Winds and convective bursts over the Indian

As the current MJO continues to evolve over the Indian Ocean, thought I would write an update before I leave for Thanksgiving (and lots of you too!).  The latest GFS run (12 ET) continues to show an upward trend in moisture convergence over the region (40-100 degrees longitude , 15-15 degrees latitude) all the way up to the middle levels (about 500 hPa). The figures below show moisture convergence for the last 10 GFS runs (ending at 12 ET today).  Convergence has increased about 36% over the last 3 days and ascending motion continues to dominate a good portion of the Indian Ocean according to the model run.

Convergence over the area at 850 hPa

Convergence over the area at 500 hPa

Moisture convergence averaged near the equator

The 500 hPa map below shows strong convergence near the equator. Irrotational winds look fairly strong for the region. This is likely one of the strongest winds/convergence I have seen since I started making these maps (they are being archived here if you are curious). It's a change in regime from the last couple of days, where the areas of maximun convergence were about 6-8 degrees south and north of the equator (the double ITCZ)

500 hPa map of moisture convergence with irrotational wind vectors

 At 200 hPa the picture is dominated by what looks like a wind "explosion" in the irrotational field, centered at about 65 degrees longitude. We can see on the map below it that the field extends close to the Maritime Continent. The explosion, as well as the rotating Rossby-like gyres are good with what a classical MJO looks like.

One interesting observation I want to mention from saving these model runs is how the wind field has changes in the last couple of days. By filtering the winds onto only the non-divergent winds. Doing that we can observe gyres which are not always apparent in the wind field. If we go back to November 15th, we observe a couple of gyres here and there, but they are fairly weak. Winds near the equator are not strong, ranging from 5-10 knots, with only a few barbs showing stronger winds.


Then during the 18th, we observe a larger gyre north of the equator, and a smaller one south (barely visible). The northern gyre actually dissipates the next day and gets replaced by another further east. What is really noticeable is that westerlies have started to pick up in that small region near the equator, with areas of 20-25 knots.

On the 21st, you can see those non-divergent winds are still going, with some areas now up to 30 knots. Organization has increased by this day. At this point, the northern gyre is still not apparen in the GFS winds, but retrievable via wind decomposition. In fact it is not until near the 22nd that this northern gyre can be seen without any filtering

This last picture is the latest one at the time of this writing. Here the MJO is very evident, with convection flares everywhere. The winds have maintained themselves strong at near 30 knots. What is even more interesting is that the area of westerly winds has increased, covering more to the north and to the south of the equator. The centers of vorticity have also migrated away from the equator and seem to be larger than previous days.

 Well that's all I have to say for now. I hope everybody has a great Thanksgiving weekend

Ángel