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 22 July to 6 August 2014. The decline is attributed to the summer mesospheric 2-day wave and interhemispheric coupling (IHC) triggered by planetary wave activity in the Antarctic stratosphere. The results indicate that the IHC in 2014 occurred via a pathway that previous studies have not emphasized. Based on Aura Microwave Limb Sounder (MLS) and Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) data, we suggest that strengthening of the summer easterly jet gave rise to baroclinic instability that supported the growth of the 2-day wave. The large 2-day wave led to enhanced meridional mixing in mid-latitudes and weakened ascent and warming at the polar summer mesopause. We also show that the 5-day planetary wave modulates the response to IHC, in that PMCs persist in the trough when zonal mean temperatures are too high to support PMCs and are absent in the ridge when mean temperatures are low enough to support PMCs.