East Asia and Western Pacific METEOROLOGY AND CLIMATE

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The works mentioned are qualitative and only thermodynamic processes
are taken account. Recently, Huang and Chou (unpublished) studied the
mechanism of analogous rhythm on monthly averaged circulation anomalies
over the Northern Hemisphere dynamically and numerically. In their
work, the evolution of monthly averaged circulation is taken to be a disturbance
supperimposed on the historical analog. The state of air and sea
can be devided into the basic and disturbed state, such as the monthly averaged
value in a historically analogous years for the latter, which may be called
analogous deviation disturbance (hereafter refer to as ADD). Thus the
study of establishment and variation of the rhythm can be transformed to
that of the evolution and stability problem of the ADD. With the
3—dimensional structure character of general circulation anomalies (i. e. the
baratropic property, stationary wave and space teleconnection property of
monthly averaged circulation anomalies), the model can be greatly simplified
and the amplitude equations of ADD for the air-sea coupled system
can be deduced. Using these equations, in an uncoupled or coupled system,
the time evolution charateristics of the ADD amplitude are studied. The results
show that in a uncoupled system with a constant SST, ADD may increase
rapidly due to linear instability. This is consistent with the analogous
evolution of circulation anomalies at initial time in the real atmosphere.
However, because of the nonlinear interaction in the atmosphere, the deviation
disturbance does not increase infinitely but tends to a steady state. This
will not bring out an analogous phenomenon. But in a coupled system,
things are different. The SST ADD can not only force the atmosphere but
be influenced by it as well and nonlinear feedback processes in an air—sea
system may produce a nonuniform fluctuation of ADD. Being forced
seasonally by the monthly averaged circulation, the coupled fluctuation of
ADD in the air-sea system is intensified and a large amplitude appears.
The result shows that the analogous rhythm phenomenon is an uneven vacillation
of ADD which is caused by nonlinear coupled interaction of air-sea
system forced by seasonal changes of the monthly mean circulation.
Considering the simplicity of the model, more sophisticated numerical
models are needed to compare the actual data with theoretical results. We
design another global air-sea coupled model wi£h a predictor of. ADD
which describes the similarity of monthly averaged circulation anomalies. It
is to input the three—dimensional structure characteristics of anomalies of
the monthly mean circulation as facts into the model, and filter the so-called
'''Climate noise 77 partly. In addition new processing methods are given on
the parameterization of diabatic heating and numerical solving process of