1. Using Interplanetary Scintillation (IPS) Magnetic Modeling to Determine Bz
Bernard V. Jackson1, Hsiu-Shan Yu1, P. Paul Hick1, Andrew Buffington1, Mario M. Bisi2, Munetoshi Tokumaru3
1Center for Astrophysics and Space Sciences, University of California, San Diego
9500 Gilman Drive #0424, La Jolla, CA , U.S.A.
Tel:
2RAL Space, Science & Technology Facilities Council, Rutherford Appleton Laboratory,
Harwell Oxford, Didcot, Oxfordshire, OX11 0QX, England (UK)
3Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku,
Nagoya , Japan
Abstract
Interplanetary scintillation (IPS) observations enable the remote determinations of velocity and density in the inner heliosphere while also providing predictions of these quantities at Earth. The global long-duration radial (Br) and tangential (Bt) heliospheric magnetic field components are determined by taking the radial magnetic field (Br) at a given source surface as derived from the Current–Sheet Source Surface (CSSS) model (Zhao and Hoeksema, J. Geophys. Res., 100, 19, 1995), and convecting this out into the heliosphere using the velocities inferred from IPS. Here we test an extension to this analysis that allows the inclusion of short-term transient effects and finds the normal (Bn) magnetic field. This extension adds closed fields from near the solar surface, also derived from the CSSS model. When traced outward from the sub-Earth point, this gives the normal (Bn) component at Earth. These are compared to in-situ magnetic fields measured near Earth for three years during the minimum between Solar Cycle 23 and 24, and are continued using recent analyses up until the present. We find a significant positive correlation with Bn field measurements. We are now well on our way to making real-time predictions of the Bn field (the major contributor to the Bz field at Earth) associated with heliospheric structures in order to refine these analyses. URLs:
1. Interplanetary Scintillation (IPS)
500 km
Interplanetary Scintillation (IPS) at meter-wave radio frequencies is the rapid variation in radio signal intensity from compact sources produced by small-scale ( km) variations in solar wind density. These density variations produce a pattern on the surface of the Earth of similar size and are transported across the Earth’s surface at solar wind propagation speeds.
The Solar-Terrestrial Environment Laboratory (STELab) radio array, Japan; the Toyokawa system is shown. USCD currently maintains a near-real-time website that analyzes and displays IPS data from this system. The UCSD real-time analysis capability is also available at the NASA/ Goddard CCMC and the Korean Space Weather Center (KSWC), Jeju Island. A 3D-MHD model driven by an IPS velocity, density and magnetic field boundary is available at George Mason University (GMU).
Speed values for the solar wind can be inferred from the intensity variation by correlating the pattern motion across the surface of the Earth and expressing this as a line-of-sight value.
Websites
Density values for the solar wind can be inferred from the ‘normalized scintillation level’ (g-level) of observations of IPS relative to a nominal average.
USCD: http//:ips.ucsd.edu/
CCMC: http//:ccmc.gsfc.nasa.gov/
KSWC: http//
For a sample of the UCSD IPS real-time global time-dependent analysis using STELab data, see demo.
GMU:
2. Time-Dependent Tomography Analysis
Velocity
Density
Velocity fisheye map Velocity ecliptic cut IPS g-level fisheye map Density ecliptic cut
jet
3. Analysis – Magnetic Field Extrapolation
The UCSD time-dependent tomography analysis (Jackson et al., 2003, 2013) 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: Zhao and Hoeksema, 1995) model to give accurate vertical fields 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 (Dunn et al., 2005). These fields are then mapped to locations where they can be measured by in-situ spacecraft monitors.
jet

2. 4. Kinematic Model Validation and Br and Bt Field Components
The Carrington rotation period in May 2007 (CR /04/26 – 2007/05/26) serves as an example.
The IPS data fits provide a precise global density and velocity mapped to in-situ observations (left). Using the CSSS model’s boundary surface at 15 Rs as a starting point and using a forward model, the IPS velocities give radial and tangential fields mapped upward from this boundary (right) and here are compared with WIND in-situ magnetic field components.
SOLIS Bt Mag SOLIS Br Mag.
Velocity Density
In these examples 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. Both the radial and tangential field components shown (above right) come from the same vertical fields on the source surface here shown as an example (right) from one of about 25 magnetograms usually available daily throughout this time period from the NSO SOLIS data set. CR
Sample Potential Field Boundary at 15 Rs
5. Bn Field Component
SOLIS Carrington map at (left). The field component directed north-south in RTN coordinates is indicated. Northward-directed fields are lighter in color than those directed southward.
Shown at the right is a Carrington map
of the magnetic field normal component
Bn at a location 15 Rs above the solar
surface as derived by the CSSS Model
from 1.6 Rs and translated upward to
15 Rs with an r falloff (see summary).
This is used as an input to the UCSD modeling that extrapolates the Bn component upward further with the same radial falloff. Comparison of this component with that of the normal component measured from the ACE in-situ fields is shown to the right. Although the data are noisy, the best-fit correlation line is close to the expected 45°.
Bn Component at 15 Rs
CR2056 Bn Field Component at ACE
6. Additional Examples
2006
2007
2008
CR2042 ND
CR2054
0.511
0.69
CR2068
0.634
0.84
CR2043
0.616
0.15
CR2055
0.558
0.80
CR2069
0.375
0.58
CR2044
0.224
0.22
CR2056
0.614
0.96
CR2070
0.589
0.94
CR2045
0.646
CR2057
0.518
0.67
CR2071
-0.318
-0.98
CR2046
0.067
0.98
CR2058
0.364
0.70
CR2072
0.029SE
1.54
CR2047
0.484
0.71
CR2059
0.414
CR2073
-0.073SE
-1.74
CR2048
0.721
0.30
CR2060
0.100
CR2074
0.381
2.62
CR2049
0.438
CR2061
0.208
0.51
CR2075
0.369
1.70
CR2050
0.505
0.34
CR2062
-0.037
-0.92
CR2076
0.382
1.31
CR2051
0.478
0.63
CR2063
0.073SE
CR2077
0.677SE
1.23
To the right is a table of correlations and slopes for additional Bn field components compared with ACE for this same method from years 2006, 2007, and We find these comparisons almost always show a positive correlation (see Jackson et al., 2015). Presumably this analysis can also be used to supplement Br and Bt field components derived using the usual CSSS model.
To the left are 12-day comparison plots of modeled Bn field with ACE (a & b) using this same method from early 2015 when a CIR passed the Earth that was associated with a geomagnetic substorm (c).
To the right are similar 12-day comparison plots of modeled Bn field with ACE (a & b) in 2015 March associated with one of the times of strongest substorm activity in the current solar cycle (c). Both examples show our modeling predicts this activity.
7. Implications and Summary
This analysis provides a simple way to partially determine Bz at Earth since the Bn normal field is the largest contributor to the Bz component in GSM coordinates that couples with the Earth’s magnetic field to provide geomagnetic storms. Thus, this technique holds significant promise for space weather forecasting.
Furthermore, while many have suggested this technique might work to provide some indication of the Bz field component in the past for CMEs (i.e., Hoeksema and Zhao, 1992; Tokumaru et al., 2007), no one to our knowledge has completed a statistical study showing its application for periods near solar minimum when CMEs are mostly absent (see Jackson et al., 2015 for details). However, in the above figure for the 2015 March 17 St. Patrick’s Day event, the modeling apparently also works for what was supposedly a CME that brushed past Earth to the east.
We speculate that, for these fields to be present in the solar wind, horizontal closed fields must somehow escape from their near solar surface configuration into the solar wind on a regular basis. The current value of the horizontal field magnitude that is present in the solar wind is somewhat arbitrary, and is here predicated by the radial falloff of the field normal component and the amplitude needed to provide a one-to-one relationship at ACE. Given that the radial falloff of r persists as measured by the Helios spacecraft (Mariani and Neubauer, 1990) all the way to near the solar surface, we find only a small fraction (~2%) of the Bn field needs to escape from closed flux regions. This field amplitude must have something to do with the physics behind its escape.
References
Dunn, T., Jackson, B.V., Hick, P.P., Buffington, A., and Zhao, X.P., 2005, “Comparative Analyses of the CSSS Calculation in the UCSD Tomographic Solar Observations”, Solar Phys., 227,
Hoeksema, J.T., and Zhao, X., 1992, “Prediction of magnetic orientation in driver gas associated −Bz events”, J. Geophys. Res., 97, , doi: /91JA02702.
Jackson, B.V., Hick, P.P., Buffington, A., Kojima, M. Tokumaru, M., Fujiki, K., Ohmi, T., and Yamashita, M., 2003, “Time-dependent tomography of hemispheric features using interplanetary scintillation (IPS) remote-sensing observations”, in Velli, M., Bruno, R., and Malara, F., Solar Wind Ten, 679,
Jackson, B.V., Hick, P.P., Buffington, A., Clover, J.M., and Tokumaru, M., 2012, “Forecasting Transient Heliospheric Solar Wind Parameters at the Locations of the Inner Planets”, Adv. in Geosciences, , 30, 93−115.
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., 285,
Jackson, B.V., Hick, P.P., Buffington, A., Yu, H.-S., Bisi, M.M., Tokumaru, M., and Zhao, X.P., 2015, “A determination of the north-south magnetic field component from inner-corona closed loop propagation”, Astrophys. J. Lett., 803:L , doi: / /803/1/L1.
Mariani, F., and Neubauer, F.M., 1990, in Physics and Chemistry in Space & Solar Physics, Physics of the Inner Heliosphere 1. Large-Scale Phenomena, Vol. 20, “The Interplanetary Magnetic Field”, ed. M. C. E. Huber, L. J. Lanzerotti, and Stoffler, D.,
Tokumaru, M., Kojima, M., Fujiki, K., Yamashita, M., and Jackson, B.V., 2007, “The source and propagation of the interplanetary disturbance associated with the full-halo coronal mass ejection on 2003 October 28”, J. Geophys. Res., 112, A05106, doi: /2006JA
Zhao, X.P., and Hoeksema, J.T., 1995, “Prediction of the interplanetary magnetic field strength,”, J. Geophys. Res., 100 (A1),