The flares associated with the abnormal rotation rates of the bipolar sunspots: Reconnection probably below the surface

Abstract

Abstract.We use the observations of Kodaikanal observatory white light pictures to study the association between the rotation rates of the bipolar sunspots and triggering of the flares. For the years 1969−1974, we compute daily rotation rates of the leading and the following spots of the bipolar sunspot groups during their life span. We find that either leading or following or both of the bipolar spot groups which have abnormal rotation rates during the course of their evolution are strongly associated with the occurrence of flares in the later stage of their life span. Other important findings are: (i) the abnormal rotation rates and the flares occur during the 50−80% of their life span of the spot group and, (ii) abnormal rotation rate of about 2• /day is required for triggering the flares. The strong relation between the occurrence of abnormal rotation rates of the sunspot groups and the occurrence of the flares enabled us to estimate the probable region of depth of reconnection below the solar surface.

Flares associated with abnormal rotation rates: Longitudinal minimum separation of leading and following sunspots

“…The errors are determined using the formula σ/(N) 1/2 , where N is the total number of events of minimum separation and flares and σ is the standard deviation. As we found in the previous study (Hiremath & Suryanarayana 2003), for the events with abnormal rotation rates, a spot with a 4 day life span experiences on average a minimum separation and correspondingly the occurrence of a flare on the second day. A spot with a life span of six days experiences the same events on the third day and so on.…”

“…A spot with a life span of six days experiences the same events on the third day and so on. In other words, abnormal rotation rates of the spots and the minimum distances of the foot points on average occur at between 50−80% of the life span during the course of their evolution, probably indicating annihilation of magnetic energy below the surface (Hiremath & Suryanarayana 2003).…”

“…By taking a clue from our previous study (Hiremath & Suryanarayana 2003) that the reconnection may be occurring below the surface at a depth of 0.935 R , from simple plane trigonometry, one can estimate the thickness (length) of the reconnecting region to be ∼10 5 cm which is in the required range of 10 5 −10 8 cm.…”

“…In order to know whether dynamics of the sunspotsespecially the dynamics due to rotational rates-give clues about the triggering of flares, we computed the daily rotation rates of sunspots (that have leaders and followers) during their life time and we have shown that the abnormal rotation rates of either leading or following spots or both eventually trigger the flares (Hiremath & Suryanarayana 2003). In that study, because of the strong association between abnormal rotation rates of sunspots and the occurrence of flares, it is possible to estimate the probable region of the depth of magnetic reconnection below the On leave under the Faculty Improvement Program.…”

Photospheric vortex flows close to the polarity inversion line of a fully emerged active region

“…On larger scales, rotational motions were observed in sunspots and they are usually associated with energy and helicity buildup and later release by flare and/or coronal mass ejection (Brown et al, 2003;Hiremath and Suryanarayana, 2003;Hiremath et al, 2005;Yan and Qu, 2007;Yan et al, 2008;Min and Chae, 2009;Yan et al, 2009;Kazachenko et al, 2010;Zhu et al, 2012;Yan et al, 2012;Jiang et al, 2012;Vemareddy et al, 2012;Hardersen et al, 2013;Wang et al, 2014;Ruan et al, 2014;Gopasyuk, 2015;Li and Liu, 2015;Suryanarayana et al, 2015;Wang et al, 2016;Vemareddy et al, 2016). The rotation of sunspots is usually very slow, this means that the evolution of the magnetic field in the corona associated to it would be slow as well.…”