Mesospheric planetary wave effects on global PMC variability inferred from AIM–CIPS and TIMED–SABER for the northern summer 2007 PMC season

Abstract

Polar Mesospheric Cloud (PMC) observations from the Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) spacecraft are used to investigate the role of planetary wave activity on global PMC variability in the summer polar mesosphere during the 2007 Northern hemisphere season. This is coupled with an analysis of contemporaneous measurements of atmospheric temperature by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere–Ionosphere–Mesosphere–Energetics and Dynamics (TIMED) spacecraft to characterize the importance of temperature as a dominant forcing mechanism of the dynamical state of the summer polar mesosphere. The study confirms results from a recent study using PMC data from the Student Nitric Oxide Explorer (SNOE) and temperature data from SABER, such that planetary wave activity is present in both PMCs and mesospheric temperature and that are strongly coherent and anti-correlated. The dominant wave present in the polar summer mesosphere in both PMCs and temperature is the 5-day wavenumber 1 Rossby normal mode. The maximum amplitude of the variation of the 5-day wave in temperature is small at 3 K but has a significant effect on PMC albedo. The phase relationship between PMC and temperature is variable between 150° and 180° out of phase, with PMC albedo reaching a maximum ∼10 h before the minimum in temperature. We have identified two additional waves, the westward propagating 2-day wavenumber 2 (2DW2) and the eastward propagating 2-day wavenumber 1 (2DE1) are both present in PMC and temperature variability in the 2007 NH season. The 2DW2 wave is consistent with a Rossby normal mode excited by the instability in the zonal mean zonal wind. However, the source of the 2DE1 wave could be a nonlinear interaction of the 2DW2 with the migrating diurnal tide. This is the first time these two wave features have been detected in coincident PMC and temperature measurements. Analysis of the zonal variation of PMC occurrence and temperature shows they are also anti-correlated and supporting the conclusion that temperature is an important forcing mechanism in zonal variability.