Characteristics of a mesospheric front observed in Polar Mesospheric Cloud fields

Abstract

We report on a Polar Mesospheric Cloud (PMC) front structure observed on July 2, 2007 over Greenland. This structure appears to be localized solitary wave, with a sharp boundary that separates a cloud and cloud-free region. Near-coincident temperature measurements indicate a 20 K temperature difference between these two regions that likely contributed to the sharp PMC front boundary. Gravity wave (GW) temperature amplitude and buoyancy frequency show that large amplitude GWs and the formation of a stable atmospheric layer between two unstable regions supported the formation of a pronounced mesospheric temperature inversion that destroyed PMCs. Given the absence of an inversion layer close to the location of PMC front, it is not clear if a similar thermal duct but with colder temperatures supported the formation of a single wave resulting in the formation of the observed PMC front. The buoyancy frequency structure with stable and unstable regions also indicates mesospheric wave propagation, and is present in both the cloud and cloud-free regions. We identify a tropospheric low-pressure area and a frontal system as potential sources of these mesospheric GWs. Ray-tracing simulations indicate that GWs from these sources propagated to the mesosphere and may have contributed to the observed PMC variability.