Tuesday, December 10, 2019

Help Me Understand the AMOC

I'm confused about the AMOC, the Atlantic Meridional Overturning Circulation. I thought it carried heat from the Gulf of Mexico northward to Europe, like this:

But now I see this University of Washington press release about a Nature paper, and the press release gives this view of the AMOC:

The directions seem reversed. So which is it??


Entropic man said...

The upper map is more detailed and closer to reality.

The key to understanding them both is in the colour coding.

Red is warm water, which tends to travel from lower to higher latitudes as surface currents.

Hence the Gulf Stream which begins in the Gulf of Mexico and ends North of Norway.

The water then moves West, cooling and sinking as it goes and then flows South along the sea floor. These cold subsurface currents are coded blue.

It is not apparent in the second image, but there are places in the North Atlantic where the Gulf Stream crosses directly over the cold water current and you have water flowing in opposite directions at different depths.


Ned said...

Agreed with Entropic Man ... the second map, although it looks more sophisticated from a graphic design perspective, is more simplified and schematic in terms of the position of the circulation "ribbon".

This one also has a nice graphic design and a more schematic feel to it, but I like it more than the one from the press release:


Victor Venema said...

Note, that the lower graph half cut off the words "Warm surface [current?]" and "Cool subsurface [current?]".

William M. Connolley said...

The graphs are only schematics, so you can't expcet miracles. I think they're both misleading, if you try to get details.

Things like the Gulf Stream are western boundary currents and this is a weirdness of (oceanic) circulations (the key being the boundary, which the atmos in general doesn't have), by which the flow ends up concentrated at the western boundary (in the analystic extreme, infinitely so). There is Maths to explain this that I never got. I think the AMOC ought to show similar features in the northwards sfc branch, but not in the southwards subsfc branch. But, all of this is hideously cut about by coastal shapes and subsfc mounts and all that stuff.

David Appell said...

Thanks a lot, everyone.