The first relativistic solar particle event of the present activity cycle observed by the network of neutron monitors!

Report by Ludwig Klein and Rolf Bütikofer

Active region NOAA 11476 produced a moderately strong (GOES class M5.1) flare at 01:25 UT on 17 May 2012 (http://www.solarmonitor.org/). The active region was located at N07 W88 at the Sun. Near 01:50 UT the worldwide network of neutron monitors (NM) detected the first enhancement caused by relativistic protons from the Sun since December 2006. The flux remained above background during about one hour. Relativistic protons travel at a speed close to the speed of light. These ‘solar cosmic rays’ are the most energetic particles that can be accelerated at or near the Sun and are a rare counterpart of solar activity. The figure below shows the time profile of the NM observations provided by the NMDB network. The event is only seen by some NM stations. The highest signal was detected at South Pole (NM operated by Bartol Research Institute, Univ. of Delaware, USA). The different signatures of different instruments give important information on the energy spectrum of the solar particles and on the anisotropy of the particle flux. The first relativistic protons that reach the Earth propagate along the interplanetary magnetic field. A network of neutron monitors all over the Earth is necessary to reveal these characteristics. The fact that some NM stations do not see the event is as important as the information of the NM stations that observe a count rate increase. The combination of the data of all NM stations of the network is needed to understand the origin of the energetic particles in the solar corona.

GLE on 17 May 2012

Ground based NMs detect the secondary hadronic component. It is generated in collisions by the primary high-energy protons and ions with the atomic nuclei of the atmosphere. To know more about cosmic rays and neutron monitors, go to www.nmdb.eu (public outreach). To follow the evolution of the cosmic ray intensity, click on `Cosmic rays now’. Protons at lower energies are observed aboard spacecraft. The GOES spacecraft operated by NOAA saw a fast rise in the flux of solar protons, followed by a slower decay, which is still ongoing on 18 May 2012. Several stronger solar proton events than that of 17 May 2012 were detected by GOES in January and March 2012. The solar energetic particle event of 17 May 2012 extended to much higher energies than these earlier ones, but was weaker at lower energies. Through our research we try to understand the reason for these differences.

Report by George Souvatzoglou and Helen Mavromichalaki

NMDB co-operation aimed at the development of services which would be useful for space weather prognosis. Ground level enhancements (GLEs), which are large solar energetic particles (SEPs) serve well this necessity, as their propagation from the Sun to the Earth depends on their energy. Due to the fact that neutron monitors (NMs) record high energy particles (> 500 MeV), GLE observations make it possible to establish a forewarning Alert signal. A GLE Alert code was implemented by NKUA (Souvatzoglou et ., 2009) and was set to operate in real-time mode (Mavromichalaki et al., 2010) within NMDB. The first GLE of solar cycle 24 was spotted by this algorithm in real-time at 02:13 UT (see this thread and the figure below for details). It is noteworthy that the relevant alert was issued by GOES, based on the >100 MeV protons exceeding 1 pfu, at 02:52 UT (see here for details). For current conditions (quiet, warning, alert), consult this link. For the evolution history of the first GLE Alert of solar cycle 24, visit this link.

Real Time GLE Alert
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