The Weibull functional form for SEP event spectra

The evolution of the kinetic energy spectra of two Solar Energetic Particle (SEP) events has been investigated through the Shannon's differential entropy during the different phases of the selected events, as proposed by [1]. Data from LET and HET instruments onboard the STEREO spacecraft were used to cover a wide energy range from ~ 4 MeV to 100 MeV, as well as EPAM and ERNE data, on board the ACE and SOHO spacecraft, respectively, in the range 1.6 ? 112 MeV. The spectral features were found to be consistent with the Weibull like shape, both during the main phase of the SEP events and over their whole duration. Comparison of results obtained for energetic particles accelerated at corotating interaction regions (CIRs) and transient-related interplanetary shocks are presented in the framework of shock acceleration

ON THE ORIGINS OF SOLAR EIT WAVES

Abstract : Approximately half of the large-scale coronal waves identified in images obtained by the Extreme-Ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory from 1997 March to 1998 June were associated with small solar flares with soft X-ray intensities below C class. The probability of a given flare of this intensity having an associated EIT wave is low. For example, of ~8,000 B-class flares occurring during this 15 month period, only 1% were linked to EIT waves. These results indicate the need for a special condition that distinguishes flares with EIT waves from the vast majority of flares that lack wave association. Various lines of evidence, including the fact that EIT waves have recently been shown to be highly associated with coronal mass ejections (CMEs), suggest that this special condition is a CME. A CME is not a sufficient condition for a detectable EIT wave, however, because we calculate that 5 times as many front-side CMEs as EIT waves occurred during this period, after taking the various visibility factors for both phenomena into account. In general, EIT wave association increases with CME speed and width

QUASI-BIENNIAL MODULATION OF GALACTIC COSMIC RAYS

The time variability of the cosmic-ray (CR) intensity at three different rigidities has been analyzed through the empirical mode decomposition technique for the period 1964-2004. Apart from the {approx}11 yr cycle, quasi-biennial oscillations (QBOs) have been detected as a prominent scale of variability in CR data, as well as in the heliomagnetic field magnitude at 1 AU and in the sunspot area. The superposition of the {approx}11 yr and QBO contributions reproduces the general features of the CR modulation, such as most of the step-like decreases and the Gnevyshev Gap phenomenon. A significant correlation has also been found between QBOs of the heliospheric magnetic field and the CR intensity during even solar activity cycles, suggesting that the former are responsible for step-like decreases in CR modulation, probably dominated by the particle diffusion/convection in such periods. In contrast, during odd-numbered cycles, no significant correlation is found. This could be explained with an enhanced drift effect also during the solar maximum or a greater influence of merged interaction regions at great heliocentric distances during odd cycles. Moreover, the QBOs of CR data are delayed with respect to sunspot activity, the lag being shorter for A > 0 periods of even cycles ({approx}1-4more » months) than for A < 0 periods of odd cycles ({approx}7-9 months); we suggest that solar QBOs also affect the recovery of the CR intensity after the solar activity maximum.« les

QUASI-BIENNIAL MODULATION OF SOLAR NEUTRINO FLUX AND SOLAR AND GALACTIC COSMIC RAYS BY SOLAR CYCLIC ACTIVITY

Using some solar activity indicators such as sunspot areas and green-line coronal emission during the period 1974-2001, we find that the quasi-biennial periodicity is a fundamental mode of solar variability. We provide evidence for the quasi-biennial modulation of the solar neutrino flux, thus supporting the hypothesis of a connection between solar neutrinos and solar magnetic fields, probably through direct interaction with the neutrino magnetic moment. The same periodic modulation has been detected when fluxes of solar energetic protons and galactic cosmic rays are investigated. These modulation results significantly correlate to that of the neutrino flux. Finally, the superposition of the quasi-biennial cycle to the eleven-year cycle can explain the Gnevyshev Gap phenomenon

Drift Effects on the Galactic Cosmic Ray Modulation

Cosmic ray (CR) modulation is driven by both solar activity and drift effects in the heliosphere, although their role is only qualitatively understood as it is difficult to connect the CR variations to their sources. In order to address this problem, the Empirical Mode Decomposition technique has been applied to the CR intensity, recorded by three neutron monitors at different rigidities (Climax, Rome, and Huancayo-Haleakala (HH)), the sunspot area, as a proxy for solar activity, the heliospheric magnetic field magnitude, directly related to CR propagation, and the tilt angle (TA) of the heliospheric current sheet (HCS), which characterizes drift effects on CRs. A prominent periodicity at ~six years is detected in all the analyzed CR data sets and it is found to be highly correlated with changes in the HCS inclination at the same timescale. In addition, this variation is found to be responsible for the main features of the CR modulation during periods of low solar activity, such as the flat (peaked) maximum in even (odd) solar cycles. The contribution of the drift effects to the global Galactic CR modulation has been estimated to be between 30% and 35%, depending on the CR particle energy. Nevertheless, the importance of the drift contribution is generally reduced in periods nearing the sunspot maximum. Finally, threshold values of ~40°, ~45°, and >55° have been derived for the TA, critical for the CR modulation at the Climax, Rome, and HH rigidity thresholds, respectively

THE GROUND-LEVEL ENHANCEMENT OF 2012 MAY 17: DERIVATION OF SOLAR PROTON EVENT PROPERTIES THROUGH THE APPLICATION OF THE NMBANGLE PPOLA MODEL

In this work, we apply an updated version of the Neutron Monitor (NM) Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model, in order to derive the characteristics of the ground-level enhancement (GLE) on 2012 May 17 (GLE71), the spectral properties of the related solar energetic particle (SEP) event, the spatial distributions of the high-energy solar cosmic ray fluxes at the top of the atmosphere, and the time evolution of the locationoftheGLEsource.Ourmodeling,baseduniquelyontheuseofground-levelNMdata,leadstothefollowing mainresults.TheSEPspectrumrelatedtoGLE71wasrathersoftduringthewholedurationoftheevent,manifesting some weak acceleration episodes only during the initial phase (at " 01:55‐02:00UT) and at " 02:30‐02:35UT and " 02:55‐03:00UT. The spectral index of the modeled SEP spectrum supports the coronal mass ejection‐shock driven particle acceleration scenario, in agreement with past results based on the analysis of satellite measurements. During the initial phase of GLE71, the solar proton source at the top of the atmosphere was located above the northernhemisphere,implyingthattheasymptoticdirectionsofviewingofthenorthernhemisphereNMsweremore favorably located for registering the event than the southern ones. The spatial distribution of the solar proton fluxes at the top of the atmosphere during the main phase manifested a large variation along longitude and latitude. At the rigidity of 1GV, the maximum primary solar protonflux resulted on the order of" 3# 10 4 part. m $2 s$ 1 sr $1 GV$ 1

Derivation of relativistic SEP properties through neutron monitor data modeling

The Ground Level Enhancement (GLE) data recorded by the worldwide Neutron Monitor (NM) network are useful resources for space weather modeling during solar extreme events. The derivation of Solar Energetic Particles (SEPs) properties through NM-data modeling is essential for the study of solar-terrestrial physics, providing information that cannot be obtained through the exclusive use of space techniques; an example is the derivation of the higher-energy part of the SEP spectrum. We briefly review how the application of the Neutron Monitor Based Anisotropic GLE Pure Power Law (NMBANGLE PPOLA) model (Plainaki et al. 2010), can provide the characteristics of the relativistic SEP flux, at a selected altitude in the Earth's atmosphere, during a GLE. Technically, the model treats the NM network as an integrated omnidirectional spectrometer and solves the inverse problem of the SEP-GLE coupling. As test cases, we present the results obtained for two different GLEs, namely GLE 60 and GLE 71, occurring at a temporal distance of ~ 11 years