A catalogue of Forbush decreases recorded on the surface of Mars from 2012 until 2016: comparison with terrestrial FDs A. Papaioannou1, A. Belov2, M. Abunina2, J. Guo3, A. Anastasiadis1, R. F. Wimmer-Schweingruber3, E. Eroshenko2, A. Melkumyan4, A. Abunin2, B. Heber3, K. Herbst3, C.T. Steigies3 1 Institute for Astronomy, Astrophysics, Space Applications and Remote Sensing (IAASARS), National Observatory of Athens, I. Metaxa & Vas. Pavlou St., GR-15236, Penteli , Greece 2 Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation (IZMIRAN), 42092 Troitsk, Moscow Region, Russia 3 Christian-Albrechts-Universität zu Kiel, Leibnizstrasse 11, 24118 Kiel, Germany p-Poster No. 29 4 Gubkin Russian State University of Oil and Gas (National Research University), Moscow, Russia Session 1

Abstract: Forbush decreases (FDs) in galactic cosmic rays (GCRs) have been recorded by neutron monitors (NMs) at Earth for more than 60 years. For the past five years, with the establishment of the Radiation Assessment Detector (RAD) on board the Mars Science Laboratory (MSL) rover Curiosity at Mars, it is possible to continuously detect, for the first time, FDs at another planet: Mars. In this work, we have compiled a catalogue of 424 FDs at Mars using RAD dose rate data, from 2012 to 2016. Furthermore, we applied a comparative statistical analysis of the FDs measured at Mars, by RAD, and at Earth, by NMs, for the same time span. One should note, though, that the Martian atmosphere shields away most of the GCRs protons that have energies < 150 MeV. This cutoff is lower than the atmospheric cutoff at Earth (~ 450 MeV) and the definite energy of 9.1 GeV that corresponds to the rigidity of 10 GV, used for the FDs at Earth in this study. A carefully chosen sample of FDs at Earth and at Mars, driven by the same ICME, led to a significant correlation (cc=0.71) and a linear regression between the sizes of the FDs at the different observing points, for the respective energies. We, further, show that the amplitude of the FD at Mars (for E>150 MeV) is higher by a factor of 1.5-2 compared to the size of the FD at Earth for (E=9.1 GeV). Finally, almost identical regressions were obtained for both Earth and Mars as concerns the dependence of the maximum hourly decrease of the CR density to the size of the FD. After S. Forbush Forbush decreases (1904-1984) A database of FD @Mars (RAD measurements)

 Forbush Decreases (FDs) are short FD > Observations of GCRs during Forbush term (≤ few days) depressions of the FD decreases from MSL/RAD @Mars surface Galactic Cosmic Ray (GCR) intensity. FD are comparable to those made @Earth B based neutron monitors.  FDs are: - not a local phenomenon but an > A new database of FDs recorded on the B interplanetary one surface of Mars has been compiled. It - of worldwide scale (simultaneously enables the scientific exploitation and measured) further usage of the novel MSL/RAD data -driven by Interplanetary Coronal Mass Figure 1. The first (ever) Forbush decrease(s). The points corresponds to the actual measurements of GCRs at by the scientific community. Ejections (ICMEs) [Non-recurrent FDs] or Huancayo and Cheltenham. The line that goes through Co-rotating Interaction Regions (CIRs) the points corresponds to GCRs at Hafelekar. The thin [Recurrent FDs] black line corresponds to the magnetic field. Richardson, AMS Conference, 2015 Forbush, Phys. Rev. 51, 1108, 1937 Figure 4. WSA-ENLIL model simulation of the ICME on January 2014 (top panel) and the resulting FDs at Non-recurrent FDs Recurrent FDs Mars and Earth (bottom panel).

Richardson & Cane, Solar Physics, 2011 Richardson, Space Science Reviews, 2004 Statistical analysis l FD @Mars (RAD) and @Earth > Schematic representation of CH GCR Variations > Distribution of FDs at Mars [mean and along trajectories median amplitude (in %) is 3.17 and 2.74] that do (A) or do not (B) encounter the ICME > Distribution of FDs at Earth [mean and

median amplitude (in %) is 1.43 and 1.10

Figure 5. Distribution of the size of Forbush decreases observed in 2012-2016 at Earth (orange colour Figure 2. GCR Figure 3. GCR histograms) and at Mars (blue coral colour histograms). Variations (non- Variations recurrent FD) (Recurrent - FD) > Martian and terrestrial FDs are along trajectory resulting from surprisingly well matched (A) and related the effect of a in-situ plasma CIR. . signatures . AM = (0.47 ± 0.07) + ( - 3.64 ± 0.32) Dmin

. AE = (0.20 ± 0.03) + ( - 3.69 ± 0.16) Dmin

Figure 6. The relation between the maximal hourly decrease in the CR density (Dmin) and the total size of the Forbush decrease

Richardson & Cane, Solar Physics, 2011

Forbush decreases l Measurements > The magnitude of the FD at Earth (AE) to the one at Mars (AM) has a correlation @ Mars MSL/RAD coefficient of cc=0.71. @ Earth Neutron Monitors Since 2012 Since 1950’s > RAD is an energetic particle > The obtained linear regression has the detector designed to measure . following expression: AM = (1.07 ± 0.24) AE > NMs are ground based galactic cosmic rays, solar + (1.70 ± 0.30) energetic particles, secondary detectors that measure galactic cosmic rays, neutrons, and other secondary and solar cosmic rays particles. Figure 7. Relation of the magnitudes for FDs caused by the same interplanetary disturbances on Earth and on Mars. (high energy [E≥433 MeV] solar energetic > RAD contains six detectors, particles). three of which (A, B, and C) are Conclusions silicon diodes arranged as a telescope. The other three (D, E, > FDs at Mars and Earth have almost identical dependencies of the values of the and F) are scintillators. maximum hourly decrease of the CR density (Dmin) to the size of the FD. > The mean amplitude of the identified FDs at Mars is 3.17%. > Dose rates are measured in > A significant correlation (cc=0.71) and a linear regression between the sizes of the FDs both silicon and plastic detectors Simpson, Space Science Rev., 2000 www.nmdb.eu Hassler et al., Space Science Rev., 2012 at the different observing points was obtained. Related papers: Guo et al., Astron. Astrophys., A79, 611, 2018 Papaioannou et al., Solar Physics, 2018 (under review) Acknowledgement: Contact: [email protected] We acknowledge the NMDB database (www.nmdb.eu), founded under the European Union's FP7 programme (contract no. 213007) for providing data.