Do Statistical models capture magnetopause dynamics during sudden magnetospheric compressions?

Abstract

<p>Under steady-state conditions the magnetopause location is described as a pressure balance between internal magnetic pressures and the external dynamic pressure of the solar wind. The question is, does this approximation hold during more dynamic solar wind features?</p><p>Under more extreme solar wind driving, such as high solar wind pressures or strong southward-directed interplanetary magnetic fields, this boundary is significantly more compressed than in steady-state, playing a significant role in the depletion of magnetospheric plasma from the Van Allen Radiation Belts, via magnetopause shadowing. Large step-changes in solar wind conditions enable the real magnetopause to have a significant time-dependence which empirical models cannot capture.</p><p>We use a database of ~20,000 magnetopause crossings, to determine how the measured magnetopause differs from a statistical model, and under which conditions. We find that observed magnetopause is on average 6% closer to the radiation belts,  with a maximum of 42%, during periods of sudden dynamic pressure enhancement, such as during storm sudden commencement. Our results demonstrate that empirical magnetopause models such as the Shue et al. [1998] model should be used cautiously to interpret energetic electron losses by magnetopause shadowing. </p>

ULF Wave Driven Radial Diffusion During Geomagnetic Storms: A Statistical Analysis of Van Allen Probes Observations

“…In Figure 3 the outermost L * values are not included as there are limited observations for L * > 6, particularly during the main phase. During storm time conditions, magnetopause shadowing reduces the number of closed drift paths (e.g., Staples et al., 2020) and the last closed drift shell is often within L * = 7 (Olifer, et al., 2018). Consequently, there are often no particles with closed drift paths in 6 ≤ L *<7 during geomagnetic storms.…”

Occurrence of EMIC Waves in the Magnetosphere According to Their Distance to the Magnetopause

“…(1998) model has a precision of about 1 R E . This precision can be worse during strong or sudden magnetosphere compression events, the magnetopause being always closer to the Earth than the predicted one (Staples et al., 2020). During such events the distance to the magnetopause is overestimated by the model: EMIC might be even closer to the magnetopause than reported in previous sections.…”

Global Magnetohydrodynamic Simulations: Performance Quantification of Magnetopause Distances and Convection Potential Predictions

“…This is in agreement with the study by Samsonov et al (2016) which found that accounting for a realistic ring current in global MHD brings values closer to the empirical MP models. However, as shown in Staples et al (2020), the validity of MP standoff distances as estimated by the empirical models during extreme events is questionable. Since the study does not employ direct comparisons with satellite crossings, a future extension of this work would compare modeled results directly against in-situ measurements from satellites like Cluster, THEMIS, MMS, or Geotail (e.g., Angelopoulos et al, 2009;Lin et al, 2010;Burch and Phan, 2016;Collado-Vega et al, 2019).…”

“…A performance analysis of many such models was presented by Lin et al (2010) to compare their model against a range of empirical models dating back to 1993. More recently, Staples et al (2020) conducted a thorough analysis of MPSD model performance, especially during extreme driving.…”