Space Weather Modeling Research Articles

RCM meets LFM: initial results of one-way coupling

While single fluid magnetohydrodynamics (MHD) is generally held to be the simplest complete first-order representation of the large-scale structure and dynamics of Earth's magnetosphere and its interaction with the solar wind, it fails to provide an adequate representation of conditions in the inner magnetosphere where energy-dependent gradient and curvature drifts become important. As part of the space environment modeling activities of the Center for Integrated Space Weather Modeling (CISM), we are working to integrate the computational machinery of the inner-magnetosphere Rice Convection Model (RCM) in the Lyon–Fedder–Mobarry (LFM) global MHD model of the magnetosphere. We describe our approach to coupling these two computational units and report on our initial application of the coupled code, a test of one-way coupling using LFM-computed magnetic and electric fields, ionospheric conductance, and plasma distribution to drive the RCM. We examine the inner magnetosphere effects of this coupling, including the formation of both the ring current and the region-2 field-aligned current system. We compare the resulting inner magnetosphere plasma distribution with LFM results obtained without RCM coupling.

Observational evidence for velocity convergence toward magnetic neutral lines as a factor in CME initiation

One of the major challenges of space weather research and modeling is the identification of the mechanism(s) for coronal mass ejections (CMEs). A leading candidate tested in several recent numerical simulations is photospheric magnetic flux cancellation by velocity convergence toward the neutral line of an active region having sheared or twisted magnetic fields. These attributes have been assumed in various combinations in modeling studies, but little observational work has been done that demonstrates their presence. In this paper, we show observational evidence that this process is at work in two different types of repetitively eruptive active regions in late 1996 and early 1997. The horizontal velocity field is obtained by applying Local Correlation Tracking (LCT) technique to sequences of photospheric line-of-sight magnetograms.

Physical models of the geospace radiation environment

A goal of predictive models of the space radiation environment is to provide advanced knowledge of significant variations in the highly energetic particle populations that form the Earth's radiation belts. The global geomagnetic field models that result from the Center for Integrated Space-weather Modeling (CISM) effort will provide a necessary input, a real-time description of the dynamic variation of the electromagnetic fields in the magnetosphere, for conducting detailed simulations of the radiation belts. In this work, we describe the issues and techniques that CISM will use to provide a physical space radiation model. An analysis of the global field configurations typical of the magneto hydrodynamic (MHD) models used in CISM suggest that much of the radiation belt modeling can proceed under a guiding center particle approximation, whereby individual, non-interacting test particles are used to track the aggregate dynamics of the radiation belts. This technique provides a relatively simple means of both conducting the necessary simulations, and coupling the relevant codes with other elements of the CISM project. The guiding center equations used to track the particles are based on a phase-space conserving approximation that conserves energy in regions of high curvature. Examples of test particle simulations with the MHD fields are given, both in the initial trapped particle population, and among the energetic particles that form the plasma sheet in the tail. These simulations suggest that multiple radiation belt models running simultaneously in the framework provided by CISM can be combined to provide an overall picture of the energetic particle environment. Finally, analysis of the spectral properties of the fields suggests how an alternate approach to modeling the global radiation belts, solution of the appropriate transport equations, might be advanced through the CISM effort.

Coupled model simulation of a Sun-to-Earth space weather event

This paper describes the 3D simulation of a space weather event using the coupled model approach adopted by the Center for Integrated Space Weather Modeling (CISM). The simulation employs corona, solar wind, and magnetosphere MHD models, and an upper atmosphere/ionosphere fluid dynamic model, with interfaces that exchange parameters specifying each component of the connected solar terrestrial system. A hypothetical coronal mass ejection is launched from the Sun by a process emulating photospheric field changes such as are observed with solar magnetographs. The associated ejected magnetic flux rope propagates into a realistically structured solar wind, producing a leading interplanetary shock, sheath, and magnetic cloud. These reach 1 AU where the solar wind and interplanetary magnetic field parameters are used to drive the magnetosphere–ionosphere–thermosphere coupled model in the same manner as upstream in situ measurements. The simulated magnetosphere responds with a magnetic storm, producing enhanced convection and auroral energy inputs to the upper atmosphere/ionosphere. These results demonstrate the potential for future studies using a modular, systemic numerical modeling approach to space weather research and forecasting.

Community Coordinated Modeling Center 2003 Workshop Report

The second biennial Community Coordinated Modeling Center (CCMC) Workshop dealt with the progress that the space weather community has made in the two years since the last gathering and the technical challenges yet to be overcome. The 28‐31 October 2003 workshop, held at the Maui High Performance Computing Center in Kihei, Hawaii, built on issues related to the Center's 2000 creation by a consortium of government agencies to enable, support, and perform the research and development needed for the next generation of space weather models.

The development of the Russian Space Weather Initiatives

Russian Space Weather Initiatives (RSWI) support different models for space weather forecastin (http://alpha.npi.msu.su/RSWI/rswi.html). The models give the long-time (months-years) and short-time (days) predictions of the solar activity, heliospheric conditions, and dynamics of the Earth's magnetic field and radiation. Many different parameters measured from the Sun to the Earth's magnetosphere are used as inputs to the space weather models. The paper is devoted to a short overview of these models.

Towards multi-dimensional space weather modeling for energetic oxygen ions in the earth's inner magnetosphere: Equilibrium configuration

We report the first 3+1 dimensional model development for energetic atomic oxygen ions in the Earth's radiation belts. Energetic Oxygen ions cans be supplied to the Earth's Inner magnetosphere from the sun (as a component of solar wind and solar energetic particles), from anomalous cosmic rays, and from acceleration processes acting on ionospheric atomic oxygen ions. We have built a multi-dimensional oxygen ion model in the following free parameters: geomagnetic L-shell, the magnetic moment, the second adiabatic invariant, and the discrete charge state number. Quiet time, steady state oxygen ion distributions have been obtained numerically from an assumed outer radiation zone boundary condition at L=7, average values of the radial diffusion coefficients, and standard values for the exospheric neutral densities due to the MSIS-86 upper atmosphere and exosphere neutral thermal particle density model. Average distributions of free electrons in the plasmasphere were also assumed with a mean plasmapause location just beyond L=4. We included the six lowest ionic charge states of atomic oxygen ( 16O) based on an existing charge exchange cross section compilation by Spjeldvik and Fritz (1978). Computed oxygen ion distributions include the resulting equilibrium structure of energy oxygen ions between 10 KeV and 100 MeV.

Improvements to the HAF solar wind model for space weather predictions

We have assembled and tested, in real time, a space weather modeling system that starts at the Sun and extends to the Earth through a set of coupled, modular components. We describe recent efforts to improve the Hakamada‐Akasofu‐Fry (HAF) solar wind model that is presently used in our geomagnetic storm prediction system. We also present some results of these improvement efforts. In a related paper, Akasofu [2001] discusses the results of the first 2 decades using this system as a research tool and for space weather predictions. One key goal of our efforts is to provide quantitative forecasts of geoeffective solar wind conditions at the L1 satellite point and at Earth. Notably, we are addressing a key problem for space weather research: the prediction of the north‐south component (Bz) of the interplanetary magnetic field. This parameter is important for the transfer of energy from the solar wind to the terrestrial environment that results in space weather impacts upon society. We describe internal improvements, the incorporation of timely and accurate boundary conditions based upon solar observations, and the prediction of solar wind speed, density, magnetic field, and dynamic pressure. HAF model predictions of shock arrival time at the L1 satellite location are compared with the prediction skill of the two operational shock propagation models: the interplanetary shock propagation model (ISPM) and the shock‐time‐of‐arrival (STOA) model. We also show model simulations of shock propagation compared with interplanetary scintillation observations. Our modeling results provide a new appreciation of the importance of accurately characterizing event drivers and for the influences of the background heliospheric plasma on propagating interplanetary disturbances.

Observation of the magnetospheric “sash” and its implications relative to solar‐wind/magnetospheric coupling: A multisatellite event analysis

Using a unique data set from the Wind, Polar, Interball 1, Magion 4, and Defense Meteorological Satellite Program (DMSP) F11 satellites, comparisons with the Integrated Space Weather Model (ISM) have provided validation of the global structure predicted by the ISM model, which in turn has allowed us to use the model to interpret the data to further understand boundary layers and magnetospheric processes. The comparisons have shown that the magnetospheric “sash” [White et al., 1998], a region of low magnetic field discovered by the MHD modeling which extends along the high‐latitude flank of the magnetopause, is related to the turbulent boundary layer on the high‐latitude magnetopause, recently mapped by Interball 1. The sash in the data and in the model has rotational discontinuity properties, expected for a reconnection site. At some point near or behind the terminator, the sash becomes a site for reconnection of open field lines, which were previously opened by merging on the dayside. This indicates that significant reconnection in the magnetotail occurs on the flanks. Polar mapped to the high‐density extension of the sash into the tilted plasma sheet. The source of the magnetosheath plasma observed by Polar on closed field lines behind the terminator was plasma entry through the low field connection of the sash to the central plasma sheet. The Polar magnetic field line footprints in each hemisphere are moving in different directions. Above and below the tilted plasma sheet the flows in the model are consistent with the corresponding flows in the ionosphere. The turbulence in the plasma sheet allows the convection patterns from each hemisphere to adjust. The boundary layer in the equatorial plane on the flank for this interplanetary magnetic field BY condition, which is below the tilted central plasma sheet, is several RE thick and is on tailward flowing open field lines. This thick boundary layer shields the magnetopause from viscous forces and must be driven by magnetic tension. Above the plasma sheet the boundary layer is dominated by the sash, and the model indicates that the open region inside the sash is considerably thinner.

Global three‐dimensional MHD simulation of a space weather event: CME formation, interplanetary propagation, and interaction with the magnetosphere

A parallel adaptive mesh refinement (AMR) finite‐volume scheme for predicting ideal MHD flows is used to simulate the initiation, structure, and evolution of a coronal mass ejection (CME) and its interaction with the magnetosphere‐ionosphere system. The simulated CME is driven by a local plasma density enhancement on the solar surface with the background initial state of the corona and solar wind represented by a newly devised “steady state” solution. The initial solution has been constructed to provide a reasonable description of the time‐averaged solar wind for conditions near solar minimum: (1) the computed magnetic field near the Sun possesses high‐latitude polar coronal holes, closed magnetic field flux tubes at low latitudes, and a helmet streamer structure with a neutral line and current sheet; (2) the Archimedean spiral topology of the interplanetary magnetic field is reproduced; (3) the observed two‐state nature of the solar wind is also reproduced with the simulation yielding fast and slow solar wind streams at high and low latitudes, respectively; and (4) the predicted solar wind plasma properties at 1 AU are consistent with observations. Starting with the generation of a CME at the Sun, the simulation follows the evolution of the solar wind disturbance as it evolves into a magnetic cloud and travels through interplanetary space and subsequently interacts with the terrestrial magnetosphere‐ionosphere system. The density‐driven CME exhibits a two‐step release process, with the front of the CME rapidly accelerating following the disruption of the near‐Sun closed magnetic field line structure and then moving at a nearly constant speed of ∼560 km/s through interplanetary space. The CME also produces a large magnetic cloud (> 100 RS across) characterized by a magnetic field that smoothly rotates northward and then back again over a period of ∼2 days at 1 AU. The cloud does not contain a sustained period with a strong southward component of the magnetic field, and, as a consequence, the simulated CME is somewhat ineffective in generating strong geo‐magnetic activity at Earth. Nevertheless, the simulation results illustrate the potential, as well as current limitations, of the MHD‐based space weather model for enhancing the understanding of coronal physics, solar wind plasma processes, magnetospheric physics, and space weather phenomena. Such models will provide the foundation for future, more comprehensive space weather prediction tools.

Global particle simulation for a space weather model: present and future

The authors report progress in the long-term effort to represent the interaction of the solar wind with the Earth's magnetosphere using a three-dimensional electromagnetic particle model (EMPM) as a space weather model. Magnetohydrodynamic (MHD) simulation models have been refined to establish quantitative global modeling in comparison with observations. The EMPM has become more feasible as the power and speed of supercomputers have improved in recent years. Simulations with southward and dawnward turning IMFs have revealed the fundamental processes which have been confirmed by MHD simulations and observations. After a quasisteady state is established with an unmagnetized solar wind, a southward IMF is switched on, which causes the magnetosphere to stretch with reconnection at the dayside magnetopause. The plasma sheet in the near-Earth magnetotail clearly thins. The cross-field current also thins and intensifies, which excites a kinetic (drift kink) instability along the dawn-dusk direction. As a result of this instability the electron compressibility effect appears to be reduced and to allow the collisionless tearing to grow rapidly with the reduced B/sub z/ component. Later, magnetic reconnection also takes place in the near-Earth magnetotail. In the case where the northward IMF is switched gradually to dawnward, magnetic reconnection takes place at both the dawnside and duskside. The arrival of dawnward IMF at the magnetopause creates a reconnection groove which causes particle entry into the deep region of the magnetosphere via field lines that go near the magnetopause. The flank weak-field region joins onto the plasma sheet and the current sheet to form a geometrical feature called the cross-tail S that structurally integrates the magnetopause and the tail interior.

The nonlinear dynamics of space weather

Studies of the nonlinear magnetospheric dynamics have led to several directions useful in understanding space physics processes, in particular those related to magnetospheric currents, and making space weather forecasts possible. Four such directions are identified: (a) empirical time series prediction with nonlinear autoregressive moving-average (ARMA) models, for which an example is given in terms of a geosynchronous electron flux index model. (b) Measurement of physical properties of the currents from the coefficients of the ARMA models, such as characteristic time scales and coupling strengths. Using a D st index model we measure the ring current decay time as a function of storm phase and activity, and identify new oscillation time scales correlating with the substorm injection activity. (c) Spatiotemporal nonlinear modeling predicts the amplitude and location of the disturbance as a function of space, as well as its time evolution. An example is given in terms of predicting the longitudinal and temporal profile of midlatitude geomagnetic disturbances. (d) Nonlinear dynamical models can be coupled to other physical or empirical approaches to build comprehensive space weather models. SWIFT, and ionospheric space weather model, is discussed as an example. Other applications of nonlinear dynamics are briefly discussed.

High performance computer methods applied to predictive space weather simulations

Taking advantage of the advent of massively parallel computers, sophisticated solution-adaptive techniques, and recent fundamental advances in basic numerical methods the authors have developed a high performance, adaptive-scale MHD code capable of resolving many of the critical processes in the Sun-Earth system which range over more than nine orders of magnitude. The development of such models are of increasing importance as the impact of space weather on vulnerable technological systems increases, and too, as the severity of space weather increases with the approach of solar maximum. There is an increasing need to develop physics-based, high performance models of the Sun-Earth system from the solar surface to the Earth's upper atmosphere which can operate faster than real time and which can provide reliable predictions of the near Earth space environment based upon solar observations and upstream solar wind measurements. They report on the status of the Michigan adaptive-scale MHD model, which is one effort whose goal is the development of an operational predictive space weather model.

On the role of electric field direction in the formation of sporadic E-layers in the southern polar cap ionosphere

Abstract Measurements of the occurrence of sporadic E (Es)-layers and F-region electric fields were obtained with a modern, HF digital ionosonde located at Casey, Antarctica (66.3 °S, 110.5 °E, 81 °S CGM latitude) during the late austral summer of 1995/96. The occurrence of Es-layers was inferred from the presence of appropriate traces in normal swept-frequency ionograms, and the electric fields were inferred from F-region “drift-mode” velocities assuming that the plasma convection velocities given by E × B B 2 were measured, on average, by the interferometer. The theory of formation of high-latitude Es-layers predicts that electric fields directed toward the south west (SW) should be particularly effective at producing thin layers in the southern hemisphere. Our measurements made at a true polar cap station are consistent with this expectation, and are contrasted with observations made by incoherent scatter radars in the northern hemisphere, which also show the importance of SW electric fields, whereas the same theory predicts that NW electric fields should be important at northern latitudes. We reconcile the interhemispheric differences with simple calculations of ion convergence driven by the electric fields specified by the IZMIRAN electrodynamic model (IZMEM) in both hemispheres. The importance of the interplanetary magnetic field in the control of high-latitude Es formation is emphasised as an important adjunct to space weather modelling and forecasting.

Space weather modelling with intelligent hybrid systems: Predicting the solar wind velocity

We are developing a space weather model to predict disturbances of the Earth's magnetosphere/ionosphere on four different time-scales: minutes, hours, 1–3 days, and 27 days. The minutes to hours predictions are made from solar-wind measurements, while predictions days in advance are made from solar observations. In this work we concentrate on predictions of solar wind velocities 3 days ahead. Using daily solar magnetograms we show how current predictions of the solar wind velocity at 1 AU can be improved with an intelligent hybrid system. The intelligent hybrid system consists of the potential field model and an artifical neural network. Solar magnetic field strengths are used as input and the output is the velocity 3 days ahead. The networks are trained and optimised on data from solar cycle 21. The hybrid system is tested on data from cycle 22 and the RMS error of the predicted daily velocity compared to the observed velocity is 90 km/s, the linear correlation is 0.58, and the average relative variance is 0.68.

A report on the community study of the early November 1993 geomagnetic storm

In anticipation of the upcoming solar maximum a large segment of the solar-terrestrial community has joined in an effort to document and benchmark the strengths and shortcomings of the community's observational and modeling capabilities. Approximately 100 scientists are participating in a study of a significant solar-terrestrial event which influenced the Earth between 2 and 11 November 1993. The goal of the study is to follow the event from its origin at the Sun, tracing the flow of particles and energy through the interplanetary medium and into the dissipative elements of the magnetosphere, ionosphere and thermosphere, thus providing a test-bed for existing space weather analysis and modeling capabilities. The geomagnetic storm of early November 1993 was identified as a candidate for study. While the study was inspired by the US National Space Weather Program, it has become an international event study. The following paper provides information about the origin and significance of the storm, the reasons for its selection as a community study event and a brief status report of the study.

Solar wind magnetosphere coupling: Predicted and modeled with intelligent hybrid systems

The solar wind-magnetosphere coupling is described as a mapping of the solar-solar wind state (input) to the magnetosphere-ionosphere state (output). The input-state is defined by solar wind parameters and the output-state is defined by geomagnetic disturbance indices. Most often are the geomagnetic disturbance indices D st and AE used. However, a new family of geomagnetic disturbance indices, CO, SO and EO, have been constructed which even might be able to describe the cusp and dayside magnetosphere. As mapper, a multi-layer backpropagation network, an Elman neural network and a radial basis function neural network, were used. Predictions of solar wind parameters and geomagnetic indices D st and AE are presented. The mapper represents a coupling function. It was found that the coupling function, learned by the neural networks, was more accurate than predefined theoretical coupling functions. In the case of modeling, it is therefore very important to explain the mapper and the trained neural network. Several methods are available: By extracting rules and decision trees from neural networks. By studying the prediction accuracy for different combinations of solar wind input parameters and for different coupling functions. By comparison with well-known mathematical methods. Integrating both data-driven and theory-driven methods into intelligent hybrid systems further improves the scientific method of studying the solar wind-magnetosphere coupling. Lund Space Weather Model is such a hybrid system. IHSs are also capable of mapping simultaneous multi-satellite observations. Such a mapping is therefore also suggested to improve the understanding of the solar wind-magnetosphere coupling.