4 September 2019, 08:30 UTC

During the course of summer 2019, there hasn't been a single flare on the Sun

Sun flares - artwork image. Sun flares — artwork image. Source - NASA.

Not a single solar flare of the x-rays class C or higher (a minimum level which is able to have an impact on Earth) has been recorded on the Sun over the past summer of the year 2019. Last, very weak surge in solar activity was observed in May 2019 and ended on 15 May, which is exactly 112 days ago. Currently, this is the fourth-longest in duration interval in the modern history of observations when a complete absence of the solar activity has been seeing. Wherein the third, longest by duration this type of interval, made of 183 days, was recorded quite recently from 6 July 2018 to 6 January 2019. However, the record-breaking intervals of activity in modern history are the two periods observed during the previous solar minimum in 2008 - 2009. The first one lasted for 214 days from April to November 2008 and the second interval lasted for 205 days from December 2008 to July 2009. In that time, such a sharp decline in activity had earnestly brought to the discussion on a possible beginning of the new Maunder minimum - long and lasting for several decades interruption of the solar activity which partially had coincided with a Little Ice Age at the turn of the XVII - XVIII centuries. Those apprehensions were not confirmed at that time though the subsequent solar cycle was one of the weakest in the entire 300-year history of observations.

A sharp decrease in the number of solar flares is one of the most prominent signs of the solar minimum alongside with a decrease in the number of sunspots. The reason for flares' disappearance, same as for the spots, is the nearly complete disappearance of a magnetic field on the Sun which is the main energy source for solar activity. Unlike the Earth's magnetic field, the field of the Sun is of a distinct variable character periodically strengthening and weakening in 11 years step pace. In our mind's eye, this solar pulse is beating for 300 years (number of years of the continuous observations of the Sun), then obviously that any of its interruptions are alarming. The concern is not about the decrease in the number of flares as such, but the fact that this may be a sign of some more serious changes in the Sun herewith, among the other things, can affect its luminosity, radiation spectrum and in the end, the climate. It should be noted that solar flares, even so often they perceived as negative phenomenon, do also play a very important role in the physics of the Earths atmosphere. In particular, their ionizing radiation is affecting the ionic and gas composition of the Earths upper atmosphere, including the concentration of the greenhouse gases. Furthermore, besides the responsibility of flares' radiation for the formation of the Earths ionosphere, it is also playing a key role in question of short-wave radio communications. In this sense, long intervals in the pace of the flares, much longer the usual ones to which our planet undoubtedly adapted to, do certainly have a destabilizing factor.

At present, the dynamics of the solar minimum is not yet alarming, notwithstanding the duration of the minimum which has already exceeded previous predictions when according to them the growth of solar activity was supposed to begin this summer. The beginning of 2020 should become quite a significant point in this matter. If by this time there won't be a distinctive outbreak registered in the solar activity, it will mean that the duration of the current minimum has equalled to the record minimum of 2008-2009. In this case, the conversation on the systemic evolutionary decrease in the Sun's level of activity may be started, which may also become a trend for the whole of the century.

Laboratory of X-ray astronomy of the Sun, Lebedev Institute, Russia