SOLAR WIND ∼20–200 keV SUPERHALO ELECTRONS AT QUIET TIMES

High-energy superhalo electrons are present in the interplanetary medium (IPM) even in the absence of any significant solar activity, carrying important information on electron acceleration in the solar wind. We present a statistical survey of ∼20–200 keV superhalo electrons measured at 1 AU by the WIND 3D Plasma & Energetic Particle instrument during quiet-time periods from 1995 January through 2013 December. The selected 242 quiet-time samples mostly occur during the rising, maximum and decay phases of solar cycles. The observed omnidirectional differential flux of these quiet-time superhalo electrons generally fits to a power-law spectrum J = A × ( E m e c 2 ) − β ?> , with β ranging from ∼1.6 to ∼3.7 and the integrated density nsup ranging from 10−8 to 10−5 cm−3. In solar cycle 23 (24), the distribution of β has a broad maximum between 2.4 and 2.8 (2.0 and 2.4). Both β and the logarithm of nsup show no obvious correlation with sunspot number, solar flares, solar wind core population, etc. These superhalo electrons may form a quiet-time energetic electron background/reservoir in the IPM. We propose that they may originate from nonthermal processes related to the acceleration of the solar wind such as nanoflares, or could be formed in the IPM due to further acceleration and/or long-distance propagation effects.

[1]  G. Zank,et al.  DIFFUSIVE SHOCK ACCELERATION AND RECONNECTION ACCELERATION PROCESSES , 2015 .

[2]  G. Zank,et al.  Dynamical small-scale magnetic islands as a source of local acceleration of particles in the solar wind , 2015 .

[3]  Jiansen He,et al.  THE ANGULAR DISTRIBUTION OF SOLAR WIND SUPERHALO ELECTRONS AT QUIET TIMES , 2015 .

[4]  G. Zank,et al.  Particle acceleration by combined diffusive shock acceleration and downstream multiple magnetic island acceleration , 2015 .

[5]  G. Zank,et al.  PARTICLE ACCELERATION VIA RECONNECTION PROCESSES IN THE SUPERSONIC SOLAR WIND , 2014 .

[6]  Shaohua Zhang,et al.  Numerical simulation of superhalo electrons generated by magnetic reconnection in the solar wind source region , 2014, 1406.4233.

[7]  D. Müller,et al.  Solar Orbiter , 2012, Solar Physics.

[8]  Glenn M. Mason,et al.  Power Law Distributions of Suprathermal Ions in the Quiet Solar Wind , 2012 .

[9]  S. Krucker,et al.  A STATISTICAL STUDY OF SOLAR ELECTRON EVENTS OVER ONE SOLAR CYCLE , 2012 .

[10]  R. Wimmer–Schweingruber,et al.  Assessment of galactic cosmic ray models , 2012 .

[11]  J. Luhmann,et al.  QUIET-TIME INTERPLANETARY ∼2–20 keV SUPERHALO ELECTRONS AT SOLAR MINIMUM , 2012 .

[12]  R. Lin,et al.  Langmuir Turbulence and Suprathermal Electrons , 2012 .

[13]  C. Russell,et al.  Comparing Solar Minimum 23/24 with Historical Solar Wind Records at 1 AU , 2011 .

[14]  D. Müller,et al.  Solar Orbiter , 2012, Solar Physics.

[15]  N. Schwadron,et al.  ON THEORIES FOR STOCHASTIC ACCELERATION IN THE SOLAR WIND , 2010 .

[16]  Christopher T. Russell,et al.  Properties of Stream Interactions at One AU During 1995 – 2004 , 2006 .

[17]  George Gloeckler,et al.  The Common Spectrum for Accelerated Ions in the Quiet-Time Solar Wind , 2006 .

[18]  R. Lin,et al.  Electron Halo and Strahl Formation in the Solar Wind by Resonant Interaction with Whistler Waves , 2005 .

[19]  T. Horbury,et al.  Measurement of the electric fluctuation spectrum of magnetohydrodynamic turbulence. , 2005, Physical review letters.

[20]  T. Armstrong,et al.  Steady‐state event‐excluded proton spectra at solar minimum at all heliolatitudes , 2003 .

[21]  E. Roelof,et al.  On electron acceleration at CIR related shock waves , 2002 .

[22]  M. Maksimović,et al.  Core, Halo and Strahl Electrons in the Solar Wind , 2001 .

[23]  R. Lin.  WIND Observations of Suprathermal Electrons in the Interplanetary Medium , 1998 .

[24]  R. Lin.  Observations of the 3D distributions of thermal to near-relativistic electrons in the interplanetary medium by the wind spacecraft , 1997 .

[25]  E. Roelof,et al.  IMF connection for energetic protons observed at Ulysses via mid-latitude solar wind rarefaction regions , 1995 .

[26]  J. M. Bosqued,et al.  A three-dimensional plasma and energetic particle investigation for the wind spacecraft , 1995 .

[27]  J. Scudder,et al.  On the causes of temperature change in inhomogeneous low-density astrophysical plasmas , 1992 .

[28]  E. Parker.  Nanoflares and the solar X-ray corona , 1988 .

[29]  H. Rosenbauer,et al.  Characteristics of electron velocity distribution functions in the solar wind derived from the helios plasma experiment , 1987 .

[30]  W. Feldman,et al.  Solar wind electrons , 1975 .

[31]  A. Hundhausen,et al.  SOLAR WIND ELECTRONS: VELA 4 MEASUREMENTS. , 1968 .

[32]  Eugene N. Parker,et al.  THE PASSAGE OF ENERGETIC CHARGED PARTICLES THROUGH INTERPLANETARY SPACE , 1965 .