Satellite observations of large atmospheric gravity waves in the Mozambique Channel

Abstract

Satellite imagery (MODIS-Terra and Aqua, ASAR and MERIS-Envisat) has revealed signatures consistent with horizontally propagating large-scale atmospheric gravity waves which are frequently observed during the winter season in the Mozambique Channel. We examine and characterize statistically the full horizontal structure of these atmospheric gravity waves. The waves were found to have dispersive average wavelengths ranging from 8.5 to 3.5 km and a mean along-crest 'coherence' length of 443 km. The propagation characteristics of these waves are examined using in situ and remote sensing measurements. The propagation speeds are estimated using two consecutive satellite images of the same wave-packet and are used as a proxy for the waves' phase speeds. The Scorer parameter vertical profiles, calculated from available atmospheric soundings nearest to the satellite observations, were found to support wave propagation conditions. The vertical structure of stability and wind determine the favourable conditions for wave propagation. Air subsidence associated with high-pressure systems is an important factor setting the pre-conditions for wave propagation. Some suggestions are presented regarding the influence of Moving Polar Highs in the generation and propagation of the observed waves.

Atmospheric frontal gravity waves observed in satellite SAR images of the Bohai Sea and Huanghai Sea

“…Near the ocean surface there is a peak in the N 2 curve under about the 1000 m level indicating stable lower atmosphere layers. The time at which these air observations were taken was close to the SAR imaging time which indicates that the local atmosphere conditions were favorable for waves propagating in horizontal wave duct (Da Silva et al, 2009).Therefore, in this case, we confirm that AGW happens within the lower atmosphere.…”

“…These characteristics are consistent with other AGWs characteristics in the literatures (Gossard and Hooke 1975). We analyze the propagation conditions of these cases with radiosonde data from weather station near the location where the wave-like patterns occurred using the method introduced by Da Silva (2009), and find that the weather conditions are favorable for the waves propagating horizontally. Therefore, we identify the wave-like patterns as imprint of atmospheric front wave packets.…”

“…In the marine atmospheric boundary layer, AGW can be defined as trapped internal wave modes propagating horizontally in atmospheric waveducts. The strong variations in stability are important mechanisms that establish favorable condition for horizontal wave propagation (Da Silva et al, 2009). There are two types of AGW patterns in the SAR images: (1) the transverse wave type where the wave crests are nearly parallel to each other and perpendicular to wind direction; and (2) the diverging wave type where the wave crests are orientated outwards from the center of the wave group in a V-shaped pattern.…”

“…Since the availability of European Remote Sensing Satellites (ERS-1/2) and the Canadian RADARSAT-1 SAR in the 1990's, AGWs have frequently been observed as well defined groups of linear waves with wavelengths ranging from a few to several tens of kilometers (Thomson et al, 1992;Vachon et al, 1994, Zheng et al, 1998Chunchuzov et al, 2000;Li et al, 2004, Da Silva et al, 2009). In the marine atmospheric boundary layer, AGW can be defined as trapped internal wave modes propagating horizontally in atmospheric waveducts.…”

Satellite Survey of Internal Waves in the Black and Caspian Seas

“…The best approach would be to employ atmospheric sounding and compute the Scorer parameter, as it was made in [66]. Unfortunately, radiosonde observations are hardly affordable for most researchers.…”