Mesoscale Variations in the Heliospheric Magnetic Field and their Consequences in the Outer Heliosphere

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 PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87299/2/365_1.pd

The Formidable Task of Developing a Predictive Capability of the Space Environment of the Solar System

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76899/1/AIAA-2005-6822-320.pd

Implications of a weak termination shock

Recent observations from the Voyager spacecraft have suggested that the spectrum of the anomalous cosmic ray component is relatively steep at the termination shock, which is believed to be responsible for accelerating these particles. This conclusion argues that the termination shock must be weak, which in turn requires that the upstream Mach number in the solar wind must be quite low, ∼2.4. It is pointed out that such conditions are unlikely to prevail at all locations along the shock front. However, it is possible for such conditions to exist at the interface between high speed streams at high heliographic latitudes and the region at low latitudes where high and low speed streams have interacted and come into equilibrium. This discussion suggests a preferred location for the injection of the anomalous component into the shock acceleration process.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43779/1/11214_2004_Article_BF00170799.pd

Exploring the heliosphere in three dimensions a keynote presentation

The 28th ESLAB Symposium marks the beginning of the sprint of the Ulysses mission to the very high heliographic latitudes and the pole-to-pole passage. The more than twenty-year quest to understand the Sun and the heliosphere in three dimensions is about to be realized. It is perhaps worthwhile, as we are poised to begin this journey, to ask how history is likely to judge this mission, or equivalently: what questions need to be answered so that the judgment will be kind?Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43778/1/11214_2004_Article_BF00768748.pd

Heating of Pickup and Solar Wind Ions at Jupiter’s Bow Shock

Interstellar pickup ions are dynamically important in the outer heliosphere where they mass‐load and heat the solar wind. Some of these pickup ions are transformed into energetic neutral atoms (ENAs) by charge exchange with the residual cold interstellar gas that is the primary constituent of the outer heliosphere. The most detailed measurements of interstellar pickup ions in the heliosphere are currently available only between ∼1 and ∼5 AU. Among the most interesting and least expected observations are those of ubiquitous suprathermal tails on the distribution of pickup and solar wind protons and all heavier ions that can be measured. Here we report new measurements of solar wind proton and alpha particle distributions and of pickup He+ spectra upstream and downstream of Jupiter’s bow shock. We find that in the magnetosheath, 27% of the total pickup H+ density is in the tail portion of the distribution, compared to only 0.4% in the upstream spectrum. For He+ the entire core distribution is apparently heated in crossing the shock. These results have important implications for particle acceleration at the heliospheric termination shock, and for predicting the fluxes of energetic neutral atoms in the inner heliosphere produced from solar wind and pickup ions heated and accelerated at the termination shock. © 2004 American Institute of PhysicsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87300/2/201_1.pd

Origin of the Solar Wind: Theory

A theory is presented for the origin of the solar wind, which is based on the behavior of the magnetic field of the Sun. The magnetic field of the Sun can be considered as having two distinct components: Open magnetic flux in which the field lines remain attached to the Sun and are dragged outward into the heliosphere with the solar wind. Closed magnetic flux in which the field remains entirely attached to the Sun, and forms loops and active regions in the solar corona. It is argued that the total open flux should tend to be constant in time, since it can be destroyed only if open flux of opposite polarity reconnect, a process that may be unlikely since the open flux is ordered into large-scale regions of uniform polarity. The behavior of open flux is thus governed by its motion on the solar surface. The motion may be due primarily to a diffusive process that results from open field lines reconnecting with randomly oriented closed loops, and also due to the usual convective motions on the solar surface such as differential rotation. The diffusion process needs to be described by a diffusion equation appropriate for transport by an external medium, which is different from the usual diffusion coefficient used in energetic particle transport. The loops required for the diffusion have been identified in recent observations of the Sun, and have properties, both in size and composition, consistent with their use in the model. The diffusive process, in which reconnection occurs between open field lines and loops, is responsible for the input of mass and energy into the solar wind.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43804/1/11214_2004_Article_338798.pd

The new heliospheric magnetic field: Observational implications

A summary of the new model of the heliospheric magnetic field and its observational implications is presented. We first introduce a global model for the steady-state configuration in the low corona and discuss solar and heliospheric implications of the resulting field configuration. Finally, we compare the effects of this model with random transport of field-lines due to reconnection on the solar surface and to the dynamic turbulent transport of magnetic field-lines. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87723/2/87_1.pd

Ubiquitous statistical acceleration in the solar wind

One of the more interesting observations by ACE is the ubiquitous presence of higher energy tails on the distribution functions of solar wind and pickup ions. The tails occur continuously in the slow solar wind, but less so in fast wind. Their presence is not correlated with the passage of shock waves. It is pointed out that statistical acceleration by transit-time damping of propagating magnitude fluctuations in the magnetic field of the solar wind is a likely mechanism to yield the observed tails. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87342/2/229_1.pd

Sources, injection and acceleration of heliospheric ion populations

A variety of heliospheric ion populations—from Anomalous Cosmic Rays (ACRs) to particles accelerated in Corotating Interaction Regions (CIRs)—have been observed and studied for several decades. It had been commonly assumed that the solar wind was the source for all of these populations, except for the ACRs, and that shock acceleration produced the energetic particles observed, including the ACRs. For the ACRs the source that had been proposed a long time ago was the interstellar gas that penetrates deep into the heliosphere. Recent measurements of the composition and spectra of suprathermal ions, primarily from Ulysses, ACE and Wind, indicate that pickup ions are likely to be an important source not only of the ACRs but for other heliospheric ion populations as well. In particular, the newly discovered “Inner Source” pickup ions may be a significant source for particles accelerated in the inner heliosphere and may also be the seed material for ACR C, Mg, Si and Fe. Furthermore, the omnipresent suprathermal tails seem to tell us that shock acceleration may not be the primary mechanism energizing particles to ∼0.1 MeV in the heliosphere. Explaining the origin of these persistent high velocity tails remains one of our challenges. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87341/2/221_1.pd

Observations of non-thermal properties of heavy ions in the solar wind

Heavy ions in the solar wind are ideal for studying injection processes in the solar wind. We use composition data from Ulysses, ACE, and Wind to examine the properties of heavy ions from thermal energies to several 100 keVs. We show that these particles are observed to gain energy without any association with shocks. This paper provides a survey of recent observations of non-thermal properties of solar wind heavy ions which are consistent with the following picture: At thermal energies coherent wave-particle interactions preferentially heat and accelerate heavy ions with collisional processes limiting subsequent non-thermal properties. At higher energies heavy ion distribution functions are characterized by ubiquitous suprathermal tails. We argue that solar wind heavy ions are a good tracer for acceleration processes which are not directly associated with shocks. These stochastic processes are observed to be relevant for predisposing ions for shock acceleration. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87338/2/215_1.pd