East Asia and Western Pacific METEOROLOGY AND CLIMATE

from the center of cyclone. Tn addition, at r* = 5 and 800
hPa, there Is a negative circulation. The reason of its
formation is not clear.
xlOOhPa 5.5
551
1 2 3 + 5 6, 7 r*
Pig, 1 The secondary circulation forced by the diabatic
heating term, with interval of stream function being 0.8*10"
!.) Turbulent flux of heat
Tt is generally accepted that the vertical flux of
heat (the 3-rd. term on the right hand side of Eq. (2)) is
much wore important than the horizontal flux (the 2-nd
t.errn)in the development of typhoons,
For the secondary circulation forced by the horizontal
turbulent flux of heat, there is a weak positive
circulation with two centers at about 750 hPa in the lower
and middle troposphere (not shown). A negative circulation
is located in the upper troposphere, with two stronger
centers found in the layer of 300-200 "'hPa .
The secondary circulation forced by the vertical
turbulent flux of heat shows a complete pair of positive
and negative circulation cells, with the center of the
former found, at 550 hPa and the center of the latter at 750
hPa (not shown), Above 300 hPa, one may observe a weak
positive circulation,
forced
greater
of heat
3)
Tt
Tn comparison, the magnitude of secondary circulation
by the vertical turbulent flux of heat is much
than that forced by the horizontal turbulent flux
Cumulus horizontal flux of heat
is generally recognized that the transport of heat
by cumulus convection (the 6-th term on the right hand side
of Eq, (2}) is much greater than that by turbulence. Kuo
(1974) suggested that this term may foe estimated according
to K-th.eory, but it is very important to -take K value
appropriately. As a rough approximation f we take this'
coefficient to be three times as great as the eddy
viscosity coefficient. The secondary circulation thus
obtained has a pattern similar to that forced by horizontal
turbulent flux of heat, only with greater magnitudes of
.(not", shown ) , •"." •' ' ... : . • ' . - . ' . .. ;'./•' • ' • . . • .; •.•;' '• • • . v ' • ' • • ' • • "