The role of particle precipitation on plasma structuring at different altitudes by in-situ measurements

Abstract

The plasma in the cusp ionosphere is subject to particle precipitation, which is important for the development of large scale irregularities in the plasma density. These irregularities can be broken down to smaller scales which have been linked to strong scintillations in the Global Navigation Satellite System (GNSS) signals. We present power spectra for the plasma density irregularities in the cusp ionosphere for regions with and without auroral particle precipitation based on in-situ measurements from the Twin Rockets to Investigate Cusp Electrodynamics-2 (TRICE-2) mission, consisting of two sounding rockets flying simultaneously at different altitudes. The electron density measurements taken from the multi-needle Langmuir probe system (m-NLP) were analyzed for the whole flight duration for both rockets. Due to their high sampling rates, the probes allow for a study of plasma irregularities down to kinetic scales.  A steepening of the slope in the power spectra may indicate two regimes, a frequency interval with a shallow slope,  where fluid-like processes are dominating, and an interval with a steeper slope which can be addressed with kinetic theory. The steepening occurs at frequencies between 20 and 100 Hz with a median similar to the oxygen gyrofrequency. Additionally, the occurrence of double slopes increases where precipitation starts and throughout the rest of the flight. In addition, strong electron density fluctuations were found in regions poleward of the cusp, thus in regions immediately after precipitation. Furthermore, by investigating the integrated power of the fluctuations within different frequency ranges, we show that at low frequencies (10-100 Hz), the power is pronounced more evenly while the rocket encounters particle precipitation, while at high frequencies (100-1000 Hz) fluctuations essentially coincide with the passing through a flow channel.