>From Lance Bosart, mid-latitude expert from the States.  To make it easier
to follow his response, I'll excerpt the three questions I asked about
this time last week:

question 1: Is this a common system?  Is it understood.... For those who
study mid-latitude weather and northern Hemisphere weather systems, is
there somewhere in Monthly Weather Review, or Petterssen or Hoskins where
the dynamics of this is described?  I had a quick look through my old
weatherbeaten copy of Pettersen: cut-offs are described in the context of
blocking, which makes sense... but this situation of the travelling, very
small scale cut-off is quite different.

Question 2: Just how common on a world-wide basis are these moving
short-wave cold pools.... They have some similarities to the travelling
CVA max in the winter situations.  Who are the mid-latitude experts out
there?  Tell us about these things..

Question 3: Back in the early-mid 1980's we (Bureau, CSIRO, Monash) held a
Cold Fronts Research Programme.  I wasn't invited to participate being too
young and belligerent back then.... But, from going to the talks, I
remember lots of discussions of conveyer belts, of density currents and of
modification of the front by the orography.  Did you CFRP people address
the 500 hPa level cut-off lows that accompany the fronts?

 ---------- Forwarded message ----------
Date: Fri, 1 Feb 2002 02:23:51 +0000
From: "Lance F. Bosart" <bosart@atmos.albany.edu>
To: jmb@bom.gov.au
Hi John,

        Been out of the loop for awhile so apologies for my delayed response.

        Did some browsing of the cases on your web sites. Nice little
mesoscale critters aloft that you have to go along with your southerly
changes.

        In response to your three questions, here are a few thoughts and
otherwise very *incomplete* response.

1. One often sees subsynoptic/mesoscale cutoffs at the equatorward ends of
middle latitude troughs in the NH. As best I can tell, the large-scale flow
pattern exerts a degree of control over cutoff development and then opening
up in conjunction with large-scale deformation processes. What appears to
be key is the degree of lateral shear (cyclonic or anticyclonic) in the
larger scale flow pattern. Thorncroft et al. (1993) used an idealized study
to show that cyclonic vs. anticyclonic wrap up was sensitive to the nature
of the lateral shear superimposed upon a uniform flow pattern.

2. Short-wave cold pools are ubiquitous. They readily form by fracture from
the equatorward ends of larger-scale troughs that move eastward and leave
the cutoff behind at lower latitudes as a trailing ridge "folds over" the
lower latiutude cold pool. In rare cases such lower latitude cold pools can
be associated with baroclinic cyclogenesis that transforms into tropical
cyclogenesis such as happened with Hurricane Diana (1984) and was desbribed
observationally by Bosart and Bartlo (1991) and simulated numerically by
Davis and Bosart (2001).

3. Looks to be an internal issue. Look up Bell and Bosart (1988) for a
description of Appalachian cold air damming and the mesoscale structures
that can accompany a trough passage across the Appalachians and Hakim
(1992) for a description of a "side door" cold front passage in the
Virginia, Maryland, and Delaware area.

        Hope this helps. Take care.

                                                        Lance