Atmospheric tides in the low-latitude E and F regions and their responses to a sudden stratospheric warming event in January 2010

An extensive analysis of atmospheric tides in the low-latitude thermosphere and their responses to a major sudden stratospheric warming (SSW) event (18-23 January 2010) is presented. The analysis is based on observational data from the Arecibo dual-beam incoherent scatter radar. Important findings of the present study are as follows. (1) The diurnal tide with an evanescent phase structure dominates the F region meridional wind field. The diurnal tide has a peak amplitude of 45 m/s occurring at about 245 km, and it is very stable throughout the nine consecutive days' observation. Below 114 km, the vertical structures of the diurnal tide in the meridional and zonal components are consistent, which resemble the classical solar S-1,S- 1 tidal mode. (2) The F region semidiurnal tide is much weaker and has larger day-to-day variability than the diurnal tide. In the E region, the semidiurnal amplitudes in the meridional and zonal components grow continuously in the altitude ranges from 106 to 121 km and from 100 to 115 km, respectively. The vertical wavelength of the zonal component is estimated to be 45 km above 100 km, which is close to the solar S-2,S- 4 and S-2,S- 5 tidal modes. (3) The semidiurnal and terdiurnal tides respond strongly to the SSW while the impact that the SSW has on the diurnal tide in the meridional wind is limited. During the SSW event, the amplitudes of the semidiurnal and terdiurnal tides are enhanced in the F region but reduced in the upper E region.