instability that you would like to contribute, please let us know. We're happy to share ideas amongst the internet community, if they lead to good science and forecasting practice.

Last update: 22 May 2001