Application Of Nonlinear Optimization Methods To The Study Of Blocking

The persistent anomaly of the general circulation often brings on large-scale disaster, while the blocking which usually occurs in the westerly is one of the most important reasons. For example, the floodwaters that occur in the Yangze River in the summer of 1954,1991,1998 are related to the blocking pattern in the east Asia(Li Shuanglin,1999), What's more, in the winter of 1976/1977, the blocking high which dominates Alaska results in the anomalously warmer winter in the west coast of North America and Alaska, and chilliness which rarely meets in the east coast(Benzi,1980), from that on, many theories about blocking are put forward. Tibaldi and Molteni(1990) indicate that one of the main reasons of the failure of the medium-range prediction models is that the frequency of blocking is underestimated. Thus it can be seen, the study of blocking has significance not only on practice, but also on theory about dynamics, numerical prediction, and climate simulation.The dynamical research of blocking can be divided into two kinds, one is based on the general theory, which mainly includes nonlinear interaction theory, multiple equilibrium theory and resonance theory. The other kind is based on the region characters, which mostly consists of 'modons' theory and KdV Rossby soliton theory. But these theories have their own "unilateralism", for example, some hypothesizes are not satisfied; only some characters can be described. The diversity of the theories just show the complexity of the blocking. Luo(1999) put forward eddy forced envelope Rossby soliton theory, which gets over the shortcomings of 'modons' theory which requests the linear relation of potential vorticity and stream function and KdV Rossby soliton which requests long wave aopproximation, What's more, the theory can describethe life cycle and multi-eddy structures of blockings.The quasi barotropic model of the interation of envelope Rossby solitions with localized synoptic-scale waves is used to simulate the occurrence, development and disappearance of blocking, and to study the conditions of occurrence of blocking. The conclusions are as follows:a) On the condition of no topography, the planetary scale waves develop into a dipole blocking pattern, while the synoptic scale waves divide into two symmetrical branches in the south and north direction, what's more, the synoptic waves are so weak in the center of blocking, Which is consistent with the theory of Luo(2000). On the condition of dipole topography, either the planetary scale field or the synoptic scale wave is influenced. The planetary scale waves develop into a blocking, and the synoptic scales divide into two braches, but the north branch is stronger than the south branch.b) The blockings are simulated through the adjustment of the amplitude, position, closing time of the wave-maker. The results show that the different life-cycle and intensity of blocking can be generated. This indicates that only under the condition of appropriate synoptic scale waves does the incipient blocking high develop into blocking event.c) Appropriate weak westerly is important to the occurrence and maintenance of blocking, which is consistent with the former results(Shutts,1983).d) The eddy forced structure with north/south minus/plus on the upstream of the blocking is essentially important to the formation of blocking.At the same time, another question is put forward, namely: under the condition of given incipient planetary scale field, what kind of synoptic scale waves can make it develop into a blocking event in the given time interval, which is the optimal precursor question. The nonlinear optimization method is applied to study this question. The conclusions are as follows:a) Nonlinear optimal method provides an advantageous tool for the study of the optimal precursors.b) The prominent character of the optimal synoptic scale field is the wave train structures in the upstream of the blocking. If the optimal interval is different, theintensity of the optimal synoptic scale field is different,...