Coupling between mesosphere and ionosphere over Beijing through semidiurnal tides during the 2009 sudden stratospheric warming

Sudden stratospheric warming (SSW) in the winter of 2008/2009 is the strongest recorded SSW event. The enhancement in semidiurnal variation of ionospheric TEC (total electron content) with phase shift forward is shown during 22 to 27 January 2009, based on the TEC observations in Beijing (40.30°N, 116.19°E geographic, 39.73°N dip latitude). We focus on finding the reason for the TEC variation. Winds observed by an all‐sky meteor radar in the same observatory are used to study mesospheric variation. The semidiurnal solar tide in the mesosphere starts to increase before the SSW and maintains oscillation with period 16–20 days during the SSW. The semidiurnal lunar tides in TEC and wind start to increase on 17 and 15 January, respectively. Although the semidiurnal lunar tide in TEC over Beijing almost dies out on 1 February, that over equatorial ionospheric anomaly crest does not vanish until 15 February when lunar tide in wind tends to be very weak. The maximum of lunar tide in wind appears on 2 February at 96 km with amplitudes of 15 m/s and 21 m/s for zonal and meridional winds. The phase comparison shows that lunar tides in TEC and zonal wind reach their maxima at almost the same time, which is 2–4 h lag behind the meridional wind. The coupling between the mesosphere and ionosphere contributes to the semidiurnal variation of TEC through both solar and semidiurnal lunar tides. The enhancement in semidiurnal lunar tide is responsible for the TEC peak shift forward during the SSW. Key PointsFirst Comparison of response of mesosphere and ionosphere in mid latitude on SSWThe results show the in‐phase variation of lunar tide in TEC and zonal wind.We provide direct evidence of coupling through semidiurnal tides during SSW.