SH32A-01
Direct Evidence for Prolonged Magnetic Reconnection at a Continuous X-Line Within the Heliospheric Current Sheet
Observations by 5 spacecraft of an exceptionally broad (1.85 x 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 x 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.
SH32A-02
Solar Wind Helium, Neon and Argon Isotopic and Elemental Composition: Data from the Metallic Glass flown on NASA's Genesis Mission
Solar wind helium, neon and argon trapped in a metallic glass target flown on NASA's Genesis mission were analyzed for their bulk composition and depth dependent distribution. The bulk isotopic and elemental composition for all elements is in good agreement with the mean values observed in the Apollo solar wind composition experiment. Adopting the measured solar wind velocity histogram during exposure, the isotopic composition of He, Ne, and Ar varies with depth within the metallic glass in a way generally consistent with ion- irradiation simulations of a solar wind of uniform composition. The similarity of the release patterns with the depth dependent distribution of trapped solar He, Ne, and Ar reported for lunar and asteroidal regolith samples shows that also the solar noble-gas record of extraterrestrial samples can be explained by mass separation of implanted solar wind with depth. This result confirms that contributions from high-energy particles to the solar wind fluence are minor, consistent with in-situ flux observations. On the other hand, a small gas fraction of the total solar gas in the metallic glass released from shallow depths is markedly enriched in the light isotopes relative to predictions from uniform isotopic implantation simulations. Contributions from interstellar gas or from the neutral solar wind are too small to explain this gas fraction. We tentatively attribute this superficially implanted gas to low-speed, current-sheet related solar wind, which was fractionated in the corona due to inefficient Coulomb drag, although the small apparent penetration depths associated to this component may be in conflict with this interpretation.
SH32A-03
Interplanetary Coronal Mass Ejections During 1996 - 2007
Interplanetary coronal mass ejections (ICMEs), the interplanetary counterparts of coronal mass ejections at the Sun, are the major drivers of interplanetary shocks in the heliosphere, and are associated with modulations of the galactic cosmic ray intensity, both short term (Forbush decreases caused by the passage of the shock, post- shock sheath, and ICME), and possibly with longer term modulation. Using several in-situ signatures of ICMEs, including plasma temperature, and composition, magnetic fields, and cosmic ray modulations, made by near- Earth spacecraft, we have compiled a "comprehensive" list of ICMEs passing the Earth since 1996, encompassing solar cycle 23. We summarize the properties of these ICMEs, such as their occurrence rate, speeds and other parameters, the fraction of ICMEs that are classic magnetic clouds, and their association with solar energetic particle events, halo CMEs, interplanetary shocks, geomagnetic storms, and cosmic ray decreases.
SH32A-04
Transport in the Interplanetary Medium of Coronal Mass Ejections
We present preliminary results of the transport study of 52 Geo-effective Interplanetary Coronal Mass Ejections (ICMEs). We analyze different CME, ICME and ambient solar wind parameters of 52 events from the Coordinated Data Analysis Workshop (CDAW) data base. We found a linear relatioship between CME and Shock speeds, which may be used to identify the related (CME and in situ) pair events. The major finding of this study is a relationship between the ambient density and the ICME driven shock speed, which apply only to low ambient densities and can be used to quantify the moment exchange between the ICME and the ambient solar wind. We discuss the implications of this finding in terms of the ICME transport in general and the Sun-Earth ICME travel time, in particular.
SH32A-05
An Analytical Three-Dimensional Field Model for Coronal Mass Ejections
We have obtained an explicit expression for the magnetic field of an upward moving 3D flux rope whose feet are anchored in the solar surface. The magnetic field in this model is rigorously line-tied. The new field model allows us to investigate the equilibrium and stability properties of line-tied flux ropes. We find that long flux ropes tend to be more unstable than short ones, and that the shape and orientation of the flux rope are likely to be significantly altered upon eruption. We are also using this model to examine the reconnection process in a situation where there is no topological distinction between field lines. Our analysis indicates that reconnection can significantly alter the appearance of the flux-rope footprint on the surface. This work is supported by NSF National Space Weather Program grants ATM0518218 and ATM0519249 to the University of New Hampshire and Helio Research.
SH32A-06
Multi-spacecraft observations of interplanetary shocks and ejecta near solar maximum
We combine observations from five different spacecraft: Helios 1, Helios 2, IMP-8, Voyager 1 and Voyager 2, from November 1977 to February 1978 (ascending phase solar cycle 21). During this period the large-scale dynamics of the solar wind near the ecliptic plane was characterized by transient forward shocks, ejecta, unstable corotating interaction regions and complex and variable magnetic sectors. We compare the solar wind observations of the five spacecraft to illuminate some aspects of the longitudinal extent and radial evolution of these large-scale events in the solar wind.
SH32A-07
Ongoing Recovery of Anomalous Cosmic Rays at 1 AU and Decreasing Radial Intensity Gradients
Using the Solar Isotope Spectrometer (SIS) on NASA's ACE spacecraft, we have measured the composition and energy spectra of anomalous cosmic rays (ACRs) near 1 AU down to energies of ~10 MeV/nucleon since late 1997. Recently these measurements have been augmented by data from the Low Energy Telescope (LET) on each of the two STEREO spacecraft, which allow us to extend the energy spectra down to ~3 MeV/nucleon. As solar minimum modulation conditions return, ACR intensities at 1 AU are recovering, although they are still a factor of ~5 lower than their peak intensities in 1997. Also, during the present A<0 magnetic polarity cycle their intensities are significantly lower relative to galactic cosmic rays (GCRs) than they were during the last A>0 cycle. We present updated measurements of the variation of the ACR oxygen intensity at 1 AU throughout the solar cycle. By comparing with observations from Voyager 1 and 2 in the outer heliosphere, we estimate the large-scale intensity gradients of ACR oxygen and GCR carbon at solar maximum, solar minimum, and during the ongoing recovery, and we investigate the role of drifts and convective processes in ACR modulation. This work was supported by NASA under grants NAG5-12929, NAS5-03131, and contract NAS7-03001.
SH32A-08
Galactic cosmic ray transport in the 3D heliosphere
Theoretical studies of cosmic-ray propagation have been to date restricted to simplified problem geometries due to certain symmetry assumptions related to the solar rotation or the relative motion between the Sun and the surrounding interstellar cloud. However, the heliosphere is an essentially three-dimensional structure lacking any symmetry owing to misalignment between the various plasma and neutral atom flows and the complex interaction between the interstellar and interplanetary magnetic fields at the heliopause. Here we present first results from the project currently underway at IGPP/UCR to develop a fully three-dimensional model of cosmic-ray propagation through the global heliosphere. Our model uses plasma and magnetic field background calculated on the basis of a complete 3D MHD-neutral global heliospheric models and includes drift and diffusive spatial transport as well as adiabatic acceleration or cooling in compressive or expanding plasma flows. Test result sets are compiled for the plasma topology corresponding to solar minimum conditions. Emphasis is placed on the role of the inner heliosheath as the region responsible for the bulk of the total heliospheric modulation.