Exploration of solar photospheric magnetic field data sets using the UCSD tomography

Abstract

This article investigates the use of two different types of National Solar Observatory magnetograms and two different coronal field modeling techniques over 10 years. Both the “open‐field” Current Sheet Source Surface (CSSS) and a “closed‐field” technique using CSSS modeling are compared. The University of California, San Diego, tomographic modeling, using interplanetary scintillation data from Japan, provides the global velocities to extrapolate these fields outward, which are then compared with fields measured in situ near Earth. Although the open‐field technique generally gives a better result for radial and tangential fields, we find that a portion of the closed extrapolated fields measured in situ near Earth comes from the direct outward mapping of these fields in the low solar corona. All three closed‐field components are nonzero at 1 AU and are compared with the appropriate magnetometer values. A significant positive correlation exists between these closed‐field components and the in situ measurements over the last 10 years. We determine that a small fraction of the static low‐coronal component flux, which includes the Bn (north‐south) component, regularly escapes from closed‐field regions. The closed‐field flux fraction varies by about a factor of 3 from a mean value during this period, relative to the magnitude of the field components measured in situ near Earth, and maximizes in 2014. This implies that a relatively more efficient process for closed‐flux escape occurs near solar maximum. We also compare and find that the popular Potential Field Source Surface and CSSS model closed fields are nearly identical in sign and strength.

Evaluation of the Interplanetary Magnetic Field Strength Using the Cosmic-Ray Shadow of the Sun

“…By calculating the average B x and B y each as a function of the Carrington longitude in every year, we examined the correlations between the simulated and observed B x and B y as shown in Figures 3(c) and 3(d). While the correlation coefficient between the simulated and observed magnetic field component in this figure is 0.93 (0.92) for B x (B y ), indicating high correlation, the regression coefficient is 1.38 ± 0.03 (1.34 ± 0.03 ) for B x (B y ), significantly larger than 1.00, implying the underestimation of the simulated B x (B y ) on the horizontal axes [13]. This underestimation is observed in every year, while the magnitude of B x or B y changes in a positive correlation with the solar activity.…”

A Daily Determination of BZ Using the Russell‐McPherron Effect to Forecast Geomagnetic Activity

“…The 3‐D reconstruction of the solar wind velocity in the UCSD time‐dependent analysis is used to forward‐model the Zhao and Hoeksema () CSSS RTN magnetic field, extending it out to the edge of the global boundary considered by the IPS analysis. As previously mentioned, more detailed descriptions are found in Dunn et al () and in Jackson et al (, ). Even though GONG synoptic maps are currently updated with a 6‐hr cadence in the UCSD time‐dependent tomography, our analysis essentially provides only background solar wind component fields.…”

“…These fields vary rather smoothly even though they are currently provided as a new source surface with a 6‐hr cadence to the UCSD 3‐D reconstructions (see section ) and are unaveraged in transit or at Earth for comparison with in situ measurements. As discussed in Jackson et al (), and known to be necessary to make field strengths match in situ measurements (e.g., Linker et al, ), GONG data are multiplied by a factor of two from the original surface fields in order to provide a more accurate amplitude comparison at Earth. In the usual CSSS modeling effort, we call “open field” in Jackson et al (), there are only radial fields present on the inner source surface.…”

“…As discussed in Jackson et al (), and known to be necessary to make field strengths match in situ measurements (e.g., Linker et al, ), GONG data are multiplied by a factor of two from the original surface fields in order to provide a more accurate amplitude comparison at Earth. In the usual CSSS modeling effort, we call “open field” in Jackson et al (), there are only radial fields present on the inner source surface. Using the Parker () solar wind equations, this field is extrapolated outward in the UCSD 3‐D reconstructions as a “frozen in” field that conserves the timing and interactions present in the UCSD time‐dependent kinematic model.…”

“…In this formulization using heliographic coordinates, there are only radial and tangential fields (RTN in heliographic radial, tangential, and normal coordinates) present; the north‐south (normal) field is zero. Jackson et al () provide a comprehensive analysis of how well these field predictions compare with Advanced Composition Explorer (ACE; Stone et al, ), or Wind (Ogilvie & Parks, ) in situ measurements over the 10‐year period of available GONG data.…”