TC Group,

    About a week ago, Johnny Chan posted a message RE the possible
Fujiwhara of TCs FengShen and Fung-Wong.  This Fujiwhara has taken place
(see attached excel graphic).  On the 21st of July the two TCs were about
1100 n mi apart, then closed to within 525 n mi on the 25th as they
completed approximately 150 degrees of mutual cyclonic orbit.
    The JTWC had identified this as a case of "one-way" TC interaction on
one of the prognostic reasoning messages that I pulled up.  This
terminology derives from the work of Carr and Elsberry.  In a paper I did
a decade or so ago, I studied the effects of unequal intensities and size
on the binary interaction of TCs, and it is not an easy task to identify
the relative "weight" that each should be given.  The relative motion
about the geographical centroid will always be symmetrical for each TC
(just as for the earth and moon about their centroid).  However, if one TC
is dominating the interaction, the centroid will undergo a cycloidal
motion (just as for the case of the centroid of the earth and moon).  For
the earth and moon, there is a point that follows a smooth curve about
which both objects orbit.  This point is approximately at the surface of
the earth for the moon-earth orbit.  The centroid of FengShen and
Fung-Wong undergoes a cycloidal loop (not shown) indicating that it is not
the center of mutual "weighted" orbit.  It loops in a manner that suggests
that Fung-Wong is the lesser TC -- not exactly irrelevant (i.e., one-way),
but certainly out-weighed by the larger Feng-Shen.

John McBride

1.  Fujiwhara:    The atmosphere certainly can be spectacular at times.  I have placed on my web-page a series of operational (TLAPS) 900 hPa vorticity analyses for the recent Fujiwhara event starring Fengshen and Fungwong. Next to each day's map, I have also placed an enhanced satellite image for approximately the same time.  The sequence on the vorticity charts is quite amazing.  Look at the sequence particularly from 00UTC 24th through 00UTC 27th whereby Fengshen "captures" Fungwong within its circulation.  As Fengshen merrily marches towards the west, Fungwong rotates around it such that  between 00 24 and 00 25 Fungwong is "advected" towards the east, and then on subsequent days it is advected northward , all within the rotational circulation of Fengshen.

2.  The "third player"
   Look however at the original configuration on 00UTC 22 July.  Besides the two storms there is a third large concentration of vorticity at approximately 15, 144 associated with a very large scale outer feeder band of Fengshen.  By the 24th this third vorticity element has become elongated into a wide filament of vorticity, emanating from Fungwong and curling around Fengshen.  I would hypothesis that a barotropic simulation of the two storms circulating round one another due to rotational-Fujiwhara dynamics would not accurately simulate the relative motion of these storms --- unless the rotation associated with this third system were  incorporated in the calculation.

3.  The monsoon gyre
    A consequence or end-result of the advection of the third vortex element into a filament circulating around Fengshen is that now (on the latest chart) we are left with an annulus of high cyclonic vorticity stretching from about 35 N down to 10 N and from about 110 E to about 145 E.  I have placed the latest (00 UTC 27 July) 850 hPa chart on my webpage, so you can have a closer look at this.  On the 850 chart you can see the annulus in the flow: a westerly monsoon stream along the bottom (10N),  southerlies along the side (45E), easterlies along the top and northerlies along 110 E... with very light winds across the middle.   This presumably is the monsoon gyre that I have heard people (particularly Mark lander) talk about on this forum and at conferences.  However, since this is the first northern hemisphere season  I have been following the charts day-by-day, this is the first time I have seen it...... and it is indeed a wonderful thing.

cheers

John McBride
 

00UTC 22 July
 

00UTC 23 July

00UTC 24 July

00UTC 25 July

00UTC 26 July

00 UTC 27 July

 
 

850 hPa flow:  00UTC 27 July