G'Day Folks,
I am very interested in JMB's comment :
"I have often wondered about
the mechanisms for this occurring: When a
summertime front crosses
southeastern Australia and moves off into the Tasman,
why does it leave a trailing
frontal zone hanging back across the continent.
It was in trying to understand
this phenomenon that I originally asked Jim
Fraser to set up the daily
maps of surface theta on the NOC site.
If anyone has any insights
on this, derived either from forecasting experience
or from dynamics, please
let us know."
My speculation is that this
is a downstream and equatorward response
to the strengthening ridge
(and surge in the trades to the south) rather
than to the cold front itself.
IE, as the post-frontal ridge strengthens,
the heat trough/monsoon
trough (to its NE) initially intensifies via an
energy dispersion process
and this intensification is amplified by locally-
induced (maybe) convective
heating.
I believe, and have seen,
and (we) are about to document some similar
processes which produce
an activation and re-location of the
monsoon trough during extreme
rain events in the tropics. I am
really interested - as I'm
sure tropical forecasters are -
in this in-situ strengthening
of the monsoon
trough and the latitudinal
movement of the trough. The processes
I speculate about above
are the only ones I can "hang my hat on"
so far, and believe it is
a useful way of interpreting midlatitude
tropical interaction. Similar
processes at upper levels may also
explain the initial acceleration
of the tropical easterlies during
active convective events.
I would be interested to
know if anyone understands
these things or has other
more realistic suggestions?
Another possible candidate
is some kind of merger between the
mid-latitude and heat troughs
- I don't subscribe to this theory
but I might tomorrow.
Another possible candidate
is the ubiquitous inertial oscillation ;
maybe Mills and Deslandes
and others might explain
this in simple terms.
The MJO guys/people/proponents
may care to comment as well -
although I have cases of
in-situ intensification and trough
movement which don't appear
linked to the MJO.
ND