Local and Remote Planetary Wave Effects on Polar Mesospheric Clouds in the Northern Hemisphere in 2014

摘要

Observations by the Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of Ice in the Mesosphere (AIM) satellite show an anomalous decline in Northern Hemisphere polar mesospheric clouds (PMCs) from 26 July to 6 August 2014. The decline is attributed to local warming associated with the quasi-two-day wave and interhemispheric coupling (IHC) triggered by planetary wave breaking in the Antarctic (winter) stratosphere. The results indicate that the IHC in 2014 occurred via a pathway that previous studies have not emphasized. Based on observations from the Aura Microwave Limb Sounder (MLS) and reanalyses from both the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) and the Navy Global Environmental Model (NAVGEM), we argue that a strengthening of the summer easterly jet gave rise to enhanced meridional and vertical shear along its equatorward flank, which supported growth of the two-day wave. The two-day wave led to enhanced meridional mixing in northern midlatitudes and a weakening of the northern branch of the mesospheric residual circulation, reducing ascent and warming the polar summer mesopause. In 2014, the five-day planetary wave modulated the response to IHC such that PMCs persisted in its cold phases even though zonal mean temperatures were too high to support PMCs, and were absent in the warm phases when zonal mean temperatures were low enough to support PMCs.