Impulse mixed down

[Helge Tuschy]

Hi everyone,

I'm wondering about this question:

This sounding shows the prefrontal situation immediately in front of an eastward racing cold front over Greece ( Athen, at 15Z ). Well, the cold front was driven by a very strong jet system ( 700hPa up to 25m/s and 500hPa up to 40m/s ---> deep layer shear (DLS) up to 35m/s / 70kt ).
Steep low level lapse rates present and I think impulse can be mixed down fine.
My question will be if someone of you knows a calculation, where you can guess the expected surface wind along the cold front ( squalline ) and how much influence this inversion will have for weaken this downward impulse somewhat...?Models forecast 925hPa wind speeds of about 25 kt ( ~ 13kt ) behind the cold front, not sampling the mesoscale convective wind field very well.
Maybe someone of you knows an abstract or a letter, which describes the problem.

Best regards,

Helge

 

[Tim Vasquez]

I don't see any downward mixing of winds (downward transfer of momentum) here, because the winds throughout the steep lapse-rate portion are pretty much the same (30 kt). The winds at 500+ mb are too high and are not being tapped by a column of steep lapse rates.

This appears to be more an environment that favors linear storms along the front. Now WITHIN the storms you can assess the potential for convective gusts:
http://meted.ucar.edu/mesoprim/cape/print.htm
http://www.wdtb.noaa.gov/courses/dloc/svrp...s/svrparams.htm (#15)

The marginal upper lapse rates, warm upper wet-bulbs, and poor instability appear to suggest weak convective gusts.

It appears that the existing pressure gradient would almost exclusively drive the winds at the surface.. I'd be looking at hand mesoscale analysis to pull out any features that might drive the winds higher.

Tim

 

[Helge Tuschy]

Hello Mr. Vasquez,

"I'd be looking at hand mesoscale analysis to pull out any features that might drive the winds higher.
"

*puh....I know that this can be done in North America, but here in Europe it is nearly impossible to draw a map with mesoscale features ( especially over the Mediterranean area ). I often get incomplete sounding reports ( like today, Athen ):
http://weather.uwyo.edu/upperair/images/20...16716.skewt.gif

But thank you very much for your answer. I see what you mean.

Helge