Unusual decrease of the cosmic ray intensity in May 2019 on the background of the minima solar activity

In May 2019 there was a long and sloping decreasing of cosmic ray’s intensity (up to ~4%), which was observed on neutron monitors. Despite this was a small decreasing compared to quasi-eleven-period variation, it stands out well in 24th cycle of solar activity. According to LASCO/SOHO and STEREO-A data from spectrometer in different UHF bands and from coronograph, there was a series of CMEs which affected on modulation of cosmic rays by creating a series of Forbush decrea - sing, which didn’t restore. This series was connected to two active regions on sun and began on April 30 from “reversed halo” CME. This CME didn’t reach the earth, but led to significant additional modulation of cosmic rays, mostly on east side. Later there was a series of smaller CMEs on May 1-6, which also didn’t reach the earth, but were gradually approaching to Earth. Recent CMEs on 8-9 and 12-13 created a normal Forbush decreasing. In May 2019, cosmic rays shown again, that they can collect information about distant objects of geliosphere and transmit it to Earth. The ground-level detectors sometimes can observe an interaction of interplanetary distur- bances, which didn‘t reach the earth. East CMEs are especially effective, because they closing magnetic field lines beyond the orbit of earth and can interfere the restoring of cosmic ray’s intensity.

Radiation environment in the interplanetary space and Mars orbit during the declining phase of 24th solar cycle and transition to 25th cycle according measurements aboard ExoMars TGO

<p>Radiation environment in the interplanetary space and Mars orbit during the declining phase of 24th solar cycle and transition to 25th cycle according measurements aboard ExoMars TGO</p><p>Jordanka Semkova1, Rositza Koleva1, Victor Benghin3, Krasimir Krastev1, Tsvetan Dachev1, Yuri Matviichuk1, Borislav Tomov1, Stephan Maltchev1, Plamen Dimitrov1, Nikolay Bankov1, Igor Mitrofanov2, Alexey Malakhov2, Dmitry Golovin2, Maxim Mokrousov2, Anton Sanin2, Maxim Litvak2, Maya Djachkova2, Sergey Nikiforov2, Denis Lisov2, Artem Anikin2, Vyacheslav Shurshakov<sup>3</sup>, Sergey Drobyshev<sup>3</sup></p><p> </p><p><sup>1</sup>Space Research and Technology Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria, [email protected]</p><p><sup>2</sup>Space Research Institute, Russian Academy of Sciences, Moscow, Russia, [email protected]</p><p><sup>3</sup>State Scientific Center of Russian Federation, Institute of Biomedical Problems, Russian Academy of Sciences, Moscow, Russia, [email protected]</p><p> </p><p>The dosimetric telescope Liulin-MO for measuring the radiation environment is a module of the Fine Resolution Epithermal Neutron Detector (FREND) onboard the ExoMars TGO.</p><p>Here we present results from measurements of the charged particle fluxes, dose rates and estimation of radiation quality factors and dose equivalent rates at ExoMars TGO science orbit (circular orbit with 400 km altitude, 74<sup>0 </sup>inclination, 2 hours orbit period), provided by Liulin-MO from May 01, 2018 to January 10, 2021.</p><p>The obtained data show that: an increase of the dose rates and fluxes is observed from May 2018 to February 2020 which corresponds to the increase of galactic cosmic rays (GCR) intensity during the declining of the solar activity in 24th solar cycle; From March to August 2020 the measured radiation values are practically equal, corresponding to the minimum of 24th cycle and transition to 25th cycle. The highest values of the dose rate (15.5/16.2 µGy h-1 at two perpendicular directions) and particle flux (3.24/3.33 cm-2s-1 at two perpendicular directions) are registered in this period; Since September 2020 a decrease of the dose rates and fluxes is observed, corresponding to the decrease of GCR intensity during the inclination phase of the 25th cycle.</p><p>The cosmic ray fluxes and doses measured in Mars orbit are recalculated into values meaningful for the deep interplanetary space at about 1.5 AU. The flux in the free space is at least 3.68 cm-2s-1 and the dose rate is 18.9 µGy h-1 in August 2020. The results demonstrate that the radiation conditions in the interplanetary space worsen in the minimum of the solar activity in 24th cycle compared to the previous solar minimum.</p><p>Liulin-MO charged particles measurements are compared for completeness to similar measurements performed by FREND neutron detectors: the instrument’s 3He neutron detectors are also a source of charged particles flux signal that can be used for correlation.</p><p>The results are of importance for benchmarking of the space radiation environment models and for assessment of the radiation risk to future manned missions to Mars.</p><p>Acknowledgements</p><p>The work in Bulgaria is supported by Project No 129 (KP-06 Russia 24) for bilateral projects of the National Science Fund of Bulgaria and Russian Foundation for Basic Research. The work in Russia is supported by Grant 19-52-18009 for bilateral projects of the National Science Fund of Bulgaria and Russian Foundation for Basic Research.</p>

From Hector Mine M7.1 to Ridgecrest M7.1 Earthquake. A Look from a 20-Year Perspective

The paper provides a comparative analysis of precursory phenomena in the ionosphere and atmosphere for two strong earthquakes of the same magnitude M7.1 that happened in the same region (North-East from Los Angeles) within a time span of 20 years, the Hector Mine and Ridgecrest earthquakes. Regardless of the similarity of their location (South-Eastern California, near 160 km one from another), there was one essential difference: the Hector Mine earthquake happened during geomagnetically disturbed conditions (essential in the sense of ionospheric precursors identification). In contrast, the quiet geomagnetic conditions characterized the period around the time of the Ridgecrest earthquake. The Hector mine earthquake happened in the middle of the rising phase of the 23-rd solar cycle characterized by high solar activity, while the Ridgecrest earthquake happened by the very end of the 24th cycle under very low solar activity conditions. We provide a comprehensive multi-factor analysis, determine the precursory period for both earthquakes and demonstrate the close similarity of ionospheric precursors. Unlike the majority of papers dealing with earthquake precursor identification based on the “abnormality” of observed time-series mainly determined by amplitude difference between “normal” (usually climatic) behavior and “abnormal” behavior with amplitudes exceeding some pre-established threshold, we used the technique of cognitive recognition of the precursors based on the physical mechanisms of their generation and the morphology of their behavior during the precursory period. These permits to uniquely identify precursors even in conditions of disturbed environment as it was around the time of the Hector Mine earthquake. We demonstrate the close similarity of precursors’ development for both events. The leading time of precursor appearance for the same region and similar magnitude was identical. For the Hector Mine it was 11 October 1999—5 days in advance—and for 2019 Ridgecrest it was 28 June—7 days before the mainshock and five days before the strongest foreshock.