Geospace Environment Modeling 2008–2009 Challenge: Geosynchronous magnetic field

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94577/1/swe422.pd

CalcDeltaB: An efficient postprocessing tool to calculate ground‐level magnetic perturbations from global magnetosphere simulations

Ground magnetic field variations can induce electric currents on long conductor systems such as high‐voltage power transmission systems. The extra electric currents can interfere with normal operation of these conductor systems; and thus, there is a great need for better specification and prediction of the field perturbations. In this publication we present CalcDeltaB, an efficient postprocessing tool to calculate magnetic perturbations Δ B at any position on the ground from snapshots of the current systems that are being produced by first‐principle models of the global magnetosphere‐ionosphere system. This tool was developed during the recent “d B /d t ” modeling challenge at the Community Coordinated Modeling Center that compared magnetic perturbations and their derivative with observational results. The calculation tool is separate from each of the magnetosphere models and ensures that the Δ B computation method is uniformly applied, and that validation studies using Δ B compare the performance of the models rather than the combination of each model and a built‐in Δ B computation tool that may exist. Using the tool, magnetic perturbations on the ground are calculated from currents in the magnetosphere, from field‐aligned currents between magnetosphere and ionosphere, and the Hall and Pedersen currents in the ionosphere. The results of the new postprocessing tool are compared with Δ B calculations within the Space Weather Modeling Framework model and are in excellent agreement. We find that a radial resolution of 1/30 R E is fine enough to represent the contribution to Δ B from the region of field‐aligned currents. Key Points Developed tool to compute magnetic perturbations on the ground Too validated using existing SWMF implementation Model validation independent from Delta‐B calculation within each modelPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/1/Contributions_E4_highlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/2/AuxiliaryMaterial_README_v2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/3/Contributions_E1_highlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/4/Contributions_E2_highlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/5/Contributions_E3_midlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/6/Contributions_E2_midlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/7/Contributions_E1_midlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/8/Contributions_E3_highlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/9/Contributions_E5_midlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/10/Contributions_E4_midlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/11/Contributions_E6_midlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/12/swe20180.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/13/Contributions_E6_highlat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109314/14/Contributions_E5_highlat.pd

Magnetohydrodynamics dynamical relaxation of coronal magnetic fields. II. 2D magnetic X-points

We provide a valid magnetohydrostatic equilibrium from the collapse of a 2D X-point in the presence of a finite plasma pressure, in which the current density is not simply concentrated in an infinitesimally thin, one-dimensional current sheet, as found in force-free solutions. In particular, we wish to determine if a finite pressure current sheet will still involve a singular current, and if so, what is the nature of the singularity. We use a full MHD code, with the resistivity set to zero, so that reconnection is not allowed, to run a series of experiments in which an X-point is perturbed and then is allowed to relax towards an equilibrium, via real, viscous damping forces. Changes to the magnitude of the perturbation and the initial plasma pressure are investigated systematically. The final state found in our experiments is a "quasi-static" equilibrium where the viscous relaxation has completely ended, but the peak current density at the null increases very slowly following an asymptotic regime towards an infinite time singularity. Using a high grid resolution allows us to resolve the current structures in this state both in width and length. In comparison with the well known pressureless studies, the system does not evolve towards a thin current sheet, but concentrates the current at the null and the separatrices. The growth rate of the singularity is found to be tD, with 0 < D < 1. This rate depends directly on the initial plasma pressure, and decreases as the pressure is increased. At the end of our study, we present an analytical description of the system in a quasi-static non-singular equilibrium at a given time, in which a finite thick current layer has formed at the null

Community‐wide validation of geospace model ground magnetic field perturbation predictions to support model transition to operations

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98787/1/swe20056.pd

Role of periodic loading‐unloading in the magnetotail versus interplanetary magnetic field B z flipping in the ring current buildup

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94813/1/jgra19183.pd

Community‐wide validation of geospace model local K‐index predictions to support model transition to operations

We present the latest result of a community‐wide space weather model validation effort coordinated among the Community Coordinated Modeling Center (CCMC), NOAA Space Weather Prediction Center (SWPC), model developers, and the broader science community. Validation of geospace models is a critical activity for both building confidence in the science results produced by the models and in assessing the suitability of the models for transition to operations. Indeed, a primary motivation of this work is supporting NOAA/SWPC’s effort to select a model or models to be transitioned into operations. Our validation efforts focus on the ability of the models to reproduce a regional index of geomagnetic disturbance, the local K‐index. Our analysis includes six events representing a range of geomagnetic activity conditions and six geomagnetic observatories representing midlatitude and high‐latitude locations. Contingency tables, skill scores, and distribution metrics are used for the quantitative analysis of model performance. We consider model performance on an event‐by‐event basis, aggregated over events, at specific station locations, and separated into high‐latitude and midlatitude domains. A summary of results is presented in this report, and an online tool for detailed analysis is available at the CCMC.Key PointsReport community‐wide model validation resultsEvaluate ability of models to predict a local index of magnetic perturbationAnalysis directly led to selection of models to transition to operations at NOAA/SWPCPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134170/1/swe20333-sup-0001-supplementary.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134170/2/swe20333_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/134170/3/swe20333.pd

Systematic evaluation of ground and geostationary magnetic field predictions generated by global magnetohydrodynamic models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95456/1/jgra20123.pd

CEDARâ GEM Challenge for Systematic Assessment of Ionosphere/Thermosphere Models in Predicting TEC During the 2006 December Storm Event

In order to assess current modeling capability of reproducing storm impacts on total electron content (TEC), we considered quantities such as TEC, TEC changes compared to quiet time values, and the maximum value of the TEC and TEC changes during a storm. We compared the quantities obtained from ionospheric models against groundâ based GPS TEC measurements during the 2006 AGU storm event (14â 15 December 2006) in the selected eight longitude sectors. We used 15 simulations obtained from eight ionospheric models, including empirical, physicsâ based, coupled ionosphereâ thermosphere, and data assimilation models. To quantitatively evaluate performance of the models in TEC prediction during the storm, we calculated skill scores such as RMS error, Normalized RMS error (NRMSE), ratio of the modeled to observed maximum increase (Yield), and the difference between the modeled peak time and observed peak time. Furthermore, to investigate latitudinal dependence of the performance of the models, the skill scores were calculated for five latitude regions. Our study shows that RMSE of TEC and TEC changes of the model simulations range from about 3 TECU (total electron content unit, 1 TECU = 1016 el mâ 2) (in high latitudes) to about 13 TECU (in low latitudes), which is larger than latitudinal average GPS TEC error of about 2 TECU. Most model simulations predict TEC better than TEC changes in terms of NRMSE and the difference in peak time, while the opposite holds true in terms of Yield. Model performance strongly depends on the quantities considered, the type of metrics used, and the latitude considered.Key PointsTEC and TEC changes during a storm predicted by ionosphere models were compared with groundâ based GPS TEC measurementsSkill scores (e.g., RMSE, NRMSE, and Yields) were calculated for five latitude regions in the selected eight longitude sectorsModel performance strongly depends on the quantities considered, the type of metrics used, and the latitude consideredPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139943/1/swe20516.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139943/2/swe20516_am.pd

Buildup of the ring current during periodic loading‐unloading cycles in the magnetotail driven by steady southward interplanetary magnetic field

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95239/1/jgra18825.pd