UPWELLING. a question for all

[rainstorm]

what causes upwelling and cooling sst's? west or wnw winds blowing offshore pushing water away from the coast or e or ene winds pushing water toward the coast?

[WXBUFFJIM]

Upwelling in our case occurs when offshore winds blow water offshore. This causes colder water temps from below to rise to near the surface much like a conveyor belt. The colder water also brings sediment up from below.

A warming of water off the east coast during the summer months occur at the waters surface while it's much colder at the bottom. That means in the event of an offshore wind, that can cause colder water from the bottom to rise to near the waters surface causing a cooling effect on the water.

Jim

[milankovitch]

what causes upwelling and cooling sst's? west or wnw winds blowing offshore pushing water away from the coast or e or ene winds pushing water toward the coast?

neither winds blowing along the coast (water to the right in the northern hemisphere) produce maximum Ekman motion away from the coast.

http://oceanworld.tamu.edu/resources/oc ... r09_04.htm

[EDR1222]

Here is an excerpt from an article from the National Weather Service in Melbourne FL regarding the upwelling event that occurred during the summer of 2003 in East Central Florida:

Upwelling Theory:
The reason upwelling occurs is because of Ekman transport. The flow of most surface currents in the oceans is driven by wind. When wind blows over water, the surface of that water is not pushed directly in front of the wind, but moves at about 45 degrees to the right of the wind's motion in the Northern Hemisphere because of the Coriolis force (which is caused by the rotation of the earth). As one descends in the water, the direction of flow continues to be deflected to the right, until ultimately a three-dimensional spiral is formed vertically in the water. The net transport of water, as explained by Ekman transport, is at an angle of roughly 90 degrees to the direction of the wind. In short, a layer of water near the surface is pulled directly away from the coast - causing cooler deep water to rise and replace it near the shore.

Reason for 2003 Event:
This year has been so extreme because of the strength and persistence of the subtropical high pressure ridge. Surface pressures in the Atlantic have been several millibars greater than average. This has produced a long period where surface winds were predominantly southeast to south. This wind flow, when combined with Ekman transport, will produce a net transport of water away from the coast (which is oriented 340-160 degrees). I have seen some web sites/news articles that show an offshore wind as the cause for upwelling. Based on the Ekman transport principle, this explanation is incorrect. The longtime Official in Charge at the Daytona Beach National Weather Service Office observed upwelling events for many years when the wind flow was southeast.