wind convergence - divergence

As the wind weight question seems to have reached a conclusion perhaps you academics out there could help me understand another wind question-

Why is there convergence on the left of the beat with a shore (parallel to the wind direction) on the left and divergence on the right when the shore is on that side .

Spend a while looking for answers yesterday without much sucess (try googleing wind convergence when you have a spare hour or 2.... ) So here's hoping there is a public spirited   out there who can explain....

Ok in researching this a little bit i managed to confuse myself but i think i have got the directions correct. (but the bit about which bank it is may be wrong)

Hopefuly this is correct and helps

The wind flows at slightly differnet angles over open water compared to the land.
Simply this is to do with the amount of drag that the surface creates.
Also at higher altitudes the wind is at yet another angle. This is a similar direction to that of the isobars on water charts.

As the wind closer to the ground gets slowed down by friction it changes angle (consevation of angular momentum) and the direction is controlled by the turn of the earth (corriolis effect) in the northern hemisphere this slower wind turns to the right.

Since the wind flowing along a bank is slowed more then the wind flowing along the water the wind on the bank is turned to the right meaning that this wind colides with the wind flowing along the river causing convergence and a similar thing happens on the right hand bank where the wind is turned to the right which means it flows inland more causeing a divergence in wind.

Not only does convergence mean a strengthening in the wind but it also changes the direction slightly so that you will get headed as you come into a left hand bank but will be lifted away from it (in stronger winds)

Similarly divergence lessens the wind strength but can provide you with a lift as you aproach the bank.

Hum its not easy is it ? I tried the first explanation yesterday but gave it up after a bit as it didn't hang together for me for the following reasons:

 According to Jim S's venue notes(amongst others) convergence is on the left looking upwind. However, if the wind flowing along the left bank is slowed and turns in the direction determined by corriolis effect, then if the wind changes by 180 degrees, won't the deflection still be in the same direction (ie the right bank now has convergent flows) - which doesn't match the facts. Similarly not clear why the faster air on the right bank turns inland when it doesn't on the left (or the slower air on the right bank wants to turn anywhere at all!)

Sorry I'm still confused - how does wave front theory help  

PS you must have an understanding boss

Hmm, I'm beginning to regret starting this   , but think you are on to something with the wind turning in the same relative direction (and like the diagram too).

According to a 505 web ref the opposite is true in the southern hemishere....

So the story so far, based on the above diagram -  something causes the wind on the left bank to turn right and flow towards the water (perhaps friction / difference in speed/pressure between it and the wind over the water, Coriolis effect) giving convergence, and something (the same effect) causes the faster wind on the right side of the course to deflect to the bank to join the slower wind over the right shore giving divergence. The something is the Coriolis effect which is acting on winds when they change speed  or not

Feeling a bit  and going for a lie down.......