barotropic instability

[JonathanBelles]

Can somebody tell me what barotropic instability (as seen in the irene report) is in simple terms?

[JonathanBelles]

anyone?

[P.K.]

I'm still trying to understand it myself, lol. To be honest I can't put it in simple terms ,you need to know a bit about potential vorticity. Are any mets with a better understanding able to explain it?

[wjs3]

I also have a layman's understanding of it. The best that I can describe it based on my simple understanding is that Barotropic Instability describes a situation where wind speed changed from north to south...

I think of it this way...the vorticity (spin) in Barotropic instability is caused by, for example, really strong winds (at the surface, let's say) blowing just north of winds that are not so strong. Imagine such a situation for a second, and you may be able to draw a mntal picture of how such a situation would cause or help "spin up" in the zone where the horizontal wind shear (change in wind speed with change in latitude) is strong.

I think that the reason it's brought up with Irene is that the NHC is kind of saying in spite of what appeared to be pretty awful conditions, Irene kept up pretty good wind speeds. this sounds like it was taking place becasue the area Irene was in (in the trades, from what I can garner) was an area of barotropic instability. This barotropic instability became the mechanism that helped the circulation together in spite of the unfavorable conditions.

Anyone else? Like I said, my grasp on this is pretty weak!

[Hybridstorm_November2001]

I think the above is a good definition of such. It is caused basically by different flows of the atmosphere clashing along a sharp boundary zone. Kind of like for example a front on which the main jet runs North to South along. On the East side wind in all levels of the Atmosphere is blowing out of the South, on the West side all winds are blowing strongly out of the North:


http://www-fpc.stanford.edu/research/insb1/node7.html

[JonathanBelles]

ok i get the picture thanx

[JonathanBelles]

would this be called an effecient short answer:

common in cold fronts. Deep north-south trade winds where either the northerlies or the southerlies are much stronger than the other.

[JonathanBelles]

also on the irene report it says "4-18 August", but many times it mentions september? typos?

[Hybridstorm_November2001]

would this be called an effecient short answer:

common in cold fronts. Deep north-south trade winds where either the northerlies or the southerlies are much stronger than the other.

Sounds about right to me