TY - GEN
T1 - Angular momentum transport and proton-alpha differential streaming in the low-latitude fast solar wind
AU - Li, Bo
AU - Li, Xing
N1 - Copyright:
Copyright 2008 Elsevier B.V., All rights reserved.
PY - 2006/7
Y1 - 2006/7
N2 - The Weber & Davis analysis on the angular momentum loss of the Sun is reconsidered for a steady-state solar wind that incorporates alpha particles and flows out of the equatorial plane. Closely following McKenzie et al. (1979), we exploit the fact that ion gyro-frequencies are many orders of magnitude larger than other frequencies in the ion momentum equations. This requires the ion velocity difference to be aligned with the magnetic field. The governing equations are derived from standard transport equations in virtue of this alignment condition. A general analysis, independent from specific energy equations, yields that the magnetic field helps the coronal plasma to achieve an effective corotation out to the Alfvénic radius, where the poloidal Alfvén Mach number MT equals one. MT however has to be defined as a composite one by Eq. (11). In a fast solar wind solution along the flux tube which lies at a colatitude of 70° at 1 AU, it is found that the angular momentum loss from the Sun is almost entirely due to magnetic stresses. The proton contribution, which can be as important as the magnetic one in interplanetary space, is canceled by the alpha particles that develop an azimuthal speed in the direction of counter-rotation with the Sun. The Poynting flux associated with the azimuthal components is negligible. Nevertheless, the solar rotation has an appreciable effect in limiting the proton-alpha differential streaming in the fast streams at low latitudes in interplanetary space. However this mechanism alone can not solely account for the Helios observations.
AB - The Weber & Davis analysis on the angular momentum loss of the Sun is reconsidered for a steady-state solar wind that incorporates alpha particles and flows out of the equatorial plane. Closely following McKenzie et al. (1979), we exploit the fact that ion gyro-frequencies are many orders of magnitude larger than other frequencies in the ion momentum equations. This requires the ion velocity difference to be aligned with the magnetic field. The governing equations are derived from standard transport equations in virtue of this alignment condition. A general analysis, independent from specific energy equations, yields that the magnetic field helps the coronal plasma to achieve an effective corotation out to the Alfvénic radius, where the poloidal Alfvén Mach number MT equals one. MT however has to be defined as a composite one by Eq. (11). In a fast solar wind solution along the flux tube which lies at a colatitude of 70° at 1 AU, it is found that the angular momentum loss from the Sun is almost entirely due to magnetic stresses. The proton contribution, which can be as important as the magnetic one in interplanetary space, is canceled by the alpha particles that develop an azimuthal speed in the direction of counter-rotation with the Sun. The Poynting flux associated with the azimuthal components is negligible. Nevertheless, the solar rotation has an appreciable effect in limiting the proton-alpha differential streaming in the fast streams at low latitudes in interplanetary space. However this mechanism alone can not solely account for the Helios observations.
KW - Alpha particles
KW - Angular momentum loss
KW - Differential streaming
KW - Solar wind
UR - http://www.scopus.com/inward/record.url?scp=33749184200&partnerID=8YFLogxK
M3 - Conference Proceeding (Non-Journal item)
AN - SCOPUS:33749184200
SN - 9290929286
SN - 9789290929284
T3 - European Space Agency, (Special Publication) ESA SP
BT - Proceedings of SOHO-17
T2 - SOHO-17: 10 Years of SOHO and Beyond
Y2 - 7 May 2006 through 12 May 2006
ER -