Estimation of cold plasma outflow during geomagnetic storms

TL;DR

This paper introduces a new method combining synoptic observations and a novel estimation technique to measure cold plasma outflow during geomagnetic storms, revealing significant variations in outflow rates and transport mechanisms.

Contribution

The study presents a novel approach to estimate cold plasma outflow during storms, overcoming measurement challenges and providing insights into ion source regions and transport dynamics.

Findings

Outflow rates increase during geomagnetic storms.

Polar cap source regions expand during storms.

Enhanced convection leads to larger cold ion supply.

Abstract

Low-energy ions of ionospheric origin constitute a significant contributor to the magnetospheric plasma population. Measuring cold ions is difficult though. Observations have to be done at sufficiently high altitudes and typically in regions of space where spacecraft attain a positive charge due to solar illumination. Cold ions are therefore shielded from the satellite particle detectors. Furthermore, spacecraft can only cover key regions of ion outflow during segments of their orbit, so additional complications arise if continuous longtime observations, such as during a geomagnetic storm, are needed. In this paper we suggest a new approach, based on a combination of synoptic observations and a novel technique to estimate the flux and total outflow during the various phases of geomagnetic storms. Our results indicate large variations in both outflow rates and transport throughout the storm. Prior to the storm main phase, outflow rates are moderate, and the cold ions are mainly emanating from moderately sized polar cap regions. Throughout the main phase of the storm, outflow rates increase and the polar cap source regions expand. Furthermore, faster transport, resulting from enhanced convection, leads to a much larger supply of cold ions to the near-Earth region during geomagnetic storms.