Oscillations in the Regions of Evershed Flows

Abstract

Authors have investigated the line-of-sight velocity difference in the radial direction of sunspot penumbrae simultaneously at two height levels, Nil 4857 and H,a by the differential method. Power spectra of time series exhibit in the range under consideration three groups of periods: 30-40, 12-15, and 8-10 minutes. Particular emphasis has been placed on the low-frequency portion of the spectrum (0.5-2 mHz). In addition to the 12-minute oscillations as detected by Rimmele the line-ofsight velocity component that is caused by Evershed motion is responsible for oscillations with periods of 15-35 minutes, which occur concurrently at the two height levels.

High-frequency oscillations in a solar active region observed with the RAPID DUAL IMAGER

“…Previous observations of Evershed oscillations have detected periods ranging from 8 to 40 min (Rimmele 2004, Makarchik & Kobanov 2001. We note that the penumbral bright-grain oscillations reported here are of much higher frequency than those observed to date.…”

“…4.1. Makarchik & Kobanov 2001). We note that the penumbral bright-grain oscillations reported here are of much higher frequency than those observed to date.…”