Preprints
https://doi.org/10.5194/egusphere-2024-485
https://doi.org/10.5194/egusphere-2024-485
21 Feb 2024
 | 21 Feb 2024

Influences of sudden stratospheric warmings on the ionosphere above Okinawa

Klemens Hocke, Wenyue Wang, and Guanyi Ma

Abstract. We analyzed the ionosonde observations at Okinawa (26.7° N, 128.1° E) for the years from 1972 to 2023. Okinawa is at the border between the low latitude and the mid-latitude ionosphere. The influences of sudden stratospheric warmings (SSWs) on the ionosphere are strong at low latitudes but less obvious at middle and high latitudes. We divided the dataset into winters with major SSWs in the northern hemisphere (SSW years) and into winters without major SSWs (no SSW years). During the SSW years, the daily cycle of the F2 region electron density maximum (NmF2) was stronger than in the no SSW years. The relative NmF2 amplitudes of solar and lunar tidal components (S2, O1, M2, MK3) are stronger by 3 to 8 % compared to no SSW years. The semidiurnal amplitude, averaged for 29 SSW events, has a significant peak at the central date of the SSW (epoch time 0 of the composite analysis). The SSW influence is not strong: the semidiurnal amplitude is about 38.2 % in SSW years and about 32.9 % in no SSW years (relative to NmF2 of the background ionosphere). However, there is a sharp decrease of the amplitude by about 10 % after the SSW peak was reached. The amplitude of the diurnal component does not show a single peak at the central date of the SSW. We present the maximal semidiurnal amplitudes of the SSWs since 1972. The SSW of 31 December 1984 has the strongest amplitude (162 %) in the ionosphere above Okinawa. The most surprising finding of the study are the strong lunar tides with relative amplitudes of about 10 % and the discovery of a terdiurnal lunar tide (5 %) in NmF2 during SSW years. The periods of the ionospheric lunar tides agree with the periods of ocean tides.

Klemens Hocke, Wenyue Wang, and Guanyi Ma

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-485', Anonymous Referee #1, 14 Mar 2024
    • AC2: 'Reply on RC1', Klemens Hocke, 22 Mar 2024
  • RC2: 'Comment on egusphere-2024-485', Anonymous Referee #2, 17 Mar 2024
    • AC1: 'Reply on RC2', Klemens Hocke, 22 Mar 2024

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-485', Anonymous Referee #1, 14 Mar 2024
    • AC2: 'Reply on RC1', Klemens Hocke, 22 Mar 2024
  • RC2: 'Comment on egusphere-2024-485', Anonymous Referee #2, 17 Mar 2024
    • AC1: 'Reply on RC2', Klemens Hocke, 22 Mar 2024
Klemens Hocke, Wenyue Wang, and Guanyi Ma
Klemens Hocke, Wenyue Wang, and Guanyi Ma

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Short summary
We find a clear SSW effect in the foF2 series at Okinawa. In the composite of 29 SSW events, the amplitude of the semidiurnal cycle of foF2 shows a peak at the SSW onset time in SSW years. For the first time, we find a lunar terdiurnal component with a relative amplitude of about 5 % in SSW years. The lunar diurnal and semidiurnal components have relative amplitudes of about 10 % in SSW years. The periods of the lunar ionospheric tidal variations are at the periods of ocean tides.