What is the Acceleration Mechanism for Anomalous Cosmic Rays and Where is it Happening?
Session Leaders: Alan Cummings(Caltech) and Randy Jokipii (U. of Arizona)
In this session we plan to examine the problems raised by recent observations by Voyagers 1 and 2 (V1 and V2) of the anomalous cosmic rays near and beyond the termination shock. Prior to V1's crossing of the solar wind termination shock in late 2004, most researchers working on anomalous cosmic rays (ACRs) thought that the energy spectrum of the ACRs (He, for example) would change from a modulated spectrum with a low-energy turnover upstream of the shock to a shock-accelerated near-power-law spectrum at and beyond the shock.
That was not observed. Similarly, before V2 crossed the shock in August 2007, some thought the spectral shape observed at V1 as it crossed the shock was due to the dynamics of the shock, either the motion of the shock in response to turbulence or transients interrupting the acceleration process, and that if left alone, the shock would deliver the power law that was expected. Since the Sun had become quieter and transients were becoming few and far between, some thought V2 would observe the power-law spectrum as it crossed the shock. But others pointed out that turbulence was still present. Still others came up with reasons why the ACR source spectrum would not be expected near the blunt nose of the termination shock and proposed the flanks or tail regions of the shock as the source location. It was also possible that the source is at a different latitude of the termination shock. Finally, others proposed that the termination shock was not the great particle accelerator almost everyone had assumed it was and that continuous acceleration occurs across the heliosheath.
From 30 August to 1 September 2007, V2 crossed the termination shock at least five times. V2 did not observe the near-power-law spectral shape for ACRs, and as of mid-February 2008, nearly 6 months after V2 crossed the shock, the shape of the energy spectrum remains with a turnover at mid-ACR energies (albeit with a turnup to a power-law at low energies). However, at V1, the shape has become a near power law as originally expected nearer the shock. This means that there is now a substantial spatial gradient between the two spacecraft at mid-ACR energies. A strong temporal change in the overall heliospheric effects (modulation) has occurred since V1's crossing and this has made interpretation difficult.
In this background, we plan a session to review the observations and recent theoretical advancements to chart a path towards understanding the ACRs.
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The Theory of Suprathermal Particle Acceleration
Session Leaders: Matt Hill (APL) and Joe Giacalone (U. of Arizona)
In the interplanetary medium, the suprathermal energy range, above bulk plasma energies of a few keV and below energetic particles of hundreds of keV, has been poorly understood due, to some extent, to the relative lack of reported observations. The dearth of data has begun to be alleviated and serious theoretic studies are maturing. One issue of considerable interest is identification of the acceleration processes responsible for the ever-present suprathermal tails in the particle spectra; stochastic vs. shock acceleration being among the dominant explanations. In this session we plan to follow up on the 2007 SHINE session in which the new observations were presented. This year will be prime time to hear from the theoretical community. The recent progress in understanding the physical mechanisms behind our in situ observations is having an impact on studies in the corona, heliosheath and even the magnetosphere.
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Where and How do Shocks Form in the Corona?
Session Leaders: Merav Opher (GMU) and Angelos Vourlidas (NRL)
This session continues the theme of coronal shocks from last year’s session. This time we focus on the theory of shock in association with CMEs and flares. We concentrate on shock formation low in the corona and the observations that support or contrast the theoretical predictions. Some of the questions we would like to discuss are:
- Where/how do shocks form?
- What is the Alfven profile in the corona? Does the bump in Alfven Speed exist?
- Does the CME shock form right at the tip of the streamer or on the side?
- What do shock remote sensing observations (spectroscopic, white light) reveal about the shock structure?
Our goal is to come up with a set of required observations for current instrumentation on how to detect shocks during the upcoming rise to solar max.
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Heliospheric Plasma Sheet
Session Leaders: Ian Richardson (GSFC) and Angelos Vourlidas (NRL)
The heliospheric plasma sheet (HPS), together with the embedded current sheet, forms an important feature of the heliosphere, separating magnetic fields and plasma from the northern and southern solar hemispheres. For more than a year, the STEREO mission has provided imaging observations of the HPS during solar minimum from two vantage points. This session will highlight and discuss the recent results from STEREO and inner heliospheric probes (Messenger, Venus Express). Studies of the HPS using data from other missions, such as ACE, IMP 8 and Helios 1 and 2, or modeling, may also contribute to this session. Important questions to explore include:
- Are HPS observations dominated by spatial or temporal variations (or both)? Are there multiple current sheets?
- How do ICMEs and CIRs interact with the HPS, and what are the consequences of this interaction?
- What are the characteristic solar features associated with the base of the HPS? What is the relationship between the streamer belt and active regions?
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CME Dynamics - What are EUV Waves?
Session Leaders: Angelos Vourlidas (NRL) and Ilia Roussev (UHI)
This session continues the energetic discussions on the nature of coronal EUV waves from last year’s session. This time we bring in new observations in soft X-rays and stereoscopic observations from SECCHI to find out whether they can help us answer the following question: Are EUV waves shocks or waves or are they the coronal footprint of the CME?
We invite researchers with an interest in this topic to participate in the discussion. A discussion on the modeling (e.g., MHD) of these waves will also take place based on the abstracts submitted for this session.
Discussion Topics:
- Soft X-ray waves: A unique SXI observations – V. Pizzo
- Stereoscopic observations of EUV waves from SECCHI – S. Patsourakos
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Turbulence in the Solar Wind
Session Leaders: Ben Chandran (UNH) and Joe Giacalone (U. Arizona)
Spacecraft observations of velocity and magnetic-field fluctuations in the solar wind provide striking evidence of large-amplitude turbulence in both the fast and slow solar wind. This turbulence is widely believed to play an important role in the heating of the solar wind and the transport of energetic particles. This session will address several key questions regarding fundamental aspects of solar-wind turbulence that are at the forefront of current research on this
problem:
1. What is the origin of the observed ``quasi-parallel waves'' in the solar wind, whose wave vectors are closely aligned with the background magnetic field?
2. How does the observed alignment between magnetic-field and velocity fluctuation vectors affect the dynamics of solar wind turbulence and the cascade of energy to small scales?
3. What are the dominant dissipation mechanisms in the collisionless solar wind, and what is the appropriate way to model the dissipation range?
4. What are the appropriate scalings to describe both the inertial-range energy spectrum and the energy-dissipation rate?
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Radio Observations of Electrons from the Corona to the Magnetosphere
Session Leaders: Justin Kasper (SAO) and Dennis Haggerty (APL)
The purpose of this working group is to examine our current understanding of the motion and acceleration of electrons through radio emission and other observational techniques. In light of the joint meeting between SHINE and GEM, this year we will examine radio observations of electrons both in the corona and in the magnetosphere.
The session will be grouped into two parts. In the first half, we will review recent radio observations of electron acceleration in the corona and interplanetary space, with a focus on the determination of electron trajectories. Are there good examples of electron beam tracking? How well do the inferred trajectories compare with models of the coronal and interplanetary field? Have the radio observations been linked to other concurrent emission, such as x-ray, UV, optical?
In the second half we will explore recent work on radio observations of electrons in the magnetospheric environment, from the ionosphere to the bow shock. In particular, we will investigate methods for determining electron density and total electron content. Presentations on density inversion techniques using GPS tomography, multiple spacecraft, or emerging low frequency radio arrays are solicited. Posters on the status of these projects are requested. This session will begin with a review of the posters by the chair, followed by a discussion of electron measurements with radio observations.
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Impulsive 3He-rich and Electron Events
Session Leaders: Dennis Haggerty (APL) and Säm Krücker (UC Berkeley)
Impulsive 3He rich events are generally small, have a short duration, can have up to 10 4 x coronal abundance of 3He/ 4He, and are associated with electron events. New observations show that the spectral slope of 3He can be different from other ions, can be associated with ultra heavy ions with huge enrichments over typical solar abundances, and are nearly continuously present in the interplanetary medium [see Mason, SHINE 2007]. Recent observations have also found that these impulsive 3He rich events may have accompanying streaming jets at the boundary of active regions where particle injection is believed to occur. All these observations can be very useful to constrain the underlying acceleration mechanisms (Oblique EM waves, second order Fermi, other…). In this session we solicit both remote and in situ observations, as well as theoretical and modeling work regarding these events.
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Hard X-rays and Particle Acceleration in Flares
Session Leaders: Säm Krücker (UC Berkeley)
Hard X-ray bursts produced by bremsstrahlung emission of flare-accelerated electrons are the most common signatures of electron acceleration in solar flares, and provide key diagnostics for the acceleration process. This session emphasizes on recent results obtained by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). Specifically, we will discuss hard X-ray emissions seen in the corona. Coronal hard X-ray sources can differ fundamentally from the classical footpoint sources of the flare impulsive phase and provide unique information about the supra-thermal electrons closest to the site in the corona where their acceleration is believed to occur. Despite the low density and hence low bremsstrahlung efficiency of the corona, RHESSI detects coronal hard X-ray emission from sources in all phases of solar flares, including sources suggesting the morphology of the Masuda flare. In major events the electron energies required may exceed one MeV. Other sources have been found by association with backside Coronal Mass Ejection events.
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Vector Magnetic Inputs to Global Models
Session Leaders: Ilia Roussev (UHI) and Marc DeRosa (LMSAL)
The increasing availability of both high-resolution and full-disk vector magnetograms (from such instruments a Hinode/SOT and SDO/HMI) will provide new ways to infer and analyze the structure and evolution of the coronal magnetic field on the sun. In this session, we will explore some aspects encountered when producing and using such data. Key questions include: What uncertainties lie in the inversion and 180-degree disambiguation processes? What effects do these have on the calculation of physical quantities, such as current densities and helicities? What is the best way to incorporate such data into models that drive coronal and heliospheric dynamics and space weather, given these uncertainties?
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Understanding Prominence Mass
Session Leaders: Holly Gilbert (Rice) and David Alexander (Rice)
In previous prominence sessions at SHINE, we have focused on dynamics. In this session we hope to address a fundamental question: why and how is prominence mass important? Topics to be addressed/challenged include what role prominence mass plays in providing a view of magnetic field structure, “anchoring” the overlying structure, understanding the thermodynamics, and understanding the chromosphere-corona TR.
The approach of this session is to start “simple” by trying to understand quiescent prominences. We hope to highlight the new prominence data offered by Hinode SOT and to address the following observational and modeling challenges:
Observational challenges
- Multi-wavelength picture- do we really know what we’re seeing?
- e.g., understanding H-alpha
- e.g., absorption vs. volume blocking of UV, EUV, SXR
- How well are we interpreting the observations?
- Difficulty that plasma motions introduce
- Structure- vertical threads vs. horizontal threads
- Understanding dynamics
- Bulk mass flows
- Wave-induced motions
Modeling challenges
- How realistic are the current models?
- Non-LTE radiative transfer in model prominences
- Are quiescent prominence fields force-free? (Anzer & Heinzel 2007)
- How to utilize the new observations for better modeling?
- Fine structure
- Mass loading
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The Magnetic and Energetic Connection Between the Solar Convection Zone and the Corona
Session Leaders: Bill Abbett (UC Berkeley)
All solar activity --- variations in energy released by the Sun, as electromagnetic radiation and energetic particles --- is mediated by the Sun's magnetic field. This activity, whether in the form of irradiance variations, modulation of the solar wind, acceleration of solar energetic particles, or flares and coronal mass ejections, ultimately arises as a result of the coupling between the Sun's magnetic field and the rotating, turbulent plasma of its convective interior. To better understand and predict space weather, we must therefore be able to describe in a quantitative way the magnetic and energetic coupling between the Sun's envelope and atmosphere. This session will focus on recent progress in this area; both theoretical and observational studies will be addressed.
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Campaign Event: 5-14 December 2006
Session Leaders: Tamitha Mulligan (Aerospace Corp) and Qiang Hu (UC Riverside)
A primary source of the highest particle intensities observed at Earth, solar energetic particles (SEPs) provide vital information on particle scattering and transport in the interplanetary medium. Although once believed to be accelerated in solar flares and diffusing across coronal and interplanetary magnetic fields, large, gradual, SEPs are now mainly thought to be accelerated at shocks driven by coronal mass ejections (CMEs) propagating through the outer solar atmosphere and interplanetary medium. Yet despite many observations and much debate over the past several decades, quantitative prediction of SEP properties remains elusive.
A series of X-class flares (and accompanying SEPs) originating from active region 930 as it rotated across the solar disk from December 5, 2006 through December 16, 2006 has presented the community with a unique opportunity to study various relationships between flare/ shock associated SEP populations and CME transport effects. What makes this group of events unique is that the series occurred during a relatively quiet solar period near solar minimum when an unprecedented barrage of spacecraft including, STEREO, ACE, Wind, SAMPEX, Polar, Cluster, and Ulysses were available to observe the series at differing latitudes and longitudes.
The focus of this session is to address a number of cross-disciplinary topics as they relate to this SEP event series:
- What is the acceleration mechanism in each event in the series (shock, flare)? Is the variability such that we can separate the two effects? (i.e. for the strong shock on the 14th, does the flare acceleration component get overwhelmed?)
- How does IP transport affect the composition and spectra in the series?
- Do the high latitude and differing longitude multipoint observations of the series complicate or simplify the picture? (Same question applies to the sunspot rotation causing each spacecraft to have a differing magnetic connection to the event. Is there a pattern, is it predictable? Is it consistent with prevailing theories?)
- CME/ICME modeling-- is there a flux rope structure? What is its role in transport?
- Is the shock geometry different at the various spacecraft? Does a changing theta_BN affect the injection threshold energies in a predictable way, consistent with theories?
- Are the statements, "Different events seen by the same s/c are different,” and, “The same event seen by different s/c are the same," borne out for the series? (Or might these statements be a function of latitude or longitude?)
The goal of this session is to utilize remote observations of the solar magnetic field and CMEs together with in situ observations of the solar wind plasma, IMF, and energetic particle spectra and composition to constrain end-to-end CME and shock acceleration models, validate numerical codes, and drive discussion of the physical mechanisms behind the series of observations.
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Relationships between Flares and CMEs
Session Leaders: Ben Lynch (UC Berkeley) and Jim McTiernan (UC Berkeley)
This session will focus on the relationships between solar flares and CME's. We will consider timing relationships, size/strength correlations, and causality --- that is, are flares/CME's byproducts of CME's/flares or are both phenomena byproducts of large-scale energy release simply manifested in different ways? In particular, we will focus on 1) the energy partitioning between various aspects of the flare-CME system, such as CME acceleration, hard X-rays, microwave bursts, thermal heating, electron beams, and SEP production; 2) the structure of eruptive events, such as topological changes due to reconnection, flare loop and ribbon evolution in 3-dimensions, and current sheet formation and dissipation; and 3) the connection between directly and indirectly observed flare and associated CME properties (e.g., reconnected magnetic flux, heavy ion charge states, SEP and ICME composition, in-situ L1, and multi-point observations).
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Introduction to Community Models
Session Leaders: Jon Linker (SAIC) and Bill Abbett (UC Berkeley)
The purpose of the session is to introduce the community to available solar & heliospheric models. After brief introductions to the available models, participants will have the opportunity to visit "stations" provided by the CCMC and model developers. Model developers will be available to show off their model web sites and/or point to where their model resides at the CCMC, explain how the different available parameters affect the solutions, and answer questions about the model.
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Modeling a “Simple” CME from its Eruption to its Interplanetary Propagation out past Earth: The May 13, 2005 Event
Session Leaders: Nick Arge (AFL)
Over the last several years the SHINE community has had a focused, coordinated effort to model a CME from its eruption at the Sun to its interplanetary propagation out past Earth. The May 12, 1997 CME was selected as the event to focus on, as it occurred near solar minimum when the Sun had a relatively simple configuration. While significant progress has been made over the years on this event, last year SHINE members decided it was time to shift the focus on the newer May 13, 2005 CME. This event is remarkably similar to May 12, 1997 (see Yurchyshyn et al., 2006, Solar Physics) in many respects, but it was much better observed by both ground and space based observatories. In this first session on the “simple” May 13, 2005 CME, a brief observational overview of the event will be provided followed by two short presentations discussing recent efforts to model it. Participants are encouraged to submit posters on this event as well as to bring one page summaries of them, since there should be time for a select few of them to be presented (i.e., depending on their relevance to the discussion during the session).
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Origin of the Structure in the Solar Wind
Session Leaders: Joe Borovsky (LANL) and Nick Arge (AFL)
Spacecraft measurements indicate that the solar-wind plasma at 1 AU is filled with discontinuities. One interpretation is that the large discontinuities seen at 1 AU have their origins at the sun and that magnetic and plasma structures in the solar wind at 1 AU are the open-flux bundles that penetrate through the magnetic carpet from the photosphere into the corona. Computer-simulations indicate that MHD turbulence can create coherent discontinuities in the solar-wind plasma via the action of cascade of fluctuation energy to smaller spatial scales.
In this working group session there will be discussions focused on:
•What structures in the solar wind at 1 AU are non-evolving fossil structure from the sun?
•What structures in the solar wind at 1 AU are created in situ by MHD turbulence or other processes?
•What is the fine-scale structure of the solar wind at distances other than 1 AU?
Any relevant measurements that have been gathered during the Whole Heliospheric Interval will be highlighted.
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The Prediction, Emergence, and Consequence of Large Active Regions
Session Leaders: Mark Rast (U. Colorado)
The emergence of large active regions often heralds significant reconfiguration of the solar magnetic field with consequent implications for the heliosphere. Moreover, large active regions are often magnetically complex and flare productive. This working group session will focus on three inter-related topics: the use of helioseismology to predict active region properties either before or after emergence, the process of active region emergence and magnetic reconfiguration, and the implications of large active region emergence for the structure and dynamics of the inner heliosphere. Discussion will center around questions such as:
- How feasible is it to predict the emergence of large active regions using helioseismic methods?
- What properties can be deduce helioseismologically, either before or after active region emergence, to understand its flare potential?
- What properties of a large active region are most important to understanding its inner heliospheric impact?
- How can careful observation of the emergence process itself lead to better understanding of an active regions subsurface structure?
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