Sunday, November 20, 2011

Double ITCZ

Here's the current infrared satellite image (1130 UTC November 20). Remarkably symmetric double ITCZ structure - two long east-west lines of convection, one on either side of the equator. The cross-equatorial symmetry is more or less typical of this time of year, the transition season when the sun is moving from one hemisphere to the other. But I don't know that we get a double ITCZ this nice all so often in the Indian ocean.
But the two hemispheres are not as similar as they might seem. This image shows approximately the same piece of real estate as the one above, but superimposed on the IR image (which has a different color scale and perhaps infrared wavelength channel than that above) are pluses indicating lightning flashes. Why are there many in the north and none in the south? Some ideas have been batted around by the scientists here, but I will leave it to you to speculate for yourself. In the bigger picture, the flow in the last couple days is looking very reminiscent of the period in late October right before the start of the active MJO phase in the Indian ocean. In fact, the RMM diagram is in a similar phase to then as well. The latest date on this plot (thanks again Matt Wheeler) is Nov. 18, a couple days ago, and we were in mid-late phase 1 then:
By today we may be getting close indeed to phase 2. We may have our second MJO onset very soon!

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