A two-dimensional Stockwell Transform for gravity wave analysis of AIRS measurements
Abstract. Gravity waves play a critical role in the dynamics of the middle atmosphere due to their ability to transport energy and momentum from their sources to great heights. The accurate parametrization of gravity wave momentum flux is of key importance to general circulation models. For the last decade, the nadir-viewing Atmospheric Infrared Sounder (AIRS) aboard NASA’s Aqua satellite has made global, two-dimensional (2-D) measurements of stratospheric radiances in which gravity waves can be detected. Current methods for gravity wave analysis of these data can introduce unwanted biases. Here, we present a new analysis method. Our method uses a 2-D Stockwell transform (2DST) to determine gravity wave horizontal wavelengths and directions in both directions simultaneously. We demonstrate that our method can accurately recover horizontal wavelengths and directions from a specified wave field. We show that the use of an elliptical spectral windowing function in the 2DST, in place of a Gaussian, can dramatically improve the recovery of wave amplitude. We measure momentum flux in two granules of AIRS measurements in two regions known to be intense hot spots of gravity wave activity: (i) the Drake Pas- sage/Antarctic Peninsula and (ii) the isolated mountainous island of South Georgia. We show that our 2DST method provides improved spatial localisation of key gravity wave properties over current methods. The added flexibility offered by alternative spectral windowing functions and scaling parameters presented here extend the usefulness of our 2DST method to other areas of geophysical data analysis.