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Title: COMPARING CORONAL AND HELIOSPHERIC MAGNETIC FIELDS OVER SEVERAL SOLAR CYCLES

Abstract

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 of 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 themore » field intensity.« less

Authors:
; ;  [1]
  1. University of Oulu, P.O. Box 3000, FI-90014 Oulu (Finland)
Publication Date:
OSTI Identifier:
22664033
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; 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; COMPARATIVE EVALUATIONS; DECAY; DISTANCE; HARMONICS; HELIOSPHERE; MAGNETIC FIELDS; MULTIPOLES; NASA; PHOTOSPHERE; SOLAR CORONA; SOLAR CYCLE; SUN; SURFACES

Citation Formats

Koskela, J. S., Virtanen, I. I., and Mursula, K., E-mail: jennimari.koskela@oulu.fi. COMPARING CORONAL AND HELIOSPHERIC MAGNETIC FIELDS OVER SEVERAL SOLAR CYCLES. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/1/63.
Koskela, J. S., Virtanen, I. I., & Mursula, K., E-mail: jennimari.koskela@oulu.fi. COMPARING CORONAL AND HELIOSPHERIC MAGNETIC FIELDS OVER SEVERAL SOLAR CYCLES. United States. doi:10.3847/1538-4357/835/1/63.
Koskela, J. S., Virtanen, I. I., and Mursula, K., E-mail: jennimari.koskela@oulu.fi. Fri . "COMPARING CORONAL AND HELIOSPHERIC MAGNETIC FIELDS OVER SEVERAL SOLAR CYCLES". United States. doi:10.3847/1538-4357/835/1/63.
@article{osti_22664033,
title = {COMPARING CORONAL AND HELIOSPHERIC MAGNETIC FIELDS OVER SEVERAL SOLAR CYCLES},
author = {Koskela, J. S. and Virtanen, I. I. and Mursula, K., E-mail: jennimari.koskela@oulu.fi},
abstractNote = {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 of 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.},
doi = {10.3847/1538-4357/835/1/63},
journal = {Astrophysical Journal},
number = 1,
volume = 835,
place = {United States},
year = {Fri Jan 20 00:00:00 EST 2017},
month = {Fri Jan 20 00:00:00 EST 2017}
}