The Numerical Research on the Disturbance Evolution before and after the South China Sea Summer Monsoon Onset
南海夏季风爆发前后扰动演变及其数值研究

Using the normal mode method,people can get the necessary condition and the increase rate of the linear instability.But,the normal mode method only can be used to deal with the small disturbance of single wavelength,and at the beginning of the disturbance evolvement.When the shearing do not exist in the basic stream fields,all the diagnostic waves are discrete spectra,in the circumstances the normal is reasonable.As there are shearing in the basic stream fields,the continuous spectra must be considered.In fact,the space structure of the disturbance correlates with time.In the finite period of time,the initial disturbance fields notably affect the produce and evolvement of disturbance.In this paper,the simple linear and nonlinear integral models are established by predigesting the spherical barotropic vorticity equation.The integral results of the spherical barotropic vorticity equation can be gotten using the linear and nonlinear integral models.The mechanisms of disturbance evolvement are investigated through setting different basic stream fields and initial disturbance fields in the integral model.The 40-year mean disturbance evolvement before and after SCSSM(the South China Sea Summer Monsoon) onset is also calculated by using the linear and nonlinear integral models.In the spherical barotropic vorticity equation,the motion and evolvement of disturbance field depend on the configuration and distribution of the basic stream field.The result of numerical experiment shows that:(1) There is the special relationship between the basic stream field and the motion and evolvement of disturbance field.Configuration of the basic stream field impacts the velocity and direction of the latitudinal and longitudinal transmittal.The large-scale disturbance moves westward,contrarily,the small-scale disturbance affected by the basic stream field moves eastward.(2) The energy transformation is related to the distribution of the basic stream field and the structure of the initial disturbance.As the basic stream field is the climatological mean basic stream before the SCSSM onset,the energy increase as time goes on,which also indicates that this kind of basic stream is of barotropic instability.(3) In the nonlinear integral model,when the basic stream is stable,the velocity and direction of the transmittal is the same as the result in the linear model.In addition, the climatological mean basic stream before the SCSM onset is barotropic instability.But,there is the upper limit of the unstable energy increase.(4) The nonlinear function is simulated in the numerical experiment.It shows that the nonlinear effect in the area where the disturbance energy goes up faster is far more obvious than that where the energy goes up slower.(5) The configuration of developing disturbance is changing with time in the initial problem,the energy increase is unsymmetrical.The action of the initial field engenders the local area increasing,which is the most different from the normal mod