Gravity waves and spreadEsobserved during the solar eclipse of 22 July 2009

[1] During the total solar eclipse of 22 July 2009, two ground-based high-frequency radio systems were applied to observe the ionospheric variations over Wuhan, China. The ionosonde recorded ionograms every 5 min; the Wuhan Ionospheric Oblique Backscattering Sounding System recorded echo range and Doppler every 1 min. Comparing the observations of the two radio systems, we found that the periodic fluctuation on the top penetration frequency of regular Es (fEs) and on the Doppler velocity of the spread Es appeared and disappeared simultaneously on the eclipse day. Moreover, wavelet analysis results show that the fEs curve and the Doppler velocity of the spread Es contain the same period of ∼35 min. The spread Es occurred owing to the off-vertical reflections from the tilted layer at the Es latitude. Atmospheric gravity waves are considered to be generated during the solar eclipse and propagate upward to deform the Es layer and produce the moving wave-like structures in the layer. The tilted plasma concentration in the moving wave-like structures induced the off-vertical HF radiowave reflections and added the Doppler modulation of also ∼35 min period on the reflected radiowave. Furthermore, the Doppler values of regular Es indicate that the layer at lower altitude was weakly disturbed and the layer at higher altitude was deeply modulated, which is in agreement with the theory that the amplitude of gravity waves increases with height.