On the relationship between energy input to the ionosphere and the ion outflow flux under different solar zenith angles

Naritoshi Kitamura,Masafumi Hirahara,Kanako Seki,Eric J. Lund,Tomoaki Hori,Robert J. Strangeway,Yukitoshi Nishimura,Kunihiro Keika,Lynn M. Kistler

doi:10.1186/s40623-021-01532-y

Naritoshi Kitamura, Masafumi Hirahara + Show 7 more

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https://doi.org/10.1186/s40623-021-01532-y

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Abstract

The ionosphere is one of the important sources for magnetospheric plasma, particularly for heavy ions with low charge states. We investigate the effect of solar illumination on the number flux of ion outflow using data obtained by the Fast Auroral SnapshoT (FAST) satellite at 3000–4150 km altitude from 7 January 1998 to 5 February 1999. We derive empirical formulas between energy inputs and outflowing ion number fluxes for various solar zenith angle ranges. We found that the outflowing ion number flux under sunlit conditions increases more steeply with increasing electron density in the loss cone or with increasing precipitating electron density (> 50 eV), compared to the ion flux under dark conditions. Under ionospheric dark conditions, weak electron precipitation can drive ion outflow with small averaged fluxes (~ 107 cm−2 s−1). The slopes of relations between the Poynting fluxes and outflowing ion number fluxes show no clear dependence on the solar zenith angle. Intense ion outflow events (> 108 cm−2 s−1) occur mostly under sunlit conditions (solar zenith angle < 90°). Thus, it is presumably difficult to drive intense ion outflows under dark conditions, because of a lack of the solar illumination (low ionospheric density and/or small scale height owing to low plasma temperature).Graphical abstract

Highlights

Quantifying the properties of outflowing ionospheric ions is one of the most important subjects for magnetospheric studies, because the physical characteristics of the magnetosphere are modulated significantly by outflowing ions
To understand how strongly ionospheric conditions affect ion outflows, we derive empirical formulas of outflowing ion number fluxes as a function of each energy input (electron density in the loss cone (> 50 eV), precipitating electron density (> 50 eV), DC and Alfvén Poynting fluxes) for a wide solar zenith angle (SZA) range (45°–145°), using data obtained by the Fast Auroral SnapshoT (FAST) satellite (3000–4150 km altitude)
Empirical formula Since the energy inputs and outflowing ion fluxes vary by multiple orders of magnitude, we investigated the relation in double logarithmic space according to the studies by Strangeway et al (2005) and Brambles et al (2011)

Summary

Introduction

Introduction Quantifying the properties of outflowing ionospheric ions is one of the most important subjects for magnetospheric studies, because the physical characteristics of the magnetosphere are modulated significantly by outflowing ions. Various modeling and observational studies have suggested that an increase in the ionospheric O + ions in the magnetosphere would affect reconnection processes (e.g., Shay and Swisdak 2004; Karimabadi et al 2011; Liu et al 2015; Fuselier et al, 2019; Tenfjord et al 2019), location of the tail reconnection (Brambles et al 2010; Garcia et al 2010; Wiltberger et al 2010; Yu and Ridley 2013), growth and propagation of electromagnetic ion cyclotron waves (e.g., Omidi et al 2013; Denton et al 2014; Nosé et al, 2020), and development and decay of the ring current (e.g., Hamilton et al 1988; Keika et al 2006; Glocer et al 2009a,b, 2013; Welling et al 2011; Ilie et al 2015; Menz et al 2019). The understanding of ion outflow from the ionosphere contributes to the understanding of atmospheric loss from magnetized planets

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