Multi-height study of the Chromospheric inverse evershed flow and its association with photospheric flows

Abstract

We analyzed the inverse Evershed flow (IEF) around a sunspot (NOAA 13131) using line scan observations in the Fe i 6173 Å and Ca ii 8542 Å spectral lines, complemented with data products from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager. Line-of-sight (LOS) velocities were obtained for different bisector levels in both spectral lines. Additionally, the Ca ii 8542 Å spectra were inverted using the Non-LTE Inversion COde using the Lorien Engine (or NICOLE) to retrieve the temperature and velocity stratification over different layers of the lower solar atmosphere. The IEF evolved dynamically in time and with height in the solar atmosphere. The flow speed associated with the IEF channels was on the order of 8 km s−1 in the upper chromosphere, which decreased in the lower layers of the atmosphere. The flow was traced to the lower chromosphere in LOS velocity maps and the upper photosphere in intensity images. The temperature enhancements associated with the IEF were up to 300 K at log τ ≈ −2 and 800 K at log τ ≈ −6 near the end point of one channel. The overall appearance of the flow along the IEF channels seems consistent with a siphon flow model. We investigated the association of the IEF with the photospheric Evershed flow, but no obvious connection was found in our analysis. We also analyzed the effect of the IEF on moving magnetic features (MMF) selected near and away from IEF channels. MMFs moved radially outward with velocities in the 0.2–1 km s−1 range, with no apparent association with the IEF.