CESE‐HLL Magnetic Field‐Driven Modeling of the Background Solar Wind During Year 2008

Abstract

In this paper, the CESE-HLL three-dimensional magnetohydrodynamic solar wind model is first modified to be able to work in a corona-heliosphere integrated approach and then used to simulate the evolution of solar wind from the solar surface to the Earth's orbit during year 2008. Here high-cadence photospheric magnetic field data are used to drive the model at the solar surface via the projected normal characteristic boundary equations. The simulated results are analyzed and quantitatively evaluated by comparing the simulated results with solar and interplanetary observations. The analyses demonstrate that our model reproduces the main pattern and the evolutionary feature of large-scale coronal structures. The simulated results show that the height of the pseudostreamer X point is positively correlated with the distance of the coronal holes connected by the pseudostreamer. During year 2008, the helmet streamer belt is found to have a net southward displacement from the equator while the pseudostreamer belts are biased to the Northern Hemisphere. Both helmet streamer belt and pseudostreamer belts exhibit a general trend of becoming more concentrated along the equator throughout 2008. The evaluation of the simulated results at the L1 point shows that the general structures can be generated by the model, and that speed is the best among the solar wind parameters reproduced. However, the temperature of the fast solar wind and the magnitude of the interplanetary magnetic field are underestimated. The success rate of prediction and arrival time error are also calculated for magnetic field polarity reversals and stream interaction regions.

Abrupt Shrinking of Solar Corona in the Late 1990s

“…The maximum-time (minimum-time) level of f au has systematically decreased from cycle 22 maximum to cycle 24 maximum (from mid-1980s to mid-2000s, respectively). This long-term decrease of the observed HMF flux density in recent decades is well documented (Smith & Balogh 2008;Lockwood 2013). The same systematic decline is seen in f ss in Figures 2(a) and (b) for all values of r ss from cycle 22 until recently.…”

“…Recently, (Koskela et al 2017) showed that the PFSS model reliably produces the HMF sector structure. Moreover, adding horizontal currents (as in the current sheet source surface (CSSS) model; Koskela et al 2019) or using an MHD model (Li & Feng 2018) does not improve the polarity match between the corona and the heliosphere. All these studies indicate that, despite its simplified assumptions (lack of currents and spherical source surface), the PFSS model can well produce the large-scale coronal magnetic field structure, even at different solar activity conditions.…”

Comparison of Synoptic Maps and PFSS Solutions for The Declining Phase of Solar Cycle 24

“…During the declining and minimum phase of solar cycle 23, both PFSS and MHD modeled results driven by GONGb synoptic maps gave satisfying results (e.g., Gressl et al., 2014; Feng et al., 2017; Jian et al., 2016, 2015; Li & Feng, 2018; Li, Feng, & Wei 2020; Li, Feng, Zuo, & Wei 2020; Wiengarten et al., 2014). However, as can be seen here, the GONGb maps do not perform well during the declining phase of solar cycle 24.…”

Revisiting the coronal current sheet model: Parameter range analysis and comparison with the potential field model

“…The long-term average polarity match with the CSSS model optimal R cs is 85.6% for a = 0.01 and 0.1, 85.4% for a = 1, and with the PFSS model optimal r ss 85.9%. For comparison, Li & Feng (2018) modelled the corona and heliosphere using a coupled coronal and heliospheric 3D MHD model, and obtained a polarity match of 85.8% in 2008. The polarity match we obtained for 2008 with the CSSS model optimal parameters was 88.2% for a = 0.01, 88.1% for a = 0.1, 88.4% for a = 1, and 87.4% for the PFSS model with the optimal r ss .…”