East Asia and Western Pacific METEOROLOGY AND CLIMATE

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the center at 200 hPa and the maximum of -0.33X10*** . The
order of magnitude of ULj * is 1 O" 1 : W * 30""*.
Tt is generally accepted that the vertical transport
of momentum i.n typhoons is accomplished by cumulus
convection while the large-scale eddy vertical transport of
momentum is less important.. Therefore.. the latter has not.
estimated in the present, paper (see the last term in F,a
(2 ) ) -
5) Cumulus vertical flux of momentum
This^ term in Eq. (2) is written as its form of
parameters ^ation:
where "UL* the dimension! ess vertical wind shear in cloud, llj*
the dimension! ess vertical wi.nd shear in the surrounding.
The secondary circulation forced by cumulus vertical
flux of momentum. (Fig. 6} is characterized by a positive
and negative secondary circulation. The center of the
negative circulation is located at p=800 hpa and r *=1,
with the maximum being -2.23XlO"*and the center of the
positive circulation at p=500 hPa and r *=2 with the
maximum being 2.53X10"*", The problem as to how the negative
circulation can occur remains to be further studied.
x 100 hPa
2
Fig.6 vSame as Fig, 1., but for the cumulus vertical flux of
momentum, with the interval of y 0.8X10"
6) Comparison among various dynamic forcing terms
From the above results, we can draw an important,
conclusion: cumulus vertical flux of and eddy horizontal
flux of momentum are basic dynamic forcing factors that
determine the secondary circulation. Tn contrast, the
turbulent flux.-of momentum (horizontal and. vertical) and
cumulus horizontal flux of '.momentum are less important.
Fig, 7 shows the secondary circulation forced by all the
dynamic factors. A complete positive circulation is located
in the middle and upper troposphere with a center of 2.97X
10""** at. p-500 hPa and r *-2.5. In the lower troposphere, a
negative circulation exists in the region from the eyewall
of the typhoon to 280 km/ with the center of -1.99xlO" a ' at