Showing papers on "Heliosphere published in 2007"
TL;DR: In this paper, the behavior and consequences of the reverse shock that terminates the supersonic expansion of the baryonic wind which is driven by neutrino heating off the surface of (non-magnetized) new-born neutron stars in supernova cores were investigated.
Abstract: We investigate the behavior and consequences of the reverse shock that terminates the supersonic expansion of the baryonic wind which is driven by neutrino heating off the surface of (non-magnetized) new-born neutron stars in supernova cores. To this end we perform long-time hydrodynamic simulations in spherical symmetry. In agreement with previous relativistic wind studies, we find that the neutrino-driven outflow accelerates to supersonic velocities and in case of a compact, ∼1.4 M ⊙ (gravitational mass) neutron star with a radius of about 10 km, the wind reaches entropies of about 100 k B per nucleon. The wind, however, is strongly influenced by the environment of the supernova core. It is decelerated and shock-heated abruptly by a termination shock that forms when the supersonic outflow collides with the slower preceding supernova ejecta. The radial position of this reverse shock varies with time and depends on the strength of the neutrino wind and the explosion conditions in progenitor stars with different masses and structure. Its basic properties and behavior can be understood by simple analytic considerations. We demonstrate that the entropy of the matter going through the reverse shock can increase to a multiple of the asymptotic wind value. Seconds after the onset of the explosion it therefore can exceed 400k B per nucleon in low-mass progenitors around 10M ⊙ , where the supernova shock and the reverse shock propagate outward quickly. The temperature of the shocked wind has typically dropped to about or less than 10 9 K, and density and temperature in the shock-decelerated matter continue to decrease only very slowly. For more massive progenitors with bigger and denser metal cores, the explosion expands more slowly so that the termination shock stays at smaller radii and affects the wind at higher temperatures and densities. In this case the termination shock might play a non-negligible, strongly time- and progenitor-dependent role in discussing supernova nucleosynthesis.
218 citations
TL;DR: In this article, a new MHD model for simulating the large-scale structure of the solar corona and solar wind under "steady state" conditions stemming from the Wang-Sheeley-Arge empirical model was presented.
Abstract: We present a new MHD model for simulating the large-scale structure of the solar corona and solar wind under "steady state" conditions stemming from the Wang-Sheeley-Arge empirical model. The processes of turbulent heating in the solar wind are parameterized using a phenomenological, thermodynamical model with a varied polytropic index. We employ the Bernoulli integral to bridge the asymptotic solar wind speed with the assumed distribution of the polytropic index on the solar surface. We successfully reproduce the mass flux from Sun to Earth, the temperature structure, and the large-scale structure of the magnetic field. We reproduce the solar wind speed bimodal structure in the inner heliosphere. However, the solar wind speed is in a quantitative agreement with observations at 1 AU for solar maximum conditions only. The magnetic field comparison demonstrates that the input magnetogram needs to be multiplied by a scaling factor in order to obtain the correct magnitude at 1 AU.
209 citations
TL;DR: The authors summarizes the observational properties of interplanetary coronal mass ejections (ICMEs) with reference to the ordinary solar wind and the progenitor CMEs, and shows that ICMEs are the most energetic phenomenon in the heliosphere and cause intense geomagnetic storms and drive fast mode shocks that accelerate charged particles.
Abstract: Interplanetary coronal mass ejections (ICMEs) originating from closed field regions on the Sun are the most energetic phenomenon in the heliosphere. They cause intense geomagnetic storms and drive fast mode shocks that accelerate charged particles. ICMEs are the interplanetary manifestations of CMEs typically remote-sensed by coronagraphs. This paper summarizes the observational properties of ICMEs with reference to the ordinary solar wind and the progenitor CMEs.
173 citations
Book•
10 Jan 2007
TL;DR: In this article, the authors present an overview of the relationship between the Earth's magnetosphere and the solar wind and the Heliosphere and its relationship with the Troposphere, as well as its effects on communication and power grids.
Abstract: 1. Introduction,- 2. Space Weather Forecasting Historically Viewed through the Lens of Meterology,- 3. The Solar and Interplanetary Drivers of Space and Storms,- 4. The Coupling of the Solar Wind to the Earth's Magnetosphere,- 5. Major Radiation Environments in the Heliosphere and their Implications for Interplanetary Travel,- 6. Radiation Belts and Ring Currents,- 7. Ionospheric Response,- 8. Solar Effects in the Middle and Lower Stratosphere and Probable Associations with the Troposphere,- 9. Space Weather Effects on Communications,- 10. Space Weather Effects on Power Grids,- 11. Space Weather Impacts on Space Radiation,- 12. Effects on Spacecraft Hardware and Operations,- 13. Effects on Satellite Navigation,- 14. Forecasting Space Weather,-15. Outlook.
164 citations
TL;DR: In this article, a detailed hydrodynamical study of the properties of the flow produced by the collision of a pulsar wind with the surrounding in a binary system is presented.
Abstract: In this paper, we present a detailed hydrodynamical study of the properties of the flow produced by the collision of a pulsar wind with the surrounding in a binary system. This work is the first attempt to simulate interaction of the ultrarelativistic flow (pulsar wind) with the nonrelativistic stellar wind. Obtained results show that the wind collision could result in the formation of an "unclosed" (at spatial scales comparable to the binary system size) pulsar wind termination shock even when the stellar wind ram pressure exceeds significantly the pulsar wind kinetical pressure. Moreover, the post-shock flow propagates in a rather narrow region, with very high bulk Lorentz factor ($\gamma\sim100$). This flow acceleration is related to adiabatical losses, which are purely hydrodynamical effects. Interestingly, in this particular case, no magnetic field is required for formation of the ultrarelativistic bulk outflow. The obtained results provide a new interpretation for the orbital variability of radio, X-ray and gamma-ray signals detected from binary pulsar system PSR 1259-63/SS2883.
134 citations
TL;DR: In this article, the implied connections between solar and heliospheric evolution have been analyzed by a powerful multisatellite solar-and heliosphere observatory that includes the Ulysses and the SOHO spacecraft, and some of these results confirmed predictions by models based on time-stationary conditions of the corona at its lowest energy state.
Abstract: The structure of the global heliospheric field reflects the physical properties of the low corona. The implied connections between solar and heliospheric evolution have been analyzed by a powerful multisatellite solar and heliospheric observatory that includes the Ulysses and the Solar and Heliospheric Observatory (SOHO) spacecraft. This coordinated investigation yielded unprecedented observational opportunities. Some of these results confirmed predictions by models based on time-stationary conditions of the corona at its lowest energy state. However, there are results that exhibit important contradictions to these models, and limit their applicability, pointing to the importance of photospheric dynamics and small-scale field emergence for the structure of the heliospheric field. The interpretation of these data provides challenges to our understanding of the physics of the energy transport from the convective layers of the Sun into the heliosphere and motivates new theoretical approaches to the e...
129 citations
TL;DR: In this article, the authors estimate the V arc solar source locations and their opening angle dynamics as tests for solar wind shearing and compare them with average properties of all SMEI ICMEs.
Abstract: [1] Since February 2003, the Solar Mass Ejection Imager (SMEI) has been observing interplanetary coronal mass ejections (ICMEs) at solar elongation angles e > 20°. The ICMEs generally appear as loops or arcs in the sky, but five show distinct outward concave shapes that we call V arcs. We expect to observe some V arcs, formed by trailing edges of ICME flux ropes or by leading ICME edges sheared by solar wind (SW) speed gradients at the heliospheric current sheet. We characterize the properties of these V arcs and compare them with average properties of all SMEI ICMEs. The typical V arc speeds argue against a slow MHD shock interpretation for their structures. We estimate the V arc solar source locations and their opening angle dynamics as tests for SW shearing. The first test contradicts but the second supports the SW shearing explanation. The implications of the small number of V arcs observed with SMEI is considered. The point P approximation used to determine the V arc locations and inferred solar source regions is critically examined in Appendix A.
127 citations
TL;DR: In this paper, the authors derived two conjectures as to the possible structure and dynamics of coronal holes: (1) coronal hole are unique in that every unipolar region on the photosphere can contain at most one CORONA, and (2) corona holes of nested polarity regions must themselves be nested.
Abstract: The solar magnetic field is the primary agent that drives solar activity and couples the Sun to the heliosphere. Although the details of this coupling depend on the quantitative properties of the field, many important aspects of the corona-solar wind connection can be understood by considering only the general topological properties of those regions on the Sun where the field extends from the photosphere out to interplanetary space, the so-called open field regions that are usually observed as coronal holes. From the simple assumptions that underlie the standard quasi-steady corona-wind theoretical models, and that are likely to hold for the Sun as well, we derive two conjectures as to the possible structure and dynamics of coronal holes: (1) coronal holes are unique in that every unipolar region on the photosphere can contain at most one coronal hole, and (2) coronal holes of nested polarity regions must themselves be nested. Magnetic reconnection plays the central role in enforcing these constraints on the field topology. From these conjectures we derive additional properties for the topology of open field regions, and propose several observational predictions for both the slowly varying and transient corona/solar wind.
112 citations
TL;DR: In this paper, the authors examined the implications of the widely used, force-free, constant-a flux rope model of interplanetary magnetic clouds for the evolution of these mesoscale (fraction 1 AU) structures in the heliosphere, with special emphasis on the inner (≤1 AU)heliosphere.
Abstract: [1] We examine the implications of the widely used, force-free, constant-a flux rope model of interplanetary magnetic clouds for the evolution of these mesoscale (fraction 1 AU) structures in the heliosphere, with special emphasis on the inner (≤1 AU) heliosphere. We employ primarily events observed by the Helios 1 and 2 probes between 0.3 and 1 AU in the ascending and maximum phases of solar cycle 21 and by Wind at 1 AU in a similar phase of solar activity cycle. We supplement these data by observations from other spacecraft (e.g., Voyagers 1 and 2, Pioneers 10 and 11, and others). Our data set consists of 130 events. We explore three different approaches. In the first, we work with ensemble averages, binning the results into radial segments of width 0.1 AU in the range 0.3 < r h ≤ 1 AU. Doing this, we find that in the inner heliosphere the modeled average central axial field strength, (B 0 ), varies with heliospheric distance r h as (B 0 ) [nT] = 18.1 ·rh -1.64 [AU], and the average diameter increases quasi-linearly as (D) [AU] = 0.23 r h 1.14 . The orientation of the axis of the underlying magnetic flux tube in our data set is generally found to lie along the east-west direction and in the ecliptic plane at all values of r h , but there is considerable scatter about these average directions. In the second, we monitor the evolution of magnetic clouds in snapshot fashion, using seven spacecraft alignments. The results are in broad agreement with the statistics reported under step 1. In the final approach, we obtain the functional dependence of By and D predicted by an analytic expression for a freely expanding Lundquist flux tube. We find D to vary linearly with r h , broadly similar to that obtained under approach 1. The maximum field strength scales as r h -2 compared to a r h -1.3 dependence obtained from statistics. We compare our findings with those of Bothmer and Schwenn (1998), who used a different methodology. The results obtained form a good background to the forthcoming Solar Terrestrial Relations Observatory (STEREO) and Sentinels missions and to multispacecraft studies of magnetic clouds.
112 citations
TL;DR: In this paper, an interdisciplinary team of scientists brings together their knowledge of the evolution and modulation of the cosmic ray flux from its origin in the Milky Way, during its propagation through the heliosphere, up to its interaction with the Earth's magnetosphere, resulting, finally, in the production of cosmogenic isotopes in the Earth’ atmosphere.
Abstract: In recent years the variability of the cosmic ray flux has become one of the main issues interpreting cosmogenic elements and especially their connection with climate. In this review, an interdisciplinary team of scientists brings together our knowledge of the evolution and modulation of the cosmic ray flux from its origin in the Milky Way, during its propagation through the heliosphere, up to its interaction with the Earth’s magnetosphere, resulting, finally, in the production of cosmogenic isotopes in the Earth’ atmosphere. The interpretation of the cosmogenic isotopes and the cosmic ray – cloud connection are also intensively discussed. Finally, we discuss some open questions.
106 citations
TL;DR: In this paper, a time-dependent model of the solar wind charge exchange (SWCX) X-ray emission was developed, based on the localization of the Solar Wind Parker spiral at each instant.
Abstract: Aims. We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emission generated by charge transfer collisions between solar wind (SW) oxygen ions and interstellar H and He neutral atoms in the inner Heliosphere. These lines which dominate the 0.3-1.0 keV energy interval are also produced by hot gas in the galactic halo (GH) and possibly the Local Interstellar Bubble (LB). Methods. We developed a time-dependent model of the Solar Wind Charge-Exchange (SWCX) X-ray emission, based on the localization of the Solar Wind Parker spiral at each instant. We include input SW conditions affecting three selected fields, as well as shadowing targets observed with XMM-Newton, Chandra and Suzaku satellites and calculate X-ray emission in the oxygen lines O VII and O VIII in order to determine the SWCX contamination and the residual emission to attribute to the galactic soft X-ray background. We obtain ground level intensities and/or simulated lightcurves for each target and compare to X-ray data from the three instruments mentioned. Results. The local 3/4 keV emission (due essentially to O VII and O VIII) detected in front of shadowing clouds is found to be entirely explained by the CX heliospheric emission. No emission from the LB is needed at these energies. The observed and modeled range of the foreground oxygen emission is 0.3-4.6 LU (Line Units = photons cm -2 s -1 sr -1 ) for OVII and 0.02-2.1 LU for OVIII depending on directions and conditions. Using the model predictions we subtract the heliospheric contribution to the measured emission and derive the halo contribution. We also correct for an error in the preliminary analysis of the Hubble Deep Field North (HDFN). We find intensities of 4.9 +1.29 -1.04 LU, 6.25 +0.63 -0.98 LU, 11.15 +2.36 -1.41 LU for OVII and 1.41 +0.60 -0.49 LU, 1.62 +0.35 -0.49 LU, 1.97 +1.11 -0.71 LU for OVIII towards the Marano Field, the Hubble Deep Field-North, and the Lockman Hole respectively.
TL;DR: The Ulysses spacecraft has been the first to orbit the Sun over its poles and to explore the heliosphere at these high heliolatitudes as discussed by the authors, which has led to several surprising discoveries concerning energetic particles.
Abstract: The Ulysses spacecraft has been the first to orbit the Sun over its poles and to explore the heliosphere at these high heliolatitudes. It has now completed two fast latitude scans, one at solar minimum and one at solar maximum. Since its launch in October 1990, this mission has led to several surprising discoveries concerning energetic particles, cosmic rays, Jovian electrons, the solar wind, the heliospheric magnetic field and the global features of the heliosphere. This review addresses mainly the propagation and modulation of cosmic rays and other charged particles, from both an observational and theoretical point of view, with emphasis on what has been learned from exploring the inner heliosphere to high heliolatitudes. This is done for solar minimum and maximum conditions. The review is concluded with a summary of the main scientific discoveries and insights gained so far from the Ulysses mission.
TL;DR: In this article, it was shown that asymmetries of the termination shock due to the influence of the interstellar magnetic field (ISMF) are considerably smaller in the presence of neutral hydrogen atoms, which tend to symmetrize the heliopause, the termination and bow shocks due to charge exchange with charged particles.
Abstract: We show that asymmetries of the termination shock due to the influence of the interstellar magnetic field (ISMF) are considerably smaller in the presence of neutral hydrogen atoms, which tend to symmetrize the heliopause, the termination shock, and the bow shock due to charge exchange with charged particles. This leads to a much stronger restriction on the ISMF direction and its strength. We demonstrate that in the presence of the interplanetary magnetic field the plane defined by the local interstellar medium (LISM) velocity and magnetic field vectors does not exactly coincide with the plane defined by the interstellar neutral helium and hydrogen velocity vectors in the supersonic solar wind region, which limits the accuracy of the inferred direction of the ISMF. We take into account the tilt of the LISM velocity vector with respect to the ecliptic plane and show that magnetic fields as strong as 3 μG or greater may be necessary to account for the observed asymmetry. Estimates are made of the longitudinal streaming anisotropy of energetic charged particles at the termination shock caused by the nonalignment of the interplanetary magnetic field with its surface. By investigating the behavior of interplanetary magnetic field lines that cross the Voyager 1 trajectory in the inner heliosheath, we estimate the length of the trajectory segment that is directly connected by these lines to the termination shock. A possible effect of the ISMF draping over the heliopause is discussed in connection with radio emission generated in the outer heliosheath.
TL;DR: In this paper, the transport properties of energetic electrons accelerated at corotating interaction regions in the solar wind considering the possibility of anomalous diffusion were studied. And the particle time decay has a power-law behavior when a non-Gaussian propagator, appropriate for superdiffusive transport, is assumed for particles accelerated at a propagating shock.
Abstract: We study the transport properties of energetic electrons accelerated at corotating interaction regions in the solar wind considering the possibility of anomalous diffusion. It is shown that the particle time decay has a power-law behavior when a non-Gaussian propagator, appropriate for superdiffusive transport, is assumed for particles accelerated at a propagating shock. Looking at shock events detected by the Ulysses spacecraft at 5 AU, we found that 42-290 keV electron time profiles are well fitted by a power law corresponding to superdiffusive transport, i.e., Δ x2(t) ∝ tα, with α = 1.02-1.38. This implies that particle propagation in the heliosphere can be intermediate between normal diffusion and ballistic motion.
Book•
05 Feb 2007TL;DR: In this article, the solar wind from the sun: an introduction and a toolkit for space plasma physics is presented, along with an overview of the outer solar atmosphere and its structure and perturbations.
Abstract: Preface 1 The wind from the sun: an introduction 2 Toolkit for space plasma physics 3 Anatomy of the sun 4 The outer solar atmosphere 5 How does the solar wind blow? 6 Structure and perturbations 7 Bodies in the wind: dust, asteroids, planets and comets 8 The solar wind in the universe Index
TL;DR: The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse almost perpendicular to the ecliptic plane (inclination 79°, perihelion distance 1.3 AU, aphelia distance 5.4 AU) since it encountered Jupiter in 1992 as mentioned in this paper.
Abstract: The Ulysses spacecraft has been orbiting the Sun on a highly inclined ellipse almost perpendicular to the ecliptic plane (inclination 79°, perihelion distance 1.3 AU, aphelion distance 5.4 AU) since it encountered Jupiter in 1992. The in situ dust detector on board continuously measured interstellar dust grains with masses up to 10−13 kg, penetrating deep into the solar system. The flow direction is close to the mean apex of the Sun’s motion through the solar system and the grains act as tracers of the physical conditions in the local interstellar cloud (LIC). While Ulysses monitored the interstellar dust stream at high ecliptic latitudes between 3 and 5 AU, interstellar impactors were also measured with the in situ dust detectors on board Cassini, Galileo and Helios, covering a heliocentric distance range between 0.3 and 3 AU in the ecliptic plane. The interstellar dust stream in the inner solar system is altered by the solar radiation pressure force, gravitational focussing and interaction of charged grains with the time varying interplanetary magnetic field. We review the results from in situ interstellar dust measurements in the solar system and present Ulysses’ latest interstellar dust data. These data indicate a 30° shift in the impact direction of interstellar grains w.r.t. the interstellar helium flow direction, the reason of which is presently unknown.
TL;DR: In this article, a 13-month stretch of Ulysses SWICS H pickup ion measurements near 5 AU close to the ecliptic right after the previous solar minimum was used to determine the neutral interstellar H density at the solar wind termination shock.
Abstract: By reevaluating a 13-month stretch of Ulysses SWICS H pickup ion measurements near 5 AU close to the ecliptic right after the previous solar minimum, this paper presents a determination of the neutral interstellar H density at the solar wind termination shock and implications for the density and ionization degree of hydrogen in the LIC. The density of neutral interstellar hydrogen at the termination shock was determined from the local pickup ion production rate as obtained close to the cut-off in the distribution function at aphelion of Ulysses. As shown in an analytical treatment for the upwind axis and through kinetic modeling of the pickup ion production rate at the observer location, with variations in the ionization rate, radiation pressure, and the modeling of the particle behavior, this analysis turns out to be very robust against uncertainties in these parameters and the modeling. Analysis using current heliospheric parameters yields the H density at the termination shock equal to $0.087\pm0.022$ cm$^{-3}$, including observational and modeling uncertainties.
TL;DR: In this paper, the authors combined radio emissions and energetic particle streaming with extensive three-dimensional magnetohydrodynamic computer simulations of magnetic field draping over the heliopause to show that the plane of the local interstellar field is ∼60° to 90° from the galactic plane.
Abstract: The orientation of the local interstellar magnetic field introduces asymmetries in the heliosphere that affect the location of heliospheric radio emissions and the streaming direction of ions from the termination shock of the solar wind. We combined observations of radio emissions and energetic particle streaming with extensive three-dimensional magnetohydrodynamic computer simulations of magnetic field draping over the heliopause to show that the plane of the local interstellar field is ∼60° to 90° from the galactic plane. This finding suggests that the field orientation in the Local Interstellar Cloud differs from that of a larger-scale interstellar magnetic field thought to parallel the galactic plane.
TL;DR: In this paper, a parametric model was used to estimate the impact of different degradation behaviors on solar sail performance for some example interplanetary missions: Mercury rendezvous missions, fast missions to Neptune and to the heliopause, and artificial Lagrange-point missions.
Abstract: The optical properties of the thin metalized polymer films that are projected for solar sails are likely to be affected by the damaging effects of the space environment, but their real degradation behavior is to a great extent unknown. The standard solar sail force models that are currently used for solar sail mission analysis and design do not take these effects into account. In this paper we use a parametric model to describe the sail film's optical degradation with its environmental history to estimate the impact of different degradation behaviors on solar sail mission performance for some example interplanetary missions: Mercury rendezvous missions, fast missions to Neptune and to the heliopause, and artificial Lagrange-point missions.
TL;DR: In this article, the authors proposed a mechanism of cosmic-ray (CR) flux modulation by the solar system vertical oscillation (64 Myr period) in the Galaxy, the Galactic north-south anisotropy of CR production in the Galactic halo/wind/termination shock (due to the Galactic motion toward the Virgo Cluster), and the shielding by Galactic magnetic fields.
Abstract: Recent work has revealed a 62 ± 3 Myr cycle in fossil diversity in the past 542 Myr; however, no plausible mechanism has been found. We propose that the cycle may be caused by modulation of cosmic-ray (CR) flux by the solar system vertical oscillation (64 Myr period) in the Galaxy, the Galactic north-south anisotropy of CR production in the Galactic halo/wind/termination shock (due to the Galactic motion toward the Virgo Cluster), and the shielding by Galactic magnetic fields. We revisit the mechanism of CR propagation and show that CR flux can vary by a factor of about 4.6 and reach a maximum at northernmost displacement of the Sun. The very high statistical significance of (1) the phase agreement between solar northward excursions and the diversity minima and (2) the correlation of the magnitude of diversity drops with CR amplitudes through all cycles provide solid support for our model. Various observational predictions which can be used to confirm or falsify our hypothesis are presented.
TL;DR: In this article, a time-dependent model of the SW charge exchange (SWCX) X-ray emission was developed, based on the localization of SW Parker spiral at each instant, and the SW conditions affecting three selected fields, as well as shadowing targets observed with XMM-Newton, Chandra and Suzaku, were analyzed.
Abstract: We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emission generated by charge transfer collisions between solar wind (SW) oxygen ions and interstellar H and He neutral atoms in the inner Heliosphere. These lines which dominate the 0.3-1.0 keV energy interval are also produced by hot gas in the galactic halo (GH) and possibly the Local Interstellar Bubble (LB). We developed a time-dependent model of the SW Charge-Exchange (SWCX) X-ray emission, based on the localization of the SW Parker spiral at each instant. We include input SW conditions affecting three selected fields, as well as shadowing targets observed with XMM-Newton, Chandra and Suzaku and calculate X-ray emission fot O VII and O VIII lines. We determine SWCX contamination and residual emission to attribute to the galactic soft X-ray background. We obtain ground level intensities and/or simulated lightcurves for each target and compare to X-ray data. The local 3/4 keV emission (O VII and O VIII) detected in front of shadowing clouds is found to be entirely explained by the CX heliospheric emission. No emission from the LB is needed at these energies. Using the model predictions we subtract the heliospheric contribution to the measured emission and derive the halo contribution. We also correct for an error in the preliminary analysis of the Hubble Deep Field North (HDFN).
TL;DR: In this paper, an exceptionally broad (1.85 × 106 km) Petschek-type reconnection exhaust within the heliospheric current sheet, HCS, in the solar wind at 1 AU on 31 August and 1 September 2001 provide convincing direct evidence for prolonged (at least 5 hours) magnetic reconnection at a continuous X-line in solar wind.
Abstract: [1] Observations by 5 spacecraft of an exceptionally broad (1.85 × 106 km) Petschek-type reconnection exhaust within the heliospheric current sheet, HCS, in the solar wind at 1 AU on 31 August and 1 September 2001 provide convincing direct evidence for prolonged (at least 5 hours) magnetic reconnection at a continuous X-line in the solar wind. At least 1.2 × 1024 ergs of magnetic energy were extracted from the HCS in this event and converted to kinetic and thermal energy of the exhaust plasma. The reconnection produced field lines disconnected from the Sun and may have originated inside the point where the solar wind became super-Alfvenic, thereby slightly reducing the amount of open magnetic flux present in the heliosphere.
TL;DR: In this article, the authors examined the energy properties of 39 flux-rope-like coronal mass ejections from the Sun using data in the distance range ∼2-20 R o from the Large Angle Spectroscopic Coronograph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO).
Abstract: Aims. We investigate whether solar coronal mass ejections are driven mainly by coupling to the ambient solar wind or through the release of internal magnetic energy. Methods. We examine the energetics of 39 flux-rope like coronal mass ejections (CMEs) from the Sun using data in the distance range ∼2-20 R o from the Large Angle Spectroscopic Coronograph (LASCO) aboard the Solar and Heliospheric Observatory (SOHO). This comprises a complete sample of the best examples of flux-rope CMEs observed by LASCO in 1996-2001. Results. We find that 69% of the CMEs in our sample experience a clearly identifiable driving power in the LASCO field of view. For those CMEs that are driven, we examine if they might be deriving most of their driving power by coupling to the solar wind. We do not find conclusive evidence in favor of this hypothesis. On the other hand, we find that their internal magnetic energy is a viable source of the required driving power. We have estimated upper and lower limits on the power that can possibly be provided by the internal magnetic field of a CME. We find that, on average, the lower limit to the available magnetic power is around 74% of what is required to drive the CMEs, while the upper limit can be as much as an order of magnitude larger.
TL;DR: In this paper, a 2.5-dimensional ideal magnetohydrodynamic (MHD) model was used to study the interplanetary multiple magnetic clouds (Multi-MC) in the heliospheric meridional plane.
Abstract: [1] Numerical studies of the interplanetary “multiple magnetic clouds (Multi-MC)” are performed by a 2.5-dimensional ideal magnetohydrodynamic (MHD) model in the heliospheric meridional plane. Both slow MC1 and fast MC2 are initially emerged along the heliospheric equator, one after another with different time intervals. The coupling of two MCs could be considered as the comprehensive interaction between two systems, each comprising of an MC body and its driven shock. The MC2-driven shock and MC2 body are successively involved into interaction with MC1 body. The momentum is transferred from MC2 to MC1. After the passage of MC2-driven shock front, magnetic field lines in MC1 medium previously compressed by MC2-driven shock are prevented from being restored by the MC2 body pushing. MC1 body undergoes the most violent compression from the ambient solar wind ahead, continuous penetration of MC2-driven shock through MC1 body, and persistent pushing of MC2 body at MC1 tail boundary. As the evolution proceeds, the MC1 body suffers from larger and larger compression, and its original vulnerable magnetic elasticity becomes stiffer and stiffer. So there exists a maximum compressibility of Multi-MC when the accumulated elasticity can balance the external compression. This cutoff limit of compressibility mainly decides the maximally available geoeffectiveness of Multi-MC because the geoeffectiveness enhancement of MCs interacting is ascribed to the compression. Particularly, the greatest geoeffectiveness is excited among all combinations of each MC helicity, if magnetic field lines in the interacting region of Multi-MC are all southward. Multi-MC completes its final evolutionary stage when the MC2-driven shock is merged with MC1-driven shock into a stronger compound shock. With respect to Multi-MC geoeffectiveness, the evolution stage is a dominant factor, whereas the collision intensity is a subordinate one. The magnetic elasticity, magnetic helicity of each MC, and compression between each other are the key physical factors for the formation, propagation, evolution, and resulting geoeffectiveness of interplanetary Multi-MC.
02 Jul 2007
TL;DR: In the attempt to understand this unexpected source of problems, it is found that solar modes are detectable in the interplanetary magnetic fields and energetic particles at the Ulysses spacecraft, five astronomical units from the Earth.
Abstract: This paper describes some unanticipated effects of the normal modes of the sun on engineering and scientific systems. We begin with historical, scientific, and statistical background, then present evidence for the effects of solar modes on various systems. Engineering evidence for these modes was first noticed in an investigation of communications satellite failures and second in a study of excessive dropped calls in cellular phone systems. The paper also includes several sections on multitaper estimates of spectra, canonical coherences, robust, and cyclostationary variants of multitapering, and related statistical techniques used to separate the various components of this complex system. In our attempt to understand this unexpected source of problems, we have found that solar modes are detectable in the interplanetary magnetic fields and energetic particles at the Ulysses spacecraft, five astronomical units from the Earth. These modes couple into the magnetosphere, the ionosphere, the geomagnetic field, and atmospheric pressure. Estimates of the power spectrum of data from solar radio telescopes and induced voltages on ocean cables show what appear to be solar modes at both lower and higher frequencies than the optically measured solar p-modes. Most surprisingly, these modes are easily detected in seismic data, where they literally shake the Earth.
TL;DR: In this paper, the authors reveal the extent of the plasma tail of comet 2P/Encke to unprecedented lengths and allow them to examine the mechanism behind a spectacular tail disconnection event driven by magnetic reconnection between the magnetic field entrained in the CME and the interplanetary field draped around the comet.
Abstract: This a discovery report of the first direct imaging of the interaction a comet with a coronal mass ejection (CME) in the inner heliosphere with high temporal and spatial resolution. The observations were obtained by the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) Heliospheric Imager-1 (HI-1) aboard the STEREO mission. They reveal the extent of the plasma tail of comet 2P/Encke to unprecedented lengths and allow us to examine the mechanism behind a spectacular tail disconnection event. Our preliminary analysis suggests that the disconnection is driven by magnetic reconnection between the magnetic field entrained in the CME and the interplanetary field draped around the comet and not by pressure effects. Further analysis is required before we can conclude whether the reconnection occurs on the day side or on the tail side of the comet. However, the observations offer strong support to the idea that large-scale tail disconnections are magnetic in origin. The online movie reveals a wealth of interactions between solar wind structures and the plasma tail beyond the collision with the CME. Future analyses of this data set should provide critical insights on the structure of the inner heliosphere.
TL;DR: In this article, a quasi-steady two-dimensional (axisymmetric) model of the heliospheric transport of galactic cosmic rays is presented, which is based on stochastic simulation techniques and includes all the modulation mechanisms that cosmic rays experience in the Heliosphere: convection, adiabatic cooling, diffusion, and drifts.
Abstract: [1] We present a quasi-steady two-dimensional (axisymmetric) model of the heliospheric transport of galactic cosmic rays. The model is based on stochastic simulation techniques and includes all the modulation mechanisms that cosmic rays experience in the heliosphere: convection, adiabatic cooling, diffusion, and drifts. A special emphasis is given to the cosmic ray transport in the vicinity of the heliospheric current sheet (HCS), and a new method to calculate the wavy current sheet drift is presented. We study cosmic ray modulation in different solar modulation conditions and levels of waviness of the current sheet. We discuss changes in the cosmic ray spectrum and the dominant streaming patterns of cosmic rays in the heliosphere for different solar polarities and HCS tilt angles.
TL;DR: In this paper, a hybrid code, Hakamada-Akasofu-Fry code version 2 (HAFv.2+3DMHD), was used to study the global interplanetary coronal mass ejection (ICME) from the 12 May 1997 solar event.
Abstract: [1] A newly developed hybrid code, HAFv.2+3DMHD, that combines two simulation codes, Hakamada-Akasofu-Fry code version 2 (HAFv.2) and a fully three-dimensional (3-D), time-dependent MHD simulation code, is used to study the global interplanetary coronal mass ejection (ICME) from the 12 May 1997 solar event. The solar wind structure is first simulated from the photosphere (1 solar radius, Rs) out to 2.5 Rs. The first step is derived from daily solar magnetograms. The HAFv.2 code is then used from 2.5 Rs to provide input at 18 Rs (0.08 AU) for the three-dimensional MHD code that calculates the evolution of solar wind plasma and interplanetary magnetic field beyond this distance into the heliosphere. A dynamic disturbance, mimicking the flare's energy output from the 12 May 1997 solar event, is then delivered to this quiescent nonuniform heliospheric structure to model the evolution and interplanetary propagation of the ICME (including its shock). We compare the derived ICME velocity and number density with the Wind spacecraft observations near Earth. We integrate the line-of-sight density in the plane of sky to compare with the white light brightness data observed by the Large-Angle Spectrometric Coronograph (LASCO) instrument on SOHO. This simulation will provide a tool to link the general cases of ICME at 1 AU to their solar sources, as well as to identify the possible origins of shock formation due to CMEs and CME/corotating interaction region interactions. In the case of complex or interacting ejecta, model interpretation is often required to accurately determine the solar sources of the ejecta at 1 AU. Because this newly developed model is performed using 3-D MHD, its results can be extended to simulate coronal and heliospheric observations, including the ambient medium's nonuniformity provided by the HAFv.2 model, from the recently launched Solar Terrestrial Relations Observatory (STEREO) mission.
TL;DR: In this paper, the effects of heliospheric disturbances on the position of the termination shock (TS) were examined using a three-dimensional MHD model, and the simulation indicated that the TS was at ~90 AU along the Sun-V1 line on 2007 August 14, the last tentative available date of the V2 data.
Abstract: The effects of heliospheric disturbances on the position of the termination shock (TS) are examined using a three-dimensional MHD model. Variations in the solar wind ram pressure due to the interplanetary shock waves drive the TS away from its steady state equilibrium position and emit shocks and waves downstream. Transmitted/emitted disturbances propagating from the TS to the heliopause (HP) are partially reflected at the HP, and the reflected waves return and collide with the TS. Thus, besides upstream solar wind disturbances, the TS location RTS changes in response to incident downstream disturbances associated with waves reflected from the HP produced by earlier supersonic solar wind disturbances. To determine the time-varying RTS, we incorporate Voyager 2 (V2) plasma data as a boundary condition into our 3D MHD simulations, which allows us to forecast the termination shock movement for nearly a year after the present V2 data. Our simulations indicate that the TS was at ~90 AU along the Sun-V1 line on 2007 August 14, the last tentative available date of the V2 data. After this, our simulation forecasts that RTS will decrease to a minimum distance in late 2007 or early 2008. This decrease will be mainly caused by the heliosheath returned pulse driven by the 2006 March event. Whether V2 will cross the TS or not in this period depends on the future solar wind ram pressure and also on the degree of the north-south asymmetry of the heliospheric structure. Some quantitative discussions are given.
TL;DR: In this paper, the authors explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured interplanetary magnetic field (IMF) and find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum.
Abstract: Photospheric observations at the Wilcox Solar Observatory (WSO) represent an uninterrupted data set of 32 years and are therefore unique for modeling variations in the magnetic structure of the corona and inner heliosphere over three solar cycles. For many years, modelers have applied a latitudinal correction factor to these data, believing that it provided a better estimate of the line-of-sight magnetic field. Its application was defended by arguing that the computed open flux matched observations of the interplanetary magnetic field (IMF) significantly better than the original WSO correction factor. However, no physically based argument could be made for its use. In this Letter we explore the implications of using the constant correction factor on the value and variation of the computed open solar flux and its relationship to the measured IMF. We find that it does not match the measured IMF at 1 AU except at and surrounding solar minimum. However, we argue that interplanetary coronal mass ejections (ICMEs) may provide sufficient additional magnetic flux to the extent that a remarkably good match is found between the sum of the computed open flux and inferred ICME flux and the measured flux at 1 AU. If further substantiated, the implications of this interpretation may be significant, including a better understanding of the structure and strength of the coronal field and I N providing constraints for theories of field line transport in the corona, the modulation of galactic cosmic rays, and even possibly terrestrial climate effects.