Real-time Flare Detection in Ground-Based Hα Imaging at Kanzelhöhe Observatory

Abstract

Kanzelhöhe Observatory (KSO) regularly performs high-cadence fulldisk imaging of the solar chromosphere in the Hα and Ca ii K spectral lines as well as the solar photosphere in white-light. In the frame of ESA's Space Situational Awareness (SSA) programme, a new system for real-time Hα data provision and automatic flare detection was developed at KSO. The data and events detected are published in near real-time at ESA's SSA Space Weather portal (http://swe.ssa.esa.int/web/guest/kso-federated). In this paper, we describe the Hα instrument, the image recognition algorithms developed, the implementation into the KSO Hα observing system and present the evaluation results of the real-time data provision and flare detection for a period of five months. The Hα data provision worked in 99.96% of the images, with a mean time lag between image recording and online provision of 4 s. Within the given criteria for the automatic image recognition system (at least three Hα images are needed for a positive detection), all flares with an area ≥50 micro-hemispheres and located within 60• of the Sun's center that occurred during the KSO observing times were detected, in total a number of 87 events. The automatically determined flare importance and brightness classes were correct in ∼85%. The mean flare positions in heliographic longitude and latitude were correct within ∼1• . The median of the absolute differences for the flare start times and peak times from the automatic detections in comparison to the official NOAA (and KSO) visual flare reports were 3 min (1 min).

Magnetic Reconnection Rates and Energy Release in a Confined X-class Flare

“…• ) in AR 12192 using three different data sets: Hα and Ca ii K filtergrams from Kanzelhöhe Observatory (Pötzi et al, 2015) and 1600Å filtergrams from AIA. The start time of the event under study is 14:02 UT and the GOES peak occurred at 14:28 UT.…”

“…The Hα images are recorded with a cadence of 6 seconds using a 12-bit 2k × 2k CCD camera, resulting in a pixel size of 1 . An automatic exposure-control system is in place to avoid saturation during flares (Pötzi et al, 2015). The KSO Ca ii K telescope (d/f = 110/1650) provides full-disk images of the Sun in the Ca ii K spectral line centered at 3934Å with an effective FWHM of 2.4Å.…”

Spectral Characteristics of the He i D3 Line in a Quiescent Prominence Observed by THEMIS

“…The prominence area in the plane of the sky, measured in the Hα broadband image (Figure 1) taken at the Kanzelhöhe Solar Observatory (KSO, Pötzi et al, 2015), is 1483 Mm 2 . After subtracting the off-limb aureole that is due to the scattered photospheric light, the prominence relative intensity in the KSO 0.7Å-wide Hα Lyot filter with respect to the disk center is within the range from 7% to 27% with a median of 17%, corresponding to a radiance of 1.0 W cm −2 sr −1 , and the prominence Hα radiant intensity is about 3.9 × 10 22 W sr −1 .…”

Statistical studies of duration of low-power solar flares

“…This makes it possible to conduct additional studies, to specify time parameters of solar flares. In recent decades, this issue has been repeatedly addressed [Temmer et al, 2001;Giersch, 2013;Potzi et al, 2014], but no detailed analysis has been made so far.…”