Analysis of Internal Gravity Waves Using GPS RO Density Profiles

GPS (Global Positioning System) radio occultation (RO) data proved to be a great tool for atmospheric monitoring and studies. In the recent decade, they were frequently used for analyses of the internal gravity waves in the upper troposphere lower stratosphere region. Internal gravity waves are widely recognized to contribute significantly to the energy and angular momentum transport. Due to their role in affecting the atmospheric circulation and turbulent mixing they are one of the main processes controlling the composition and structure even of the UT/LS region.

Atmospheric density is the first quantity of state gained in the GPS RO retrieval process and is not burdened by any additional assumptions. However, there are no studies elaborating in details the utilization of GPS RO density profiles for gravity waves analyses. In the presented study, we introduce a method for the density background separation and a methodology for the internal gravity waves analysis using the GPS RO density profiles. Correspondence between analytical forms of the density and widely used temperature background profiles is examined. Comparison between the power spectrum of the normalized density and normalized dry temperature fluctuations in the lower stratospheric region further confirms the advantages of the density profiles utilization. In the vertical range of 8 km 40 km, to avoid possible violation of the WKB approximation around the tropopause, results of the continuous wavelet transform are presented and discussed. In the LS region, analysis of global and temporal variation of gravity wave activity is done and regions of breakdown of IGWs are examined. Specific behavior of IGW activity in the Northern Pacific / Eastern Asia region is revealed, possible wave sources are examined and its influence on the UT/LS region is discussed. Finally, the limits of our approach are discussed and the advantages of the density usage are listed.