标题： 基于COCONUT的高效、时间演化、全局MHD日冕模型 显示英文标题

标题： An efficient, time-evolving, global MHD coronal model based on COCONUT

摘要： 磁流体动力学日冕模型在太阳到地球的模型链中至关重要，是其中最复杂且计算量最大的组成部分，尤其是随时间演化的日冕模型，通常由一系列随时间演化的光球磁场图驱动。 迫切需要开发高效且可靠的随时间演化的磁流体动力学日冕模型，以进一步提高我们预测空间天气的能力。 COCONUT是一个快速发展的磁流体动力学日冕模型。 采用高效的隐式算法使其适用于进行计算密集型的随时间演化的日冕模拟。 本文旨在将COCONUT扩展为一种高效的随时间演化的磁流体动力学日冕模型。 在这个磁流体动力学模型中，通常采用隐式时间积分算法以避免CFL稳定性限制，并通过大时间步长提高计算效率。 在每个时间步内应用牛顿迭代法以提高时间精度。 使用非结构化测地网格以提高网格划分的灵活性并避免极点处的退化问题。 此外，采用具有自适应耗散项的HLL黎曼求解器以适应低速和高速流动。 利用一系列随时间演化的光球磁场图，在惯性坐标系中，围绕2019年日食的两个卡灵顿旋转（CRs）期间，驱动从太阳表面到25Rs的日冕结构演化。 结果显示，COCONUT可以在9小时内（1080个CPU核心，1.5M个单元）模拟完整卡灵顿旋转期间的日冕演化。 我们还比较了热力学磁流体动力学模型中随时间演化与准稳态日冕模拟的结果，以验证随时间演化的方法。 此外，我们评估了时间步长对模拟结果的影响，以找到一个同时保持高效率和必要数值稳定性和准确性的最优时间步长。 显示英文摘要

摘要： MHD coronal models are critical in the Sun-to-Earth model chain and the most complex and computationally intensive component, particularly the time-evolving coronal models, typically driven by a series of time-evolving photospheric magnetograms. There is an urgent need to develop efficient and reliable time-evolving MHD coronal models to further improve our ability to predict space weather. COCONUT is a rapidly developing MHD coronal model. Adopting the efficient implicit algorithm makes it suitable for performing computationally intensive time-evolving coronal simulations. This paper aims to extend COCONUT to an efficient time-evolving MHD coronal model. In this MHD model, as usual, an implicit temporal integration algorithm is adopted to avoid the CFL stability restriction and increase computational efficiency by large time steps. The Newton iteration method is applied within each time step to enhance the temporal accuracy. The unstructured geodesic mesh is used for flexibility in mesh division and to avoid degeneracy at the poles. Furthermore, an HLL Riemann solver with a self-adjustable dissipation term accommodates both low- and high-speed flows. A series of time-evolving photospheric magnetograms are utilized to drive the evolution of coronal structures from the solar surface to 25Rs during two Carrington rotations (CRs) around the 2019 eclipse in an inertial coordinate system. It shows that COCONUT can mimic the coronal evolution during a full CR within 9 hours (1080 CPU cores, 1.5M cells). We also compare the simulation results of time-evolving versus quasi-steady-state coronal simulations in the thermodynamic MHD model to validate the time-evolving approach. Additionally, we evaluate the effect of time steps on the simulation results to find an optimal time step that simultaneously maintains high efficiency and necessary numerical stability and accuracy.