Study on solar sources and polar cap absorption events recorded in Antarctica

Particularly intense events occurred on the Sun in a period around minimum of solar activity during cycle 23. We investigated the characteristics of September 2005 and December 2006 events and the properties of the correlated observations of ionospheric absorption, obtained by a 30 MHz riometer installed at Mario Zucchelli Station (MZS-Antarctica), and of geomagnetic activity recorded at Scott Base (Antarctica). Solar events are studied using the characteristics of CMEs measured with SoHO/LASCO coronagraphs and the temporal evolution of solar energetic protons in different energy ranges measured by GOES 11 spacecraft.     

Launch and commissioning of the PAMELA experiment on board the Resurs-DK1 satellite

PAMELA is a satellite borne experiment designed to study with great accuracy cosmic rays of galactic, solar, and trapped nature in a wide energy range (protons: 80 MeV–700 GeV, electrons 50 MeV–400 GeV). Main objective is the study of the antimatter component: antiprotons (80 MeV–190 GeV), positrons (50 MeV–270 GeV) and search for antimatter (with a precision of the order of 10⁻⁸). The experiment, housed on board the Russian Resurs-DK1 satellite, was launched on June, 15th 2006 in a 350 × 600 km orbit with an inclination of 70°. The detector consists of a permanent magnet spectrometer core to provide rigidity and charge sign information, a Time-of-Flight system for velocity and charge information, a silicon–tungsten calorimeter and a neutron detector for lepton/hadron identification. An anticounter system is used off-line to reject false triggers coming from the satellite. In self-trigger mode the calorimeter, the neutron detector and a shower tail catcher are capable of an independent measure of the lepton (e⁺ + e⁻) component up to 2 TeV. In this work we focus on the first months of operations of the experiment during the commissioning phase.     

Evolution of magnetic fields and cosmic ray acceleration in supernova remnants

Observations show that the magnetic field in young supernova remnants (SNRs) is significantly stronger than can be expected from the compression of the circumstellar medium (CSM) by a factor of four expected for strong blast waves. Additionally, the polarization is mainly radial, which is also contrary to expectation from compression of the CSM magnetic field. Cosmic rays (CRs) may help to explain these two observed features. They can increase the compression ratio to factors well over those of regular strong shocks by adding a relativistic plasma component to the pressure, and by draining the shock of energy when CRs escape from the region. The higher compression ratio will also allow for the contact discontinuity, which is subject to the Rayleigh–Taylor (R–T) instability, to reach much further out to the forward shock. This could create a preferred radial polarization of the magnetic field. With an Adaptive Mesh Refinement MHD code (AMRVAC), we simulate the evolution of SNRs with three different configurations of the initial CSM magnetic field, and look at two different equations of state in order to look at the possible influence of a CR plasma component. The spectrum of CRs can be simulated using test particles, of which we also show some preliminary results that agree well with available analytical solutions.     

Fluctuations of cosmic rays and IMF in the vicinity of interplanetary shocks

Fluctuations of cosmic rays and interplanetary magnetic field upstream of interplanetary shocks are studied using data of ground-based polar neutron monitors as well as measurements of energetic particles and solar wind plasma parameters aboard the ACE spacecraft. It is shown that coherent cosmic ray fluctuations in the energy range from 10 keV to 1 GeV are often observed at the Earth’s orbit before the arrival of interplanetary shocks. This corresponds to an increase of solar wind turbulence level by more than the order of magnitude upstream of the shock. We suggest a scenario where the cosmic ray fluctuation spectrum is modulated by fast magnetosonic waves generated by flux of low-energy cosmic rays which are reflected and/or accelerated by an interplanetary shock.     

The charge-sign dependent effect in the solar modulation of cosmic rays

The centennial anniversary of the discovery of cosmic rays was in 2012. Since this discovery considerable progress has been made on several aspects related to galactic cosmic rays in the heliosphere. It is known that they encounter a turbulent solar wind with an imbedded heliospheric magnetic field when entering the Sun’s domain. This leads to significant global and temporal changes in their intensity inside the heliosphere, a process known as the solar modulation of cosmic rays. The prediction of a charge-sign dependent effect in solar modulation in the late 1970s and the confirmatory observational discoveries can also be considered as a milestone. A short review is given of these predictions based on theoretical and numerical modelling work, the observational confirmation and related issues.     

Long-term (50 years) measurements of cosmic ray fluxes in the atmosphere

Since the middle of 1957 till present time the group of researchers of P.N. Lebedev Physical Institute of the Russian Academy of Sciences has carried out the regular balloon borne measurements of charged particle fluxes in the atmosphere. The measurements are performed at polar (northern and southern) and middle latitudes and cover the interval of heights from the ground level up to 30–35 km. Standard detectors of particles (gas-discharged counters) have been used. More than 80,000 measurements of cosmic ray fluxes in the atmosphere have been performed to the present time. In the data analysis the geomagnetic field and the Earth’s atmosphere are used as cosmic ray spectrometers.     

Detection of the high energy component of Jovian electrons in Low Earth Orbit with the PAMELA experiment

The PAMELA experiment is devoted to the study of cosmic rays in Low Earth Orbit with an apparatus optimized to perform a precise determination of the galactic antimatter component of c.r. It is constituted by a number of detectors built around a permanent magnet spectrometer. PAMELA was launched in space on June 15th 2006 on board the Russian Resurs-DK1 satellite for a mission duration of 3 years. The characteristics of the detectors, the long lifetime and the orbit of the satellite, will allow to address several aspects of cosmic-ray physics. In this work we discuss the observational capabilities of PAMELA to detect the electron component above 50 MeV. The magnetic spectrometer allows a detailed measurement of the energy spectrum of electrons of galactic and Jovian origin. Long term measurements and correlations with Earth–Jupiter 13 months synodic period will allow to separate these two contributions and to measure the primary electron Jovian component, dominant in the 50–70 MeV energy range. With this technique it will also be possible to study the contribution to the electron spectrum of Jovian e⁻ reaccelerated up to 2 GeV at the Solar Wind Termination Shock.     

The scaler mode in the Pierre Auger Observatory to study heliospheric modulation of cosmic rays

The impact of the solar activity on the heliosphere has a strong influence on the modulation of the flux of low energy galactic cosmic rays arriving at Earth. Different instruments, such as neutron monitors or muon detectors, have been recording the variability of the cosmic ray flux at ground level for several decades. Although the Pierre Auger Observatory was designed to observe cosmic rays at the highest energies, it also records the count rates of low energy secondary particles (the scaler mode) for the self-calibration of its surface detector array. From observations using the scaler mode at the Pierre Auger Observatory, modulation of galactic cosmic rays due to solar transient activity has been observed (e.g., Forbush decreases). Due to the high total count rate coming from the combined area of its detectors, the Pierre Auger Observatory (its detectors have a total area greater than 16,000 m²) detects a flux of secondary particles of the order of ∼10⁸ counts per minute. Time variations of the cosmic ray flux related to the activity of the heliosphere can be determined with high accuracy. In this paper we briefly describe the scaler mode and analyze a Forbush decrease together with the interplanetary coronal mass ejection that originated it. The Auger scaler data are now publicly available.     

Fluxes and nuclear abundances of cosmic rays inside the magnetosphere using a transmission function approach

At 1 AU and outside the Earth’s magnetosphere, the relative abundances to protons for He (He/p), C (C/p) and Fe (Fe/p) nuclei were calculated using the observation data of AMS-01 (for p and He) and HEAO-3 (for C and Fe) above 0.8 GeV/nucleon. In addition, the transmission function (TF) for the GCR propagation inside the magnetosphere was evaluated using the IGRF and T96 (introduced by Tsyganenko and Stern) models to obtain permitted and forbidden trajectories inside the magnetosphere. The TF allowed one to derive the primary He-nuclei fluxes in the same geomagnetic regions of AMS-01 observations. These fluxes were found in good agreement with the observation data. Furthermore inside the magnetosphere in addition to the flux of helium, it allowed one to obtain those of the primary p, C, and Fe nuclei and the relative abundances of He, C and Fe nuclei to protons from the same observation data of AMS-01 and HEAO-3 above ≈0.8 GeV/nucleon. Up to a geomagnetic latitude of ≈45.84°, the relative isotopic abundances were found to depend on the mass number I_isot and, on average, range from a factor ≈2.31 up to ≈3.35 larger than those outside the magnetosphere at 1 AU. Thus, the magnetospheric isotopic/nuclear relative abundances differ from those inside the solar cavity and those in the interstellar space. The usage of the TF approach can allow one to determine the nuclear abundances in the magnetosphere at any geomagnetic latitude and, thus, any orbit, provided that the CR spectra are determined at 1 AU.     

Sawtooth substorms generated under conditions of the steadily high solar wind energy input into the magnetosphere: Relationship between PC, AL and ASYM indices

Periodicity in occurrence of magnetic disturbances in polar cap and auroral zone under conditions of steady and powerful solar wind influence on the magnetosphere is analyzed on the example of 9 storm events with distinctly expressed sawtooth substorms (N = 48). Relationships between the polar cap magnetic activity (PC-index), magnetic disturbances in the auroral zone (AL-index) and value of the ring current asymmetry (ASYM index) were examined within the intervals of the PC growth phase and the PC decline phase inherent to each substorm. It is shown that the substorm sudden onsets are always preceded by the PC growth and that the substorm development does not affect the PC growth rate. On achieving the disturbance maximum, the PC and AL indices are simultaneously fall down to the level preceding the substorm, so that the higher the substorm intensity, the larger is the AL and PC drop in the decline phase. The ASYM index increases and decreases in conformity with the PC and AL behavior, the correlation between ASYM and PC being better than between ASYM and AL. Level of the solar wind energy input into the magnetosphere determines periodicity and intensity of disturbances: the higher the coupling function E_KL, the higher is substorm intensity and shorter is substorm length. Taking into account the permanently high level of auroral activity and inconsistency of aurora behavior and magnetic onsets during sawtooth substorms, the conclusion is made that auroral ionosphere conductivity is typically high and ensures an extremely high intensity of field-aligned currents in R1 FAC system. The periodicity of sawtooth substorms is determined by recurrent depletions and restorations of R1 currents, which are responsible for coordinated variations of magnetic activity in the polar cap and auroral zone.     

A statistical analysis of low frequency geomagnetic field pulsations at two Antarctic geomagnetic observatories in the polar cap region

The aim of this study is to investigate the characteristics of low frequency (∼0.5–5 mHz) geomagnetic field fluctuations as recorded at two Antarctic stations within the polar cap: the Italian observatory Mario Zucchelli Station (TNB) and the French–Italian observatory Dome C (DMC) in order to investigate the spatial extension and propagation characteristics of the phenomena observed at very high latitude. The stations have approximately the same geographic latitude, but a very different corrected geomagnetic latitude, being DMC close to the geomagnetic pole and TNB closer to the auroral oval.     

Stratospheric polar vortex as a possible reason for temporal variations of solar activity and galactic cosmic ray effects on the lower atmosphere circulation

Possible reasons for the temporal instability of long-term effects of solar activity (SA) and galactic cosmic ray (GCR) variations on the lower atmosphere circulation were studied. It was shown that the detected earlier ∼60-year oscillations of the amplitude and sign of SA/GCR effects on the troposphere pressure at high and middle latitudes (Veretenenko and Ogurtsov, Adv.Space Res., 2012) are closely related to the state of a cyclonic vortex forming in the polar stratosphere. The intensity of the vortex was found to reveal a roughly 60-year periodicity affecting the evolution of the large-scale atmospheric circulation and the character of SA/GCR effects. An intensification of both Arctic anticyclones and mid-latitudinal cyclones associated with an increase of GCR fluxes at minima of the 11-year solar cycles is observed in the epochs of a strong polar vortex. In the epochs of a weak polar vortex SA/GCR effects on the development of baric systems at middle and high latitudes were found to change the sign. The results obtained provide evidence that the mechanism of solar activity and cosmic ray influences on the lower atmosphere circulation involves changes in the evolution of the stratospheric polar vortex.     

Physical implications of discrepancy between summer and winter PC indices observed in the course of magnetospheric substorms

The PC index based on a statistically justified relationship between the polar cap magnetic activity and the interplanetary electric field E_KL has been derived as a value standardized for the E_KL intensity regardless of season, UT and hemisphere. As a result, the summer and winter PC indices are consistent with one another under ordinary conditions. Discrepancies between the summer and winter PC indices arising in the course of magnetospheric substorms are analyzed in this paper. It is argued that the channel of enhanced conductivity, formed in the auroral oval owing to intense auroral particle precipitation, strongly improves the conditions for closure of the Region 1 field-aligned currents in the winter dark polar region but only trivially affects the conditions of the Region 1 FAC closure in the summer sunlit ionosphere. Since the coefficients describing the relationship between E_KL and the polar cap magnetic activity were derived for statistically justified (i.e., mean) conditions, their application to such abnormal situation, as intense field-aligned currents in the winter dark polar region, leads to overestimation of the winter PC index. The summer and winter PC indices level off as soon as the intense auroral particle precipitation terminates and the auroral ionosphere in the winter and summer polar caps returns to the ordinary (statistically justified) state.     

Tilts and polarity separation in the sunspot groups and active regions at the ascending and descending phases of the cycle 23

The Solar Feature Catalogues for sunspots and active regions measured with SOHO/MDI instrument and Ca II K3 spectroheliograph of the Paris-Meudon Observatory are analyzed with the automated classification technique for sunspot groups and active region polarities. We report the first classification results for daily variations of tilt angles (normal and trigonometric ones) in sunspot groups (SG) and active (AR) regions in the cycle 23. The average normal tilts are presented for every year at the ascending and descending phases of the cycle 23 which are similar to those deduced by other authors for the cycles 19–22. The normal tilts of both the sunspot groups and active regions are shown to increase in the ascending phase and a decrease in the descending phase. Similar to SG and AR areas, the trigonometric tilts are shown to have the noticeable North–South asymmetry with the Southern hemisphere dominant in the selected ascending and descending periods. The normal tilt variations with latitude follow Joy’s law revealing a periodicity along the meridian of about 10° and reaching the maximum of 14° at the latitude of about 32° corresponding to the top of the ‘royal zone’ where the sunspots appear. The variations of polarity separation with a latitude are in an anti-phase with those of the tilts reaching a maximum at the latitude of 35° and showing a small positive separation for the groups/active regions in a vicinity of the average tilts ±40°. The ratio R of the polarity separation to the trigonometric tilt fits the linear function of a latitude φ as R = −0.0213φ − 0.1245 confirming positive separation for the polarities of active regions with the average tilts, or the dominance of activity in the Southern hemisphere activity, for the selected period of observations.     

The structure of the solar cycle maximum phase in the galactic cosmic ray 11-year variation

Two phenomena connected with the maximum phase of the 11-year solar cycle in the galactic cosmic ray intensity – the change in the energy dependence of the intensity variations and the double-peak structure in the intensity modulation time profile – are considered for the last five solar cycles (Nos. 19–23). The distinct 22-year cycle in the magnitude of the so called energy hysteresis is observed.The periods of the solar cycle maximum phase in the galactic cosmic ray intensity, characterized by the specific energy dependence of the intensity, are estimated. It is found that the double-peak structures belonging to the solar cycle maximum phase and those around it are very similar both in the amplitude and in its energy dependence.     

Cluster observations of earthward propagating plasmoid and flux ropes in the near-tail during the course of a substorm event

We analyze the magnetic structures in the near-tail at Xgsm = −17.5 Re on September 19, 2003 by Cluster. During the course of a substorm event, the earthward propagating plasmoid and flux ropes in the near-tail are observed. The earthward propagating plasmoid is associated with the bipolar Bz and By signatures. The two flux ropes are embedded within the earthward plasma flows, which might be referred to the population as ‘‘BBF-type’’ flux ropes. The first flux rope diameter is about 0.7 Re and duration based upon the Bz signature is ∼20 s, while the second one diameter is about 1.4 Re and duration is ∼30 s. The earthward propagating plasmoid and flux ropes could have influence upon the dipolarization and injection in inner magnetosphere. The Cluster observations of earthward propagating plasmoid and flux ropes can be interpreted as strong evidence for multiple X-lines. Our observations are consistent with that multiple plasmoids or flux ropes are formed repeatedly and ejected tailward in the course of geomagnetically active time.     

Physics of ion acceleration in the solar flare on 2005 September 7 determines γ-ray and neutron production

Relativistic neutrons were observed by the neutron monitors at Mt. Chacaltaya and Mexico City and by the solar neutron telescopes at Chacaltaya and Mt. Sierra Negra in association with an X17.0 flare on 2005 September 7. The neutron signal continued for more than 20 min with high statistical significance. Intense emissions of γ-rays were also registered by INTEGRAL, and during the decay phase by RHESSI. We analyzed these data using the solar-flare magnetic-loop transport and interaction model of Hua et al. [Hua, X.-M., Kozlovsky, B., Lingenfelter, R.E. et al. Angular and energy-dependent neutron emission from solar flare magnetic loops, Astrophys. J. Suppl. Ser. 140, 563–579, 2002], and found that the model could successfully fit the data with intermediate values of loop magnetic convergence and pitch-angle scattering parameters. These results indicate that solar neutrons were produced at the same time as the γ-ray line emission and that ions were continuously accelerated at the emission site.     

Estimation of the bias of the Minimum Variance technique in the determination of magnetic clouds global quantities and orientation

Magnetic clouds (MCs) are highly magnetized plasma structures that have a low proton temperature and a magnetic field vector that rotates when seen by a heliospheric observer. More than 25 years of observations of magnetic and plasma properties of MCs at 1 AU have provided significant knowledge of their magnetic structure. However, because in situ observations only give information along the trajectory of the spacecraft, their real 3D magnetic configuration remains still partially unknown. We generate a set of synthetic clouds, exploring the space of parameters that represents the possible orientations and minimum distances of the satellite trajectory to the cloud axis, p. The synthetic clouds have a local cylindrical symmetry and a linear force-free magnetic configuration. From the analysis of synthetic clouds, we quantify the errors introduced in the determination of the orientation/size (and, consequently, of the global magnetohydrodynamic quantities) by the Minimum Variance method when p is not zero.     

Global electric circuit modulation of winter cyclone vorticity in the northern high latitudes

Small changes in extended winter (November–March) 500 hPa vorticity area index (VAI) values for the 60–80°N latitude band are shown to be positively correlated with changes in a proxy for the high latitude ionosphere-to-surface current density _Jz$J_z$.