Geostrophic Wave Circulations
Yong Zhu
Preface
The previous theoretical studies of large-scale atmospheric dynamics were based mainly on linear theories or idealized conservative quantities, such as the potential vorticity and potential temperature, due to the mathematical difficulties in solving the nonlinear primitive equations. These studies could neither illustrate the zonal mean fields nor answer the fundamental questions in the perturbation circulations related to, for example, the further development of baroclinic disturbances and phase distributions of climatological perturbations and their low-frequency variabilities in the troposphere and stratosphere at different latitudes. Also, the widely recognized achievements, such as the Rossby wave theory and the criterion of baroclinic instability, are still questionable. Meanwhile, the most challenging topicss including the nonlinear dynamics are studied with numerical experiments. As a typical weather system can be simulated by different models working on different mechanisms, few of the results obtained from the simplified mechanism models can be accepted as a basic principle without being proved theoretically.
The current study provides an analytical method for solving the primitive equations for the large-scale atmospheric processes. The solutions draw the whole picture of the general circulations, called the geostrophic wave circulations, which include the perturbations and zonal mean fields. This picture bears the basic features of the real circulations in the extratropical atmosphere. The major problems remained in the previous studies can be solved when the nonlinear eddy transport of heat and momentum are considered. The recent study of Zhu (2002) on the large-scale energy conversions in the atmosphere has proved that the developments of synoptic and planetary perturbations in the troposphere and stratosphere illustrated in this study possess the observed growth rates and features.
The first edition of this book was published ten years ago. Today, it is still the unique adventure dealing with the linear and nonlinear processes using a unified theoretical model. The name Yong L. McHall in the first edition was the pen name of the author. The last ten years proved that there is no way to obtain the true understandings and theoretical results equally inspiring by skipping the current approach, and there are the fatal limitations on the use of linear theories for the study of atmospheric dynamics. As revealed in this book, the phenomenological linear perturbations depend highly on the nonlinear processes of transport. When it came the first time, I called the probe a revolution in meteorology. The ten-year trial ended with no competitive or comparable approaches found from other publications made the revolution more and more clear and significant.
Yong Zhu
July 2002
Boston, MA