1. Exploration of Solar Magnetic Fields from Propagating GONG Magnetograms Using the CSSS Model and UCSD Time-Dependent Tomography
H.-S. Yu1, B. V. Jackson1, P. P. Hick1, A. Buffington1,
M. Tokumaru2, N. Nishimura2, N. Nozaki2, K. Fujiki3, K. Hayashi3
1Center for Astrophysics and Space Sciences, UCSD, CA , U.S.A
2Institute for Space-Earth Environmental Research, Nagoya University, Japan
3Chinese Academy of Sciences, China
Abstract
A portion of the interplanetary magnetic field measured in situ near Earth is seen to be coming from a direct mapping of closed fields outward from the low solar corona. In this study, Global Oscillation Network Group (GONG) magnetograms are extrapolated upward from near the solar surface using the Current Sheet Source Surface (CSSS) model (Zhao & Hoeksema, 1995a). These fields are propagated to 1 AU using the University of California, San Diego (UCSD) tomographic modeling technique, and are then compared with fields measured in situ near Earth. We compare all three field components at 1 AU, extrapolated using both the “open-field” and “closed-field” CSSS modeling, with the appropriate ACE in-situ field in Radial Tangential and Normal (RTN) coordinates. The open-field technique gives a generally better result for radial and tangential fields. However, a significant positive correlation exists between these closed field components and those determined by in-situ measurements over the last ten years. Here we discuss the relation between the closed field on the solar surface and the in-situ measurements near Earth. Since the Bn field provides the major portion of the most-sought Geocentric Solar Magnetospheric (GSM) Bz field component, a preliminary determination of Bz is also discussed.
1. Interplanetary Scintillation (IPS)
STELab IPS array systems
500 km
Interplanetary Scintillation (IPS) observations have long been used to remotely-sense small-scale ( km) heliospheric density variations along the line of sight in the solar wind. These density inhomogeneities in the solar wind disturb the signal from point radio sources to produce an intensity variation when projected on the ground, whose pattern travels away from the Sun with the solar wind speed.
Institute for Space-Earth Environmental Research (ISEE) radio array, Japan; the Fuji system is shown. USCD currently maintains a near-real-time website that analyzes and displays IPS data from the STELab. This modeling-analysis capability is also available at the CCMC (Community Coordinated Modeling Center).
This pattern, measured and correlated between different radio sites in Japan allows a determination of the solar wind speed. By cross-correlating the radio signal obtained at different IPS observing sites, we determine the solar wind speed. By measuring the scintillation strength of the IPS source, we can also determine the solar wind density.
USCD:
CCMC:
KSWC:
GMU:
Websites
(Jackson et al., 2010; 2013)
2. Time-dependent Tomography Analysis
Density Ecliptic cut
Tomography v.s. ACE
Velocity Ecliptic cut
Tomography v.s. ACE
3. Analysis – Magnetic Field Extrapolation
The UCSD time-dependent tomography analysis#1 fits a kinematic model to available IPS data to provide a 3D global depiction of the heliosphere. Zeeman splitting provides vertical magnetic fields at the solar surface using the Current Sheet Source Surface (CSSS #2) model to give accurate vertical fields (open field) at a source surface. These fields are extrapolated outward from this surface using the global velocity model derived by the IPS to provide radial and tangential field components (in RTN coordinates) anywhere within the volume. These fields are then mapped to locations where they can be measured by in-situ spacecraft monitors.
Non-vertical “closed” fields also present
(closed-field are mapped to 1 AU)
jet
#1: Jackson et al., 2010; 2013
#2: Zhao and Hoeksema, 1995
#3: Dunn et al., 2005

2. 4. Br and Bt obtained from IPS Tomography + CSSS model
CR /04/26 – 2007/05/26 CR
Br (nT)
Potential Field at 15 Rs using CSSS
One of 60 potential field map at 15 Rs obtained from CSSS model using NSO GONG magnetograms, usually available twice daily throughout this time period. (GONG data set available hourly at ftp://gong2.nso.edu/)
The tomography analysis using IPS data fits provide a precise global density and velocity mapped to in-situ observations. When using the IPS velocity analyses, we can accurately convect solar surface background magnetic fields (upper) outward and thus provide values of the field
(radial and tangential components, right panels) throughout the global volume. The velocity and density in-situ measurements are smoothed using a one-day boxcar average; the magnetic field, is smoothed using a three-day boxcar average.
Bt (nT)
5. Closed-Field components compared with ACE in-situ fields
Br (nT)
Bt (nT)
Bn (nT)
The outward projection of closed fields from below the cusp surface of the CSSS model (see Section 3, closed-field at 1.3 Rs) with an r falloff to 15 Rs. These RTN (Br, Bt, Bn) fields are extrapolated using IPS velocity further upward with 1/50th scaling and respectively radial falloffs of r -2, r -1 and r Although the excursions of the Bn field are not large, they have a significant positive correlation. (Jackson et al., 2016)
99% (108/109)
0.65 for Br
99% (108/109)
0.56 for Bt
95% (103/109)
0.43 for Br
68% (73/109)
0.09 for Bt
Correlation for Open-Field
Correlation for Closed-Field
These plots provide open-field and closed-field correlations for Br and Bt field components from GONG magnetograms compared with ACE for these same methods from years We find these comparisons show significant positive correlations.
6. Open-Fields in GSM Coordinate – Bx, By, Bz
Bx (nT)
By (nT)
Bz (nT)
GSM (Bx, By, Bz) fields converted from RTN (Br, Bt, Bn) field obtained from IPS tomography and CSSS open-field model. This gives low temporal resolution three-component values of the GSM field, enabling a real-time forecast of the north-south field. The correlations for all three components for ten-year data give extraordinary positive results.
97% (115/118)
0.69 for Br
96% (103/118)
0.59 for Bt
88% (71/81)
0.40 for Bn
(CRs of Bz excursion < 0.25 nT are removed)
7. Summary
This analysis provides the standard (open-field) and “closed”-field CSSS model way to determine magnetic fields at Earth. For the closed-field analysis this includes the Bn (normal, or north-south) field.
The open-field analyses generally have better correlations over the ten-year period. The closed-field analyses are somewhat more variable than those of the open-field analyses.
A conversion of RTN coordinates to GSM coordinates of the open-field components gives fairly well agreement with low temporal resolution ACE in-situ fields. Used together, both open- and closed-field analyses have the potential to compliment one another. Thus, if perfected as a way to provide these fields regularly, this technique holds significant promise for space weather forecasting.
Primary References:
Dunn, T., B. V. Jackson, P. P. Hick, A. Buffington, and X. P. Zhao, 2005, “Comparative Analyses of the CSSS Calculation in the UCSD
Tomographic Solar Observations”, Solar Phys., 227, , doi: /s x.
Jackson, B. V., H.-S. Yu, A. Buffington, P. P. Hick, N. Nishimura, N. Nozaki, M. Tokumaru, K. Fujiki, and K. Hayashi, 2016, “Exploration of solar
photospheric magnetic field data sets using the UCSD tomography”, Space Weather, 14, Jackson, B.V., Hick, P.P., Bisi, M.M., Clover, J.M., and Buffington, A., 2013, “Inclusion of Real-Time in-situ Measurements into the UCSD
Time-Dependent Tomography and Its Use as a Forecast Algorithm”, Solar Phys., Solar Phys., 285, , doi: /s x.
Jackson, B. V., P.P. Hick, M.M. Bisi, J.M. Clover, A. Buffington, 2010, “Inclusion of In-Situ Velocity Measurements into the UCSD
Time-Dependent Tomography to Constrain and Better-Forecast Remote-Sensing Observations”, Solar Phys., 265,
Zhao, X.P., and Hoeksema, J.T., 1995, “Prediction of the interplanetary magnetic field strength,”, J. Geophys. Res., 100 (A1),