Two-dimensional UHF radar studies of post-midnight ESF at the Jicamarca Radio Observatory

Equatorial spread F (ESF) is the general name given to a wide range, in scale sizes, of ionospheric F-region irregularities observed at low latitudes. ESF events have been more commonly observed during evening hours and have been associated with the pre-reversal enhancement (PRE) of the equatorial F-region vertical drifts which occurs around sunset. More recently, however, studies have pointed out the occurrence of F-region irregularities during post-midnight hours which have yet to be better understood.
Of main relevance to the present study is the work by Zhan et al. (2018) which presented cases of post-midnight ESF but pointed out difficulties of conventional (single beam) radar observations to determine, unequivocally, whether the ESF events were generated locally (near the observation site) or non-locally and drifted zonally into the field-of-view of the radar. We emphasize that the distinction is crucial when trying to understand the conditions under which these events developed based on local measurements of ionospheric or thermospheric parameters.
We have been processing and analyzing new two-dimensional (2D) observations of F-region echoes made by a 14-panel version of the AMISR system installed at JRO. Semi-routine (~ 200 nights per year) have been made since July 2021. Of importance here is that AMISR-14 scans the magnetic equatorial plane and produces “images” of ESF echoes over a zonal distance of +/- 200 km with respect to JRO. Therefore, the images allow us to determine, unambiguously, whether radar ESF was generated locally or not. Here, we use these images to better understand the post-midnight ESF events.
In this poster, we will present and discuss results of the analyses of 2D observations of post-midnight ESF made by AMISR-14 between July 2021 and August 2023. The results include occurrence rates of post-midnight ESF events detected by the system, the seasonal and geomagnetic conditions under which these events developed and our findings about the local versus non-local development of these events.

Zhan, W., Rodrigues, F., & Milla, M. (2018). On the genesis of postmidnight equatorial spread F: Results for the American/Peruvian sector. Geophysical Research Letters, 45, 7354–7361. https://doi.org/10.1029/2018GL078822.

Acknowledgment: This work was supported by NSF award AGS-1916055 and by a NDSEG fellowship.