Noel Davidson

Hello John and others,

1. The 989 low to the SW of WA that JMB spoke about seemed related to the humungus (is that a word?) low of around 940 hPa that developed near 55S, 100E on 11 September. My interest in
these high latitude cyclogenesis events has been stimulated by some tantalising evidence that such developments during
southern summer may eventually influence/modulate - in the presence of a subtropical jet - the short-term
behaviour of the monsoon? Such high latitude events have preceded every monsoon onset event that we have looked at
(~ 8 now). Further, Kevin Tory has done some very nice work running idealised dry simulations using a model that he and
Michael Reeder developed to study extra-tropical cyclogenesis. He uses periodic boundary conditions and initialises with zonally symmetric flow - a baroclinically unstable polar front jet at ~50S, (stable) STJ at 25S, weak monsoon trough at 12S. Very similar to what is observed.
The idealised simulation produces a humungus high latitude low (not unlike the Sept 11 low), but more interesting is that
eventually (~ 5 days) the location and structure (vorticity and divergence) of the MT are affected (more cyclonic, more convergent). The presence of the STJ seems critical for the process to affect the tropics.
Further the process evolves via the development of the STR and the equatorward extension
of an (albeit broad) upper trough to about 15S - much as has been documented
in observational studies. The dry process sets up a very nice broad scale monsoon trough structure favourable for further enhancement by moist processes. {More work needed, but interesting}.

Has work been done on these SHEM high latitude cyclogenesis events? Climatology, dynamics (besides Tory and Reeder, Reeder et al, 1991)?
What is the subtropical response?
The southern Indian Ocean seems like a prefered area for cyclogenesis.

2. I've often thought that there were windy lows and rainy lows. Is this stupid? If so (not stupid), why do they develop in this way?

3. We (mostly Kevin T. but also with invaluable input from Jeff Kepert, Peter Steinle, Graham Mills, Chris Tingwell, Brett Harris, hope I haven't left anyone out) also have some interesting results on mesoscale data assimilation
generally (use of scat data, surface wind obs, GMS IR data, mesoscale initialisation), and TC genesis specifically. But more details can wait for another time.

4. Perhaps it would be good to use synoptic_discussion to broadcast interesting results/observations not necessarily related to the current weather. Am I out of line here?

Jeff Callaghan

Noel and others
I wonder if this has anything to do with work Ian James did in the 1980s
(QJRMet Soc 1988 114, 619-337) where he linked the drainage flow out of
east Antarctica (South of Indian Ocean ) with the split flow in the ANZ
region (Blocking region0
Jeff