New Cycle, the Sun Begins To Stretch (Planetary Science)

On July 3, at 4:29 pm Italian time, our star emitted an intense solar flare – the first of the X-class of the new solar cycle. Among the instruments that recorded it there are also those of the Swelto space weather laboratory, of INAF in Turin

After the minimum reached in 2020, the solar activity cycle ( number 25 ) is slowly restarting following its quasi-periodic trend of about 11 years . In recent months, the number of active regions on the Sun (i.e. regions with a high concentration of magnetic fields and possible sites of solar flares) has progressively increased. After some first so-called “class M” flares (of medium-high intensity), two weeks ago one of these regions produced the first “class X” (ie high intensity) solar flare of the new cycle of solar activity. The event took place in particular on 3 July, with an intensity peak at 14:29 Ut (16:29 in Italy) and a duration of about 16 minutes as measured by NASA’s Goes satellite, and was observed in particular by the Sdo probe also by NASA which, in orbit around to the Earth, it monitors the Sun 24 hours a day.

When the flare occurred, the active region was near the western edge of the Sun, in a position that could make the event more dangerous for the Earth, because the high-energy particles (the so-called Seps ) eventually accelerated in the event. they are more likely to propagate towards our planet following the spiral of the interplanetary magnetic field (called Parker’s spiral ). This is why it is important to monitor not only solar activity, but also the shape of the Parker spiral. This is reconstructed day by day by the Swelto project through a magnetohydrodynamic numerical simulation based on a model called Rimap, developed in a collaboration between the INAF of Turin and the University of Palermo. The image below shows the shape of this spiral as reconstructed in real time by Rimap for July 3 and displayed in the distribution on the ecliptic plane of the density (left) and speed (right) of the solar wind. In these figures the yellow dot shows the position of the Sun, while the blue dot (both not to scale) shows the position of the Earth.

Parker spiral reconstructed in real time with the Rimap model for 3 July. Credits: Swelto / Inaf Torino

The effects of this event also reverberated on Earth, causing a radio emission burst and a very particular geomagnetic field disturbance called magnetic crochet . This type of disturbance in the Earth’s magnetic field is observed only rarely, and has the unique characteristic of occurring not a few days after the eruptive event on the Sun, as sometimes happens when the solar eruption spreading from the Sun to the Earth finally hits our magnetosphere. On the contrary, in the case of a magnetic crochetthe disturbance on the ground occurs in immediate concomitance with the flare itself. In the case of particularly intense solar flares and with a particularly rapid increase in brightness in the X-rays, the arrival of high-energy photons (which propagate from the Sun to the Earth in just over 8 minutes) causes a sudden increase in the ionization of the high Earth’s atmosphere, the ionosphere. This causes a sudden intensification of the electric currents flowing through it, which are associated with magnetic fields which in turn disturb the earth’s field.

23.4 kHz radio signal observed by the Sid monitor in Turin on 3/7/2021. Credits: Swelto / Inaf Torino

The associated ionospheric disturbance – referred to as Sudden ionospheric disturbance, or  Sid– it was also very fast and intense, and was also observed by the Sid monitor still in operation as part of the Swelto project at the INAF in Turin. The two graphs on the side show in particular the 23.4 kHz radio signal observed by the Sid monitor in Turin on the day of the event (bottom) and for comparison also the previous day (top). In addition to the typical variation in the signal due to changes in ionospheric density between day (region in orange) and night (region in blue) and observable in both cases, the graph of July 3 shows a very evident peak around 15 Ut and due precisely to the ionospheric disturbance associated with the solar flare of the same day observed about half an hour earlier from space. The effects on Earth of this event were therefore also observed by us.

In the coming months and years, solar activity will become increasingly important, and phenomena of this type will occur with increasing frequency. The monitoring and study of the Sun continues with observations from Earth and from space, through large international projects – (such as the ESA probe and Nasa Solar Orbiter – but also with small local projects, such as Swelto, which can still make their contribution. .

To know more:

Provided by INAF

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s