Horizontal velocities and propagation directions of gravity waves in the ionosphere over the Czech Republic

Abstract

[1] Using a five-point continuous Doppler sounding system operating at 3.59 MHz, developed at the Institute of Atmospheric Physics AS CR (IAP), we investigate propagation directions and velocities of gravity waves (GWs) at altitudes from ∼150 to ∼250 km over the western part of the Czech Republic. The velocities and directions are computed from the time delays between the observations of corresponding GWs at different reflection points that correspond to various sounding paths. We focused on the GWs that produce an S-shaped trace in Doppler shift spectrograms and are observed close to sunrise and sunset. We have selected about 100 of such events. Our results show that the analyzed GWs propagate with typical horizontal velocities from ∼100 to ∼200 m/s. The north-south component of GW velocities depends on the season, it is directed northward in the summer and southward in the winter. At the same time, the north-south component of the neutral winds calculated by the horizontal wind model HWM07 has the opposite sign. Typical observed periods of the analyzed waves range from ∼10 to ∼30 min.

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.…”

“…1. A more detailed description of similar Doppler sounding systems operating in other locations can be found in Chum et al (2010Chum et al ( , 2012, and Doppler sounding theory is described in more detail in Chum et al (2016).…”

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

“…It is necessary to stress that the given uncertainties concern the propagation of the dominant wave and they are not related to the width (span) of the slowness vector which is usually much wider as can be seen in Figure . The velocity determined from time differences of the S‐shaped signatures [ Chum et al ., ] is 133 ± 31 m/s with azimuth 4 ± 14° for the S‐shaped signatures occurring around 21:24 UT, and the velocity estimated from the time differences of steep positive slopes [ Chum et al ., ] is 139 ± 17 m/s with azimuth 28 ± 8° for the swelling occurring around 22:00 UT. The results obtained by different methods are therefore consistent.…”

Ionospheric disturbances (infrasound waves) over the Czech Republic excited by the 2011 Tohoku earthquake

“…The used transmitted frequencies f are as follows: f (Tx1) = 3.594500 MHz, f (Tx2) = 3.594504 MHz, f (Tx3) = 3.594496 MHz, f (Tx4) = 3.594508 MHz, f (Tx5) = 3.594492 MHz. A short description of this system, developed at the Institute of Atmospheric Physics, Czech Republic, with a short introduction to Doppler sounding measurements can be found in Chum et al [2010]. The reflection height of sounding radio waves is estimated from the ionograms obtained by the digital model DPS–4 ionosonde (http://ulcar.uml.edu/digisonde_dps.html) located in Pruhonice, ∼1 km away from the transmitter Tx2, and ∼7 km from the receiver Rx.…”