Atmospheric Gravity Waves over the Caspian Sea Studied using Envisat and Radarsat-1/2 SAR Images and Atmospheric Model
Ivanov, Andrei1; Barabanov, Vladyslav2
1P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, RUSSIAN FEDERATION; 2Marine Hydrophysical Institute, National Academy of Sciences of Ukraine, UKRAINE

Atmospheric gravity waves (AGW) play significant role in controlling middle and low atmospheric dynamics. Synthetic aperture radars (SAR) are proven to be powerful tools to study the low atmosphere AGW using their sea surface manifestations. Numerous sea surface signatures of AGW have been often detected on series of consecutive SAR images acquired by Envisat and Radarsat-1/2 satellites over the Northern Caspian Sea during it monitoring. In favorable atmospheric conditions they are frequently observed over this region every day, especially during the summer (April - September) seasons of 2009-2012. The vertical structure o the atmospheric, i.e. stability and wind determines the favorable conditions for wave generation and propagation. According to SAR image analysis the wave periods are ranging from 30-100 min, the wavelengths up to several kilometers and the propagation velocity estimated from consecutive satellite images is 2-8 m/s. The atmospheric conditions before, during and after their generation were modeled using regional application of high resolution WRF model. This modeling was supported by in-situ meteorological measurements, atmospheric soundings and by Terra and Aqua MODIS imagery. The detailed analysis of a number of SAR images showed good correlation between simulated low atmosphere wind fields and AGW patterns seen in the imagery. Typical cases of AGW propagating in the lower atmosphere over the sea are suggested to be explained by generation mechanism similar to undular bore. SAR imagery also shows evidence that this marine region is prone to very high occurrence of AGW, and for this reason the Northern Caspian Sea can be considered as a new hot spot for AGW.