Magnetic field configurations associated with fast solar wind

Abstract

In this paper, we consider the implications of the observed inverse correlation between solar wind speed at Earth and the expansion rate of the Sun-Earth flux tube as it passes through the corona. We find that the coronal expansion rate depends critically on the large-scale photospheric field distribution around the footpoint of the flux tube, with the smallest expansions occurring in tubes that are rooted near a local minimum in the field. This suggests that the fastest wind streams originate from regions where large coronal holes are about to break apart and from the facing edges of adjacent like-polarity holes, whose field lines converge as they transit the corona. These ideas lead to the following predictions:(1) Weak holes and fragmentary holes can be sources of very fast wind.(2) Fast wind with steep latitudinal gradients may be generated where the field lines from the polar hole and a lower-latitude hole of like polarity converge to form a mid-latitude 'apex'.(3) The fastest polar wind should occur shortly after sunspot maximum, when trailing-polarity flux converges onto the poles and begins to establish the new polar fields.

The evolution of the interplanetary sector structure in 1992

“…It is known (Hoeksema, 1986) must clearly be affected by it. This same transition is likely to be related to the development of the polar coronal field structure and the associated development and equatorward expansion of the polar coronal hole with its characteristically high solar wind velocities as predicted by Sheeley and Wang (1991) and observed by Bame et al, (1993). While the long-term evolution of the sector structure as observed by Ulysses in 1992 can be seen in terms of the gradual evolution of the main te•xns in the solar magnetic field, the suddenness of the change reflects a more abrupt reorganisation of the large scale coronal fields.…”

The Solar Wind and Its Magnetic Sources at Sunspot Maximum

“…The low-f exp flux tubes at solar maximum are generally rooted around weak-field regions located within or between small coronal holes of a given polarity; instead of diverging steadily with height like the flux tubes inside the polar holes, they initially fan out rapidly but subsequently '' collide '' with each other and are deflected upward again, so that their net expansion remains small (see Fig. 2 in Sheeley & Wang 1991). We speculate that this combination of rapid initial expansion and subsequent reconvergence lowers the height of the temperature maximum compared to that inside the polar holes, causing the fast wind at ACE to have composition properties intermediate between those of the polar wind near sunspot minimum and the slow wind at sunspot maximum.…”

STEREO IMPACT Investigation Goals, Measurements, and Data Products Overview

“…A version of such a model developed by Arge and Pizzo (2000), based on Sheeley and Wang's (1991) empirical relationship between coronal open field divergence and solar wind speed, is currently used to predict solar wind sources, solar wind velocities, and interplanetary field polarity at L1 at the NOAA SEC Rapid Prototyping Center (http://solar.sec.noaa.gov/ws/). Figure 22 shows sample products from this model, which is based on synoptic maps of the photospheric field available from a number of ground based observatories.…”