Thursday, December 6, 2012

Tactical Use of Scatterometer Data

We will be watching the tropical Atlantic winds very closely for the next 3  months as we assist in the tactical routing of the OAR Northwest expedition from Dakar to Miami. This will bring up many examples of the value of scatterometer winds, about which we have several posts. Here we will just document a few as we proceed, starting with the one below. We highlight the importance of this analysis in our text Modern Marine Weather.

The top picture is our best surface analysis map of the ITCZ (doldrums) just SW of Dakar valid at 18z. The closest ASCAT pass (hi-res from KNMI)  is some hours earlier at 1030z, but this pattern does not change rapidly and our point for now is just to show the type of detail we can see. Searching around the data, we can often find cases closer in time.

The blue rectangle marks the region shown below in the ASCAT data.

The surface analysis does not tell us much about the winds at all, but we can guess that since this is the ITCZ, we would expect the NE trades to be meeting the SE trades, as they are indeed doing. This we see from the ASCAT winds, but notice how much more detail we get.  If you are rowing or sailing in this area, this is tremendously valuable information. Notice how the zone really splits up wind-wise on the eastern end of the region measured, which we have no idea at all about from the surface analysis alone.

Below we see the GFS model wind for 18z, which is effectively a surface analysis for this 18z run, but we do not learn much from it. In short, the scatterometer winds are the most precise wind data we can get at sea... or get at home for a particular part of the ocean.

This is the end of this example. We will add more as we run across them or share ones we actually use in routing.

Study  on your own 
To make a comparison of this type on your own for any location:

(1) get the top picture:

(2) get the middle picture:

(3) get the bottom picture:

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