A note on the current situation.

Looking at the time-latitude plot 60-90e, we are still in a monsoon active period over the Indian ocean.

The 850 hPa analysis for last night (1200 8 JUly UTC) still shows a good westerly current across the eastern Indian ocean and there is now a pronounced southwesterly stream across Indo-China.  The flow in the eastern part of the Indian Ocean is interesting in that it has the structure of a an equatorial gyre with southerly flow along the African coast and northerly flow south of Sri Lanka.  To some extent this is a climatological feature, as can be seen on the climatological hovmoller for meridional wind along the equator on my web-page.  Looking at the hovmoller for the last 40 or so days (the left-hand hovmoller on my web-page), the northerly flow around 80-90 east is a lot stronger than normal.  It actually looks like there has been a propagation into this "monsoon gyre" of an equatorially-trapped mixed Rossby-Gravity wave, as discussed in the papers by Hendon and Liebmann JAS 1991, and more recently by Dickinson and Molinari, JAS, 2002.  More explicitly. the equatorial northerlies currently at about 70 E on the left-hand hovmoller look like they propagated in from about 140E on 30 June.  Looking at the individual charts (which I do not show), you can see a distinct single cell vortex located on the equator and moving westward on the daily charts.
 

Current equatorial v-wind Hovmoller                           Climatological v-Hovmoller

 In terms of zonal winds. there is still an equatorial easterly anomaly across most of the Asian monsoon region, as can be seen on the zonal-wind hovmoller on Matt Wheeler's page (http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom/NCEP+GASP/hov.last6m.an.EQ.u850.gif)   The convection/monsoon active period in western and central Indian ocean shows up as an MJO event on his real-time diagnostics, but as discussed last time, it has not generated any eastward moving wind-surge, nor has the convective region itself moved eastwards.  Going back to the current large scale analysis at the top of the page, despite the southwesterly flow over Indochina and Vietnam, the monsoon trough in the northwest Pacific has not developed yet, as shown for example by the lack of good south-westerlies across the South China Sea. This must be considered a late onset in the South China Sea, and shows up as an easterly anomaly at about 120E on the Hovmoller of zonal wind for 10-15N on my web-page:

 Looking at larger time and space scale, the OLR anomaly for the last 3 months is interesting.

The convection associated with the Indian monsoon active period shows up as a good 3-month OLR negative anomaly spanning the equator in the western Indian Ocean, whereas the Indonesian-maritime continent region (where we have had an easterly wind anomaly) shows up as having been quite dry.  Looking further east at the date line, the cold anomaly (blue) north of the warm (yellow) anomaly means the SPCZ is further north than normal.  The combination of the dry zone over the maritime continent and the displaced SPCZ has gone along with high pressure over Darwin and low over Tahiti, so the SOI is actually negative, i.e having the sign of  a warm event.

The Eastern pacific sea surfaces temperatures have been acting quite differently however, to the extent that through April-May-June there was a pronounced cold anomaly, consistent with an ENSO cold phase.  On my page I have reproduced the Hovmoller plot of zonal wind, SST and 20C isotherm depth from the TAO array page (http://www.pmel.noaa.gov/tao/jsdisplay/).  In the middle (SST) plot you can see the cold anomalies (blue area) in the east at Pacific in May-June. Comparing with the left-hand (zonal wind) plot, you can see the westerly wind event at about 150E in May set off  an equatorial Kelvin wave (shown as the eastward propagating disturbance at the bottom of the right-hand isotherm depth plot), which apparently removed most of the eastern Pacific cold anomaly.
 

 There are a lot of other interesting things happening... I could go on for another page or so. As I said last time, if anyone else has something to add, especially any forecasters out there from the monsoon region, please do.

cheers

John mcBride

Comment by Professor Takio Murakami

Date: Mon, 14 Jul 2003 05:53:10 +0900
From: murakami takio <takionobuko@hotmail.com>
To: J.Mcbride@bom.gov.au
Subject: Re: [Monsoon] The state of the monsoon : 9 July UTC

Hello John :
 I enjoyed reading your report on the state of the monsoon on 9 July 2003 . As you stressed ,
the 850 hPa wind field is dominated by a well organized equatorial gyre over the western Indian Ocean
with cross-equatorial southerlies ( northerlies ) near 40 ( 80 ) E . However , an exact mechanism
through which the gyre is maintained still remains unknown . An observational information has also been
scanty pertaining to its structural features . It seems to
be of quite different character when compared with the stationary equatorial symmetric mode forced by
convections ( Lim and Chang , JAS ,1983 ) . I wish you to further elaborate on the
structure of the gyre by presenting additional synoptic maps not only for winds , but also for pressure
, temperature , moisture , and vertical velocity . Of particular interest is the cross-equatorial
distribution of pressure and meridional wind along 40 and 80 E . I am looking forward to seeing your
next report on the state of the monsoon .
You also commented on the transient nature of  the gyre . Your postulation that a westward
propagating mixed Rossby-gravity wave could be responsible for accelerating northerlies near 80 E on the
9-th of July is quite interesting . However , how can you explain the simultaneous intensification of
southerlies near 40 E on the same day .  If  possible , I want to see a series of daily synoptic maps
showing the westward propagation of  v - perturbations .

Takio Murakami

John McBride Reply: 18 July

Dear Takio,

Thanks for your comments. I don't really have access to good charts for this system other than the streamline and vorticity analyses I showed you at 850 hP and at 200 hPa......I guess with a bit of playing around on the web, I (we?) could retrieve the surface pressure data you requested from the NCEP analyses (or for past years from the reanalyses)... but I haven't figured out how to do it yet.

Anyway, stimulated by your question on the vertical structure, I went to the NOAA CDC site and  generated a few climatological time sections of meridional wind along the equator, and have put them on my web-page.
 

Hovmollers of climatological values of meridional wind along the equator for the past 1 1/2 months:

                 850 hPa                                                           700 hPa    
 
                                500 hPa                                                            200hPa

Unfortunately I can't control the shading on the images from these interactive sites; so it is not consistent from image to image.  Anyway, looking at the time-longitude sections, one can see at 850 hPa there is strong southerly flow (red colouring) from about 35 to 50 E and northerly flow between about 65E and 75 E.  This southerly-northerly coupling represents the main western Indian Ocean equatorial gyre. Moving eastwards across the longitudes of India, there is a second southerly regime between about 75 E and 90 E and northerly (return) flow between about 92E and 100 E, constituting a second (weaker) gyre between the longitudes of India and Sumatra.

Moving upwards in the atmosphere, the same pattern is there at 700 hPa with no discernible tilt in the vertical. It's still there at 500, but weaker, and has gone completely at 200 hPa.  As to what causes it........ hmm...... something to ponder over.

 On to your second question re the transient nature of the gyre and the influence of the westward propagating mixed Rossby gravity wave.  Based on the literature I cited and on several examples of mixed Rossby gravity waves we saw on individual charts during 2002, personally I am convinced the disturbance I referred to is an MRG.   However, taking up your challenge, I have to admit is is difficult to see on the individual daily charts.  I can easily put up a daily chart where you can see it, but then on the next day's analysis its not there.

I began this business of looking at the daily weather early last year when I was setting up the Australian synoptic discussion list.  During the 2002 Northern summer we saw many examples of equatorially-trapped waves the characteristic patterns of which stood out clearly on individual daily charts.  So far this season, however, we have seen nothing as clear cut, and in a comparative sense this season has been marked by the lack of discernible equatiorially-trapped wave activity.

 Regards

John McBride