wind convergence - divergence

lol soz about the green it was either that or somethign which was too dark for the arrows to show properly.

woohoo  status ... should i be happy or not?

Hi

I'm intrigued by the varied discussion on convergence/divergence. I'm a meteorologist by profession and spent some time looking at such matters a decade or so ago. Knightmares's diagram could have come out of some text books except for two big problems: -

Big Problem 1 Temperature. The drawing assumes the wind experiences more drag over land than over water. All things equal that might be the case but temperature differences dominate the atmosphere. Given cooler water than land the opposite will usually be the case and your diagram will then work in reverse. In fact round chilly UK waters the common rule that offshore winds always veer right away from the coast is pretty likely to be wrong.

Big Problem 2 Scale. How big is the lake in your drawing? The effects w'ere talking about take at least kilometres and ideally tens of kilometres to work. You're unlikely to see these effects on Grafham Water, you might in the Caspian.

Sorry for such an academic tome but I would be interested to hear if anyone thinks they can consistently predict and use coastal convergence (or coastal jets as the 'trade' now likes to call them). 

So are we saying that where we have a cold sea, say early in the seaon, we will find that the wind doesn't change speed and therfore direction.  But doesn't that assume that the temp difference is able to take immeadiate affect rather than the air coming off the land being cooled as it passed over the sea.  So in effect we would almost see a 'S'  as the wind turns right as it accelerates as as the drag decreases as it crosses the coast then swinging left again as it is cooled by the sea temp???

The second question about scale.  Its one of those weird things which doesn't quite obey accepted physics.  It shouldn't work at small lake and river size butI 'm sure i've seen it (or something) happen  even on lakes the size of grafham and over narrow rivers.  Now this can't be anything to do with the coriolis force at this scale but somethings going on!!