A filtering method to improve the global gravity wave activity calculation in the troposphere and stratosphere from radio occultations

ALEXANDER, P.; DE LA TORRE, A.; LLAMEDO, P.; HIERRO, R.; SCHMIDT, T.; WICKERT, J.; HASER, A.

Taiwan

Workshop; 5th FORMOSAT‐3 / COSMIC Data User Workshop and ICGPSRO 2011; 2011

International Program Committee Member for the 5th FORMOSAT‐3 / COSMIC Data User Workshop and ICGPSRO 2011

Reliable estimations of global gravity wave activity from GPS radio occultations are needed in order to obtain realistic climatologies. We study the global tropospheric and stratospheric gravity wave activity by the calculation of the specific potential energy derived from GPS radio occultation data, as retrieved by COSMIC low Earth orbit satellites between 2006 and 2010. Systematic annual and interannual features as a function of longitude, latitude and time are shown. Possible artifacts produced by the temperature data processing around the tropopause due to the sharp change in lapse rate are remarked. Our work aims an improvement in the extraction of the perturbation components of the individual measured profiles. Different filtering options were tested. A new double filtering procedure that considerably reduces a systematically observed bias in the gravity wave activity around the tropopause in standard filtering methods is presented. After applying a bandpass filter, the perturbation component is processed again with a low pass filter. The suggested method was tested with synthetic perturbation components added to known background temperature profiles. It was found that the performance of the other filtering methods that were used was lower. The new climatologies were compared with previous ones in order to assess the changes implied by the new filtering method. The possible improvements may allow the inclusion of waves with longer vertical wavelengths in future calculations along the troposphere and stratosphere.