Revisiting Evershed Flows with CHASE Spectroscopic Observations

Abstract The Evershed flow (EF), since its discovery in 1909, represents a longstanding issue in solar physics, with its three-dimensional velocity fields and underlying physical mechanisms still not fully understood. We present a comprehensive analysis of the velocity fields for 20 sunspots, using the full-disk spectroscopic observations from the Chinese H α Solar Explorer (CHASE). The height-dependent velocity fields are derived from the bisector analysis of the Si i 6560.58 Å, Fe i 6569.21 Å, and H α 6562.81 Å spectral lines, which are formed from the deep photosphere (∼70 km) to the upper chromosphere (∼1340 km). The statistical results based on CHASE observations reveal that the photospheric EF manifests as a nearly horizontal outflow with the maximum radial flow velocities of 2.5–2.9 km s −1 at the outer penumbral boundaries, and the inverse EF (IEF) at the chromosphere shows predominant inward flows of 1.6–3.5 km s −1 , with substantial downward flows. EF-like flows above the penumbra are found in all sunspots in the H α far wings, with a velocity reversal shown by the bisector analysis at H α ±0.65 Å (corresponding to a normalized line depth intensity of ∼0.6) in the limb-side region, and a small reversal in the center-side region, suggesting the coexistence of the EF outflows and IEF downflows at the flow reversal layers. We finally construct a three-dimensional schematic of the EF and IEF above sunspots, depicting the height-dependent flows from the deep photosphere to the upper chromosphere.