850mb wind vs 10M wind

[jgf]

is there a way to make a _rough_ prediction of surface (10m) winds from 850mb winds?

 

what factor would you use for reducing the wind speed?

 

what about direction? 10m wind should be rotated a bit counterclockwise from the 850mb winds. about how many degrees? I would guess that the rotation might be a function of speed, but I need a constant rotation.

 

I am mostly interested in winds over the ocean, where there is less friction than over land, so not as much speed reduction or rotation as over land.

 

I understand this is probably going to be a crude estimate. but what's your best guess?

[wxmeddler]

For wind speed and indirectly direction, much of it depends on the temperature profile between 850mb and the surface. For the speed, considering the open ocean and a dry adiabatic lapse rate (Cooling at a rate of 9.8°C per km of altitude) to 850mb, the winds should be around 65% to 100% of the 850mb wind speed.

 

For wind direction, it's likely best to use a surface weather map. When the winds are high (say, 35kts+) the wind over the open ocean should be roughly parallel to the isobars with a slight angle inwards to the lower pressure. When winds are low (5kts) winds should be pointing directly towards the area of lower pressure with a bit of an angle (say 10-15°?) parallel to the isobars. For speeds in between just use a greater angle towards the isobars with higher winds speeds.

 

If there is an inversion, surface winds can, and likely will, be at a different speed and direction than at 850mb. In this case you can use the winds at the top of the surface mixing layer. In all cases, wind gust's will be veered towards the direction of the wind at whatever height the air is mixing from.

 

 

Question: What area of the world are you concerned about particularly?