East Asia and Western Pacific METEOROLOGY AND CLIMATE

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Fig. 4 Same as Fig, 1, but for the vertical turbulent flux
of moment!]. Interval of ^ i s 0.8X10*",
3) CuTm.il us horizontal flux of momentum
K"-theory may he used to estimate this term
approximately (the 10-th term, on the right hand side of
Eq.(2) ). The secondary circulation forced by this term is
mainly a positive circulation located in the middle and
upper troposphere {not shown).
4}Fddy horizontal flux of momentum
When there is a significant inward momentum flux in
the tropical cyclone, it is mainly caused by the asymmetry
of large-scale eddy. McBri.de {1981} calculated this kind of
momentum flux (the last second term on, the right hand side
of Flq. (P.)}. Normally; one may use actual data to estimate
the perturbation quantities along azxmuthal direction and
then to obtain the secondary circulation forced by this
asymmetric distribution of physical quantities. But the
data set used here is two-dimensional by which it is
impossible to derive the average perturbation along \ .
instead, an empirical function is se3.ect.ed to rpresent the
distribution of —r * [U&.* ViL*] that is very close to the
results calculated based on real data by McBride, -r * [Uo,*
Vk*] is assumed to be a, function of r * and Z * and is set
to be zero at boundaries. At 200 hPa, it has a maximum of
2.68*l£T*st r * =4(about 20 latitude degree m* s~* in the
dimensional case).
This distribution is equivalent to a quadratic
surface. Below 200 hPa, it is part of an ellipsoid whereas
above 200 hPa it is a sloping surface that intersects with
the ellipsoid, at 200 hPa,
HxlOOhPa *-0-2 .._
—.0
1 2 3 4 5- 6 , 7 J
Fig, B Same as Fig. V, but for the eddy horizontal flux of
momentum; with the interval of 3P being Q.2x10
Fig, 5 is the secondary circulation forced by the eddy
horizontal flux of momentum defined with the abovedescribed
empirical function. It can be seen that there is
basically a positive circulation in the entire domain with
^the center at 700 hPa and r *=3,5, and the maximum
*•'. At the top there is a negative circulation, with