Active region upflows

Abstract

Context.Observations of many active regions show a slow systematic outflow/upflow from their edges lasting from hours to days. At present no physical explanation has been proven, while several suggestions have been put forward. Aims. This paper investigates one possible method for maintaining these upflows assuming, that convective motions drive the magnetic field to initiate them through magnetic reconnection. Methods. We use Helioseismic and Magnetic Imager (HMI) data to provide an initial potential 3D magnetic field of the active region NOAA 11123 on 2010 November 13 where the characteristic upflow velocities are observed. A simple 1D hydrostatic atmospheric model covering the region from the photosphere to the corona is derived. Local correlation tracking of the magnetic features in the HMI data is used to derive a proxy for the time dependent velocity field. The time dependent evolution of the system is solved using a resistive 3D magnetohydrodynamic code. Results. The magnetic field contains several null points located well above the photosphere, with their fan planes dividing the magnetic field into independent open and closed flux domains. The stressing of the interfaces between the different flux domains is expected to provide locations where magnetic reconnection can take place and drive systematic flows. In this case, the region between the closed and open flux is identified as the region where observations find the systematic upflows. Conclusions. In the present experiment, the driving only initiates magneto-acoustic waves without driving any systematic upflows at any of the flux interfaces.

Testing the Accuracy of Data-driven MHD Simulations of Active Region Evolution

“…At t = 0 a potential field extrapolation is used to fill the coronal volume, and after each update of the normal field and velocities on the boundary, the system is allowed to relax to a new equilibrium. The boundary velocities are derived from either (a) local correlation tracking methods [2,3,9], (b) imposed density perturbations proportional to the horizontal magnetic field magnitude at the surface [10,11], or (c) by the method of MHD characteristics [27].…”

Investigating the Magnetic Imprints of Major Solar Eruptions with SDO/HMI High-cadence Vector Magnetograms

“…Knowledge of the coronal magnetic field is vital to our understanding of solar eruptions and our capability to predict major space weather events. New-generation data-driven models (e.g., Cheung & DeRosa 2012;Inoue et al 2014;Fisher et al 2015;Galsgaard et al 2015;Jiang et al 2016) aim to take advantage of the observed evolution of the magnetic and velocity fields and model the evolution of the coronal field with sufficient accuracy and efficiency. Leake et al (2017) have investigated the effect of the driving time scale, i.e., the input data cadence, on the modeling accuracy using their newly developed, data-driven MHD framework.…”

Apparent and Intrinsic Evolution of Active Region Upflows

“…Several other mechanisms have been proposed as direct or indirect drivers of AR upflows observed by Hinode/EIS such as AR expansion (Murray et al, 2010), waves (e.g. Wang et al, 2009;Verwichte et al, 2010;Ofman, Wang, and Davila, 2012;Galsgaard et al, 2015), coronal plasma circulation (Marsch et al, 2008), chromospheric evaporation (Del Zanna, 2008), and type II spicules (e.g. De De Pontieu and McIntosh, 2010;Tian et al, 2012), among others.…”