PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
ON A CLOSE RELATION BETWEEN THE STATIONARY SOLAR WIND
VELOCITIES AND THE SOLAR MAGNETIC FIELDS
K. I. Nikolskaya
Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Russian
Academy of Sci., Russia, 142190, Troitsk of Moscow region, IZMIRAN;
e-mail: knikol@izmiran.troitsk.ru
Abstract. The purpose of this paper is to elucidate a possible role of the solar magnetic field in
the formation of the stationary solar wind (SW). An analysis of the SW proton velocities
measured by Ulysses for the period of ~1.5 activity cycle in combination with SW speed IPSobservations
as well as the XUV corona images and solar magnetic field data has been
performed. The main result of this study is the finding of inverse relation between the SW speeds
and solar magnetic field strengths: the stronger the closed magnetic fields the slower the solar
wind and vice versa, that points to direct interactions of the solar wind plasma flows with solar
magnetic fields. Thus, solar magnetic fields are responsible not only for the solar corona
formation via plasma trapping and heating but also for the SW velocity ranging. A few examples
of SW velocity – solar magnetic field connection are presented.
Introduction
A goal of this paper is to present results of a study of the relationship between the solar wind) velocities in
the inner and outer heliosphere and the magnetic events on the Sun by the way of the analysis of the SW
velocity behavior in different phases of activity cycles. An analysis has been carried out of SW velocity data
for the outer heliosphere taken from Ulysses’ archive and those for inner heliosphere deduced from IPS
observations and taken from literature.
Designated to probe the extra-ecliptic outer heliosphere space-craft Ulysses after passage by Jupiter in
February1992 climbed to high southerly latitudes until it reached -80.2° on September 12, 1994. It then
proceeded to fly northward reaching perihelion near the ecliptic plane in March 12, 1995, and peak northern
latitude at +80.2° on July 31, 1995. Hitherto Ulysses has made nearly 3 rotations over the Sun: the first and
third rotations – around the activity minimum and the second one – within the maximum. SW parameters
including the proton velocities and densities were measured by the device SWOOPS on board Ulysses
(device SWOOPS – Solar Wind Observations Over Poles of the Sun). IPS observations in south and north
high latitude heliosphere were performed with the stations EISCAT (North Finland) and VLBA (USA)
in1994 and 1995 when Ulysses passed from south to North Pole on its first orbit. In addition, XUV solar disk
images by Yohkoh and EIT/SOHO, full disk magnetograms (NSO/Kitt Peak and MDI/SOHO) and coronal
hole (CH) maps (NSO/KP, USA) taken from internet-archive were utilized too.
Solar wind velocities in the activity cycles No. 22-23
Coupling between the stationary SW velocity and solar magnetic fields (MF) is very well seen in the Fig.1
where SW speed latitudinal distribution are represented for low activity phase of 22-th cycle (left panel) and
high activity phase of 23-th cycle, for the first and second Ulysses’ rotations around the Sun. Pictures of the
SW velocity distribution over latitudes on the left and right panels in Fig.1 are completely different. Left
panel that is referred to the quiet Sun epoch reveals stable SW speeds within 700–800 km/s at all
heliographic latitudes beyond streamer belt and mainly slow SW inside it (≤±20° of latitude) with isolated
high speed peaks caused by low latitude coronal holes. Contrary, as right panel shows, the heliosphere of the
active Sun epoch was dominated by the slow solar wind except for the regions over the North Pole where the
coronal hole situated, and irregular high velocity peaks over middle- and low-latitude coronal holes.
The second Ulysses’ flight in the quiet Sun epoch (during declining phase of the 23-th cycle) took place on
the third space-craft orbit with passages over solar South and North Poles in ~ 2007 January and December
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