Middle atmospheric water vapor and ozone anomalies during the 2010 major sudden stratospheric warming

Abstract

Abstract. A major sudden stratospheric warming (SSW) occurred in the Northern Hemisphere in January 2010. The warming started on 26 January 2010, was most pronounced by the end of January and was accompanied by a polar vortex shift towards Europe. After the warming, the polar vortex split into two weaker vortices. The zonal mean temperature in the polar upper stratosphere (35–45 km) increased by approximately 25 K in a few days, while there was a decrease in temperature in the lower stratosphere and mesosphere. Local temperature maxima were around 325 K in the upper stratosphere and minima around 175 and 155 K in the lower stratosphere and mesosphere, respectively. In this study, we present middle atmospheric water vapor and ozone measurements obtained by a meridional chain of European ground-based microwave radiometers in Bern (47° N), Onsala (57° N) and Sodankylä (67° N). The instruments in Bern and Onsala are part of the Network for the Detection of Atmospheric Composition Change (NDACC). Effects of the SSW were observed at all three locations and we perform a combined analysis in order to reveal transport processes in the middle atmosphere above Europe during the SSW event. Further we investigate the chemical and dynamical influences of the SSW event. We find that the anomalies during the warming in water vapor and ozone were different for each location. A few days before the beginning of the major SSW, we observed a decrease in mesospheric water vapor above Bern, which we attribute to movement of the mesospheric polar vortex towards Central Europe. The most prominent H2O anomaly observed in Bern was an increase in stratospheric water vapor during the warming. In Onsala and Sodankylä, mesospheric water vapor increased within a few days during the warming and slowly decreased afterwards. Upper stratospheric ozone decreased during the warming over Bern by approximately 30% and by approximately 20% over Onsala. Over Sodankylä, a decrease in ozone below 30 km altitude was observed. This decrease is assumed to be caused by heterogeneous chemistry on polar stratospheric clouds. After the SSW, stratospheric ozone increased to higher levels than before at all three locations. The observed anomalies are explained by a trajectory analysis with reanalysis data from the European Center for Medium-Range Weather Forecasts (ECMWF). Most of the observed anomalies in water vapor and ozone during the warming are attributed to the location of the polar vortex, depending on whether a measurement site was inside or outside the polar vortex. The observed increase in mesospheric water vapor at high latitudes is explained by advection of relatively moist air from lower latitudes, whereas the observed increase in stratospheric water vapor at midlatitudes is explained by advection from high latitudes, i.e. from the moist stratospheric polar vortex.