A study on stratospheric gravity waves generated by TyphoonEwiniar: Numerical simulations and satellite observations

摘要

Characteristics of stratospheric gravity waves generated by Typhoon Ewiniar (2006) areinvestigated using the Weather Research and Forecasting (WRF) model, high-resolutionEuropean Center for Medium-Range Weather Forecasts (ECMWF) analysis data, andthe Atmospheric Infrared Sounder (AIRS) observations. In the numerical simulations,convective forcing in the troposphere shows nearly isotropic features, which propagate invarious directions with a maximum in the typhoon-moving direction. However, stratosphericgravity waves are anisotropic since only the wave components that satisfy the verticalpropagation condition of gravity waves can reach the upper stratosphere. The lowerstratospheric background winds play the key role in filtering the wave spectrum generatedby the typhoon. During the mature stage of the typhoon, stratospheric waves propagatemainly eastward with significant power in the northeastward and southeastward directions.During the decaying stage of the typhoon, northeastward propagating waves are dominantdue to fast movement of the typhoon in the same direction after landfall. The modeledwave patterns are also found in the AIRS and ECMWF data sets at similar locations,directions, wavelengths, and timing, although the wave amplitude differs among the threedata sets. This is likely due to different typhoon intensities and the distributions of convectiveforcing in each data set, owing to different spatial resolution as well as limitations in themodel physics.