Gravity wave signature inside upper-level clouds over Arctic region: implications from AIRS observations

Gravity waves (GWs) are one of the most important dynamic phenomena in middle to upper atmosphere, and have nontrivial impacts in the troposphere if they interact with weather phenomena. Mountain is one of the most dominant GW sources at high latitudes. Despite the famous "lee-wave" clouds, it remains unclear how GWs organize upper-level cloud structures at high latitudes. Using the radiance data from Atmospheric Infrared Sounder (AIRS), we are able to derive and infer some cloud structural properties in the cross-track direction (nearly meridional) in the polar region. Because AIRS instrument has a narrow (1.1 degree) beamwidth, small-scale (<45 km) GWs in the lower stratosphere and GW-induced cloud structures in the upper troposphere region can be obtained independently from each AIRS scan.

In this study, we focus on the Greenland area, where the largest GW amplitudes are found in the lower stratosphere Arctic region during boreal winters. Upper troposphere cloud perturbations are also found high in this region, but with summer peaks, these clouds are closely associated with convections generated over mountains. We will present evidence of systematically tilted banded cloud structures inside upper tropophere clouds, which are believed to be related with mountain GWs. These band structures are prominant at local noon when deep convection begin to initiate at mountain regions, and are much weaker during midnight. Moreover, they tilt in different ways right at the lee side of the high topography and further downstream, which might help the propagation of convective cells. These results have important implications for cloud dynamics as well as general circulations.