Aims. Magnetic clouds are large interplanetary flux ropes that propagate in the solar wind from the Sun and that expand during their propagation. We check how magnetic cloud models, represented by cylindrical magnetic flux ropes, which include expansion, correspond to in situ observations.Methods. Spacecraft measurements of magnetic field and velocity components inside magnetic clouds with clearly expressed expansion are studied in detail and fit by models. The models include expanding cylindrical linear force-free flux ropes with circular or elliptic cross sections.Results. From the period of 1995-2009, 26 magnetic clouds were tit by the force-free model of an expanding circular cylindrical flux rope. Expansion velocity profiles qualitatively correspond to model ones in the majority of cases (81%) and quantitatively in more than half of them (587). In four cases an elliptic cross section significantly improved a match between observed and modeled expansion velocity profiles.Conclusions. Analysis of velocity components tests magnetic cloud models more strictly and may reveal information on magnetic cloud shapes.

Ultra-High Energy Cosmic Rays (UHECR) (E ≥ 5 × 1019 eV ) are detected through Extensive Air Showers that are created when a primary cosmic ray particle interacts with the atmosphere of the Earth. The energy of the primary particle can be estimated experimentally based on simulations. In this paper, we attempt to estimate the energy of UHECR gamma ray photons by applying a Monte Carlo simulation code and we compare the results with the ones derived in our previous papers for hadron initiated showers. The scenario of simulations is adapted to the P. Auger Observatory site.

Energy is among the characteristics of Ultra High Energy Cosmic Rays (E > 5 ×10 19 eV ) which could be estimated experimentally based on simulations. This paper attempts to estimate the energy of an UHECR proton by applying a Monte Carlo simulation code. A number of extensive air showers, vertical and inclined, are simulated to derive the lateral distribution functions of the shower particles. The scenario of simulations is adapted to the P. Auger Observatory site.

Magnetic clouds are important objects for space weather forecasters due to their impact on the Earth's magnetosphere and their consequences during geomagnetic storms. Being considered as cylindrical or toroidal flux ropes, their size, velocity, magnetic field strength, and axis orientation determine its impact on Earth. Above mentioned parameters are usually extracted from model fits using measurements from one-spacecraft crossings of these structures. In order to relate solar events with these spacecraft observations, the parameters are then compared to situation at the Sun around a most probable source region with a goal to correlate them with near-Sun observed quantities for prediction purposes. In the past we performed three-dimensional simulations of magnetic cloud propagation in the inner heliosphere. Simulated spacecraft measurements are fitted by models of magnetic clouds and resulting parameters are compared with real shapes of magnetic clouds which can be directly obtained from our simulations. The comparison shows that cloud parameters are determined quite reliably for spacecraft crossings near the cloud axis.

Magnetic clouds are supposed to be large interplanetary flux ropes propagating away from the Sun.Due to enhanced inner magnetic pressure, they expand during their travel.We have analyzed 21 magnetic clouds from Wind observations and fitted them by our model.Comparison of the time-dependent model with observations is shown for several cases with a detailed discussion.The model describes behavior of compared quantities satisfactorily.In addition to magnetic field vectors, also velocity vectors were modeled and it was found that radial velocity component behaves as expected.Analysis of velocity components put models under a more strict test and yields more confidence into models and derived magnetic cloud parameters.

Recent observations by the H.E.S.S. collaboration of the Galactic Centre region have revealed what appears to be γ-ray emission from the decay of pions produced by interactions of recently accelerated cosmic rays with local molecular hydrogen clouds. Synthesizing a 3D hydrogen cloud map from the available data and assuming a diffusion coefficient of the form κ(E) = κ0(E/E0)δ, we performed Monte Carlo simulations of cosmic ray diffusion for various propagation times and values of κ0 and δ. By fitting the model γ-ray spectra to the observed one we were able to infer the value of the diffusion coefficient in that environment (κ = 3.0 ± 0.2 kpc2 Myr−1 for E = 1012.5 eV and for total propagation time 104 yr) as well as the source spectrum (2.1 ⩽ γ ⩽ 2.3). Also, we found that proton losses can be substantial, which justifies our approach to the problem.

We report observations of solar energetic particles obtained by the HI-SCALE and COSPIN/LET instruments onboard Ulysses during the period of isolated but intense solar activity in 2006 December, in the declining phase of the solar activity cycle. We present measurements of particle intensities and also discuss observations of particle anisotropies and composition in selected energy ranges. Active Region 10930 produced a series of major solar flares with the strongest one (X9.0) recorded on December 5 after it rotated into view on the solar east limb. Located over the South Pole of the Sun, at >72°S heliographic latitude and 2.8 AU radial distance, Ulysses provided unique measurements for assessing the nature of particle propagation to high latitudes under near-minimum solar activity conditions, in a relatively undisturbed heliosphere. The observations seem to exclude the possibility that magnetic field lines originating at low latitudes reached Ulysses, suggesting either that the energetic particles observed as large solar energetic particle (SEP) events over the South Pole of the Sun in 2006 December were released when propagating coronal waves reached high-latitude field lines connected to Ulysses, or underwent perpendicular diffusion. We also discuss comparisons with energetic particle data acquired by the STEREO and Advanced Composition Explorer in the ecliptic plane near 1 AU during this period.

Ulysses, the first spacecraft ever to fly over the poles of the Sun, plays a central role in the Heliospheric Network, the international fleet of spacecraft to explore the Sun and Heliosphere. In No- vember 2006, Ulysses began its passage over the Sun's south pole for the third time. Although like during the first polar passes in 1994/1995 the Sun is again close to its activity minimum, an unex- pected rise of solar activity occurred in December 2006. Active Region 0930 produced a series of ma- jor solar flares with the strongest one (X9.0) recorded on December 5 after it rotated into view on the solar east limb. We present energetic particle observations by Ulysses located at >70 deg south heli- olatitude during this period and discuss their implications for particle propagation to solar polar re- gions. The observed events are also compared with previous Ulysses high latitude measurements ob- tained close to solar maximum. Furthermore, comparisons with data acquired from ACE - another spacecraft of the Heliospheric Network - near the ecliptic plane are discussed.

We report recent observations of energetic particles at energies 1–40 MeV/n made by the COSPIN/LET instrument onboard the Ulysses spacecraft during the period of intense solar activity in August/September 2005 during the declining phase of solar cycle 23. Ulysses, having started its climb to high southern latitudes for the third time, was located at ~5 AU, at a helio-latitude of ~30 degrees south. It detected the arrival of a solar wind compound stream resulting from the merging of a series of fast halo CMEs ejected from the Sun in late August and early September 2005 and their interaction with the pre-existing pattern of solar wind Stream Interaction Regions (SIRs) in the ambient medium through which they propagated. The heavy ion intensities are observed by COSPIN/LET to remain elevated for at least 20 days following the very intense X17.0/3B solar flare on 7 September and its associated very fast CME (plane of sky projected CME speed ~2400 km s−1). We carry out an analysis of the composition of the particle increases observed at the location of the spacecraft. Although the composition signatures were predominantly Solar Energetic Particle (SEP)-like, after the passage of the compound stream over Ulysses, in association with a characteristic forward and reverse shock pair, the observations showed evidence of an enhanced He content.

The efficiency of a pixel detector using optical UV filters is determined in this work. Based on the Auger fluorescence detector geometry, we have calculated the overall efficiency of the pixel detector using an appropriate method that takes into account the particular spectral functions and the dependence on the angle of incidence of the optical filter used. Assuming extensive air shower (EAS) events developed with various inclinations generated by AIRES code, we calculated the number of electrons and positrons produced during the development of the EAS's. The detection efficiency of the pixel detector is taken into account in estimating the recorded signal (number of photoelectrons) for two sets of EAS simulations, corresponding to protons and iron nuclei, as primary particles.

Diffuse VHE gamma radiation from the Galactic Centre ridge observed by the H.E.S.S. telescope has been convincingly linked with the propagation of recently accelerated cosmic rays that interact with molecular hydrogen clouds during their diffusion. Through a series of time-dependent simulations of that diffusion for different propagation parameters we have obtained the most probable values of the diffusion coefficient for the Galactic Centre region. Assuming that the diffusion coefficient is of the form kappa(E) = kappa_0*(E/E_0)^delta, then for different optimal combinations of kappa_0 and delta its value is obtained for cosmic rays originating from a central point (possibly Sgr A East) 10 kyr ago.

The energy is among the characteristics of Ultra High Energy Cosmic Rays (E>5 x 1019 eV) which could be estimated experimentally. The following paper attempts to estimate the energy of an UHECR proton by applying a Monte Carlo simulation code. A number of extensive air showers, vertical and inclined, is simulated to derive the Lateral Distribution Functions of the shower muons. The scenario of simulations is adopted to the Cerenkov surface detector of the P. AUGER Observatory. Due to the fact that the Lateral Distribution Functions show minimal fluctuations of the muon density at a distance larger than 800 m from the core of the showers, and due to the fact that at a distance of 900 m the distribution functions for inclined showers coincide (which means that it does not change with the zenith angle of the showers), we select the muon density at 900 m to derive the energy of the primary protons. (The project is co-funded by the European Social Fund and National Resources (EPEAEK II) PYTHAGORAS II.)

We report recent observations of energetic parti- cles at energies 1-40 MeV/n made by the COSPIN/LET in- strument onboard the Ulysses spacecraft during the period of intense solar activity in August/September 2005 during the declining phase of solar cycle 23. Ulysses, having started its climb to high southern latitudes for the third time, was lo- cated at 5 AU, at a helio-latitude of 30 degrees south. It detected the arrival of a solar wind compound stream result- ing from the merging of a series of fast halo CMEs ejected from the Sun in late August and early September 2005 and their interaction with the pre-existing pattern of solar wind Stream Interaction Regions (SIRs) in the ambient medium through which they propagated. The heavy ion intensities are observed by COSPIN/LET to remain elevated for at least 20 days following the very intense X17.0/3B solar flare on 7 September and its associated very fast CME (plane of sky projected CME speed 2400 km s 1 ). We carry out an anal- ysis of the composition of the particle increases observed at the location of the spacecraft. Although the composition sig- natures were predominantly Solar Energetic Particle (SEP)- like, after the passage of the compound stream over Ulysses, in association with a characteristic forward and reverse shock pair, the observations showed evidence of an enhanced He content.

Abstract We present unique observations obtained by the Magnetospheric Imaging Instrument (MIMI) on the Cassini spacecraft, of the energetic ion population in the environment upstream from the dawn-to-noon sector of the Kronian magnetosphere during the approach phase and subsequent several orbits of the Cassini spacecraft around the planet. High sensitivity observations of energetic ion directional intensities, energy spectra, and ion composition were obtained by the Ion and Neutral Camera (INCA) of the MIMI instrument complement with a geometry factor of ~2.5 cm2sr. Charge state information was provided by the Charge-Energy-Mass-Spectrometer (CHEMS) over the range ~3 to 220 keV per charge. The observations revealed the presence of distinct upstream bursts of energetic hydrogen and oxygen ions up to distances of ~135 RS. The observations are presented and their theoretical implications are addressed.

Data from the Pierre Auger Observatory are analyzed to search for anisotropies near the direction of the Galactic Centre at EeV energies. The exposure of the surface array in this part of the sky is already significantly larger than that of the fore-runner experiments. Our results do not support previous findings of localized excesses in the AGASA and SUGAR data. We set an upper bound on a point-like flux of cosmic rays arriving from the Galactic Centre which excludes several scenarios predicting sources of EeV neutrons from Sagittarius A. Also the events detected simultaneously by the surface and fluorescence detectors (the `hybrid' data set), which have better pointing accuracy but are less numerous than those of the surface array alone, do not show any significant localized excess from this direction.

We present recent energetic particle measurements from 1–20 MeV/n recorded by the Ulysses/COSPIN/LET instrument from mid‐October to the end of November 2003 and from May 2004 to the end of February 2005. Long‐lasting periods with enhanced solar activity occurred during the declining phase of the current solar cycle contributing to the high‐intensity particle events and heavy ion signatures observed by Ulysses near the ecliptic plane, at ∼5 AU from the Sun. The energetic particles injected from the Sun during the January 2005 intense solar activity were not observed at Ulysses until a stream interface that acted as a barrier for the particles reached the spacecraft. Our observations during this period thus show that the propagation of energetic particles is largely governed by the existence of large‐scale solar wind structures that impede the transport of the particles. We use the elemental composition of the particle fluxes recorded by COSPIN/LET to gain insight into the possible origin of the particle events. We study and provide a possible interpretation of the composition signatures observed at ∼5 AU during periods of CME/CIR combinations. Although predominantly SEP‐like, the observed composition showed evidence for enhancements in He, which we suggest is of interstellar origin, consistent with CIR shocks accelerating ions from multiple sources.

Ulysses, the first spacecraft ever to fly over the poles of the Sun, plays a central role in the Heliospheric Network, the international fleet of spacecraft to explore the Sun and Heliosphere. In No- vember 2006, Ulysses began its passage over the Sun's south pole for the third time. Although like during the first polar passes in 1994/1995 the Sun is again close to its activity minimum, an unex- pected rise of solar activity occurred in December 2006. Active Region 0930 produced a series of ma- jor solar flares with the strongest one (X9.0) recorded on December 5 after it rotated into view on the solar east limb. We present energetic particle observations by Ulysses located at >70 deg south heli- olatitude during this period and discuss their implications for particle propagation to solar polar re- gions. The observed events are also compared with previous Ulysses high latitude measurements ob- tained close to solar maximum. Furthermore, comparisons with data acquired from ACE - another spacecraft of the Heliospheric Network - near the ecliptic plane are discussed.