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Title: Magnetic flux density in the heliosphere through several solar cycles

Abstract

We studied the magnetic flux density carried by solar wind to various locations in the heliosphere, covering a heliospheric distance range of 0.3-5.4 AU and a heliolatitudinal range from 80° south to 80° north. Distributions of the radial component of the magnetic field, B{sub R} , were determined over long intervals from the Helios, ACE, STEREO, and Ulysses missions, as well as from using the 1 AU OMNI data set. We show that at larger distances from the Sun, the fluctuations of the magnetic field around the average Parker field line distort the distribution of B{sub R} to such an extent that the determination of the unsigned, open solar magnetic flux density from the average (|B{sub R} |) is no longer justified. We analyze in detail two methods for reducing the effect of fluctuations. The two methods are tested using magnetic field and plasma velocity measurements in the OMNI database and in the Ulysses observations, normalized to 1 AU. It is shown that without such corrections for the fluctuations, the magnetic flux density measured by Ulysses around the aphelion phase of the orbit is significantly overestimated. However, the matching between the in-ecliptic magnetic flux density at 1 AU (OMNI data)more » and the off-ecliptic, more distant, normalized flux density by Ulysses is remarkably good if corrections are made for the fluctuations using either method. The main finding of the analysis is that the magnetic flux density in the heliosphere is fairly uniform, with no significant variations having been observed either in heliocentric distance or heliographic latitude.« less

Authors:
 [1];  [2]
  1. Wigner Research Centre for Physics, Hungarian Academy of Sciences, P.O. Box 49, H-1525 Budapest (Hungary)
  2. The Blackett Laboratory, Imperial College London, London SW7 2BZ (United Kingdom)
Publication Date:
OSTI Identifier:
22348151
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 781; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CORRECTIONS; DISTRIBUTION; FLUCTUATIONS; FLUX DENSITY; HELIOSPHERE; MAGNETIC FIELDS; MAGNETIC FLUX; ORBITS; PLASMA; RECREATIONAL AREAS; SOLAR CYCLE; SOLAR WIND; SUN; VELOCITY

Citation Formats

Erdős, G., and Balogh, A., E-mail: erdos.geza@wigner.mta.hu. Magnetic flux density in the heliosphere through several solar cycles. United States: N. p., 2014. Web. doi:10.1088/0004-637X/781/1/50.
Erdős, G., & Balogh, A., E-mail: erdos.geza@wigner.mta.hu. Magnetic flux density in the heliosphere through several solar cycles. United States. doi:10.1088/0004-637X/781/1/50.
Erdős, G., and Balogh, A., E-mail: erdos.geza@wigner.mta.hu. Mon . "Magnetic flux density in the heliosphere through several solar cycles". United States. doi:10.1088/0004-637X/781/1/50.
@article{osti_22348151,
title = {Magnetic flux density in the heliosphere through several solar cycles},
author = {Erdős, G. and Balogh, A., E-mail: erdos.geza@wigner.mta.hu},
abstractNote = {We studied the magnetic flux density carried by solar wind to various locations in the heliosphere, covering a heliospheric distance range of 0.3-5.4 AU and a heliolatitudinal range from 80° south to 80° north. Distributions of the radial component of the magnetic field, B{sub R} , were determined over long intervals from the Helios, ACE, STEREO, and Ulysses missions, as well as from using the 1 AU OMNI data set. We show that at larger distances from the Sun, the fluctuations of the magnetic field around the average Parker field line distort the distribution of B{sub R} to such an extent that the determination of the unsigned, open solar magnetic flux density from the average (|B{sub R} |) is no longer justified. We analyze in detail two methods for reducing the effect of fluctuations. The two methods are tested using magnetic field and plasma velocity measurements in the OMNI database and in the Ulysses observations, normalized to 1 AU. It is shown that without such corrections for the fluctuations, the magnetic flux density measured by Ulysses around the aphelion phase of the orbit is significantly overestimated. However, the matching between the in-ecliptic magnetic flux density at 1 AU (OMNI data) and the off-ecliptic, more distant, normalized flux density by Ulysses is remarkably good if corrections are made for the fluctuations using either method. The main finding of the analysis is that the magnetic flux density in the heliosphere is fairly uniform, with no significant variations having been observed either in heliocentric distance or heliographic latitude.},
doi = {10.1088/0004-637X/781/1/50},
journal = {Astrophysical Journal},
number = 1,
volume = 781,
place = {United States},
year = {Mon Jan 20 00:00:00 EST 2014},
month = {Mon Jan 20 00:00:00 EST 2014}
}
  • Open magnetic flux in the heliosphere is determined from the radial component of the magnetic field vector measured onboard interplanetary space probes. Previous Ulysses research has shown remarkable independence of the flux density from heliographic latitude, explained by super-radial expansion of plasma. Here we are investigating whether any longitudinal variation exists in the 50 year long OMNI magnetic data set. The heliographic longitude of origin of the plasma package was determined by applying a correction according to the solar wind travel time. Significant recurrent enhancements of the magnetic flux density were observed throughout solar cycle 23, lasting for several years.more » Similar, long-lasting recurring features were observed in the solar wind velocity, temperature and the deviation angle of the solar wind velocity vector from the radial direction. Each of the recurrent features has a recurrence period slightly differing from the Carrington rotation rate, although they show a common trend in time. Examining the coronal temperature data of ACE leads to the possible explanation that these long-term structures are caused by slow–fast solar wind interaction regions. A comparison with MESSENGER data measured at 0.5 au shows that these longitudinal magnetic modulations do not exist closer to the Sun, but are the result of propagation.« less
  • Here we use the PFSS model and photospheric data from Wilcox Solar Observatory, SOHO /MDI, SDO/HMI, and SOLIS to compare the coronal field with heliospheric magnetic field measured at 1 au, compiled in the NASA/NSSDC OMNI 2 data set. We calculate their mutual polarity match and the power of the radial decay, p , of the radial field using different source surface distances and different number of harmonic multipoles. We find the average polarity match of 82% for the declining phase, 78%–79% for maxima, 76%–78% for the ascending phase, and 74%–76% for minima. On an average, the source surface ofmore » 3.25 R{sub S} gives the best polarity match. We also find strong evidence for solar cycle variation of the optimal source surface distance, with highest values (3.3 R{sub S}) during solar minima and lowest values (2.6 R{sub S}–2.7 R{sub S}) during the other three solar cycle phases. Raising the number of harmonic terms beyond 2 rarely improves the polarity match, showing that the structure of the HMF at 1 au is most of the time rather simple. All four data sets yield fairly similar polarity matches. Thus, polarity comparison is not affected by photospheric field scaling, unlike comparisons of the field intensity.« less
  • The variability of hourly values of solar wind number density, number density variation, speed, speed variation and dynamic pressure with IMF B{sub z} and magnitude {vert bar}B{vert bar} has been examined for the period 1965-1986. The authors wish to draw attention to a strong correlation in number density and number density fluctuation with IMF B{sub z} characterized by a symmetric increasing trend in these quantities away from B{sub z} = O nT. The fluctuation level in solar wind speed is found to be relatively independent of B{sub z}. They infer that number density and number density variability dominate in controllingmore » solar wind dynamic pressure and dynamic pressure variability. It is also found that dynamic pressure is correlated with each component of IMF and that there is evidence of morphological differences between the variation with each component. Finally, they examine the variation of number density, speed, dynamic pressure and fluctuation level in number density and speed with IMF magnitude {vert bar}B{vert bar}. Again they find that number density variation dominates over solar wind speed in controlling dynamic pressure.« less
  • It is normally believed that a magnetic field transfers helicity from the solar subatmosphere into interplanetary space. This is based on the calculation of the injected magnetic helicity near the center of the solar disk between latitude {+-}30 Degree-Sign of both solar hemispheres in the period 1996-2009. As one follows the long-term injection of magnetic helicity, one finds that the transfer of magnetic helicity does not have a monotonic sign in the northern and southern hemispheres, and that the bulk of the helicity contributed goes to the active region, while the contribution to the quiet Sun is insignificant. The consistencymore » between the total injected magnetic helicity and the sunspot numbers has also been found statistically in the solar cycle. The estimated total injected magnetic helicity flux in our calculation is of the order of or larger than 5.0 Multiplication-Sign 10{sup 46} Mx{sup 2} in the 23rd solar cycle.« less
  • Observed meridional plasma flow and its connection with other plasma parameters in the outer heliosphere are discussed. The dynamics of the flow are examined locally and compared with observed plasma parameters and a global flow model which predicts such flows in a steady solar wind. The observational evidence supports stream dynamics and associated pressure gradients as responsible for driving the flow. Such a meridional flow may result in a net transport of magnetic flux from regions near the heliographic equator. The amplitude of the observed meridional component of solar wind flow is consistent with observed magnetic flux deficits in themore » outer heliosphere. The limited coverage of heliographic latitude by Voyager 2 precludes a direct measurement of the full flow pattern; however, the magnitude of reported magnetic flux deficits and the unambiguous, regular variations in the meridional flow suggest that the stream interactions do produce a net movement of magnetic flux away from the heliographic equator. copyright American Geophysical Union 1988« less