Evidence of low‐latitude daytime large‐scale traveling ionospheric disturbances observed by high‐frequency multistatic backscatter sounding system during a geomagnetically quiet period

Abstract

Observations from the high‐frequency multistatic backscatter sounding radars on a geomagnetically quiet day (minimum Dst = −14 nT) captured the anti‐equatorward propagation of daytime large‐scale traveling ionospheric disturbance (LSTID) at the low‐latitude regions. The observed LSTID was characterized approximately by a meridional propagation speed of 347 ± 78 m/s and azimuthal angle of −4.7 ± 27.6° (counterclockwise from north), with a period of 76 min and a wavelength of 1583 ± 354 km by means of maximum entropy cross‐spectral analysis. Vertical phase velocity was also evaluated to be <∼42 m/s through the Doppler measurements. These results provide evidence that the low‐latitude ionosphere can undergo large‐scale perturbations even under geomagnetically quiet conditions. We suggest that this observed LSTID could be due to the secondary gravity waves from thermospheric body forces created from the dissipation of primary gravity waves from deep tropospheric convection.