Linear and nonlinear barotropic vorticity model frameworks are constructed to understand the formation of the monsoon trough in boreal summer over the western North Pacific. The governing equation is written with respect to specified zonal background flows, and a wave perturbation is prescribed in the eastern boundary. Whereas a uniform background mean flow leads no scale contraction, a confluent background zonal flow causes the contraction of zonal wavelength. Under linear dynamics, the wave contraction leads to the development of smaller scale vorticity perturbations. As a result, there is no upscale cascade. Under nonlinear dynamics, cyclonic (anticyclonic) wave disturbances shift northward (southward) away from the central latitude due to the vorticity segregation process. The merging of small-scale cyclonic and anticyclonic perturbations finally leads to the generation of a pair of large-scale cyclonic and anti-cyclonic vorticity gyres, straddling across the central latitude. The large-scale cyclonic circulation due to nonlinear upscale cascade can be further strengthened through a positive convection-circulation feedback.
Day-to-day precipitation data of Junes during the 43 years of 1958-2000 from stations to the
south of Yangtze River are used to divide regions and run statistical analysis of sustained torrential rainfall
processes. A preliminary analysis is then made based on it and the results show that June is the month in
which torrential rains in the southern half of China take place frequently and sustained torrential rains
occur at the same time in South China and the area to the south of Yangtze River. In addition, the analysis
gives the basic features of sustained torrential rains of June in China and their interannual variability
patterns, with the suggestion that the amount of these events increases significantly after the 1990s. Lastly,
the sustained torrential rains occurring in Junes of 1994, 1998 and 2005 in the southern half of China are
taken as examples in the research on the basic patterns and formation mechanisms of the evolution of
double rain-bands during the rain season in South China and the area to the south of Yangtze River. The
analysis shows that the large scale environment field in which sustained torrential rains occur is related to
the stable sustaining of the South Asia High and upper level jet streams. 相似文献
In this study, a fuzzy-Markov-chain-based stochastic dynamic programming (FM-SDP) method is developed for tackling uncertainties
expressed as fuzzy sets and distributions with fuzzy probability (DFPs) in reservoir operation. The concept of DFPs used in
Markov chain is presented as an extended form for expressing uncertainties including both stochastic and fuzzy characteristics.
A fuzzy dominance index analysis approach is proposed for solving multiple fuzzy sets and DPFs in the proposed FM-SDP model.
Solutions under a set of α-cut levels and fuzzy dominance indices can be generated by solving a series of deterministic submodels.
The developed method is applied to a case study of a reservoir operation system. Solutions from FM-SDP provide a range of
desired water-release policies under various system conditions for reservoir operation decision makers, reflecting dynamic
and dual uncertain features of water availability simultaneously. The results indicate that the FM-SDP method could be applicable
to practical problems for decision makers to obtain insight regarding the tradeoffs between economic and system reliability
criteria. Willingness to obtain a lower benefit may guarantee meeting system-constraint demands; conversely, a desire to acquire
a higher benefit could run into a higher risk of violating system constraints. 相似文献