High Altitude ISR Experiments at Jicamarca in Low Solar Flux Conditions

Abstract:

We present recent data and advances in high altitude ISR experiments at Jicamarca that allow high altitude estimates of ionospheric parameters of the equatorial topside ionosphere and lower plasmasphere during low solar flux conditions. The low solar flux conditions, in particular the current deep solar minimum have brought unique challenges in signal processing due to lower SNR in the return signals. These ionospheric estimates are a crucial step in complimenting data from higher solar flux periods, validating the output of models, and allowing us to build a more comprehensive understanding of the equatorial upper atmosphere during a full solar cycle.

Ionospheric parameter altitude profiles (N_e, T_e, T_i and O⁺, H⁺ , He⁺ ion composition) that span heights of up to 1500 km will be presented. We will elaborate on the modifications made to the experimental setup and signal processing techniques to accommodate conditions of extremely low solar flux.

Advances in the data processing techniques will be explained, which include improved initial guess estimation using functions informed by the SAMI2-PE model output, and constrained with satellite data, the use of more advanced clutter elimination techniques, and incorporation of an updated IGRF model (2019-2024) that reflects the recent changes to the magnetic field.

Revisions to the SAMI2-PE model will also be presented, prompted due to discrepancies between the model output and the Jicamarca data for periods of low solar flux. Temperatures at sunrise are higher in the ISR data and satellite data than in the model, and a mid-afternoon drop is seen in the ISR data that exceeds that which is observed in the model. Some of our ongoing research in this area will be discussed, such as the inclusion of additional terms in the transport equations.

Finally another phenomenon picked up by Jicamarca’s ISR antenna will be briefly introduced, that of high altitude coherent echoes in the range of 1000 - 2200 km observed only during conditions of low solar flux in the post-midnight sector. It is distinct from ESF in terms of its altitudes of occurrence and the presence of LH electrostatic waves which appear as prominent bands in the spectrogram of the backscatter.