Planetary-scale wave observations over a low-latitude E region using simultaneous observations of VHF radar and ionosonde over Sanya (18.34°N, 109.62°E)

[1] The planetary-scale oscillations of the field-aligned irregularities (FAI) and the sporadic E (Es) layers in the low-latitude E region were studied in terms of the observations from 8 June to 22 August 2009 using coherent backscatter radar and a digital ionosonde installed at Sanya (18.34°N, 109.62°E), Hainan Island, China. Quasi 2 day waves were observed both in the meridional wind and in daytime backscatter echo occurrence. Simultaneous observations on sporadic E layers in daytime showed a planetary-scale wave signature in the low-latitude region for the first time. Close correlation between echo occurrence and the mean critical frequency (foEs) was found when the quasi 2 day planetary wave (QTPW) existed. These results suggest that the Es plays an important role in determining the long-term variability of the low-latitude E region FAI. To test the nonlinear interactions between tides and QTPW, the hourly meridional and zonal winds are analyzed. The subsidiary waves with anticipated frequencies and their height evolutions provide evidence of tide-QTPW interactions. Bispectral analysis on the winds further validates the strong nonlinear interactions between tides and the QTPW in the meridional wind. Our results suggest that the mechanism proposed by Pancheva et al. [2003] is a reasonable explanation for the planetary-scale variability of the low-latitude E region FAI and Es. The different responses of the Es layers and the E region FAIs on the QTPW between day and night can be attributed to diurnal variations in ion densities in the region between 100 and 160 km.

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