Solar Rotation Period Driven Modulations of Plasmaspheric Density and Convective Electric Field in the Inner Magnetosphere

Abstract

This paper presents the first analysis of Van Allen Probes measurements of the cold plasma density and electric field in the inner magnetosphere to show that intervals of strong modulation at the solar rotation period occur in the locations of the outer plasmasphere and plasmapause (~0.7 R E peak-to-peak), in the large-scale electric field (~0.24 mV/m peak-to-peak), and in the cold plasma density (~250 to~70 cm −3 peak-to-peak). Solar rotation modulation of the inner magnetosphere is more apparent in the declining phase of the solar cycle than near solar maximum. The periodicities in these parameters are compared to solar extreme ultraviolet irradiance, solar wind dawn-dusk electric field, and Kp. The variations in the plasmapause location at the solar rotation period anticorrelate with solar wind electric field, magnetospheric electric field, and Kp, but not with extreme ultraviolet irradiance, indicating that convective erosion is the dominant physical process controlling the plasmapause at these timescales.Plain Language Summary As the Sun rotates with a 27-day period, it also emits winds of ionized gas. In some places these winds are leaving at faster speeds than in other places. These winds flow out to the Earth and beyond, and because the Sun rotates, the Earth is hit with each stream of fast wind every 27 days. A region of cooler ionized gas in space surrounding Earth, called the plasmasphere, shrinks when the effects of the fast wind on Earth's magnetic field cause the removal of the outer part of the plasmasphere. When the wind speeds decrease, the plasmasphere grows in size again. The result is that the plasmasphere breathes in and out at the solar rotation period. We use the Van Allen Probe-B satellite to measure the size and density of the plasmasphere and to show for the first time with direct measurements the 27-day variation in the plasmasphere and its connection to the fast winds from the Sun. This result is important, as the behavior of the plasmasphere affects various kinds of waves that can exist in space around Earth, some of which are responsible for the creation and loss of energetic electrons that can damage spacecraft.

Particle Dynamics in the Earth's Radiation Belts: Review of Current Research and Open Questions

“…In addition to the wave environment, we seek to understand the local plasma conditions (e.g., Thaller et al, ; Hwang & Yoon, , in this collection) that lead to the enhancement or suppression of these various wave modes and the consequences therein for the precipitation of the trapped populations. For instance, Greeley et al () in this collection have found that the plasmapause is likely a better indicator of microburst location than L‐shell.…”

Multi‐Event Studies of Sudden Energetic Electron Enhancements in the Inner Magnetosphere and Its Association With Plasmapause Positions

“…An alternative to this L pp definition is to use a density threshold (n e ) of 100 cm −3 to infer the plasmapause. Many studies have utilized the density threshold as a proxy of the plasmapause position (Chappell et al, 1970;Malaspina et al, 2016;Thaller et al, 2019). In Thaller et al (2019), they derived the plasmapause using both the plasma density gradient and density threshold methods and demonstrated that these two quantities are comparable.…”

“…Many studies have utilized the density threshold as a proxy of the plasmapause position (Chappell et al, 1970;Malaspina et al, 2016;Thaller et al, 2019). In Thaller et al (2019), they derived the plasmapause using both the plasma density gradient and density threshold methods and demonstrated that these two quantities are comparable. They further noted that the plasmapause derived from the density threshold has fewer gaps, thanks to its simplicity of implementation.…”

“…An alternative to this L pp definition is to use a density threshold ( n e ) of 100 cm −3 to infer the plasmapause. Many studies have utilized the density threshold as a proxy of the plasmapause position (Chappell et al., 1970; Malaspina et al., 2016; Thaller et al., 2019). In Thaller et al.…”

“…In Thaller et al. (2019), they derived the plasmapause using both the plasma density gradient and density threshold methods and demonstrated that these two quantities are comparable. They further noted that the plasmapause derived from the density threshold has fewer gaps, thanks to its simplicity of implementation.…”