Distribution of low-power solar flares by brightness rise time

Abstract

For brightness classes this trend is less pronounced. We have found that flares with explosive phase and flares with one brilliant point have the shortest flash phases; two-ribbon flares and flares with several intensity maxima, the longest ones. We have separated 572 cases when the brightness rise time was more than 60 min; 80 % of such ultra-long flares have a shorter brightness decay time (main phase). We have established that low-power flares in terms of developmental features do not differ from large flares. Low-power solar flares, as well as large flares, can be followed by filament activation or disappearance, and can have an explosive phase and several intensity maxima. Two-ribbon flares, white-light flares, and flares covering sunspot umbra can also have low power.

The Processes of Energy Release in Low-Power Solar Flares

“…There is no relationship between the time of brightness rise to maximum and the time of its decay (according to our estimates, the correlation coefficient is less than 0.4). Borovik, Zhdanov [2017b, 2018a, 2018b] using a great body of data have obtained distributions of solar flares by the time of brightness rise to maximum, decay time, and total duration in accordance with the international classification of chromospheric flares. According to the optical classification, flares are divided by area into five classes: S, 1, 2, 3, 4.…”

“…All the T rel distributions have a positive asymmetry and an extended decrease and, like time parameters of flares [Borovik, Zhdanov, 2017b, 2018a, 2018b, exhibit a significant mutual overlap of distributions ( Figure 3, a, b). This implies that the high percentage of flares with increasing area class does not show the general tendency.…”

“…The mean relative brightness rise time for D-and G-flares is longer than that for flares of other types (Table 5, Figure 7). Note that neither the distribution by brightness rise time of flares nor the distribution by their total duration are discrete [Borovik, Zhdanov, 2018a, 2018b. The maxima are likely to de unrelated with the observation time discretenessspread of time parameters of flares within the maxima is quite significant.…”

“…In this paper, we analyze the results obtained in [Borovik, Zhdanov, 2017b, 2018a, 2018b, present a number of important, in our opinion, conclusions about dynamics and power of flare processes.…”