TY - JOUR
T1 - The Characteristic Pitch Angle Distributions of 1 eV to 600 keV Protons Near the Equator Based On Van Allen Probes Observations
AU - Yue, Chao
AU - Bortnik, Jacob
AU - Thorne, Richard M.
AU - Ma, Qianli
AU - An, Xin
AU - Chappell, C. R.
AU - Gerrard, Andrew
AU - Lanzerotti, Louis J.
AU - Shi, Quanqi
AU - Reeves, Geoffrey D.
AU - Spence, Harlan E.
AU - Mitchell, Donald G.
AU - Gkioulidou, Matina
AU - Kletzing, Craig A.
N1 - Funding Information:
This work was supported by the NASA Living With a Star Jack Eddy Postdoctoral Fellowship Program, administered by the UCAR Visiting Scientist Programs. Jacob Bortnik gratefully acknowledges support from NASA LWS grant NNX13AI61G and NASA NNX16AG21G. We acknowledge use of Van Allen Probes data of the Level 3 HOPE unidimensional particle flux data obtained from the RBSP-ECT website (rbsp-ect.lanl.gov/data_pub/ rbspb/hope/level3/PA/), made publicly available through NASA prime contract NAS5-01072; the Level 3 RBSPICE unidimensional particle flux data obtained from the RBSPICE website (http://rbspicea.ftecs.com/Level_3PAP/); the Level 3 magnetometer data obtained from the RBSP EMFISIS website (emfisis.physics.uiowa.edu/Flight/ RBSP-B/L3). We thank the Space Physics Data Facility at the NASA Goddard Space Flight Center for providing the OMNI data (ftp://spdf.gsfc.nasa.gov/ pub/data/omni/omni_cdaweb/).
Publisher Copyright:
©2017. American Geophysical Union. All Rights Reserved.
PY - 2017/9
Y1 - 2017/9
N2 - Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here we statistically analyze ~1 eV to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L shells except for dawn sector; (2) a bidirectional field-aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly, and isotropic distributions depending on their energy, MLT, and L shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L shell increases, which is primarily caused by adiabatic transport. Furthermore, energetic H+ (>10 keV) PADs become more isotropic following the substorm injections, indicating wave-particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L > 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations.
AB - Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here we statistically analyze ~1 eV to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L shells except for dawn sector; (2) a bidirectional field-aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly, and isotropic distributions depending on their energy, MLT, and L shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L shell increases, which is primarily caused by adiabatic transport. Furthermore, energetic H+ (>10 keV) PADs become more isotropic following the substorm injections, indicating wave-particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L > 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations.
KW - H pitch angle distributions
KW - bidirectional field aligned
KW - plasmaspheric H
KW - radiation belt H
KW - ring current
KW - warm plasma cloak
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U2 - 10.1002/2017JA024421
DO - 10.1002/2017JA024421
M3 - Article
AN - SCOPUS:85030158836
SN - 2169-9380
VL - 122
SP - 9464
EP - 9473
JO - Journal of Geophysical Research: Space Physics
JF - Journal of Geophysical Research: Space Physics
IS - 9
ER -