Title: Quantifying the Effect of Magnetic Field Line Curvature Scattering on the Loss of Ring Current Ions

Abstract

During geomagnetic storms, the ring current ions sometimes exhibit rapid loss as suggested by the fast recovery of the Dst index on a time scale of a few hours. Here, the effects of magnetic field line curvature (FLC) scattering on the loss of ring current ions, which have not been well quantified, are studied here by test particle simulations under the T89c magnetic field model. Our simulation results show that the prediction of ion loss based on a single–value cutoff of the κ parameter or maximum of δμ/μ of a single FLC scattering is not accurate. Instead, the e–folding lifetime (τ) for the loss of ring current ions due to cumulative FLC scattering has been calculated for different initial ion energies, equatorial pitch angles, and L shells under different geomagnetic conditions. The results show that in general the FLC scattering loss is faster for ions of higher energy, higher mass, smaller pitch angle, higher L, and at high Kp level. Specifically, we find that at Kp = 6 the lifetime can be <10 h at L > 5 for 100 s keV protons and at L > 4 for 100 s keV O⁺, which demonstrates that FLC scattering can bemore » an important mechanism for the observed fast loss (τ < 10 h) of ring current ions during geomagnetic storms. Furthermore, we formulate an empirical formula for τ as a function of ion energy, pitch angle, position, species, and Kp. The empirical formula can be directly included in ring current models to account for the FLC scattering effects.« less

Authors:

Eshetu, Wondwossen W.  ^[1];

• Search DOE PAGES for author "Eshetu, Wondwossen W."
• Search DOE PAGES for ORCID "0000-0002-4075-059X"

Tu, Weichao  ^[1];

• Search DOE PAGES for author "Tu, Weichao"
• Search DOE PAGES for ORCID "0000-0003-4547-3269"

Jordanova, Vania Koleva  ^[2];

• Search DOE PAGES for author "Jordanova, Vania Koleva"
• Search DOE PAGES for ORCID "0000-0003-0475-8743"

Cowee, Misa  ^[2]

• Search DOE PAGES for author "Cowee, Misa"
• Search DOE PAGES for ORCID "0000-0003-3117-4030"

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+ Show Author Affiliations

1. West Virginia Univ., Morgantown, WV (United States)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Publication Date:

Thu Dec 10 00:00:00 EST 2020

Research Org.:

Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Sponsoring Org.:

National Aeronautics and Space Administration (NASA); National Science Foundation (NSF)

OSTI Identifier:

1760608

Report Number(s):

LA-UR-20-25795
Journal ID: ISSN 2169-9380; TRN: US2205762

Grant/Contract Number:  

89233218CNA000001; AGS 1752736; 80NSSC18K1284; 80NSSC19K0908; NNH16AC501

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Space Physics

Additional Journal Information:

Journal Volume: 126; Journal Issue: 1; Journal ID: ISSN 2169-9380

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

79 ASTRONOMY AND ASTROPHYSICS; Heliospheric and Magnetospheric Physics