Center For Integrated Space Weather Modeling Research Articles

The role of dayside merging in generating the ionospheric potential during the Whole Heliospheric Interval

In this paper we examine the role of dayside merging between the interplanetary magnetic field (IMF) and the geomagnetic field in the generation of the polar cap potential in the ionosphere during the Whole Heliospheric Interval using the Coupled Magnetosphere Ionosphere Thermosphere (CMIT) and Lyon–Fedder–Mobarry (LFM) global simulations of the geospace system from the Center for Integrated Space Weather Modeling (CISM). We isolate the portion of the total ionospheric potential due to the viscous interaction by simulating the interval with a zero IMF, but with the same solar wind plasma conditions. For southward IMF, the cross polar cap potential is the sum of the merging potential and the viscous potential, so we can determine the merging potential by subtracting the viscous potential from the total potential. From the dependence of the merging potential on southward IMF we calculate a geoeffective length of 5 RE. For northward IMF the situation is more complicated since the cross polar cap potential, defined as the peak to peak potential, will be almost always either the value of the viscous potential or of the merging potential, whichever is larger. We find that during periods of northward IMF the cross polar cap potential can be less than what the viscous interaction would produce with no IMF present. This means that the viscous interaction is weakened by the cycle of merging and reconnection for northward IMF. Our results also indicate that current representations of merging rates or electric fields are flawed in the manner in which they describe northward IMF. Typical representations simply produce a weak reconnection rate when the IMF is northward that adds to the viscous potential to create a cross polar cap potential that is larger than the viscous potential, whereas the effect of merging for northward IMF reduces the viscous interaction so that the cross polar cap potential for moderate northward IMF values is smaller than the value that would be expected from solar wind plasma conditions of the viscous potential in isolation.

Corotating interaction regions during the recent solar minimum: The power and limitations of global MHD modeling

The declining phase of solar activity cycle 23 has provided an unprecedented opportunity to study the evolution and properties of corotating interaction regions (CIRs) during unique and relatively steady conditions. The absence of significant transient activity has allowed modelers to test ambient solar wind models, but has also challenged them to reproduce structure that was qualitatively different than had been observed previously (at least within the space era). In this study, we present and analyze global magnetohydrodynamic (MHD) solutions of the inner heliosphere (from 1RS to 1AU) for several intervals defined as part of a Center for Integrated Space weather Modeling (CISM) interdisciplinary campaign study, and, in particular, Carrington rotation 2060. We compare in situ measurements from ACE and STEREO A and B with the model results to illustrate both the capabilities and limitations of current numerical techniques. We show that, overall, the models do capture the essential structural features of the solar wind for specific time periods; however, there are times when the models and observations diverge. We describe, and, to some extent assess the sources of error in the modeling chain from the input photospheric magnetograms to the numerical schemes used to propagate structure through the heliosphere, and speculate on how they may be resolved, or at least mitigated in the future.

Space Weather Model Moves Into Prime Time

Space Weather Model Moves Into Prime Time

Solar energetic particle cutoff variations during the 29-31 October 2003 geomagnetic storm

[1] At low latitudes to midlatitudes the Earth's magnetic field usually shields the upper atmosphere and spacecraft in low Earth orbit from solar energetic particles (SEPs). During severe geomagnetic storms, distortion of the Earth's field suppresses geomagnetic shielding, allowing SEPs access to the midlatitudes. A case study of the 26–31 October 2003 solar-geomagnetic event is used to examine how a severe geomagnetic storm affects SEP access to the Earth. Geomagnetic cutoffs are numerically determined in model geomagnetic fields using code developed by the Center for Integrated Space Weather Modeling (CISM) at Dartmouth College. The CISM-Dartmouth geomagnetic cutoff model is being used in conjunction with the High Energy and Charge Transport code (HZETRN) at the NASA Langley Research Center to develop a real-time data-driven prediction of radiation exposure at commercial airline altitudes. In this work, cutoff rigidities are computed on global grids and along several high-latitude flight routes before and during the geomagnetic storm. It is found that significant variations in SEP access to the midlatitudes and high latitudes can occur on time scales of an hour or less in response to changes in the solar wind dynamic pressure and interplanetary magnetic field. The maximum suppression of the cutoff is ∼1 GV occurring in the midlatitudes during the main phase of the storm. The cutoff is also significantly suppressed by the arrival of an interplanetary shock. The maximum suppression of the cutoff due to the shock is approximately one half of the maximum suppression during the main phase of the storm.

Cone model-based SEP event calculations for applications to multipoint observations

The problem of modeling solar energetic particle (SEP) events is important to both space weather research and forecasting, and yet it has seen relatively little progress. Most important SEP events are associated with coronal mass ejections (CMEs) that drive coronal and interplanetary shocks. These shocks can continuously produce accelerated particles from the ambient medium to well beyond 1 AU. This paper describes an effort to model real SEP events using a Center for Integrated Space weather Modeling (CISM) MHD solar wind simulation including a cone model of CMEs to initiate the related shocks. In addition to providing observation-inspired shock geometry and characteristics, this MHD simulation describes the time-dependent observer field line connections to the shock source. As a first approximation, we assume a shock jump-parameterized source strength and spectrum, and that scatter-free transport occurs outside of the shock source, thus emphasizing the role the shock evolution plays in determining the modeled SEP event profile. Three halo CME events on May 12, 1997, November 4, 1997 and December 13, 2006 are used to test the modeling approach. While challenges arise in the identification and characterization of the shocks in the MHD model results, this approach illustrates the importance to SEP event modeling of globally simulating the underlying heliospheric event. The results also suggest the potential utility of such a model for forcasting and for interpretation of separated multipoint measurements such as those expected from the STEREO mission. Published by Elsevier Ltd. on behalf of COSPAR.

Operational Space Weather Entering a New Era

U.S. operational space weather maturing because of two competing factors. On one hand, directed agency funding at about $1 billion for model development over the past decade has brought modeling maturity to !ve broad Sun-toEarth domains, i.e., Sun, heliosphere, magnetosphere, ionosphere, and thermosphere. On the other hand, agency funding for transitioning these models into operations has been a small fraction of the level provided for model development. is situation has le# implementation of operational space weather largely unfunded and woefully undirected, with the exception of a few U.S. Air Force Weather Agency projects. A new vision needed so that operational space weather can help solve 21st-century challenges. e current paradigm for operational space weather began in the 1990s, when the idea was to build complete systems at single facilities. ese rapid prototyping centers were envisioned as a means for implementing new operational systems, but this path was unsuccessful. Although increased funding for operational space weather would have bene!ted the community, this did not happen, and in the lopsided funding pro!le, operational space weather was forced to develop an unusual but robust architecture. is architecture consists of distributed networks—automated systems of models, data streams, and algorithms at multiple, geographically dispersed facilities linked by operational servers. A central server manages the network and uses a database enabling remote nodes to deposit output data and access input data at their geophysical or measurement cadences and latencies. e emergence of distributed networks represents a paradigm shi# from 1995, when the National Space Weather Program (NSWP) strategic plan was !rst published. At that time, very few models existed that could be even considered for use in operations. Model development increased due to the funding surge, and by 2000 seventy-three models characterizing 15 space environment domains were listed in the NSWP implementation plan (2nd edition). During the past decade some of these models were implemented operationally and became important components of distributed networks. Early examples were the Magnetospheric Spec!cation Model (MSM; 2000), SOLAR2000 (S2K; 2001), and High Accuracy Satellite Drag Model (HASDM; 2004). More recently, systems of coupled models and data streams have been created, including Global Assimilation of Ionospheric Measurements (GAIM; 2006), HakamadaAkasofuFry (HAF; 2007), and Communication Alert and Prediction System (CAPS; 2008). Coupled model/ data systems that are currently being implemented include the JacchiaBowman 2008 (JB2008), the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS), U.S. Geological Survey Dst, ENLIL with Cone, and Ionosphere Operational System (IONS; i.e., the commercial version of GAIM at the Utah Science Technology and Research (USTAR) Center for Space Weather). Of added note that the Space Weather Modeling Framework (SWMF) and the Center for Integrated Space Weather Modeling (CISM) have developed multi domain systems to represent the entire Sunto-Earth environment, in which some of the models have been running for years. e need to test coupled systems existed even without funding, and the lack of funds drove small businesses, universities, and the multiagency Community Coordinated Modeling Center to create innovative, cost-e$ective solutions. Basically, these organizations had to !nd cheaper ways to accomplish testing and operational implementation. e result was the development of distributed networks to close the Technology Readiness Level (TRL) 7–9 gap. TRL the concept used by agencies and companies to assess the maturity of evolving technologies. TRL 7 models and data can operate in stand-alone mode within the context of an operational environment. TRL 8 signi!es the completion of a fully functional system prototype, and TRL 9 describes a fully delivered, operational system. e distributed network systems at TRL 7–9 are linked in a way that allows developers to maintain versioning and proprietary control over their models, permits data streams to be integrated at their own measurement cadence, results in testing %exibility, enables rapid

Building and Using Coupled Models for the Space Weather System: Lessons Learned

Building and Using Coupled Models for the Space Weather System: Lessons Learned

Metrics for solar wind prediction models: Comparison of empirical, hybrid, and physics‐based schemes with 8 years of L1 observations

Space weather effects on technological systems originate with energy carried from the Sun to the terrestrial environment by the solar wind. In this study, we present results of modeling of solar corona‐heliosphere processes to predict solar wind conditions at the L1 Lagrangian point upstream of Earth. In particular we calculate performance metrics for (1) empirical, (2) hybrid empirical/physics‐based, and (3) full physics‐based coupled corona‐heliosphere models over an 8‐year period (1995–2002). L1 measurements of the radial solar wind speed are the primary basis for validation of the coronal and heliosphere models studied, though other solar wind parameters are also considered. The models are from the Center for Integrated Space‐Weather Modeling (CISM) which has developed a coupled model of the whole Sun‐to‐Earth system, from the solar photosphere to the terrestrial thermosphere. Simple point‐by‐point analysis techniques, such as mean‐square‐error and correlation coefficients, indicate that the empirical coronal‐heliosphere model currently gives the best forecast of solar wind speed at 1 AU. A more detailed analysis shows that errors in the physics‐based models are predominately the result of small timing offsets to solar wind structures and that the large‐scale features of the solar wind are actually well modeled. We suggest that additional “tuning” of the coupling between the coronal and heliosphere models could lead to a significant improvement of their accuracy. Furthermore, we note that the physics‐based models accurately capture dynamic effects at solar wind stream interaction regions, such as magnetic field compression, flow deflection, and density buildup, which the empirical scheme cannot.

An event‐based approach to validating solar wind speed predictions: High‐speed enhancements in the Wang‐Sheeley‐Arge model

One of the primary goals of the Center for Integrated Space Weather Modeling (CISM) effort is to assess and improve prediction of the solar wind conditions in near‐Earth space, arising from both quasi‐steady and transient structures. We compare 8 years of L1 in situ observations to predictions of the solar wind speed made by the Wang‐Sheeley‐Arge (WSA) empirical model. The mean‐square error (MSE) between the observed and model predictions is used to reach a number of useful conclusions: there is no systematic lag in the WSA predictions, the MSE is found to be highest at solar minimum and lowest during the rise to solar maximum, and the optimal lead time for 1 AU solar wind speed predictions is found to be 3 days. However, MSE is shown to frequently be an inadequate “figure of merit” for assessing solar wind speed predictions. A complementary, event‐based analysis technique is developed in which high‐speed enhancements (HSEs) are systematically selected and associated from observed and model time series. WSA model is validated using comparisons of the number of hit, missed, and false HSEs, along with the timing and speed magnitude errors between the forecasted and observed events. Morphological differences between the different HSE populations are investigated to aid interpretation of the results and improvements to the model. Finally, by defining discrete events in the time series, model predictions from above and below the ecliptic plane can be used to estimate an uncertainty in the predicted HSE arrival times.

Center for integrated space weather modeling metrics plan and initial model validation results

Metrics and model validation represent two key elements upon which the success of the Center for Integrated Space Weather Modeling (CISM) hinges. The routine calculation of important operationally- and scientifically-motivated metrics permits us to objectively measure and track the ability of coupled CISM models to predict essential space weather quantities. The rationale for CISM metrics selection is developed and the list of 29 metrics, along with the baseline models, first-generation physics models, and the data sets needed to compute skill scores, are outlined. While metrics provide a means for the objective assessment of long-term model improvement, model validation—the comprehensive, systematic quantitative comparison of model output with observations—is required for identifying and documenting model strengths and weaknesses. Two representative examples of initial validation efforts are summarized. The first uses case study analysis techniques and comparison with in situ observations during real events to explore the range of validity of the Lyon–Fedder–Mobarry (LFM) MHD simulation during magnetic storms. The second uses a statistical approach to compare the climatology of plasma sheet bulk properties (density, temperature, magnetic field, flows) deduced from both spacecraft observation and modeled by the LFM code.

The CISM code coupling strategy

The success of the Center for Integrated Space Weather Modeling (CISM) depends on the production of an ever-improving series of comprehensive scientific models describing the Solar Terrestrial environment from the solar surface to the upper atmosphere of earth. We describe here our strategy for coupling the codes we have selected as the basis for these models, which include core global codes which address the corona, heliosphere, the earth's magnetosphere, and ionosphere, and codes which model important local processes such as magnetic reconnection. Coupling these codes requires four separate functions: efficient transmission of information among codes, interpolation of grid quantities, translation of physical variables between codes with differing physical models, and control mechanisms to synchronize the interaction of codes. The characteristics of these codes dictate an approach involving loosely coupled groups of independently running programs. We have selected two existing software packages, InterComm and Overture, to provide the basis of our coupling framework. By combining the strengths of these packages, we obtain the benefits of simplified coding of translation routines and inter-grid communication between distinct codes with minimal code modification. The NASA Living With a Star program shares both the scientific goals and code coupling challenges of CISM, and is equally involved in the coupling strategy and development we present.

Initial results from the coupled magnetosphere ionosphere thermosphere model: magnetospheric and ionospheric responses

The Center for Integrated Space Weather Modeling (CISM) is developing a simulation package of the coupled Sun–Earth system by connecting existing models within each region. The Coupled Magnetosphere Ionosphere Thermosphere (CMIT) model combines the Lyon–Fedder–Mobarry global magnetohydrodynamic (MHD) magnetospheric (LFM) model with the Thermosphere Ionosphere Nested Grid (TING) model. The LFM uses the ideal MHD equations to model the interaction between the magnetospheric plasma and the solar wind. It includes the magnetosphere–ionosphere interaction by requiring the conservation of current flowing between the magnetosphere and a two dimensional ionosphere. TING is a three dimensional code designed to simulate the thermosphere–ionosphere system by solving the mass, momentum, and thermodynamic energy equations for the global thermosphere and ionosphere. Normally, TING uses parameterized models to describe the magnetospheric input into the ionosphere. We begin this paper with a description of how the TING model is used to replace the simple two dimensional ionosphere within the LFM to produce the CISM CMIT Model. The results from the coupled model for a series of steady IMF conditions are compared with the results from the LFM to show that these models have been successfully combined. The problem of high cross polar cap potentials remains, but the structure of the magnetosphere is not dramatically altered by the coupling and the ionospheric conductances show a more realistic distribution driven by EUV radiation as well as a more clearly defined auroral oval.

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.

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.