NG31A-1176
Active Regions and Solar Cycles: Topologically Explored
Solar magnetic activity is the driver of space weather, and herewith of great importance to be able to predict. However, before being able to make predictions, we need to know the present state (on short and long- terms) and to define it as precisely as possible. We believe topological methods can contribute to that. We will discuss the state of solar magnetic active regions and that of the solar magnetic cycle in terms of topology. We study null points of solar vector magnetic fields. This allow us to study the state of active regions and the relation to CMEs and solar flares. We study the flow with Poincare maps and show that the flow has an attractor. This allow us to study the variations of the periods of quasiperiodic orbits and variations of solar magnetic cycles. These precise topological descriptions of the states will then be presented to neural networks, aimed at making predictions. An outline will be presented.
NG31A-1177
Magnetic Charge Topology Analysis for Space Weather Forecasting
Magnetic Charge Topology (MCT) models represent each concentration of flux at the surface of the Sun by a magnetic point source; the field due to these point sources is then used as a model for the coronal magnetic field. This class of model has the advantage that the coronal magnetic topology becomes particularly simple: with a few special exceptions, each field line must start on a source of one polarity, and end on a source of the opposite polarity. The exceptions are topologically interesting field lines that are either separators or lie in separatrix surfaces. We summarize an automated method for partitioning active regions into flux concentrations and implementing an MCT model. We have applied this approach to a data base of magnetograms, and present here an analysis of some of the topological features as related to the occurrence of solar energetic events. This work was funded by the Air Force Office of Scientific Research under contract FA9550-06-C-0019, and by the NASA/JSC Space Radiation Analysis Group.
NG31A-1178
Spatial Structures Of Magnetic Clouds From The Helicity Conservation Law
We present a clue of spatial structures of magnetic clouds estimated from the helicity conservation law. Spatial structures of magnetic clouds are an enigma in the interplanetary physics because of a few, at least one, in-situ data points. It is difficult to clearly decide spatial structures of magnetic clouds from in-situ data fitting, because we can fit in-situ data either by using closed structures (e.g., torus model) or by using the magnetic flux model rooting in the solar corona (e.g., Marubashi & Lepping, 2007, Ann. Geophys., 25, 2453). Additional restrictions are needed. The helicity conservation law is one of promising restrictions for magnetic cloud structures. Magnetic helicity is a quantitative measure of the magnetic field helicalness, and is a conserved quantity in the corona and in the interplanetary space. Recently magnetic helicities in the solar atmosphere have been quantitatively measured by several authors. Field pitch angles or values of force-free parameter α in magnetic clouds are also obtained from model fitting. Applying the magnetic flux tube model whose spatial scale length is longer than 2 AU, total helicities in magnetic clouds are much larger than those in solar active regions (10.--100. >> 0.01-1.0; e.g., Leamon et al., 2004, JGR, 109, A05106). However, by using the helicity conservation law and data of Leamon et al., we can estimate spatial scale lengths of magnetic clouds, 0.01--0.1 AU. From the short scale lengths, we propose two possible candidates of magnetic cloud structures. One is the spheromak, and another is the magnetic flux tube having partial helical structure around the apex. Several sample events supporting our hypothesis are shown to discuss in detail.
NG31A-1179
Magnetic Helicity and Free Magnetic Energy: Their Relation and Predictive Power in Eruptive Solar Magnetic Configurations
Solar and space weather forecasting seek metrics with predictive power that can help mitigate the adverse effects of solar eruptions and their consequences. These metrics often rely on a reduced, simplified physical background, but this does not mean that space weather itself should necessarily trade well-founded physics for operational convenience. Solar eruptions are triggered in tangled, helical, solar magnetic fields stressed well beyond their minimum energy state. We aim to precisely calculate the two physical quantities thought to be responsible for eruptions, namely, the relative magnetic helicity and the free magnetic energy of the source active regions. Using the nonlinear force-free approximation, we first relate the magnetic free energy to the relative helicity and then we proceed to distinguish eruptive from non-eruptive active regions purely from their free energy and helicity values. Results with sufficient statistics, pending the availability of high-quality solar vector magnetograms, can establish "all-clear" free-energy and helicity thresholds. Moreover, the free energy/helicity buildup in the absence of eruptions in solar active regions can be viewed as a course through a sequence of metastable states with eruptions occurring spontaneously when the system reaches local or global minimal stability. This allows the careful use of the self-organized criticality (SOC) concept to describe the dynamics of the system and leads to important conclusions about how far we can go when predicting solar eruptions.
NG31A-1180
Conversion Between Self- and Mutual Magnetic Helicities in the Stepwise Evolution of Cellular Flux Systems Towards Solar Eruption
Structures observed in the solar atmosphere are generally of smaller scales than those structures that are observed in solar eruptions, such as CME loops and erupting prominences. Although an eruption intrinsically involves a volume expansion of the structure to erupt, there is observational evidence that the erupting structure forms by interaction and merging of smaller scale structures in steps. In this paper, the evolution of an idealized solar active region composed of a number of flux tubes is investigated by three dimensional magnetohydrodynamic simulations. Under low electrical resistivity as in the solar atmosphere, the partitional structure of the active region magnetic field is not readily destroyed. Thus, the corrosion of the current sheets, which partition individual flux systems, proceeds slowly but continuously until a rather fast magnetic reconnection process abruptly changes the global topology of the system. However, a total merging of the cellular flux systems cannot be achieved all at once. The system evolves into intermediate stages, which consist of cellular flux systems of incrementally larger sizes. An eruptive phase eventually sets in when partitional flux systems are fused to form a highly self-wound magnetic structure of the largest scale. A relevant observation will be presented with simulation results.
NG31A-1181
Injection of magnetic helicity in active regions: a possible forecasting tool for solar activity
The largest phenomena of the solar activity, Coronal mass ejections (CMEs) and flares, originate from the accumulation of magnetic flux in solar active regions. Twist being necessary for flux tubes cross the convection zone, helicity also accumulates throughout the lifetime of an active region. Magnetic helicity, as a well preserved quantity, even during reconnection, unlike twist and writhe, appears as a key quantity to follow. Only recently, it has been realized that the magnetic helicity flux can be derived from time series of magnetograms. After briefly describing the advances made in measuring the helicity injection rate at the photospheric level, we review some results obtained from the study of magnetic helicity in active region, focusing on the different way magnetic helicity can be used as a forecasting tool for the prediction of CMEs and flares.
NG31A-1182
Interaction between emerging magnetic flux and the ambient solar coronal field
We study the interaction between emerging magnetic flux and pre-existing coronal field by means of numerical simulations using the magneto-frictional method. By advancing the induction equation, the magneto-frictional method models the coronal magnetic field as a quasi-static sequence of non-linear force- free field configurations evolving in response to photospheric driving. A general feature of the simulations is the spontaneous formation of tangential discontinuities, interfaces where the field line torsional coefficient changes abruptly across separate domains of connectivity. Since the method evolves the vector potential, we can follow the evolution of the relative magnetic helicity and examine its relation to the magnetic free energy. Other tools, such as the squashing factor of Titov and Démoulin, are also used to study the topology of the field configurations.
NG31A-1183
The Role of Twisted Magnetic Flux Tubes in Topological Space Weather Forecasting
More and more twisted magnetic flux tubes are being identified in the solar active regions of solar cycle 23 utilizing imagery from high resolution satellite instrumentation, such as TRACE, Hinode, and SOHO/MDI. The twisted flux tubes carry energy and helicity via the Poynting Flux from below the photosphere up into the corona, where much of it is stored in the non-potentiality of the fields, many times visible in the form of sigmoidal and anti-sigmoidal shapes, until dissipation occurs mostly following eruptive events. The twisted flux tubes are easily observed and measured in TRACE whitelight in cross section as sunspots at the photosphere, which rotate about their umbral centers. The first results presented at the 2007 Fall AGU from a statistical study on the number of rotating sunspots showed that almost all of the measurable sunspots during the solar maximum year of 2000 were rotating. Here we extend the study to include halo coronal mass ejections (CMEs) observed by SOHO/LASCO, of which 80% are associated with rotating sunspots and twisted magnetic flux tubes in 2000. Many of the CMEs, consisting of very energetic particles normally captured within a magnetic cloud of twisted flux tubes, accelerate out into the heliosphere where the Earth and its magnetic fields can encounter them, causing large geomagnetic events, such as geomagnetic storms, Solar Particle Events (SPEs), and other space weather effects. The amount of twist, or helicity, and its directionality may play important roles in solar eruptions and in the CME's interaction with the magnetosphere. Within the next year the Solar Dynamics Observatory (SDO) will launch and the HMI and AIA instruments will be available to observe the rotating sunspots and twisted magnetic flux tubes in greater detail than is currently being done to improve our understanding of these processes. Examples of such events and topological features will be shown and discussed with respect to the role that twisted magnetic flux tubes play in topological space weather forecasting. This work was supported by NASA under the TRACE contract NAS5-38099.
NG31A-1184
Impulsive Magnetic Reconnection in Solar and Laboratory Plasmas
Impulsive magnetic reconnection has been considered as the mechanism responsible for impulsive non- thermal emission in hard X-rays (HXR) and millimeter/submillimeter waves during the soft X-ray (SXR) flare rise phase. The impulsive non-thermal emission also correlates temporarily with impulsive acceleration of coronal mass ejectionˇ¦s (or flux ropeˇ¦s) upward motion via the impulsive magnetic reconnection process. The magnitude of impulsive magnetic reconnection rate and the magnetic reconnection electric field at the reconnecting X-line can be computed from the rate of change in magnetic flux swept by the evolution of H- alpha ribbons or EUV ribbons or HXR footpoints. By averaging the magnetic flux change rate over the ribbons the peak reconnection electric field during the HXR impulsive phase is ~ 1 kV/m for X-class flares. Further studies show that the magnetic flux change rate of reconnected field lines varies along the ribbons and the peak value is located near the HXR footpoint and can be several times larger than the averaged value. However, solar flare observations provide ˇ§indirectˇ¨ measurement of impulsive reconnection. In this paper we also report results of recent laboratory experiments performed at the University of Tokyo that directly observed and measured the impulsive magnetic reconnection process associated with accelerated ejection of flux ropes. The combined results from both solar observations and laboratory plasma experiments thus provide a much stronger support of the impulsive magnetic reconnection theory for explaining impulsive phenomena in solar flares and CMEs.
NG31A-1185
Statistical Approach to Coronal Magnetic Field
In this contribution we attempt to develop a self-consistent statistical description of a force-free magnetic field in the corona above a turbulent dense medium (the photosphere). The field is represented by a statistical ensemble of loops tied to the solar surface. Each loop evolves under several physical processes: flux emergence/submergence, turbulent random walk of the disk footpoints, and reconnection with other loops. To build a statistical description, we introduce the distribution function of loops over their sizes and construct a kinetic equation for this function. This Loop Kinetic Equation is similar to Boltzmann's kinetic equation, with reconnection described by a binary collision integral. We solve the equation numerically and obtain a statistical steady state. This allows us to calculate self-consistently the distribution of magnetic pressure with height, the equilibrium shapes of loops of different sizes, and the energy associated with a given loop.
NG31A-1186
Systematic Independent Validation of Inner Heliospheric Models
This presentation is the first in a series which will provide independent validation of community models of the outer corona and inner heliosphere. In this work we establish a set of measures to be used in validating this group of models. We use these procedures to generate a comprehensive set of results from the Wang- Sheeley-Arge (WSA) model which will be used as a baseline, or reference, against which to compare all other models. We also run a test of the validation procedures by applying them to a small set of results produced by the ENLIL Magnetohydrodynamic (MHD) model. In future presentations we will validate other models currently hosted by the Community Coordinated Modeling Center(CCMC), including a comprehensive validation of the ENLIL model. The Wang-Sheeley-Arge (WSA) model is widely used to model the Solar wind, and is used by a number of agencies to predict Solar wind conditions at Earth as much as four days into the future. Because it is so important to both the research and space weather forecasting communities, it is essential that its performance be measured systematically, and independently. In this paper we offer just such an independent and systematic validation. We report skill scores for the model's predictions of wind speed and IMF polarity for a large set of Carrington rotations. The model was run in all its routinely used configurations. It ingests line of sight magnetograms. For this study we generated model results for monthly magnetograms from the National Solar Observatory (SOLIS), Mount Wilson Observatory and the GONG network, spanning the Carrington rotation range from 1650 to 2068. We compare the influence of the different magnetogram sources, performance at quiet and active times, and estimate the effect of different empirical wind speed tunings. We also consider the ability of the WSA model to identify sharp transitions in wind speed from slow to fast wind. These results will serve as a baseline against which to compare future versions of the model as well as the current and future generation of MHD models under development for use in forecasting.
NG31A-1187
Field-line Torsion (FLT) / (SOC) Self-Organized Criticality Correspondence and Duality
Magnetic potential energy is stored when an incident disturbance such as the propagating solar wind interacts with the undisturbed magnetosphere resulting in the twisting and bending of the Earth's magnetic field. The energy that is stored in turn becomes a reservoir for dissipative wave interactions and instabilities that ultimately result in auroral phenomena that are observed on Earth. The topological structure of the Earth's magnetic field can provide clues about the timing and intensity of these events even during relatively quiescent periods. In particular, the presence of magnetic field-line torsion (FLT), a putative signature of magnetic storms and sub-storms, results in an increase in the fundamental standing Alfvén wave (SAW) field-line resonance (FLR) frequencies corresponding to a particular Alfvén speed profile. These frequencies can be dynamically calculated in an arbitrary boundary-constrained non-orthogonal geomagnetic flux coordinate (GFC) system in conjunction with chronological magnetic field data, provided by magnetospheric models such as BATSRUS and Tsyganenko (T05). A comparison of these frequencies to those computed in a purely meridional geometry yields a parameter that is useful in forecasting the triggering and evolution of ionospheric phenomena, such as the formation of localized auroral density cavities, which interact with lower and upper hybrid waves or Z modes resulting in mode conversion processes that lead to the formation of discrete auroral arcs via an escaping electromagnetic mode. There is strong evidence that this evolution describes a dynamical self-organized critical (SOC) phase transition due to an abrupt change in the pressure distribution in the near-Earth plasma sheet and the intrusion of convective flows into the inner magnetosphere.
NG31A-1188
The effects of geomagnetic field line geometry on resonant frequencies near the open- closed boundary.
Magnetometer data from Davis, Antarctica (74.49°S, 100.03°E CGM) often exhibit spectral characteristics which can be interpreted as field line resonance (FLR) signatures of the last closed field-lines in the dayside magnetosphere. Diurnal variations in the frequency at which maximum power occurs in the Pc5 (1-10 mHz) band, often shows an arch-shaped variation with local magnetic time. It has been suggested that in high latitude ULF data, the length of closed field lines threading the ground stations is a major factor that determines the frequency of FLRs. The general topology of the dayside magnetopause results in longer field lines and therefore lower resonant frequencies on the dawn and dusk flanks, and the shortest field lines/ highest resonant frequency for field lines near noon, passing through the sub-solar point. We present a rigorous eigenfunction solution of ULF wave modes, accounting for the curvature and torsion in the geomagnetic field lines which have their footprint at Davis. This provides an explanation for our observations of a saddle in the Pc5 arch, observed as a decrease in frequency centred on local magnetic noon that is often seen in Davis magnetometer data.
NG31A-1189
Global Topology and Convection of a Northward IMF Reconnection Event
Using a global resistive MHD simulation and ionospheric satellite data, we examine a northward IMF reconnection event at global separator length scales. This allows a full 3D interpretation of where reconnection occurs on the magnetopause for northward IMF with Bx and By components and for a significant dipole tilt. It also demonstrates that 3D separator reconnection with a northward IMF couples the reconnection electric field and field-aligned currents to the ionosphere to drive sunward convection in a manner that agrees with the satellite measurements of ionospheric sunward flows. We find antiparallel reconnection of the IMF to both open and closed field lines near global nulls in both hemispheres. The reconnection in turn produces both open and closed field lines, propelling both steady and non-steady convection. We discuss for the first time how line tying in the ionosphere and draping of open and IMF field lines over the dusk and dawn flanks of the magnetopause produce torsion within the magnetopause of the reconnected magnetic field lines. The models show that, consistent with Cluster observations, the reconnection geometry is not necessarily a simple two-dimensional hyperbolic structure.
NG31A-1190
Interchange Reconnection at Small IMF Clock Angles, as Identified by PolarDARN/SuperDARN
When the interplanetary magnetic field (IMF) clock angle θ c = atan2(BY, BZ) lies in the range of 0° < |θ c| < 30°, there only persist IMF-lobe and lobe-closed reconnection (both of which we call interchange-type), with Dungey-type reconnection (IMF-closed and lobe-lobe) being absent. In the ionosphere, the coupling of IMF-lobe and lobe-closed reconnection (which we call the interchange cycle) produces a lobe cell, an interchange-type merging cell, and a reciprocal cell. The reciprocal cell circulates exclusively in the closed field line region and can be used uniquely as an identifier of the interchange cycle. The recent deployment of the PolarDARN radar pair as part of SuperDARN has made it possible to measure all three types of cells in the two-dimensional convection pattern at high latitudes with detail not available previously. In this paper we demonstrate two examples of reciprocal cell observation by PolarDARN (one for IMF BY > 0 and the other for BY < 0). Concurrent precipitating particle data from polar-orbiting satellites are also used to locate the open-closed field line boundary.
NG31A-1191
The relationship between solar wind driving of ionospheric convection and the open flux
The open flux is estimated from SuperDARN observations of the convection reversal boundary (CRB). (The CRB as a proxy for the OCB was established by Sotirelis et al. [2005].) The correlation of ionospheric convection with solar wind/IMF driving using this scheme is shown. Within the expanding–contracting polar cap paradigm, this correlation should depend on whether the polar cap is expanding or contracting. This proposition is tested by examining the convection-solar wind/IMF correlation under expanding and contracting conditions.
NG31A-1192
3D Asymmetric Magnetopause Modeling from Support Vector Regression Machine and MineTool
As the inner boundary of the magnetosheath, the magnetopause is the location for energy, mass, and momentum transfer between the solar wind and the magnetosphere. The location of the magnetopause as well as its dependence on solar wind and geophysical conditions is critical for solar wind-magnetosphere interaction and global magnetosphere dynamics. Since the first theoretical solution of the shape and size of the magnetopause, many models have been proposed for magnetopause location. However, none of these models make use of new magnetopause crossings with much better coverage of high-latitude magnetopause and the cusps, as well as solar wind conditions. Previous studies also usually mandated analytical descriptions of magnetopause shape, which were then fit to subsets of crossings. This leaves much room for improvement, especially for unusual upstream conditions. In this study, we use the biggest magnetopause crossing database ever used by magnetopause modeling, including both older magnetopause crossings mainly from Space Physics Data Facility (SPDF) and earlier studies, and new magnetopause crossings from Cluster, THEMIS, Wind, Geotail, Polar, and Interball-1 with better high-latitude magnetopause and cusp coverage and corresponding solar wind conditions. Advanced machine learning technique, Support Vector Regression Machine (SVRM), and machine learning tool, MineTool, are used in this study to explore this big database for the control of the magnetopause locations by various solar wind and geophysical factors, including Earth's dipole tilt, the vector solar wind velocity, and the vector IMF, solar wind dynamic pressure, Beta, and Alfven Mach number. Comparison of our new magnetopause model with some leading earlier models shows that the new model has the smallest error, very well captures the subsolar magnetopause, high-latitude magnetopause, and cusps. Behavior of the new magnetopause model, including its asymmetry, magnetopause and cusp locations, is further studied under various typical solar wind conditions.
NG31A-1193
Real-time Kp prediction using the Boyle Index through artificial neural networks
We present four new algorithms with an improvement in the accuracy and lead-time in short term space
weather predictions by coupling the Boyle Index, Φ=10-4ν2 + 11.7{B}sin3(θ/2) kV, to
artificial neural networks. The Boyle Index is available in near-real-time from
http://space.rice.edu/ISTP/wind.html and has been in use for nearly five years to predict geomagnetic activity.
The logarithm of both 3-hour and 1-hour averages of the Boyle Index correlates well with the following Kp:
Kp = 8.93 log10
http://space.rice.edu/ISTP/wind.html