Comparison of Synoptic Maps and PFSS Solutions for The Declining Phase of Solar Cycle 24
Huichao Li, Xueshang Feng, Fengsi Wei
Abstract
Abstract The global distributions of photospheric magnetic field are routinely provided by synoptic maps, which often serve as fundamental observational input for coronal and heliospheric models. In this paper, we compare synoptic maps and PFSS‐derived magnetic field results obtained during 2017/12/06–2018/12/06, a period at the declining phase of solar cycle 24. We use four kinds of synoptic maps, the Helioseismic and Magnetic Imager (HMI) maps, the Air Force Data Assimilative Photospheric Flux Transport (ADAPT) maps, the Global Oscillation Network Group (GONG) maps with their zero‐point uncertainty corrected (GONGz maps) or uncorrected (GONGb maps). Qualitatively similarity among the four maps are found in the low‐latitude region, but the polar fields have notable differences. While the polar fields of HMI, ADAPT and GONGz maps are unipolar and relative stable in large scale, those of the GONGb maps are variable. The PFSS results of HMI, ADAPT, and GONGz compare reasonably with coronal remote observations and near‐Earth in situ data, and the HMI maps perform slightly better. There is generally no significant difference among results of the 12 ADAPT ensemble maps, but exceptions are also found. The PFSS results of GONGb maps deviate from observation significantly. The deviations are attributed to the problematic polar field, and the source of the problem may be the zero‐point uncertainty of the magnetograms. As GONGb maps perform well in the declining phase of solar cycle 23, results in this study highlight the importance of continuous assessment of synoptic map data quality.