On Low Energy Cosmic Rays and Energetic Particles Near Earth K

Contrib. Astron. Obs. SkalnatéPleso 46, 15 { 70, (2016) On low energy cosmic rays and energetic particles near Earth K. Kudela Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Koˇsice, Slovakia Received: September 14, 2016 Abstract. This paper is an update of the review paper (Kudela, 2009) including selected results and activities over the past 7 years related to ground based measurements of Cosmic Rays (CR), modulation of CR by the he- liosphere, solar CR, transitional CR variations, geomagnetic filtering, energetic/suprathermal particles in the Earth's surrounding, and relations of CR to space weather effects and atmospheric processes. Key words: cosmic rays 1. Introduction In 2012 a century since the discovery of cosmic rays (CR) by Victor F. Hess (1912) was celebrated. Several reviews on CR and on history of its research were published around that anniversary (e.g. Walter and Wolfendale, 2012; Müller, 2012; Grupen 2013; de Angelis 2014; Bazilevskaya 2014; Muraki 2011; Logachev et al. 2013 among others). History of CR research is described in several books and papers. One of the recent extensive and detailed reviews is in the book (Dorman and Dorman, 2014). This paper is an attempt to update the papers (Kudela, 2009; 2012) and to include some specific parts not covered earlier. It is not an exhaustive/complete review on energetic particles in space. In the subsequent sections some of new papers published after 2009 are mentioned. Very high energy CR results are not included, and only the direct CR measurements are inserted with references. Since the main point here is CR and energetic particles in the surrounding of the Earth, there are not mentioned results from several important missions to planets and e.g. the STEREO mission. Variations on long term scales (> several tens of years) are the subject using indirect methods of CR measurements, based mainly on a cosmogenic nuclide analysis in materials exposed to CR for a long time. These topics, very useful for estimates of e.g. solar activity in the past are not included in the current review. Overviews on that can be found e.g. in papers (Gosse and Phillips, 2001; Ivy-Ochs and Kober, 2008) as well as in the books (Dunai, 2010; Beer et al., 2012). Important new results on CR were obtained from PAMELA complex instru- ments as well as by AMS-02 detectors on low altitude orbits. One of them is 16 K. Kudela the precise measurement of CR proton and He spectra at energies from those below the sensitivity of ground based measurements up to very high energies (Adriani et al. 2011; Aguilar et al. 2015). An upper limit of the antihelium flux in CR is reported by Mayorov et al. (2011). The flux of antiprotons in the energy range from 60 MeV to 350 GeV has been obtained too (Adriani et al. 2012). Electron and positron fluxes in primary CR have been reported from both ex- periments, AMS-02 and PAMELA (Aguilar et al. 2014; Adriani et al., 2016). Gusev et al. (2001), by the study of the nuclear interactions of CR in the atmosphere, suggested a source of positrons with a possibility of their trapping in the magnetosphere. Mikhailov et al. (2016) present spatial distributions of trapped, quasi-trapped and short-lived albedo electrons and positrons in the near Earth space according to PAMELA observations. In the following chapters we present a short review of selected results and sci- entific activities with references on the ground based measurements (chap.2), the heliospheric modulation of CR (chap. 3), contribution to the CR flux from solar and interplanetary acceleration (chap. 4), short term or transitional CR variations (chap.5), geomagnetic filtering of CR (chap. 6), energetic and suprathermal particles within the magnetosphere of the Earth and near its boundary regions (chap. 7), and, finally, CR relations to selected space weather effects and atmospheric processes (chap.8). 2. Measurements by neutron monitors and muon detectors After 50 years of measurements by neutron monitors (NM) at different sites, at various altitudes and for different periods of time, the network of those in- struments still remains to be an important tool for the study of primary CR variations in the rigidity range between 1 and 15 GV. History of a half of the century of measurements by NMs and of results obtained from them has been the subject of papers collected in a special issue of Advances in Space Research (Storini, 2009). In recent years new NMs have been put into operation and collection of the data has been updated. In October 2011, an NM64-type NM with a vertical cutoff rigidity of 11.2 GV started the measurements at Daejeon in Korea (Kang et al., 2012). Until 2014, 37 Forbush decreases (FDs) at Daejeon and at the position with a lower geomagnetic cut-off rigidity, namely Oulu have been reported (Kang et al., 2016). The Castilla-La Mancha neutron monitor (CaLMa) in Spain, with a vertical cut-off rigidity of 6.95 GV started its full operation in July 2012 (Medina et al., 2013; Blanco et al., 2015) and observed at least 29 FDs. A new NM with He3 tubes used for CR observatories in Chile is described by (Cordaro et al., 2012). While energy spectra and anisotropy of CR are deduced from many NMs with individual characteristics, the calibrations of NMs producing data over a long time period, is of importance (Krügerand Moraal, 2010; 2013). Semikh et al. (2012) report the NM design at Plateau de On low energy cosmic rays and energetic particles near Earth 17 Bure, France (2555 m a.s.l., in operation since 2008) and complete a numerical simulation obtaining in detail the NM detection response function for neutrons, muons, protons and pions at that altitude. The NM data processing center in Athens is introduced by Mavromichalaki et al. (2009). In addition to "classical" NMs a new design with a smaller size and weight and with rather high sensitivity, and thus being of importance for inter-calibration of NMs at different positions, namely mini neutron monitors, have been developed in past years and installed in operation (Poluianov et al., 2015; Heber et al., 2015, Krüger et al., 2015). The altitude profile has been obtained recently with a mini NM (Lara et al., 2016). Assuming different characteristics of NMs from those obtained from cosmogenic nuclides, the use of the 10Be flux to study heliospheric phenomena as an extension of NM records in the past are discussed by (Beer et al., 2013). Secondary neutrons are of interest since they contribute up to 60% to the dose from CR at flight altitudes and they are important also at high mountain positions (Rühm et al., 2009). Bonner Sphere Spectrometers (BSS) are used for monitoring neutrons at Zugspitze. Comparison with a high mountain NM and with other measurements indicates that BSS measurements could be used to monitor the flux of secondary neutrons from CR if the data are restricted to neutrons E > 20 MeV (Rühm et al., 2012). BSS measurements are compared with NM ones also at a high geomagnetic latitude (Pioch et al., 2011). Hubert (2016) described recently new high-altitude platforms operated in the Concordia stations since December 2015. By comparison with Pic-du-Midi, Pico dos Dias and the reference laboratory in Toulouse, the author reports a first neutron network dedicated to study the atmospheric radiation field based on neutron spectrometry. A BSS extended to high energies (HERMEIS) was set up at the summit of the Pic du Midi de Bigorre in the French Pyrenees (2,885 m a.s.l.; geomagnetic cutoff 5.6 GV) in May 2011 (Cheminet et al., 2013). The authors analyzed FDs and derived an analytical model to estimate the atmospheric neutron spectrum at the the site according to primary spectra depending on the solar modulation potential. Relations between the variability of the primary CR flux and that measured by NMs as well as by muon detectors is of essential interest. In addition to earlier works (e.g. Clem, 2004; Clem and Dorman, 2000; Nagashima et al., 1990; Flückiger et al., 2008 and references therein), the recalculation of the primary CR flux variations above the atmosphere deduced from those measured by NM on the ground has been checked by new computations/simulations of the yield and response functions and compared in some cases with a latitudinal profile of the count rate by NM(s) in past years. Gil et al. (2015) verified the new yield function of NM using data from the PAMELA satellite measurements of CR during 2006-2009 and the NM latitude survey in 1994-2007 including intervals with high solar activity. The authors found a very good agreement between the measured count rates of sea level NMs and the modeled ones in different conditions. Maurin et al. (2015) discuss the uncertainty for NMs related to the 18 K. Kudela yield function and to other effects. Functions useful for inferring the primary CR variability from ground based NMs and from muon detectors can be found e.g. in papers (Mishev et al., 2013; Caballero-Lopez and Moraal, 2012; Mangeard et al., 2016; Caballero-Lopez, 2016). The surrounding structure of NM is important for the count rate measured. Monte Carlo simulations of the count rate inside and outside the building with NM and the use of the calibration detector provided validation of the model of the yield functions of NMs (Aiemsa-ad et al., 2015). Lead-free NMs with different sensitivity to energies of the primary CR than usual NMs (e.g.

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