J/A+A/679/A64 Heliospheric density and magnetic field model (Mann+, 2023)
A heliospheric density and magnetic field model.
Mann G., Warmuth A., Vocks C., Rouillard A.P.
<Astron. Astrophys. 679, A64 (2023)>
=2023A&A...679A..64M 2023A&A...679A..64M (SIMBAD/NED BibCode)
ADC_Keywords: Sun ; Models
Keywords: Sun: corona - Sun: heliosphere - Sun: magnetic fields -
solar-terrestrial relations - solar wind
Abstract:
The radial evolution of the density of the plasma and the magnetic
field in the heliosphere, especially in the region between the solar
corona and the Earth's orbit, has been a topic of active research
for several decades. Both remote-sensing observations and in situ
measurements by spacecraft such as HELIOS, Ulysses, and WIND have
provided critical data on this subject. The NASA space mission Parker
Solar Probe (PSP), which will approach the Sun down to a distance of
9.9 solar radii on December 24, 2024, gives new insights into the
structure of the plasma density and magnetic field in the heliosphere,
especially in the near-Sun interplanetary space. This region is of
particular interest because the launch and evolution of coronal mass
ejections (CMEs), which can influence the environment of our Earth
(usually called space weather), takes place there.
Because of the new data from PSP, it is time to revisit the subject of
the radial evolution of the plasma density and magnetic field in the
heliosphere. To do this, we derive a radial heliospheric density and
magnetic field model in the vicinity of the ecliptic plane above quiet
equatorial regions. The model agrees well with the measurements in the
sense of a global long-term average.
The radial evolution of the density and solar wind velocity is
described in terms of Parker's wind equation. A special solution of
this equation includes two integration constants that are fitted by
the measurements. For the magnetic field, we employed a previous model
in which the magnetic field is described by 0a superposition of the
magnetic fields of a dipole and a quadrupole of the quiet Sun and a
current sheet in the heliosphere.
We find the radial evolution of the electron and proton number density
as well as the radial component of the magnetic field and the total
field strength in the heliosphere from the bottom of the corona up to
a heliocentric distance of 250 solar radii. The modelled values are
consistent with coronal observations, measurements at 1AU, and with
the recent data from the inner heliosphere provided by PSP.
With the knowledge of the radial evolution of the plasma density and
the magnetic field in the heliosphere the radial behaviour of the
local Alfven speed can be calculated. It can can reach a local maximum
of 392km/s at a distance of approximately 4 solar radii, and it
exceeds the local solar wind speed at distances in the range of
3.6-13.7 solar radii from the centre of the Sun.
Description:
Radial behaviour of the electron number density, solar wind (i.e,
proton) velocity, the radial component of the magnetic field, the
total magnetic field strength, and the Alfven speed as given by the
model of the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table8.dat 57 2491 Model results
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Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 5 F5.1 Rsun R Distance from Sun normalized by solar radius
7- 18 A12 cm-3 Ne Electron density
20- 26 F7.3 km/s Vsw Solar wind speed
28- 37 F10.5 nT Brad ? Radial magnetic field strength
39- 48 F10.5 nT Btot ? Total magnetic field strength
50- 57 F8.4 km/s VA ? Alfven speed
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Acknowledgements:
Alexander Warmuth, awarmuth(at)aip.de
(End) Patricia Vannier [CDS] 02-Nov-2023