Concentric gravity waves in polar mesospheric clouds from the Cloud Imaging and Particle Size experiment

Abstract

AbstractFive concentric atmospheric gravity wave (AGW) events have been identified in Polar Mesospheric Cloud (PMC) images of the summer mesopause region (~82–84 km) made by the Cloud Imaging and Particle Size (CIPS) instrument on board the Aeronomy of Ice in the Mesosphere satellite during the Northern Hemisphere 2007 and 2009 PMC seasons. The AGWs modulate the PMC albedo, ice water content, and particle size, creating concentric ring patterns. On only one occasion (13 July 2007), the concentric AGWs in PMCs were aligned with AGWs with similar shapes observed in 4.3 µm radiance in the lower stratosphere, as measured by Atmospheric Infrared Sounder (AIRS). Coincident AIRS and Infrared Atmospheric Sounding Interferometer nadir measurements of 8.1 µm radiance reveal a region of deep convection in the troposphere close to the estimated centers of the AGWs in the stratosphere, strongly suggesting that convection is the wave source. The AGWs in CIPS on 13 July 2007 were ~1000 km away from the observed deep convection. Three other concentric AGWs in PMCs were 500–1000 km away from deep convection in the troposphere, while no convection was observed related to the wave on 29 July 2009. We perform a 2‐D ray tracing study for the AGW event on 13 July 2007. The calculated propagation distance is much shorter than the distance between the AGWs in PMCs and the observed convection. The 2‐D ray tracing study indicates that the AGWs in PMCs and in the stratosphere are probably excited by different tropospheric convective systems.