Climatology and seasonal variation of the thermospheric tides and their response to solar activities over Arecibo

Abstract A long-term statistical analysis of thermospheric tides in an altitude range from 150 to 400 km is presented. The analysis is based on a dataset with 31 multi-day experiments conducted from an incoherent scatter radar at Arecibo Observatory between 1984 and 2015. This is the first time that the climatological mean and seasonal variations of the thermospheric tides and their response to solar activities are reported using an extensive dataset. The climatological mean amplitude of diurnal tide (DT) is dominant while the amplitudes of the semidiurnal tide (SDT) and terdiurnal tide (TDT) are comparable. Below 250 km, the SDT and TDT phases show downward propagation with vertical wavelengths of 300 and 240 km, respectively. Above 250 km, the DT is the most prominent component except in autumn while the SDT dominates below 250 km except in winter. Above 250 km, the DT is the strongest in winter and its amplitude varies around 28 m/s. Below 250 km, the SDT is prominent in autumn and fluctuates around 35 m/s. The TDT is the most important in winter compared to the other three seasons and its amplitude is slightly less than 20 m/s. The DT and SDT amplitudes show the opposite response to solar activity. Above 250 km, the former increases with increasing solar activity while the latter is the opposite. The enhanced DT amplitude and its phase structure under the high solar activity indicates that the in-situ EUV radiation plays a major role in generating the thermospheric DT over Arecibo.