Consistency between Fourier transform and small-volume few-wave decomposition for spectral and spatial variability of gravity waves above a typhoon

[摘要] Convective gravity wave (GW) sources are spatially localized and emit at thesame time waves with a wide spectrum of phase speeds. Any wave analysistherefore compromises between spectral and spatial resolution. Futuresatellite borne limb imagers will for a first time provide real 3-D volumes ofobservations. These volumes will be however limited which will impose furtherconstraints on the analysis technique. In this study a three dimensionalfew-wave approach fitting sinusoidal waves to limited 3-D volumes isintroduced. The method is applied to simulated GWs above typhoon Ewiniar andGW momentum flux is estimated from temperature fluctuations. Phase speedspectra as well as average profiles of positive, negative and net momentumfluxes are compared to momentum flux estimated by Fourier transform as wellas spatial averaging of wind fluctuations. The results agree within10–20%. The few-wave method can also reveal the spatial orientation ofthe GWs with respect to the source. The relevance of the results fordifferent types of measurements as well as its applicability to model data isdiscussed.

[学科分类] 几何与拓扑