East Asia and Western Pacific METEOROLOGY AND CLIMATE

557
vertical turbulent flux of momentum should also be taken
into account, for the forced secondary circulation. Table 1
also indicates that the effect of cumulus convection is
very important., due to the fact that the first three terms
related to it.
Table 1 A 1 i st of realti.ve importance of
dynamic and thermal forcing in descending order.
Forcing terms
Order of magnitue
of forced decondary
circulation
di.abatic heating
lO*^
CM vertical flux of heat 10"**
Cu vertical flux of momentum
ID"*
eddy horizontal flux of momentum 10"*
vertical trubulent flux of momentum. 10"*
eddy horizon tal. flux of heat 10"^
Cu horizontal flux of momentum 10"*
horizontal, trubulent flux of momentum 10"*
Cu horizontal flux of heat 10* 7
horizontal turbulent flux of heat 10"""*
total thermal forcing 10"*
total dvnamic forcing 1.0**
sum of thermal and dynamic forcing 10"'
various
i
j Maxi mum
\ of
j
9.15x10'*
3.0 X1Q-*
2.53*10*
0.95x10*
7.72*10"*
4.6 XlO"*
2.58X1CT*
0.9 XLO"*
4.5 *10" 7
1.5 xi cr 7
11.6x10"*
2.97X10*
1.43X10*'
V.CONCLUSIONS
The present paper used non-dimensional equations to
study secondary circulation in typhoons and 11-yr composite
typhoon data to estimate the relative role of thermal and
dynamical forcing in these secondary circulations. The main
results are as follows:
1 . The effect, of turbulent horizotal flux and cumulus
horizontal mixing of heat are of minor importance and may
be neglected.
9.. The trubulent vertical flux of heat may force a
positive circulation in the lower and middle troposphere
with the order of magnitude ofj'being 10.
3. The dlabatlo heating and cumulus vertical mixing of
heat are major thermal forcing factors, Thet both may force
the vigorous secondary ci rculation with y being of 10"t
4. Cumulus vertical momentum mixing and eddy
horizontal momentum flux play an important role in the
development and maintenance of typhoons. They may force a
stronger secondary circulation. The former has more
significant effects than the latter, Tt can help enhance
large-scale low-level convergence, thus intensifying
positive feedback processes relevant to CTSK me.chani.sm.
6. Vertical and horizontal turbulent fluxes of
momentum and "/cumulus horizontal flux of momentum can force
nosi tive ci rculation eel Is, but with less significant
effect than the two terms discussed above.