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

Characteristics of stratospheric gravity waves generated by Typhoon Ewiniar (2006) are investigated using the Weather Research and Forecasting (WRF) model, high-resolution European Center for Medium-Range Weather Forecasts (ECMWF) analysis data, and the Atmospheric Infrared Sounder (AIRS) observations. In the numerical simulations, convective forcing in the troposphere shows nearly isotropic features, which propagate in various directions with a maximum in the typhoon-moving direction. However, stratospheric gravity waves are anisotropic since only the wave components that satisfy the vertical propagation condition of gravity waves can reach the upper stratosphere. The lower stratospheric background winds play the key role in filtering the wave spectrum generated by the typhoon. During the mature stage of the typhoon, stratospheric waves propagate mainly eastward with significant power in the northeastward and southeastward directions. During the decaying stage of the typhoon, northeastward propagating waves are dominant due to fast movement of the typhoon in the same direction after landfall. The modeled wave 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 three data sets. This is likely due to different typhoon intensities and the distributions of convective forcing in each data set, owing to different spatial resolution as well as limitations in the model physics.