Dependence of lunar tide of the equatorial electrojet on the winter-time polar vortex, solar flux and QBO

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Thursday, April 5, 2018

The lower atmospheric forcing effects on the ionosphere are particularly evident during extreme meteorological events known as sudden stratospheric warmings (SSWs). During SSWs, the polar stratosphere and ionosphere, two distant atmospheric regions, are coupled through the SSW induced modulation of atmospheric migrating and non-migrating tides.

Dependence of lunar tide image
a) Composite of the lunar tidal power from Huancayo recordings for SSWs in the easterly phase of QBO. The red (blue) line shows the mean lunar tidal power when solar flux values are < (>) 120 s.f.u. (b) Composite of the area-weighted ZMZW anomaly (m/s) between 60 deg - 90 deg N for SSWs that are recorded during the easterly QBO phase when the solar flux values < 120 s.f.u. (c) Same as (b) but for SSWs recorded during the easterly QBO phase when the solar flux values > 120 s.f.u. (d-f) Same as (a-c) except for SSWs in the westerly phase of QBO. The dashed vertical black lines indicate the central day of the composites.

The changes in the migrating semidiurnal solar and lunar tides are the major source of ionospheric variabilities during SSWs. In this study, we use 55 years of ground-magnetometer observations to investigate the composite characteristics of the lunar tide of the equatorial electrojet (EEJ) during SSWs. These long-term observations allow us to capture the EEJ lunar tidal response to the SSWs in a statistical sense. Further, we examine the influence of solar flux conditions and the phases of Quasi-Biennial Oscillation (QBO) on the lunar tide and find that the QBO phases and solar flux conditions modulate the EEJ lunar tidal response during SSWs in a similar way as they modulate the winter-time Arctic polar vortex. This work provides first evidence of modulation of the EEJ lunar tide due to QBO.

Publication Name: Geophysical Research Letters

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