On vertical plasma drift measurements made by a new medium power incoherent scatter radar (MP ISR) mode at the Jicamarca Radio Observatory

Abstract

A new medium power (MP) mode of the incoherent scatter radar (ISR) at the Jicamarca Radio Observatory has been recently implemented. The MP ISR mode uses comparatively small transmitters (∼0.2 MW peak power) to allow routine observations (200 to 300 days per year) of ionospheric plasma drifts that were not possible with the original larger transmitters. Here, we present results of an analysis of the first year (October 2023-October 2024) of vertical drift measurements made with the standard version of this new mode. The analysis was carried out to verify the ability of the new measurements to reproduce the expected features of the equatorial ionospheric vertical drifts despite the reduction in transmitter power. Our analysis shows that the diurnal and seasonal variation of the climatological MP ISR vertical drifts matches expectations based on previous experimental and modeling studies of the equatorial vertical drifts. For instance, the MP ISR reproduces the diurnal variation of the vertical drifts that includes the development of the well-known pre-reversal enhancement (PRE) near sunset. The MP ISR mode also shows that the PRE peak reaches maximum values in December solstice and equinox. Peak PRE values are reduced in June solstice. Therefore, the climatological vertical drifts indicate that, despite the reduced transmitter power, the new MP ISR mode is capable of capturing the main features of the equatorial vertical drifts. To better evaluate the MP ISR mode, we also compare the MP ISR climatology with vertical drifts output from two empirical models that were created using independent data sets and different mathematical techniques. Good overall agreement was obtained between the measurements and model predictions. Here, we highlight that the new MP ISR measurements show a rapid variation in the vertical drifts near sunrise that was predicted by one of the models. We point out that this rapid change can also be seen in vertical drifts simulated by physics-based numerical models. The new, routine MP ISR measurements will enable a better understanding of the equatorial drifts under a wide range of geophysical conditions.