Comparison of ionosonde and incoherent scatter drift measurements at the magnetic equator

Abstract

It has been proposed that ionosondes can be used to measure vectorial nighttime ionospheric drifts at F region altitudes. These measurements have been validated at mid and high magnetic latitudes on campaign basis. Here we report concurrent F-region drift measurements made at Jicamarca (11.95°S, 76.87°W), under the magnetic equator, using the main Incoherent scatter radar (ISR) and a digisonde portable ionosonde (DPS). As far as the vertical drift measurements, we show a fair agreement between the two techniques at periods when convection dominates other factors (e.g., around pre-reversal enhancement). At other times, production and recombination dominate, and DPS vertical drifts are not reliable. For the horizontal drift component, we limited our measurements to the zonal component. We find poor agreement, being worse at times when the E region electron density is high (e.g., during the day). The amplitude of DPS zonal velocities are significantly larger than ISR zonal drifts. During the day, we find that the DPS zonal drifts are in better agreement with the drift velocity of the long wavelength equatorial electrojet (EEJ) instabilities. This is to be expected since, the diffraction pattern on the ground - to which any reflection HF drift technique will be sensitive to - is mainly, if not solely, dependent on the electron density structure at EEJ heights, where the electron irregularity density is sufficiently high to diffract the phase front of the F region reflected wave.