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Alfvénicity is a feature characterizing solar wind fluctuations and is defined by a high correlation between velocity and magnetic field components and in ideal conditions by equipartition between kinetic and magnetic energies. It is a feature characterizing especially the fast wind while slow wind shows usually lower correlation between velocity and magnetic field components. However this is not always the case. Under certain conditions a high degree of Alfvénicity can be found also within slow wind. In the present paper, we show the existence of two kinds of slow solar wind with similar velocities but which display different characteristics. The different degree of Alfvénicity is a feature discrimanating the two types of slow wind. This feature is always linked to a low magnetic field compressibility as shown in the present paper using a case study. It is found that the Alfvénic slow wind is more similar to fast wind rather than to the standard slow wind apart from velocity. This fact can be attributed to a different source region on the solar surface. Actually the standard slow wind comes from coronal streamers or active regions while the Alfvénic slow wind originates from the boundary of coronal holes sharing characteristics typical of fast wind. [ABSTRACT FROM AUTHOR]

We analyze the two-hour resolution solar wind proton speed (Vp) and charge state ratio of O7+/O6+ measured by ACE (SWICS and SWEPAM) from 1998 to 2011 at 1 AU. By applying a two-step mapping method, we link the solar wind in-situ observations to the corona images captured by SOHO and STEREO, in which we identify the different plasma structures, such as active regions (ARs), coronal holes (CHs) and quiet Sun regions (QS), using a classification scheme based on pixel brightness. Then we determine from which region in the corona the solar wind originates. We examine the in-situ properties of the solar wind streams associated with CHs, ARs and QS regions. We find that more than half of CH associated wind is actually slow wind, and O7+/O6+ ratio has a strong coherent correlation with the location of the solar wind coronal sources. Therefore, we conclude that O7+/O6+ ratio can be used as a much more effective discriminator to identify solar wind coronal sources region than Vp. [ABSTRACT FROM AUTHOR]

The Interface Region Imaging Spectrograph (IRIS) reveals numerous small-scale (sub-arcsecond) brightenings that appear as bright dots sparkling the solar transition region in active regions. Here, we report a statistical study on these transitionregion bright dots. We use an automatic approach to identify 2742 dots in a Si IV raster image. We find that the average spatial size of the dots is 0.8 arcsec² and most of them are located in the faculae area. Their Doppler velocities obtained from the Si IV 1394 Åline range from -20 to 20 km s-1. Among these 2742 dots, 1224 are predominantly blue-shifted and 1518 are red-shifted. Their nonthermal velocities range from 4 to 50 km s-1 with an average of 24 km s-1. We speculate that the bright dots studied here are small-scale impulsive energetic events that can heat the active region corona. [ABSTRACT FROM AUTHOR]

We investigated the relationship between heavy-ion composition variability in gradual solar energetic particle (SEP) events and the source regions of the associated interplanetary magnetic field (IMF) along which these SEPs are transported. In particular, we found that the SEP elemental composition has a positive correlation with the unsigned photospheric magnetic field strength around the IMF footpoints. Furthermore, the IMF source region can be generally categorized into two classes, depending on whether the associated solar wind, and correspondingly the footpoints of the open magnetic field along which the SEPs are transported, are from a coronal hole (CH) near an active region (an 'AR field-source') or from a CH without an AR in its close proximity (a 'CH field-source'). This study is based on 24 events observed in years 1998 and 2003-2006. We present in this paper the results for Fe/O as an example, and show that the observed SEP Fe/O ratio at 3-30 MeV/nucleon is preferentially enhanced in the case of AR field-source. By contrast, the distributions of Fe/O for the in-situ solar-wind thermal particles in these time intervals are essentially indistinguishable between the two field-sources. Our results suggest that suprathermal ions are the preferred seed particles for shock acceleration, and the composition of these suprathermals depends on the magnetic field where they are generated, with suprathermals associated with active regions, i.e. stronger photospheric magnetic field, having larger heavy-ion enhancements than suprathermals associated with coronal holes with weak magnetic field. These results open a new window in understanding the origin and production of the suprathermal seed particles for SEPs. [ABSTRACT FROM AUTHOR]

Multipoint SEP (Solar Energetic Particle) event measurements continue to suggest that even modest flarerelated impulsive energetic particle events can have greater-than-expected longitudinal extents. This raises questions concerning the flare source nature and size as well as the possible roles of transport mechanisms including perpendicular diffusion. However it is well-established that open coronal magnetic fields can exhibit large divergence between points near the solar surface and the radius where solar wind dominates, and that this can spread SEP fluxes from a small source over a broad heliospheric volume. Potential Field Source Surface (PFSS) models are often used to determine whether open coronal field lines connecting the observer to a flaring active region can explain widely separated impulsive SEP event observations. But while such 'mappings' of suspected sources to the observation sites can succeed, as many others seem to fail. The reasons may be physical but they may also be related to the model applications. We examine some potential sources of error related to the users' choices of assumptions and parameters in the PFSS model field mappings including the size and location of the flare source footprint at the Sun, the order of the spherical harmonic reconstruction of the coronal field, and the chosen radius of the model source surface. An example from August 2010 is used to illustrate the sensitivity of the results to these choices, providing insights and cautionary notes for model users. [ABSTRACT FROM AUTHOR]

Eclipse observations of the W-L corona show linear rays above active regions at times of solar maximum. We show that these linear rays are also observed in the field-of-view of the C2-LASCO coronagraph, in perfect correspondence with the eclipse results. A selected prominent case taken from the 2001 eclipse observation in Angola is analysed with several different methods, including the use of a synoptic map constructed using SoHO/LASCO C2 images. A clear signature of time variations near the eclipse observation is detected, suggesting that at least some parts of the beam are collimated. These observations strongly suggest high speed streams that apparently ignore the potential large scale coronal magnetic field rooted rather low in the corona. A possible origin is the neutral magnetic points located above the active region. Several mechanisms exist to explain how the plasma is accelerated in these regions to large quasi-relativistic velocities, possibly related to the occurrence of type III radio bursts. We point out a curious analogy with phenomena occurring inside coronal holes. [ABSTRACT FROM AUTHOR]

The present study concerns a comparison between the slow solar wind plasma parameters obtained in the extended corona by the UV spectroscopic data from the Ultraviolet Coronagraph Spectrometer (UVCS) onboard SOHO during the minimum of solar activity (1996) and the results of a time-dependent 2.5 D three-fluid MHD model of coronal streamer belt. The aim of the study is to improve the knowledge of the slow solar wind acceleration mechanism and the origin of its variability. [ABSTRACT FROM AUTHOR]

It is widely accepted that magnetic disturbances around fast interplanetary magnetic clouds can play an important role in their geo-effectiveness. An analytical solution for magnetic field in the sheath region of a cylindrical magnetic cloud with an elliptical cross-section is proposed. Upstream magnetic field can have an arbitrary direction. Normal magnetic field components are conserved through the bow shock with a high accuracy. [ABSTRACT FROM AUTHOR]

Between February 2008 and February 2009 solar activity remained very low, providing an excellent opportunity for multi-point studies of CIRs combining observations from STEREO and near-Earth spacecraft. In-situ energetic particle and plasma data from STEREO and ACE were ballistically mapped back to the Sun and compared. The observations were also correlated with remote-sensing observations of the parent coronal holes and synoptic maps of the coronal magnetic field. We found telltale discrepancies in the structures observed by different spacecraft which can not always be explained by the heliographic latitudinal separation between the spacecraft. The observations suggest that temporal evolution of the parent coronal holes as well as the interaction between CIRs and transient solar wind structures in the interplanetary medium also play an important role structuring the inner heliosphere. [ABSTRACT FROM AUTHOR]

We present generalized structure function (GSF) analysis of magnetic and velocity field fluctuations measured in situ in the solar wind at ∼ 1 AU with the ACE spacecraft. We decompose the fluctuations into directions parallel and perpendicular to the mean local background magnetic field. GSF plots based on these quantities are shown to provide a clear indicator of the spectral break between the inertial range and “1/f“ range of scaling. In GSF plots, the projected velocity and magnetic field fluctuations track each other closely in the inertial range in both fast and slow solar wind and at solar maximum and minimum. At longer timescales the “1/f” range is easily identified, because the magnetic field fluctuations display a flattening of the GSFs (exponents become zero) consistent with a ∼1/f PSD. The velocity fluctuations on the other hand have GSFs which steepen, consistent with a PSD of ∼1/fα where α as determined by GSF varies with solar wind speed and solar cycle but is closer to two. The extent of the inertial range determined in this manner differs between fast and slow solar wind streams, and between periods of maximum and minimum solar activity. [ABSTRACT FROM AUTHOR]

We have surveyed the spectral and compositional properties of suprathermal (∼40–320 keV nucleon-1) heavy ions during quiet times from 1995 January 1 to 2008 December 31 using instruments on board ACE and Wind spacecraft in the interplanetary (IP) medium near 1 AU. We find that the composition of the quiet-time suprathermal heavy ion population (3He and C-Fe) depends on the level of solar activity: the ions exhibit SEP-like composition signatures during solar maximum and CIR or solar-wind like composition during solar minimum. In addition, we find that during quietest times in the IP medium, all ion species exhibit suprathermal tails with power-law spectral indices ranging from 1.27 to 2.29, i.e., significantly different from recent observations and theoretical predictions of a unique 1.5 index. We discuss the implications of these new observations for the origin of the suprathermal ion population near 1 AU. [ABSTRACT FROM AUTHOR]

Interplanetary scintillation (IPS) allows us to determine solar wind velocity and density structures over a relatively short time by employing computer assisted tomography. This method can be applied to forecast solar wind changes for a few days prior to its reaching Earth. We have been attempting solar wind forecasting by using IPS data observed at Solar-Terrestrial Environment Laboratory (STELab), Japan. Here we introduce the solar wind forecast using STELab-IPS and evaluated dependences of the accuracy of the STELab-IPS forecasts on a number of line-of-sight observed with IPS and a solar activity by comparing comparing them with in situ measurements. [ABSTRACT FROM AUTHOR]

Energetic Solar particles and Geomagnetic Indices during the last two cycles were given. The data of the grouped flares and 10.7 cm radio flux were obtained from Solar Geophysical data reports by the US Department of Commerce, during the solar cycle 22 and 23. Power spectrum analyses method were used for the data treatments, to find the intermediate-term periodicities, 14, 28, 35 are significant. Long-term periodicities periodicity 154 days appeared, and confirmed with the other results. Halloween storms during Nov. 2003 and its effects on the geomagnetic storms have been studied analytically. The data of amplitude and phase of most common indicators of geomagnetic activities during solar cycle 23 has been analyzed. [ABSTRACT FROM AUTHOR]

Solar rotational tomography is applied to almost eleven years of LASCO C2/SOHO data, revealing for the first time the structural behavior of streamers over almost a full solar activity cycle. Streamers are most often shaped as extended, narrow plasma sheets. The sheets can be extremely narrow at times (<=0.14×106 km at 4R⊙). This is over twice their heliocentric angular thickness at 1 AU. For most of the activity cycle, streamers share the same latitudinal extent as filaments on the disk, showing that large-scale stable streamers are closely linked to the same large-scale photospheric magnetic configuration which give rise to large filaments. There is considerable differential rotation of streamers at high latitudes, which makes comparison between disk and coronal structure complicated. The presence of differential rotation has implications for many areas of coronal and heliospheric research. [ABSTRACT FROM AUTHOR]

The edge of a solar active region (AR) is considered as a possible source region of the slow solar wind. Winebarger et al. (2001) observed outflows from an AR with velocities between 5 and 20 km/s. Recently, Sakao et al. (2007) reported the outflow of X-ray-emitting plasma from the edge of an AR. This outflow was inferred from the observation of outward traveling intensity enhancements. However, in Robbrecht et al. (2001), propagation of slow magnetoacoustic waves along the strand was considered as the possible cause for the longitudinal extension of the strand. Whether this phenomenon relates to a slow-mode wave or the outflow of plasma or a heating process of different parts of the strand is still an open question. Here we try to identify the nature of such a traveling event through studying the longitudinal motions of certain intensity level fronts in the strand. We find that the intensity front is oscillating like a sinusoidal signal along the strand with a period of 11 minutes. This result suggests that the oscillation might be partly related with the 5-minute p-mode oscillation in the photosphere. Moreover, we find that such oscillation of intensity-level fronts can be described by a model in which the strand has periodic extension. Yet, the relation between the extending strand and slow solar wind needs to be further studied. [ABSTRACT FROM AUTHOR]

Coronal radio sounding observations were carried out with the radio science experiment MaRS on the ESA spacecraft Mars Express during the period from 25 August to 22 October 2004. Differential frequency and log-amplitude fluctuations of the dual-frequency signals were recorded during a period of low solar activity. The data are applicable to low heliographic latitudes, i.e. to slow solar wind. The mean frequency fluctuation and power law index of the frequency fluctuation temporal spectra are determined as a function of heliocentric distance. The radial dependence of the frequency fluctuation spectral index α reflects the previously documented flattening of the scintillation power spectra in the solar wind acceleration region. Temporal spectra of S-band and X-band normalized log-amplitude fluctuations were investigated over the range of fluctuation frequencies 0.01 Hz<ν<0.5 Hz, where the spectral density is approximately constant. The radial variation of the spectral density is analyzed and compared with Ulysses 1991 data, a period of high solar activity. Ranging measurements are presented and compared with frequency and log-amplitude scintillation data. Evidence for a weak increase in the fractional electron density turbulence level is obtained in the range 10–40 solar radii. [ABSTRACT FROM AUTHOR]

Cosmic ray detectors are widely used, for educational purposes, in order to motivate students to the physics of elementary particles and astrophysics. Using a “telescope” of scintillation counters, the directional characteristics, diurnal variation, correlation with solar activity, can be determined, and conclusions about the composition, origin and interaction of elementary particles with the magnetic field of earth can be inferred. A telescope was built from two rectangular scintillator panels with dimensions: 91.6×1.9×3.7 cm3. The scintillators are placed on top of each other, separated by a fixed distance of 34.6 cm. They are supported by a wooden frame which can be rotated around a horizontal axis. Direction is determined by the coincidence of the signals of the two PMTs. Standard NIM modules are used for readout. This device is to be used in the undergraduate nuclear and particle physics laboratory. The design and construction of the telescope as well as some preliminary results are presented. [ABSTRACT FROM AUTHOR]

Results of study of the continuum radio emission of the Sun in the decameter range are presented. Observations were carried out with radio telescope URAN-2 in summer months in 2008–2009. Radio fluxes at frequencies 20 MHz and 25 MHz in frequency band 250 kHz were obtained during the time, when there were no active regions on the solar disk. Their average values for two years were 670 Jy and 850 Jy at frequencies 20 MHz and 25 MHz correspondingly. These fluxes are in agreement with high frequency values. [ABSTRACT FROM AUTHOR]

We have surveyed the spectral and compositional properties of suprathermal heavy ions during quiet times from 1995 January 1 to 2008 December 31 using instruments on board ACE and Wind spacecraft in the interplanetary (IP) medium near 1 AU. We find that the composition of the quiet-time suprathermal heavy ion population (3He and C-Fe) depends on the level of solar activity: the ions exhibit SEP-like composition signatures during solar maximum and CIR or solar-wind like composition during solar minimum. In addition, we find that during quietest times in the IP medium, all ion species exhibit suprathermal tails with power-law spectral indices ranging from 1.27 to 2.29, i.e., significantly different from recent observations and theoretical predictions of a unique 1.5 index. We discuss the implications of these new observations for the origin of the suprathermal ion population near 1 AU. [ABSTRACT FROM AUTHOR]

We have studied the evolution and decay of the active region 09778, as well as the evolution of the filament below it and its possible relation with the active region. Using data from SOHO—LASCO, BBSO, Mauna Loa, we analyzed the evolution of active region in different wavelengths. The AR presented high flare productivity. From MDI magnetograms we extrapolate the magnetic field in order to obtain a 3D configuration and to understand flare occurrence. [ABSTRACT FROM AUTHOR]

The magnetic fields in solar active regions are known to be helical. The current helicity, as measured from magnetograms, is negative on the northern and positive in the southern hemisphere, its normalized mean value being αp≡B·(∇×B)/B2∼10-8 m-1. Recent observations have convincingly demonstrated that the helicity originates in subsurface regions and the flux tubes emerge in an already helical form. One possible contribution to this helicity is the accretion of the weak general poloidal magnetic field of the Sun by the rising toroidal flux loop. For this process to work, the field lines of the background field first need to be wrapped around the rising flux tube, which assumes that freezing-in holds to a good degree of approximation. The wrapped-up field then has to diffuse into the flux tube, giving rise to a twisted magnetic field structure. The conflict between the requirements of freezing-in (for wrapup) and diffusion (for penetration into the tube) is only apparent. The role of diffusion is likely to be limited during most of the rise of the tube, allowing a significant amount of flux to be swept up; then, in the uppermost 20–30% of the tube's path through the convective zone diffusion prevails, allowing penetration of the wrapped up flux. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to evidence, from a statistical point of view, the different periods of solar activity. The well known period is that of 150–160 days, but many others were detected between 9 and 4750 days (length of solar cycle). We tabulated 49 articles revealing 231 periods. In order to explain them, different hypotheses were suggested. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

The MHD numerical simulations started to be performed at the Astronomical Institute of Romanian Academy eleven years ago. We present here the main results obtained during this period. The 2D numerical experiments were performed by the Alfvén code. We have obtained the main active phenomena of the solar activity: flares, prominences, CMEs, coronal streamers and coronal holes. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]

We present a statistical study of the evolution of active regions observed at microwave wavelengths during the 23rd solar cycle (1992–2004). Active regions are sites of increased magnetic fields, thus the radio emission at microwave wavelengths is mostly due to gyro-resonance of thermal electrons around relatively strong magnetic fields. We analyze active regions observed in full Sun images obtained daily by the Nobeyama Radioheliograph (NoRH) at 17 GHz. Additional information is obtained from photospheric magnetograms of the same day. Also a multiwavelength study provides a global view of the solar atmosphere above active regions, the radio images will be further compared to ultraviolet (SOHO) and H-alpha images. The active regions are characterized by: position, area, maximum and mean brightness temperatures, and magnetic field. The inferred magnetic fields are used to estimate the contribution to the emission at 17 GHz. We discuss the results of the correlation among these physical parameters. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

According to their timescale, emission from the Sun can be divided into three types. There is the slowly varying emission which changes on a timescale of 11 years and follows the solar cycle. A more rapidly varying radiation on timescale of weeks, known as quiescent emission, is related to the occurrence of active regions. Last but not least is the very abrupt emission produced by solar activity such as flares and coronal mass ejections on timescales of second to hours. All three kinds of behavior can also be observed at radio wavelength, each being produced mostly by different mechanisms. At microwave and millimeter wavelengths, the quiet Sun emission, which varies on 11 years timescale, is due to thermal bremsstrahlung. Nevertheless, the quiescent radio emission has a strong contribution from thermal gyro-resonance especially at microwaves, whereas thermal bremsstrahlung dominates the millimetric and submillimetric waves. On the other hand, gyro-synchrotron radiation from non-thermal electrons is the main mechanism producing the flare emission at wavelengths shorter than cm, whereas the metric and decimetric emission from radio burst are due to coherent plasma radiation. Especial emphasis will be given to the newest findings in solar radio astronomy by the Solar Group at CRAAM. These results were obtained mainly from two radio telescopes: the Submillimeter Solar Telescope (SST) operating at 212 and 405 GHz and the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The magnetic field lines were never so depicted as in the recent results about active regions on the sun from the EUV experiments on board of SOHO and TRACE satellites. The main result is a clear complexity of the, as called, magnetic arcs on top of the sunspots with arc second spatial resolution of the field lines connecting different magnetic polarities. The microwave solar bursts occurring in this magnetic ambient have been treated, in most of analysis, as a homogeneous source of gyrosynchrotron emission. We developed a numerical code for the emission, self-absorption and transfer equation of the ordinary and extraordinary modes for this complex ambient to calculate the flux density map and spectrum of the emitting region. We applied our code for a non-thermal distribution of electrons, with number density typical for solar flares, with anisotropic pitch angle distribution, a hydrostatic ambient density and analyzed the spectrum for many viewing angles. For the magnetic field configuration we idealized a complex array of magnetic arcs simulating one of these observed scenarios for our first result presented here. The code is also prepared to use a non-linear extrapolation of photospheric magnetic field. Our main concern in this analysis was to show some of the geometric dependence of the spectrum shape as an alternative for the general interpretation based on a composition of many isotropic sources with distinct magnetic field or bremsstrahlung competition to broad and/or reinforce the emission in specific frequency bands. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The observations on magnetic field fluctuations and suprathermal ion spectra near the shocks driven by the coronal mass ejections during the time periods of the Bastille Day 2000 event and the Halloween 2003 events are summarized. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Solar cycle 23 was notable for two periods of intense solar activity (or ‘events’ as we shall hereafter refer to them): the ‘Bastille Day Event’ of 2000 and the ‘Halloween Event’ of 2003. In this paper we look at the signatures of the interplanetary shocks produced by these events, in particular the plasma parameters, as observed by Voyager 2 (V2) some six months after the events occurred at Sun. We compare these shocks with other large events observed by V2 during the preceding decade. We note that the plasma parameters, most notably the plasma density, are frequently not as might be expected for “typical” events. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

In astrophysical settings, termination shocks where strong stellar wind outflows interact with the surrounding environments tend to take place in dusty regions. Just to name a few, star formation regions, planetary nebulae, supernova remnants and active galactic nuclei are all good examples. Dynamics and evolution of the associated dust clouds could have important influences on the acceleration and composition of energetic particles resulting from the diffusive shock acceleration at the termination shocks. In this note we provide a brief review of previous work predating the recent detection of ACR Mg, Na, Si and S ions which might have originated from the Kuiper belt dust. Their compositional abundance might be diagnostic of the collisional history of the Kupier belt objects. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper considers several different aspects of the magnetic field in the outer heliosphere and their consequences. It is noted first that many features of the heliospheric magnetic field are set back at the Sun, and that these processes result in variations in the heliospheric field on several distinct spatial scales. An equation is discussed that describes the interactions of mesoscale variations in the magnetic field with small-scale turbulence, and it is argued that this interaction can account for the creation of the observed superthermal tails on the particle distributions, and alter the expected behavior of the magnetic field at the termination shock. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

The distribution of the magnetic field on the solar surface from 1975 up to 2002 is analyzed using the observations taken on the WSO observatory, revealing remarkable latitudinal zonal structure in both the northern and southern hemisphere. A preliminary model combining the dipole, quadrupole, octupole and other components for the longitude distribution is discussed. The active longitude problem has been investigated. The new active regions seem to appear with the sideral period of about 25.0 ± .1 days, corresponding to the solar rotation rate at 10 degree latitude at the 0.85±.03 solar radii. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]

Modeling dynamics underlying the sunspot numbers is an important problem because such data indicate the relative activity of the Sun. A key point in modeling sunspot data, which follows an 11-year cycle, is the need to take into account the reversal of the Sun’s magnetic field, which follows a 22-year cycle. This can be done using an appropriate coordinate transformation applied to the phase portrait reconstructed from the sunspot numbers. Such a transformation introduces symmetry in the phase portrait and has the advantage of unfolding the structure of the dynamics. Global models have been obtained from such data. It is shown that the models capture the basic dynamical structure underlying the data which appears to be the structure of a Rössler attractor with an additional half twist. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]