Date: Tue, 24 Oct 2000 16:06:54 -0500 (CDT) From: David Schultz To: map@atmos.albany.edu, map_disco@nssl.noaa.gov, ddowell@ou.edu, hblue@ou.edu, wicker@nssl.noaa.gov MIME-Version: 1.0 Content-MD5: 1gbBtvHbRuEwvrNuLYozRw== Subject: [Map_disco] map discussion items: The Kicker and the Kickee X-BeenThere: map_disco@optical X-Mailman-Version: 2.0beta5 List-Id: Lance et al., It's interesting to sit on the sidelines and listen in on the Albany map discussions vicariously. Ours at NSSL have been heating up recently and I thought I would share some observations with you all (and hopefully get some answers). (1) Heavy rain event Sunday night over Oklahoma This was a very interesting event. Initially meridionally elongated scattered showers formed in southerly flow. A zonally oriented band moves through this sea of showers and spawns an F1 tornado over the mall. Then a group of cells start rotating and clumping together to form a line of storms with a much larger-scale MCV along its northern extent. Another phase in the evolution begins when this line starts moving eastward and looking like a bow echo, although few strong winds are observed behind the line. In fact, winds are still 5 knots out of the east behind the line! Very weird. Outstanding questions include the causes of the evolution, why the bowing occurred without any strong winds, how could tornadoes have been predicted ahead of time, what was the cause of the MCV, etc. (2) Henry's rule As I learned in your class, Henry's rule (Bluestein, Vol. II, p. 68) says that a stationary trough over the southwestern U.S. will be kicked out when a kicker (shortwave trough upstream) gets within 2200 km upstream of the kickee. Howie's book says that the stationary trough becomes progressive as the geostrophic vorticity advection becomes significant. In response to a question posed by Mike Kay of how he would explain Henry's rule to his sister, I tried to calculate the vorticity advection from the upstream trough on the downstream trough. No luck. The forcing wasn't even close to the location of the downstream trough. Thus, it seemed that Howie's explanation wouldn't hold up for the case presenting occuring over the SW U.S. Even if you were to hypothesize that low-level warm advection was increasing in advance of the upstream trough, forcing heights to rise and making the system more progressive, the GEMPAK diagnostics on the Eta model forecast couldn't really explain the progressive nature of the troughs currently over the SW U.S. The best explanation we could come up with in map discussion was using PV thinking. With the upstream trough, an induced flow is associated with it that extends beyond the reaches of the PV anomaly itself. It is this induced flow that forces the downstream trough to become more progressive. Clearly, PV inversion would be required to prove this point, but I was wondering if there were simpler diagnostics that could be used to demonstrate the physical reasoning for Henry's rule. What do you think of this argument? Are there any references for Henry's rule or for this concept of discontinuous retrogression? Thanks, Dave -------------------------------------------------------------------------- Dr. David Schultz phone: (405) 366-0453 NOAA/National Severe Storms Laboratory fax: (405) 366-0472 1313 Halley Circle schultz@nssl.noaa.gov Norman, OK 73069 USA http://www.cimms.ou.edu/~schultz "A master of the art of living draws no sharp distinction between work and play. His labor and leisure, his mind and body, his education and recreation, he hardly knows which is which. He simply pursues his vision of excellence through whatever he is doing and leaves others to determine whether he is working or playing. To him, he always seems to be doing both." -- unknown --------------------------------------------------------------------------