Comparison of potential field solutions for Carrington Rotation 2144

Abstract

We examined differences among the coronal magnetic field structures derived with the potential field source surface (PFSS) model for Carrington Rotation 2144, from 21 November to 19 December 2013. We used the synoptic maps of solar photospheric magnetic field from four observatories, the Huairou Solar Observing Station (HSOS), Global Oscillation Network Group (GONG), Helioseismic Magnetic Imager (HMI), and Wilcox Solar Observatory (WSO). We tested two smoothing methods, Gaussian and boxcar averaging, and correction of unbalanced net magnetic flux. The solutions of three‐dimensional coronal magnetic field are significantly different each other. An open‐field region derived with HSOS data agrees best with the corresponding coronal hole observed by Solar Dynamics Observatories/Atmospheric Imaging Assembly, while HMI data yielded best agreements with the near‐Earth OMNI database. The GONG data overall gave agreements as good as the HMI. The PFSS calculations using WSO data were least sensitive to the choices we examined in this work. Differences in PFSS solutions using different choices and parameters in smoothing imply that the photospheric magnetic field distributions with size of several degrees at midlatitude and low‐latitude regions can be decisive, at least, in the examined period. To better determine the global solar corona, therefore, further evaluation of influences from compact bipolar magnetic field is needed.

On Solutions of the PFSS Model With GONG Synoptic Maps for 2006–2018

“…Therefore, correction coefficients, which depend on the magnetic field observatory, are applied to obtain agreement with observations of the magnetic field at 1 AU (Wang & Sheeley, ; Riley, ). The fact that there are differences in measurements of the solar magnetic field can lead to some inconsistency between results from numerical models which use synoptic maps from different observatories (see, e.g., Hayashi et al, ). Recently, Riley et al (), for example, studied line‐of‐sight synoptic maps from several solar observatories and derived conversion factors between the maps.…”

Prediction of Solar Wind Speed at 1 AU Using an Artificial Neural Network

“…The recent improvements in space and ground‐based instruments have enabled solar and heliospheric observations with much higher temporal and spatial resolution, which can improve the performance of data‐driven models. For example, the accuracy of the PFSS model in modeling the coronal magnetic field depends on the quality of the magnetogram that was used as input of the model (Liu et al, ; Hayashi, Yang, et al, ; Riley et al, ). The PFSS modeling accuracy also depends on some other factors, such as the magnetogram smoothing procedures (Hayashi, Yang, et al, ), the hypothesis of source‐surface radius (Lee et al, ), and the spherical polynomial calculation method (Tóth et al, ).…”

Possibilities and problems of solar magnetic field observations for space weather forecast

“…This very fact may explain the rather inaccurate forecasts made with WSA-Enlil+Cone, where basically GONG data are used. Also illustrative in [Hayashi et al, 2016] is Figure 10, which demonstrates the comparison between real observations and results of calculations of the radial magnetic field component near Earth's orbit for different data series with and without zero-level shift correction. It is easy to see that without correction (the validity of which, as done in [Hayashi et al, 2016], in my opinion, is far from obvious), the calculation results for GONG and HSOS differ considerably from experimental data.…”

“…Let us discuss in more detail the results of [Hayashi et al, 2016], which analyzes differences in calculations (performed in the potential approximation, i.e. by the PFSS model) of the heliosphere structure and solar wind parameters in Earth's orbit, using synoptic maps from four observatories: WSO, GONG, SDO/HMI, and Huairou Solar Observation Station (HSOS).…”

“…the number of points on a synoptic map was 72 (longitude) and 30 (sine latitude). The authors of [Hayashi et al, 2016] applied an important procedure -respective average (over the entire map) values of ΔB were subtracted from all synoptic maps to correct the unbalanced magnetic flux. This procedure for correcting zero-level shift had practically no effect on WSO and HMI data (ΔB=-0.08 and -0.11 G respectively), but markedly affected HSOS data (ΔB=-1.13 G) and GONG (ΔB=-1.21 G).…”