Fast solar wind after the rapid acceleration

Abstract

[1] We have studied the radial dependence of the velocity of high-latitude fast solar wind in the heliocentric distance range of 0.13-0.9 AU. For this study a new tomographic analysis method which can evaluate uncertainties was developed to obtain velocity distribution maps on two reference spheres at 0.13 and 0.3 AU using interplanetary scintillation (IPS) observations. First of all, it is tested that this tomographic method has enough sensitivity and reliability to investigate the radial dependence of the wind velocity. The analysis was made for the IPS observations during 3 years, from 1995 to 1997, when solar activity was minimum. From this analysis, average velocities of 770-780 km s À1 were obtained at distances of 0.13-0.3 AU, which were 19 ± 17 km s À1 lower than those at 0.3-0.9 AU. The results from this work, taken together with measurements of SOHO/ LASCO, EISCAT and MERLIN [Breen et al., 2002], Helios [Schwenn et al., 1978], and Ulysses [McComas et al., 2000], indicate that the fast wind is accelerated almost to its final flow velocity within 20 R s and a small but not negligible acceleration exists beyond 30 R s which tends to become smaller at farther heliocentric distances.

Three-dimensional exploration of the solar wind using observations of interplanetary scintillation

“…We have investigated the radial gradient of the speed of high-latitude fast solar wind in the distance range of 0.13–0.9 AU using the two-reference sphere CAT analysis of STEL IPS observations. 24) As a result, a small but measurable increase in the solar wind speed, 19 ± 17 km/s, is detected between 0.13–0.3 AU and 0.3–0.9 AU. This result suggests that the fast wind is accelerated almost to its terminal speed within 20 Rs, but that the acceleration is not fully complete at this solar distance, and continues beyond 30 Rs.…”

“…We have developed the computer-assisted tomography (CAT) method to deconvolve LOS integration of IPS data and to retrieve the intrinsic solar wind distribution. 19–22) At present, various versions of the IPS CAT method are available, including the multi-step CAT, 23) two-reference-sphere CAT, 24) time-sequence CAT, 25) MHD-IPS tomography, 26) and time-dependent tomography. 27) …”

Coronal heating and wind acceleration by nonlinear Alfvén waves – global simulations with gravity, radiation, and conduction

“…A dark blue open square with errors is velocity by IPS measurements averaged in 0.13-0.3 AU of high-latitude regions (Kojima et al, 2004). Light blue data are taken from Grall et al (1996); crossed bars are IPS measurements by EISCAT, crossed bars with open circles are by VLBA measurements, and vertical error bars with open circles are data based on observation by SPARTAN 201-01 (Habbal et al, 1994).…”

Astrophysics in 2004

“…Supporting data of the proton temperature anisotropy are modeled from Helios (Marsch et al 2004;Tu et al 2004). The fast solar wind seems to be accelerated almost to its final flow velocity within 20 solar radii (Kojima et al 2004). A simple robust scaling law explains the anticorrelation between the final solar wind speed and freezing-in temperature results (Schwadron & McComas 2003).…”