You are going to have to forgive my ignorance on this one.  Growing out of the discussions of the large scale tropics posted to this list, I now find when I arrive at the office each day, I look  Geostationary satellite images and  large scale analyses for the global tropics from various sites on the web.

Looking at last night's 200hPa flow for the Atlantic there is an interesting feature.  I have put the GASP analysis for 1200 UTC 3 November up on my web-page.  There is an interesting upper cyclonic trough (marked on our analysis by the yellow-orange cyclonic vorticity) stretching across the Atlantic from Panama across to the African coast (at about 25N). The associated upper level westerly jet over western Africa is interesting as it is not associated with the circumpolar subtropical jet.

To check its existence wasn't just a function of our local/GASP analysis I have also put up the superimposed satllite image/300hPa NOGAP winds from the Naval Research Lab site.  On that you'll see the trough IS there and has a strong satellite signature in the form of jet-stream type cirrus on its equatorward (westerly winds) side.

To all you peopel who live and breathe US and Atlantic meteorology, this is presumably a common feature.  However, I have never heard of it or noticed it before.  Is there anything much known about these tropical Atlantic upper level troughs?

John McB

Indian Ocean Double ITCZ
As a p.s of sorts, the current eumetsat image is also interesting in that it shows a beautiful Southern Hemisphere ITCZ stretching across the entire width of the Indian Ocean (also reproduced on my web-page).  It is part of a double ITCZ across the Indian Ocean, which seems a little rare, though I don't have statistics to hand.  I have put the GASP eastern hemisphere low level chart below the image on my page.  In both hemispheres the ITCZ cloud line is associated with a band of cyclonic -partial-U/partial-y vorticity at the equatorward edge of bands of trade winds.  Interestingly there is an n=1 Rossby wave structure at the western end, off the African coast, except that the higher latitude easterlies (at 10N and 10S) are much stronger than the equatorial westerlies, whereas in the classical structure (e.g Matsuno's solutions) it should be the other way around.  Before posting this I wandered around the corridor to see Matt the Wonder Boy and ask what he thought.  He says the stronger easterlies can be considered as the backgroud state on which the n=1 Rossby wave is superimposed.... Hmmm... perhaps. ).
 

Geostationary IR image of Indian Ocean for 1030UTC 3 November (copyright 2002 EUMETSAT)

Concurrent GASP eastern hemisphere 850 hPa analysis: