A whole atmosphere model (WAM) has been used to determine the physical processes driving the change in electrodynamics during the January 2009 sudden stratospheric warming (SSW). Previously the WAM model was integrated into the National Weather Service Gridpoint Statistical Interpolation (GSI) data assimilation scheme to enable the observed changes in amplitude of planetary wavenumber one and two in the lower atmosphere to be followed. The modeled changes in ozone concentration, which act as a tracer of the middle atmosphere dynamics, agree well with observations from the ground-based station at Bern, Switzerland, which supports the accuracy of the modeled middle atmosphere dynamics. The model showed that the amplitude and phase of both the semi-diurnal and terdiurnal migrating tides SW2 and TW3 varied through the period. The change in phase of SW2 and TW3 follows the reversals in direction of the stratospheric longitudinally averaged zonal winds. As the stratospheric zonal winds reverse from eastward to westward, the SW2 and TW3 tidal phases move to earlier local times. Similarly, as the zonal winds slowly recover to the more typical eastward direction expected for the season, the tidal phases gradually move to later local times. The reasonable correlation suggests the tidal phase changes are due to the zonal winds in the stratosphere pushing the tide to earlier or later local times as it propagates from its source at lower altitudes. The phase changes of the SW2 during the SSW recovery period is similar to that expected from the lunar gravitational tide. Since WAM does not explicitly include the lunar tide, the change in phase of the solar-driven SW2 could be mistaken for an increase in the amplitude of the lunar gravitational semidiurnal M-2 mode. The apparent signature of the lunar tide in the model simulation is actually due to the gradual change in phase each day of the solar heating-driven semidiurnal tide as it propagates through the slowing changing zonal wind. The WAM winds drove electrodynamics in the dynamo region reasonably consistent with observations from the Jicamarca longitude sector. Near the peak of the SSW, the winds drove a stronger eastward electric field (upward plasma drift) early in the morning, reversing to westward (downward plasma drift) in the afternoon. The peak in upward plasma drift gradually moved back to later local times during the 2- or 3-week recovery from the SSW. The model tidal fields were separated into their components to determine what aspects of the tidal wind changes (i.e., SW2 or TW3 amplitude and phase) caused the shift in phase of the vertical plasma drift at the magnetic equator to earlier local times, and what drove the increases in amplitude. The results show the SW2 tide is the dominant mode producing agreement between observations and modeled electrodynamics, and that the model changes in TW3 hinder rather than help in the comparison. The model also shows that, although the increase in magnitude of the SW2 drives a stronger upward plasma drift, part of the increase in magnitude at the earlier local times comes from the phase change, from a more efficient dynamo action. Key Points: Sudden stratospheric warmings (SSW) modulate vertical propagation of migrating tides. WAM simulated the planetary wave and ozone response to the 2009 SSW. Phase changes of the migrating semidiurnal tide (SW2) in the lower thermosphere follow the changes in the stratospheric zonal winds. The phase change of SW2 is similar to that expected from the lunar gravitational tide. The SW2 tidal winds in the dynamo region drove electrodynamics reasonably consist with Jicamarca incoherent scatter observations.

GROMOS, the ground-based millimeter-wave ozone spectrometer, continuously measures the stratospheric ozone profile between the altitudes of 20 and 65km above Bern (46°57′N, 7°27′E) since November 1994. Characteristics of intraseasonal oscillations of stratospheric ozone are derived from the long-term data set. Spectral analysis gives evidence for a dominant oscillation period of about 20 days in the lower and middle stratosphere during winter time. A strong 20-day wave is also found in collocated geopotential height measurements of the microwave limb sounder onboard the Aura satellite (Aura/MLS) confirming the ground-based observations of GROMOS and underlining the link between ozone and dynamics. Remarkably, the ozone series of GROMOS show an interannual variability of the strength of intraseasonal oscillations of stratospheric ozone. The interannual variability of ozone fluctuations is possibly due to influences of planetary wave forcing and the quasi-biennial oscillation (QBO) on the meridional Brewer–Dobson circulation of the middle atmosphere. In detail, time series of the mean amplitude of ozone fluctuations with periods ranging from 10 to 60 days are derived at fixed pressure levels. The mean amplitude series are regarded as a measure of the strength of intraseasonal oscillations of stratospheric ozone above Bern. After deseasonalizing the mean amplitude series, we find QBO-like amplitude modulations of the intraseasonal oscillations of ozone. The amplitudes of the intraseasonal oscillations are enhanced by a factor of 2 in 1997, 2001, 2003, and 2005. QBO-like variations of intraseasonal oscillations are also present in wind, temperature and other parameters above Bern as indicated by meteorological reanalyses of the European Centre for Medium-range Weather Forecasts (ECMWF). Further, intercomparisons of interannual variability of intraseasonal tropospheric and stratospheric oscillations are performed where the NAO index (North-Atlantic oscillation) and the MJO index (Madden–Julian oscillation) are taken as proxies for tropospheric oscillations. As a result, interannual variability of intraseasonal oscillations of the stratosphere seems not to be well correlated with respect to that of the troposphere.