Propagation of gravity waves and spread F in the low‐latitude ionosphere over Tucumán, Argentina, by continuous Doppler sounding: First results

Abstract

Results of systematic analysis of propagation directions and horizontal velocities of gravity waves (GWs) and spread F structures in low-latitude ionosphere (magnetic inclination~27°) in Tucumán region, Argentina, are presented. Measurements were carried out by multipoint continuous Doppler system during 1 year from December 2012 to November 2013. It was found that meridian propagation of GWs dominated and that southward propagation prevailed in the local summer. Oblique spread structures observed in Doppler shift spectrograms and associated with spread F propagated roughly eastward at velocities from 70 to~180 m/s and were observed at night from~September to~March. The velocities were computed for 182 events and the azimuths for 64 events. Continuous Doppler sounding makes it possible to analyze more events compared to optical observations often used for propagation studies since the measurements do not depend on weather.

Medium-scale traveling ionospheric disturbances over Taiwan observed with HF Doppler sounding

“…Similar seasonal behavior, i.e., poleward propagation in summer and equatorward in winter, was observed in previous studies using HF Doppler sounding over the Czech Republic, South Africa, and Argentina (Chum et al 2010(Chum et al , 2012(Chum et al , 2014. Ding et al (2011) investigated MSTIDs over Central China using GPS-TEC measurements.…”

“…The method is based on shifting the signals measured at each point in the array to the reference point with various values of slowness, the inverse of velocity, and summing them together. This method has been successfully used for analyzing GW propagation in Chum et al (2014), who also verified that the obtained propagation velocities were consistent with those observed with other methods. In the 2-D case, the outcome is a two-dimensional function of slowness components W(s x ,s y ), which is calculated as:…”

“…The maximum of the function, which in this case corresponds to the velocity of 267 ms −1 and bearing of 140°, is considered the best estimate of the disturbance's horizontal propagation parameters. The parameter uncertainties are determined by calculating the parameters over slightly different time intervals (Chum et al 2014). This method is applied to all selected intervals.…”

Ground-based measurements of ionospheric dynamics

“…The temporal evolution of the spectrum with time is usually presented in the form of a spectrogram. Several spatially separated transmitter-receiver (sounding) paths are usually used to determine horizontal velocities of ionospheric disturbances from the time delays between the observations of corresponding disturbances on different sounding paths (Chum et al, 2014).…”

“…Moreover, the CDS allows to obtain the basic TID characteristics. The speed and direction of TIDs caused by atmospheric gravity waves can be estimated from comparison of the signals recorded on different sounding paths (Chum et al, 2014). TIDs were also studied from TEC perturbations caused by acoustic gravity waves by using dense networks of dual-frequency GPS (GNSS) receivers Otsuka et al, 2013;Lay et al, 2015).…”