The interplanetary space

Structures which are found in the interplanetary space are fast solar winds (Figure 4), slow solar winds, interaction regions between fast and slow solar wind, structures (Figure 4) caused by transients such as coronal mass ejections, the heliospheric current sheet (Figure 3) between outward and inward directed solar magnetic fields and Alfvén waves. The solar wind has typically a velocity of 450 km/s, a density of 5 particles/cm3, a temperature of 105K (depending on particle type) and a magnetic field strength of 5 nT. The solar wind consists mainly of protons, electrons and alpha particles (3-4 %, relative to the protons).

Maps of the solar magnetic field at source surface (2.5Rs) can tell us where CMEs and CHs may occur. Earth's orbit projected on the maps tell us when Earth will cross the heliospheric current sheet and interact with the plasma clouds from the CMEs and the plasma streams from the CHs. These maps are therefore very important for forecasting the space weather. Notice in the synoptic charts below, how warped the current sheet is at times of solar maximum 1980 (Figure 2) compared to at times of solar minimum 1976 (Figure 1).


Figure 1 shows the source surface magnetic field, calculated from Wilcox Solar Observatory (WSO) photospheric magnetic field observations. The synoptic chart covers the period May 28 to June 23, 1976, i.e. Carrington Rotation 1642. Dashed lines represent negative magnetic field, solid lines positive field and the thick line the coronal neutral line (heliospheric current sheet).


Figure 2 shows source surface magnetic field, calculated from WSO photospheric magnetic field observations. The synoptic chart covers the period October 23 to November 18, 1980, i.e. Carrington Rotation 1701.


Figure 3 shows a painting, made at Stanford, of the warped heliospheric current sheet.


Figure 4 shows the solar wind variation between September 5 and September 25, 1996. A fast solar wind, caused by a coronal hole, starts on September 19/20. "Courtesy of SOHO CELIAS consortium".


Further Reading:

Tongues, bottles, and disconnected loops: The opening and closing of the interplanetary magnetic field, by D.J. McComas.

Solar wind corotating interaction regions, by J.T. Gosling

Solar wind composition, by K.W. Olgivie and M.A. Coplan.