The very slow solar wind: Properties, origin and variability

Solar wind slower than 300 km/s, hereafter termed very slow solar wind (VSSW), is seldom observed at 1 AU. It was, however, commonly measured inside 0.7 AU by the two Helios spacecraft, particularly during solar maximum. Magnetohydrodynamic (MHD) modeling reveals that the disappearance of VSSW at 1 AU is the result of its interaction with faster solar wind. The acceleration and compression of the VSSW contributes to the observed highly variable structure of the slow solar wind at 1 AU. The VSSW usually contains the heliospheric plasma sheet and current sheet. It has higher density and lower temperature than the regular slow solar wind, extending the known scaling laws below 300 km/s. Its helium abundance increases with solar activity even more significantly than the slow solar wind. Contrary to faster solar winds, the helium ions in the VSSW are slower than the dominant protons. Combining a Potential Field Source Surface (PFSS) model with ballistic back tracing, we study the source region of the VSSW. We show that the proton density flux for the VSSW is much higher than for the faster winds, particularly at solar maximum.

[1]  L. Ofman,et al.  Relative drifts and temperature anisotropies of protons and α particles in the expanding solar wind: 2.5D hybrid simulations , 2014, 1410.3358.

[2]  J. Sauvaud,et al.  The Heliospheric Plasma Sheet Observed in situ by Three Spacecraft over Four Solar Rotations , 2012 .

[3]  N. Schwadron,et al.  EVOLUTION OF THE RELATIONSHIPS BETWEEN HELIUM ABUNDANCE, MINOR ION CHARGE STATE, AND SOLAR WIND SPEED OVER THE SOLAR CYCLE , 2012 .

[4]  G. Toma.  Evolution of Coronal Holes and Implications for High-Speed Solar Wind During the Minimum Between Cycles 23 and 24 , 2011 .

[5]  J. Sauvaud,et al.  THE SOLAR ORIGIN OF SMALL INTERPLANETARY TRANSIENTS , 2011 .

[6]  Y.-M. Wang.  ON THE RELATIVE CONSTANCY OF THE SOLAR WIND MASS FLUX AT 1 AU , 2010 .

[7]  M. Lockwood,et al.  Intermittent release of transients in the slow solar wind: 2. In situ evidence , 2010 .

[8]  M. Tokumaru,et al.  Solar cycle evolution of the solar wind speed distribution from 1985 to 2008 , 2010 .

[9]  M. Lockwood,et al.  Intermittent release of transients in the slow solar wind: 1. Remote sensing observations , 2010 .

[10]  N. Sheeley,et al.  ON THE WEAKENING OF THE POLAR MAGNETIC FIELDS DURING SOLAR CYCLE 23 , 2009 .

[11]  R. Pinto,et al.  Time-dependent hydrodynamical simulations of slow solar wind, coronal inflows, and polar plumes , 2009 .

[12]  A. Lazarus,et al.  Hot solar-wind helium: direct evidence for local heating by Alfvén-cyclotron dissipation. , 2008, Physical review letters.

[13]  R. Skoug,et al.  Weaker solar wind from the polar coronal holes and the whole Sun , 2008 .

[14]  J. Steinberg,et al.  Solar Wind Helium Abundance as a Function of Speed and Heliographic Latitude: Variation through a Solar Cycle , 2007 .

[15]  Yukihiro Takahashi,et al.  Magnetic field variations in the Jovian magnetotail induced by solar wind dynamic pressure enhancements , 2005 .

[16]  Nathan A. Schwadron,et al.  On the sources of fast and slow solar wind , 2005 .

[17]  H. Spence,et al.  Heliospheric plasma sheets , 2004 .

[18]  V. Hansteen,et al.  Helium Abundance in the Corona and Solar Wind: Gyrotropic Modeling from the Chromosphere to 1 AU , 2003 .

[19]  J. Sapp.  The Evolution of Relationships , 2003 .

[20]  P. Isenberg,et al.  Generation of the fast solar wind: A review with emphasis on the resonant cyclotron interaction , 2002 .

[21]  Alan J. Lazarus,et al.  The solar wind helium abundance: Variation with wind speed and the solar cycle , 2001 .

[22]  U. Feldman,et al.  On the Rate of Abundance Modifications versus Time in Active Region Plasmas , 2001 .

[23]  J. Geiss,et al.  Composition of quasi‐stationary solar wind flows from Ulysses/Solar Wind Ion Composition Spectrometer , 2000 .

[24]  B. Barraclough,et al.  Solar wind observations over Ulysses' first full polar orbit , 2000 .

[25]  J. Gosling,et al.  Formation and Evolution of Corotating Interaction Regions and their Three Dimensional Structure , 1999 .

[26]  Scott H. Hawley,et al.  Measurements of Flow Speeds in the Corona Between 2 and 30 R☉ , 1997 .

[27]  R. Woo,et al.  Heliospheric plasma sheet and coronal streamers , 1997 .

[28]  Y.-M. Wang,et al.  Empirical Relationship between the Magnetic Field and the Mass and Energy Flux in the Source Regions of the Solar Wind , 1995 .

[29]  J. Geiss,et al.  Origin of the solar wind from composition data , 1995 .

[30]  H. Rosenbauer,et al.  Estimates of alpha particle heating in the solar wind inside 0.3 AU , 1989 .

[31]  J. Freeman,et al.  Solar wind proton temperature‐velocity relationship , 1986 .

[32]  J. Mihalov,et al.  Radial variation of the solar wind speed between 1 and 15 AU , 1982 .

[33]  W. Feldman,et al.  Solar wind helium and hydrogen structure near the heliospheric current sheet: A signal of coronal streamers at 1 AU , 1981 .

[34]  V. Pizzo.  A three-dimensional model of co-rotating streams in the solar wind. 2: Hydrodynamic streams , 1979 .

[35]  V. Pizzo.  A three-dimensional model of corotating streams in the solar wind. 1: Theoretical foundations , 1978 .

[36]  G. Ousley,et al.  The Helios program and the sun , 1976 .

[37]  S. Sydoriak,et al.  SOLAR-WIND PROTON PROPERTIES: VELA 3 OBSERVATIONS FROM JULY 1965 TO JUNE 1967. , 1970 .

[38]  J. Wilcox,et al.  A model of interplanetary and coronal magnetic fields , 1969 .

[39]  J. Wilcox,et al.  Solar source of the interplanetary sector structure , 1967 .

[40]  V. Pizzo.  A Three-Dimensional Model of Corotating Streams in the Solar Wind II . Hydrodynamic Streams ( NASA-TM-80276 ) A THREE-DIMENSIONAL MODEL N 79-28 110 OF CO-ROTATING STREAMS ° IN THE SOLAR WIND , 2010 .

[41]  Robert W. Ebert,et al.  Bulk properties of the slow and fast solar wind and interplanetary coronal mass ejections measured by Ulysses: Three polar orbits of observations , 2009 .

[42]  John W. Belcher,et al.  A statistical study of the properties of interplanetary coronal mass ejections from 0.3 to 5.4 AU , 2005 .

[43]  T. Zurbuchen,et al.  The Transition Between Fast and Slow Solar Wind from Composition Data , 1999 .

[44]  H. Rosenbauer,et al.  Solar wind protons: Three-dimensional velocity distributions and derived plasma parameters measured between 0.3 and 1 AU , 1982 .

[45]  A. Geranios.  Long-period observations of the solar wind plasma between 0.3 and 1.0 AU — Solar activity , 1982 .

[46]  H. Rosenbauer,et al.  Solar Wind Helium Ions: Observations of the Helios Solar Probes Between 0.3 and 1 AU E. MARSCH, 1 K.-H. MOHLHXUSER, 2 H. ROSENBAUER, 1 , 1982 .

[47]  J. Hollweg,et al.  Ion-cyclotron heating and acceleration of solar wind minor ions , 1981 .

[48]  A. Barnes.  COLLISIONLESS HEATING OF THE SOLAR-WIND PLASMA. I. THEORY OF THE HEATING OF COLLISIONLESS PLASMA BY HYDROMAGNETIC WAVES. , 1968 .