Re: Persistent Low over Midwest?

I R A Darth Aggie wrote:

On Sun, 14 May 2006 23:43:28 GMT,
Ron Hardin <rhhardin@xxxxxxxxxxxxxx>, in
<4467C09D.7F31@xxxxxxxxxxxxxx> wrote:
+ What's causing this cold rainy low to sit isolated over the Great
+ Lakes for days, instead of moving somewhere else?

It is cut off from the normal mid-latitude flow in the upper levels,
so it sits and spins.

http://weather.unisys.com/upper_air/ua_500.html

You can go back thru the previous 72 hours and see a very slow
west-southwest motion. You can see there is a split flow occuring over
the Canadian prairie provences. The good news is that the low looks
like it is about to get picked up by the southern branch of that flow.

If so, it'll probably exit the CONUS over North Carolina/Virginia.

http://www.srh.noaa.gov/fwd/glossary/def/cutofflow.htm

Would it be more correct to say that the low _is_ the cutting off of
upper level winds?

The idea would be that a strong enough low produces a stream function that
includes cutting off of upper level winds.

The philosophical problem (as to causality) is that the stream function is
something of a fiction, as is, as a result, identification of the ``same''
wind.

So the problem is then how to decide if a low is one of the lingering
variety or not, since obviously most lows are carried along and move out.

What I remember from 2d imcompressible flows long ago, is that same-sign
rotations attract and differing-sign rotations repel, as to dynamics. As
well, of course, as simply adding some constant velocity to everything causes
everything to drift that way, which seems to be the usual drift causality.

For some reason, then, the constant went to zero. Perhaps it is part of some
very very large scale vortex over which the ``constant'' serves as a constant?

I'm not sure how to do causality in fluid flows, in short.
--
Ron Hardin
rhhardin@xxxxxxxxxxxxxx

On the internet, nobody knows you're a jerk.
.