Modulation of galactic protons in the heliosphere during the unusual solar minimum of 2006 to 2009

The last solar minimum activity period, and the consequent minimum modulation conditions for cosmic rays, was unusual. The highest levels of galactic protons were recorded at Earth in late 2009 in contrast to expectations. Proton spectra observed for 2006 to 2009 from the PAMELA cosmic ray detector on-board the Resurs-DK1 satellite are presented together with the solutions of a comprehensive numerical model for the solar modulation of cosmic rays. The model is used to determine what mechanisms were mainly responsible for the modulation of protons during this period, and why the observed spectrum for 2009 was the highest ever recorded. From mid-2006 until December 2009 we find that the spectra became significantly softer because increasingly more low energy protons had reached Earth. To simulate this effect, the rigidity dependence of the diffusion coefficients had to decrease significantly below ~3 GeV. The modulation minimum period of 2009 can thus be described as relatively more "diffusion dominated" than previous solar minima. However, we illustrate that drifts still had played a significant role but that the observable modulation effects were not as well correlated with the waviness of the heliospheric current sheet as before. Protons still experienced global gradient and curvature drifts as the heliospheric magnetic field had decreased significantly until the end of 2009, in contrast to the moderate decreases observed during previous minimum periods. We conclude that all modulation processes contributed to the observed increases in the proton spectra for this period, exhibiting an intriguing interplay of these major mechanisms

AMS-02 on the International Space Station: Recent results and perspectives

The AMS-02 (Alpha Magnetic Spectrometer) is a magnetic spectrometer built for the precision study of the energy spectrum and chemical composition of cosmic rays (CRs) in the GeV to TeV energy range. AMS-02 was installed on the ISS on May 19th 2011, and has been collecting data since then, collecting 17 billion CR triggers every year. With its large acceptance, long exposure time and excellent subdetector performance, AMS-02 can measure CRs fluxes with unprecedented precision in a wide energy range. In this contribution the main results achieved by AMS-02 in 5 years of operations will be presented and discussed

Vulnerability analysis of satellite-based synchronized smart grids monitoring systems

The large-scale deployment of wide-area monitoring systems could play a strategic role in supporting the evolution of traditional power systems toward smarter and self-healing grids. The correct operation of these synchronized monitoring systems requires a common and accurate timing reference usually provided by a satellite-based global positioning system. Although these satellites signals provide timing accuracy that easily exceeds the needs of the power industry, they are extremely vulnerable to radio frequency interference. Consequently, a comprehensive analysis aimed at identifying their potential vulnerabilities is of paramount importance for correct and safe wide-area monitoring system operation. Armed with such a vision, this article presents and discusses the results of an experimental analysis aimed at characterizing the vulnerability of global positioning system based wide-area monitoring systems to external interferences. The article outlines the potential strategies that could be adopted to protect global positioning system receivers from external cyber-attacks and proposes decentralized defense strategies based on self-organizing sensor networks aimed at assuring correct time synchronization in the presence of external attacks

Time dependence of the e^- flux measured by PAMELA during the July 2006 - December 2009 solar minimum

Precision measurements of the electron component in the cosmic radiation provide important information about the origin and propagation of cosmic rays in the Galaxy not accessible from the study of the cosmic-ray nuclear components due to their differing diffusion and energy-loss processes. However, when measured near Earth, the effects of propagation and modulation of galactic cosmic rays in the heliosphere, particularly significant for energies up to at least 30 GeV, must be properly taken into account. In this paper the electron (e^-) spectra measured by PAMELA down to 70 MeV from July 2006 to December 2009 over six-months time intervals are presented. Fluxes are compared with a state-of-the-art three-dimensional model of solar modulation that reproduces the observations remarkably well.Comment: 40 pages, 18 figures, 1 tabl

Search for anisotropies in cosmic-ray positrons detected by the PAMELA experiment

The PAMELA detector was launched on board of the Russian Resurs-DK1 satellite on June 15, 2006. Data collected during the first four years have been used to search for large-scale anisotropies in the arrival directions of cosmic-ray positrons. The PAMELA experiment allows for a full sky investigation, with sensitivity to global anisotropies in any angular window of the celestial sphere. Data samples of positrons in the rigidity range 10 GV $\leq$ R $\leq$ 200 GV were analyzed. This article discusses the method and the results of the search for possible local sources through analysis of anisotropy in positron data compared to the proton background. The resulting distributions of arrival directions are found to be isotropic. Starting from the angular power spectrum, a dipole anisotropy upper limit \delta = 0.166 at 95% C.L. is determined. Additional search is carried out around the Sun. No evidence of an excess correlated with that direction was found.Comment: The value of the dipole anisotropy upper limit has been changed. The method is correct but there was a miscalculation in the relative formul

Measurement of boron and carbon fluxes in cosmic rays with the PAMELA experiment

The propagation of cosmic rays inside our galaxy plays a fundamental role in shaping their injection spectra into those observed at Earth. One of the best tools to investigate this issue is the ratio of fluxes for secondary and primary species. The boron-to-carbon (B/C) ratio, in particular, is a sensitive probe to investigate propagation mechanisms. This paper presents new measurements of the absolute fluxes of boron and carbon nuclei, as well as the B/C ratio, from the PAMELA space experiment. The results span the range 0.44 - 129 GeV/n in kinetic energy for data taken in the period July 2006 - March 2008

Trapped proton fluxes at low Earth orbits measured by the PAMELA experiment

We report an accurate measurement of the geomagnetically trapped proton fluxes for kinetic energy above > 70 MeV performed by the PAMELA mission at low Earth orbits (350-610 km). Data were analyzed in the frame of the adiabatic theory of charged particle motion in the geomagnetic field. Flux properties were investigated in detail, providing a full characterization of the particle radiation in the South Atlantic Anomaly region, including locations, energy spectra and pitch angle distributions. PAMELA results significantly improve the description of the Earth's radiation environment at low altitudes placing important constraints on the trapping and interaction processes, and can be used to validate current trapped particle radiation models.Comment: 22 pages, 5 figure

PAMELA's measurements of geomagnetic cutoff variations during solar energetic particle events

Data from the PAMELA satellite experiment were used to measure the geomagnetic cutoff for high-energy ($\gtrsim$ 80 MeV) protons during the solar particle events on 2006 December 13 and 14. The variations of the cutoff latitude as a function of rigidity were studied on relatively short timescales, corresponding to single spacecraft orbits (about 94 minutes). Estimated cutoff values were cross-checked with those obtained by means of a trajectory tracing approach based on dynamical empirical modeling of the Earth's magnetosphere. We find significant variations in the cutoff latitude, with a maximum suppression of about 6 deg for $\sim$80 MeV protons during the main phase of the storm. The observed reduction in the geomagnetic shielding and its temporal evolution were compared with the changes in the magnetosphere configuration, investigating the role of IMF, solar wind and geomagnetic (Kp, Dst and Sym-H indexes) variables and their correlation with PAMELA cutoff results.Comment: Conference: The 34th International Cosmic Ray Conference (ICRC2015), 30 July - 6 August, 2015, The Hague, The Netherlands, Volume: PoS(ICRC2015)28

Time dependence of the proton flux measured by PAMELA during the July 2006 - December 2009 solar minimum

The energy spectra of galactic cosmic rays carry fundamental information regarding their origin and propagation. These spectra, when measured near Earth, are significantly affected by the solar magnetic field. A comprehensive description of the cosmic radiation must therefore include the transport and modulation of cosmic rays inside the heliosphere. During the end of the last decade the Sun underwent a peculiarly long quiet phase well suited to study modulation processes. In this paper we present proton spectra measured from July 2006 to December 2009 by PAMELA. The large collected statistics of protons allowed the time variation to be followed on a nearly monthly basis down to 400 MV. Data are compared with a state-of-the-art three-dimensional model of solar modulation.Comment: 17 pages, 5 figures, 1 table, to appear in Astrophysical Journal. Corrected two elements of Table