F region drift observations from Athens Digisonde

Abstract

[1] Ionospheric drift measurements are of significant importance in the monitoring of the upper atmosphere dynamics and an important contributor toward the deeper understanding of the ionospheric electrodynamics. An interesting perspective for operational ionospheric drift measurements comes from the HF radars, such as the Digisondes. Nevertheless, when interpreting velocity measurements obtained from the Digisonde drift analysis method, care must be taken in relating the motion to the effects of photoionization, recombination, gravity waves, and plasma motion. In this paper we investigate the effect of all different mechanisms contributing to the apparent velocity measured by the Athens Digisonde. As a first step, the daily drift pattern over Athens under quiet magnetospheric conditions is preliminarily determined for the equinox months. Moreover, the substorm effect on the extracted pattern is also investigated. Our results provide some evidence for the direct effect of traveling atmospheric disturbances in the vertical component, while in the horizontal plane, the disturbance could be attributed to other substorm-related mechanisms.

A comparison of ground and satellite observations of F region vertical velocity near the dip equator

“…Digisonde appears to be another means of getting ionospheric drifts, during day and night [ Belehaki et al , 2006; Bertoni et al , 2006]. At equatorial latitudes, comparison and validation studies have not been yet conducted on the digisonde drift measurement [ Woodman et al , 2006].…”

F-region vertical drift measurements at Ebro, Spain

“…Therefore, dynamics and auroral energy input would partly explain the larger systematic variability we observe during nighttime, and the enhancement of this nighttime variability during winter because the nights are longer. However, other physical mechanisms may account for the above variability like ionospheric electric fields, traveling ionospheric disturbances, and substorm phenomena (Belehaki et al, 2006;and references therein). Lastly, we conclude from Fig.…”

“…However, the model represents the (E · B) drifts produced by electric fields, while Digisondes measure the apparent velocity Va. The Digisonde F-region drift is obtained from Doppler frequency shifts of HF radio waves reflected from the ionosphere, which are caused by plasma redistributions as a result of electric fields, ionization/recombination, substorm effects, neutral winds, and traveling ionospheric disturbances (Belehaki et al (2006)). Therefore, Va is not necessarily equal to the E · B drift, but it does include its effect on the plasma redistribution.…”

“…The Generalized Digisonde Drift Analysis (GDDA) proposed by Reinisch et al (1998) overcomes some of the problems of the previous method, and it gives more reliable results for the estimation of all three components of the ionospheric drift velocities: the vertical (Vz), and magnetic meridional (Vn) and zonal (Ve). However, as explained by Scali et al (1997) and Belehaki et al (2006), the Digisondes measure the ''apparent'' velocity Va which is a complicated function of a number of time varying properties of the radio wave propagation medium and, therefore, when interpreting HF Doppler measurements, care must be taken to account for the effects of photoionization, recombination, gravity waves, and plasma motion. Belehaki et al (2006) assessed the Digisonde drift measurements and they were able to obtain the daily drift pattern over Athens under quiet magnetospheric conditions during equinox, and to extract the substorm effects from the obtained daily pattern.…”

“…However, as explained by Scali et al (1997) and Belehaki et al (2006), the Digisondes measure the ''apparent'' velocity Va which is a complicated function of a number of time varying properties of the radio wave propagation medium and, therefore, when interpreting HF Doppler measurements, care must be taken to account for the effects of photoionization, recombination, gravity waves, and plasma motion. Belehaki et al (2006) assessed the Digisonde drift measurements and they were able to obtain the daily drift pattern over Athens under quiet magnetospheric conditions during equinox, and to extract the substorm effects from the obtained daily pattern. The daily pattern was clearly identified for both the eastward and northward components of the F-region drift velocities, with a dominant semidiurnal behavior for the magnetic meridional component, and a dominant diurnal behavior for the zonal component.…”