Study On Typhoon Simulation And Assimilation Of Northwest Pacific Based On SCVT Grid

Numerical weather prediction model and its data assimilation technology are important ways to improve the accuracy of weather forecast.In this paper,the MPAS-A global atmospheric model based on SCVT grid is used to study three aspects of typhoon simulation and assimilation in the Northwest Pacific Ocean.First,the effects of three cumulus parameterization schemes of New-Tiedt,Grell-Freitas and Kain-Fritsch on MPAS-A typhoon simulation were studied on the track and intensity.Experiments show that the typhoon track and intensity is more sensitive to the selection of cumulus convection parameterization schemes.Considering the overall simulation results of track and intensity,the New-Tiedt scheme is optimal.The difference in the large-scale situation field simulated by the various schemes is the reason for the difference in the typhoon track.That is,the difference in the location of the simulated Western Pacific Subtropical High makes the typhoon guide airflow different,and ultimately makes the typhoon track different.The difference in simulated vertical heating structure is the reason for the difference in typhoon intensity.On the other word,the simulated height of convection instability is different,resulting in different latent heat transported and released differently,ultimately makes the typhoon intensity different.Second,comparing the effects of SCVT grids generated by the Frontal-Delaunay refinement algorithm and the Llody type algorithm,as well as quasi-uniform grids and variable resolution grids in simulating typhoons.The SCVT grids generated by the two algorithms are similar in terms of computational resources,typhoon track and intensity errors.Com-pared with the global quasi-uniform 24 km grid,the variable resolution grid can significantly save computing resources,and the typhoon track error can also be reduced by 10 km on average.The SCVT grid generated by different algorithms and the global quasi-uniform 24 km or variable resolution grid 96-24 km,no matter whether they simulate the global large-scale environmental field or the typhoon mesoscale structure in the refined area,there is no obvious the difference.Third,based on the developed grid conversion module,the MPAS-GSI global assimilation and forecast system was established.On the basis of verifying the accuracy of the grid conversion module and the single observation test,the research of assimilation conventional observation and AMSU-A microwave radiometer were studied.The assimilation test of typhoon MERBOK shows that the assimilation of conventional observation and AMSU-A data can improve the track and intensity.After assimilating the data,the RMSE of the main variables of the model have been improved to varying degrees.The assimilation of the AMSU-A data has a larger decrease in RMSE than the conventional observation data.At the analysis time,the increment of sea level pressure field,potential height,and wind speed by assimilated conventional observations and AMSU-A data show the characteristics of large-scale structures.At the forecast time,the incremental field generated by assimilation has developed mesoscale structure,and the structure of the incremental field is basically consistent with the typhoon track and intensity improvement direction of the assimilation experiment.The assimilation test of typhoon NESAT shows that the typhoon track simulated by the MPAS model is better than the WRF,and the intensity of the WRF simulation is better than the MPAS simulation.Whether MPAS-GSI model only assimilate conventional observations,or assimilate both of conventional observations and AMSU-A data,its improvement effect in track and intensity is superior to WRF-GSI model.