[1] Polar mesospheric cloud (PMC) observations have revealed that interannual variability near the polar summer mesopause can be forced by planetary wave activity in the winter stratosphere. We use data from the Aeronomy of Ice in the Mesosphere (AIM) satellite to investigate coupling between the Arctic winter stratosphere and PMC variability in the Antarctic summer of 2007 -2008. We find a high correlation between zonal mean PMC frequency and Arctic winter zonal mean winds from the Goddard Earth Observing System, as well as Microwave Limb Sounder zonal mean temperatures. The time lag between changes in the winter stratosphere and the connected response in PMCs varies from 2 to 8 days. We suggest that the differences in lag times are related to the evolution of cloud altitudes throughout the season. The results here are the first to show evidence for intra-seasonal PMC variability forced by interhemispheric coupling.

We have investigated the 5 day wave in both temperature and water vapor in the stratosphere and mesosphere as seen in the Navy Operational Global Atmospheric Prediction System–Advanced Level Physics High Altitude (NOGAPS‐ALPHA) analysis fields for summer 2007. We have compared these fields and the derived saturation ratios with polar mesospheric cloud (PMC) measurements from the AIM satellite. We find that the 5 day wave is variable in both time and space, with significant amplitudes in the temperature wave in August (up to ∼6 K). By contrast, the 5 day wave–induced water vapor anomalies remain at a near‐constant level throughout the season. During August, the 5 day wave in the NOGAPS‐ALPHA saturation ratio and in the occurrence of clouds in the AIM data shows a clear anticorrelation with bright PMCs forming in the trough of the temperature wave. The analysis shows that the August enhancement in the 5 day wave amplitude acts to extend the PMC season past the time when zonal mean temperatures are saturated with respect to ice. The increased wave amplitude in August is attributed to in situ wave generation and amplification due to baroclinic instability of mean winds at around 0.1–0.01 hPa. The late‐season extension of cloud occurrence due to the 5 day wave may explain previous ground‐based reports of bright noctilucent cloud displays in August.

[1] Polar mesospheric clouds (PMC) routinely form in the cold summer mesopause region when water vapor condenses to form ice. We use a three-dimensional chemistry-climate model based on the Whole-Atmosphere Community Climate Model (WACCM) with sectional microphysics from the Community Aerosol and Radiation Model for Atmospheres (CARMA) to study the distribution and characteristics of PMCs formed by heterogeneous nucleation of water vapor onto meteoric smoke particles. We find good agreement between these simulations and cloud properties for the Northern Hemisphere in 2007 retrieved from the Solar Occultation for Ice Experiment (SOFIE) and the Cloud Imaging and Particle Size (CIPS) experiment from the Aeronomy of Ice in the Mesosphere (AIM) mission. The main discrepancy is that simulated ice number densities are less than those retrieved by SOFIE. This discrepancy may indicate an underprediction of nucleation rates in the model, the lack of small-scale gravity waves in the model, or a bias in the SOFIE results. The WACCM/CARMA simulations are not very sensitive to large changes in the barrier to heterogeneous nucleation, which suggests that large supersaturations in the model nucleate smaller meteoric smoke particles than are traditionally assumed. Our simulations are very sensitive to the temperature structure of the summer mesopause, which in the model is largely dependent upon vertically propagating gravity waves that reach the mesopause region, break, and deposit momentum. We find that cloud radiative heating is important, with heating rates of up to 8 K/d.