1Institute of Applied Physics, University of Bern, Bern, Switzerland
2Oeschger Center for Climate Change Research, University of Bern, Bern, Switzerland
3Atmospheric Chemistry Division, National Center for Atmospheric Research, Boulder, CO, USA
Abstract. The transportable ground based microwave radiometer MIAWARA-C monitored the upper stratospheric and lower mesospheric (USLM) water vapor distribution over Sodankylä, Finland (67.4° N, 26.6° N) from January to June 2010. At the end of January, approximately 2 weeks after MIAWARA-C's start of operation in Finland, a stratospheric sudden warming (SSW) disturbed the circulation of the middle atmosphere. Shortly after the onset of the SSW water vapor in the USLM rapidly increased from approximately 5.5 to 7 ppmv in the end of January. Backward trajectory calculations show that this strong increase is due to the break down of the polar vortex and meridional advection of subtropical air to the arctic USLM region. In addition, mesospheric upwelling in the course of the SSW led to an increase in observed water vapor between 0.1 and 0.03 hPa.
After the SSW MIAWARA-C observed a decrease in mesospheric water vapor volume mixing ratio (VMR) due to the subsidence of H2O poor air masses in the polar region. Backward trajectory analysis and the zonal mean water vapor distribution from the Microwave Limb Sounder on the Aura satellite (Aura/MLS) indicate the occurrence of two regimes of circulation from 50° N to the north pole: 1) regime of enhanced meridional mixing throughout February and 2) regime of an eastward circulation in the USLM region reestablished between early March and equinox. The polar descent rate determined from MIAWARA-C's 5.2 ppmv isopleth is 350 m d−1 in the pressure range 0.6 to 0.06 hPa between mid February and early March. For the same time interval the descent rate was determined using trajectories calculated from the Transformed Eulerian Mean (TEM) wind fields simulated by means of the Whole Atmosphere Community Climate Model (WACCM). The values found using these different methods are in good agreement.