摘要
针对暴雨天气的发生、发展都伴随着对流层中低层有很强的气流与水汽辐合持续的天气事实,摒弃传统研究中把散度方程局限于水平动力方程约束的观念,从湿斜压原始方程出发,导出了包含热、动力耦合强迫作用的散度演化方程,揭示了正压大气非平衡强迫和湿斜压大气热、动力耦合强迫在暴雨激发和维持中的重要作用,阐明了持续性暴雨过程中对流层中低层强烈的气流与水汽辐合长时间维持的动力机制。
Torrential rain and flood are the main meteorological disasters in China, which cause enormous losses coming to hundreds of million yuan every year. So it is the main object of the weather-forecasting organ in the flood season to predict the heavy rain accurately. According to analysis, during the development of a heavy rain system, it is usually accompanied by strong convergence of air flow and vapor in the lower troposphere, so analyzing the dynarnic process of convergence increase is conducive to reveal physical mechanism of the evolution of torrential rain process. The fact that there are connections between the continual rainfall and the low jet as well as the energy front with strong baroclinity indicates that not only the dynamic fields of the atmosphere can change the divergent field, but also the interaction of the dynamic field and the thermodynamic field can be regarded as a result of their different distributions. So when studying the excitation and maintenance of heavy rain according to the evolvement of the divergence of air flow, the interaction between the dynamic field and the thermodynamic field must be considered.
Traditionally, the divergence equation is obtained from the horizontal dynamic equations. In this paper, based on the thermodynamic equation, which can strongly connect the dynamic field （containing the horizontal wind and the vertical velocity） and the thermodynamic field, a new type of divergence equation is deduced from the primitive equation with the wet and baroclinic features. The divergence equation includes obviously the coupling effect of dynamic fields and thermodynamic fields. From the divergence equation, the authors can conclude that the evolvement of divergent field is a result of the actions of the dynamic field and the thermodynamic field, and the latter is a direct factor. Further more, the stratified stability also plays an important role in the divergence evolvement. With different stability, it may diverges or converges and the velocity of the air flow may be also different. It is a new theory that offers an explanation for the thermodynamic fields forcing the divergence fields.
The vapor that provides the rain is mainly conveyed by the convergent flow between the surface and the undivergent level. Based on this, the authors make an integral of the new divergence equation from the surface to the undivergent level depend on the air pressure, and get an equation that is able to describe the evolution of the divergence in the air column between the two levels. Meanwhile, the authors find the main factors that dominate the excitation and maintenance mechanisms of the heavy rain, and illustrate its dynamic mechanisms.
In conclusion, the barotropic imbalance forcing of the lower atmospheric motion is close related to the change of mesoscale flow, which has a relatively faster speed and lasts a shorter time, thus it has an impact on the excitation of the heavy rain. Contrarily, the terms that have close connection with the baroclinic thermodynamic effects vary slowly and can be maintained easily. It is associated with the distribution of the weather systems and can cause the continuous convergence of the air flow, thus lead it to grow. It is the main dynamic mechanism on the maintenance of the heavy rain.
出处
《大气科学》
CSCD
北大核心
2007年第2期291-297,共7页
Chinese Journal of Atmospheric Sciences
基金
国家自然科学基金资助项目40275017
40433007
40675032
四川省青年科技基金后续项目
关键词
暴雨天气
散度演化
正压非平衡强迫
热动力耦合强迫
heavy rain, evolvement of divergence, barotropic non-equilibrium force, coupling forces between dynamic and thermodynamic fields
