[1] We present an observational study of stratospheric gravity wave spectra and seasonal variations of potential energy density at the South Pole (90°S) and Rothera (67.5°S, 68.0°W), Antarctica. The gravity wave spectra are derived from the atmospheric relative density perturbation in the altitude range of 30-45 km measured by an iron Boltzmann lidar. The ground-relative wave characteristics obtained at each location are comparable, with an annual mean vertical wavelength of $4.1 km, vertical phase speed of $0.7 m s À1 , and period of $104 min. Approximately 44% of the observed waves show an upward phase progression while the rest display a downward phase progression in ground-based reference for both locations. Gravity wave potential energy density (GW-E P ) at Rothera is $4 times higher than the South Pole in winter but is comparable in summer. Clear seasonal variations of GW-E P are observed at Rothera with the winter average being 6 times larger than that of summer. The seasonal variations of GW-E P at the South Pole are significantly smaller than those at Rothera. The absence of seasonal variations in wave sources and critical level filtering at the South Pole is likely to be responsible for the nearly constant GW-E P . The minimum critical level filtering in winter at Rothera is likely to be a main cause for the winter enhanced GW-E P , as this would allow more orography-generated waves to reach the 30 to 45 km range. The stratospheric jet streams may also contribute to the winter enhancement at Rothera.

The meridional transport of water vapor into the High Arctic, accompanied by dry enthalpy and clouds, impacts the surface radiative forcing. The evolution of one such moist intrusion over 9–11 February 2010 is presented. The event is analyzed using a unique blend of measurements including a new pan‐Arctic retrieval of column water vapor from the Microwave Humidity Sounders, water vapor profiles from a Raman lidar and a ground‐based microwave radiometer at the Polar Environment Atmospheric Research Laboratory (PEARL), in Eureka (80°N, 86°W), on Ellesmere Island in the Canadian High Arctic. A radiation model reveals the intrusion is associated with a 17 W m−2 average increase in downwelling longwave irradiance. Optically thin clouds, as observed by the lidar, contribute a further 20 W m−2 to the downwelling longwave irradiance at their peak. Intrusion events are shown to be a regular occurrence in the Arctic winter with implications for the understanding of the mechanisms driving Arctic Amplification.

[1] Lidar observations of polar mesospheric clouds (PMC) were made at Rothera, Antarctica, from December 2002 to March 2005. Overall, 128 hours of PMC were detected among the 459 hours of observations, giving a mean occurrence frequency of 27.9%. The mean PMC centroid altitude is 84.12 ± 0.12 km, the mean PMC total backscatter coefficient is 2.34 ± 0.11 Â 10 À6 sr À1 , and the mean layer RMS width is 0.93 ± 0.03 km. The distribution of PMC centroid altitudes over all observations is symmetric (nearly Gaussian), with the most probable altitude ($84 km) near the center of the distribution. The distribution of PMC brightness is non-Gaussian and is dominated by weak PMC. The observed PMC altitudes at Rothera support the earlier lidar findings that Southern Hemispheric PMC are on average 1 km higher than corresponding Northern Hemispheric PMC, and higher PMC occur at higher latitudes. Significant interannual and diurnal variations are observed in PMC centroid altitude and brightness. Mean PMC altitude varies more than 1 km from one year to another. In addition, 24-hour, 12-hour, and 8-hour oscillations are clearly shown in PMC centroid altitude and brightness. The altitude distribution of PMC brightness peaks at a nearly constant altitude of 84 km, with weaker PMC found on either side of this altitude. The mean PMC altitudes averaged in brightness bins are anticorrelated with the PMC brightness, where weaker PMC occur at higher altitude and the PMC altitudes are proportional to the logarithm of the PMC brightness.

[1] Aerosols from the Sarychev Peak volcano entered the Arctic region less than a week after the strongest SO 2 eruption on June 15 and 16, 2009 and had, by the first week in July, spread out over the entire Arctic region. These predominantly stratospheric aerosols were determined to be sub-micron in size and inferred to be composed of sulphates produced from the condensation of SO 2 gases emitted during the eruption. Average (500 nm) Sarychev-induced stratospheric optical depths (SOD) over the Polar Environmental Atmospheric Research Laboratory (PEARL) at Eureka (Nunavut, Canada) were found to be between 0.03 and 0.05 during the months of July and August, 2009. This estimate, derived from sunphotometry and integrated lidar backscatter profiles was consistent with averages derived from lidar estimates over Ny-Ålesund (Spitsbergen). The Sarychev SOD e-folding time at Eureka, deduced from lidar profiles, was found to be approximately 4 months relative to a regression start date of July 27. These profiles initially revealed the presence of multiple Sarychev plumes between the tropopause and about 17 km altitude. After about two months, the complex vertical plume structures had collapsed into fewer, more homogeneous plumes located near the tropopause. It was found that the noisy character of daytime backscatter returns induced an artifactual minimum in the temporal, pan-Arctic, CALIOP SOD response to Sarychev sulphates. A depolarization ratio discrimination criterion was used to separate the CALIOP stratospheric layer class into a low depolarization subclass which was more representative of Sarychev sulphates. Post-SAT (post Sarychev Arrival Time) retrievals of the fine mode effective radius (r eff,f ) and the logarithmic standard deviation for two Eureka sites and Thule (Greenland) were all close to 0.25 mm and 1.6 respectively. The stratospheric analogue to the columnar r eff,f average was estimated to be r eff,f (+) = 0.29 mm for Eureka data. Stratospheric, Raman lidar retrievals at Ny-Ålesund, yielded a post-SAT average of r eff,f (+) = 0.27 mm. These results are $50% larger than the background stratospheric-aerosol value. They are also about a factor of two larger than modeling values used in recent publications or about a factor of five larger in terms of (per particle) backscatter cross section.