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  • 1
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    Ensemble forecasting of major solar flares – First results (2015)
    Wiley
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    Publication Date: 2015-09-11
    Description: We present the results from the first ensemble prediction model for major solar flares (M and X classes). The primary aim of this investigation is to explore the construction of an ensemble for an initial prototyping of this new concept. Using the probabilistic forecasts from three models hosted at the Community Coordinated Modeling Center (NASA-GSFC) and the NOAA forecasts, we developed an ensemble forecast by linearly combining the flaring probabilities from all four methods. Performance-based combination weights were calculated using a Monte-Carlo-type algorithm that applies a decision threshold P t h to the combined probabilities and maximizing the Heidke Skill Score (HSS). Using the data for 13 recent solar active regions between years 2012 - 2014, we found that linear combination methods can improve the overall probabilistic prediction and improve the categorical prediction for certain values of decision thresholds. Combination weights vary with the applied threshold and none of the tested individual forecasting models seem to provide more accurate predictions than the others for all values of P t h . According to the maximum values of HSS, a performance-based weights calculated by averaging over the sample, performed similarly to a equally weighted model. The values P t h for which the ensemble forecast performs the best are 25 % for M-class flares and 15 % for X-class flares. When the human-adjusted probabilities from NOAA are excluded from the ensemble, the ensemble performance in terms of the Heidke score, is reduced.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Solar Storm GIC Forecasting: Solar Shield Extension—Development of the End-User Forecasting System Requirements (2015)
    Wiley
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    Publication Date: 2015-09-24
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
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  • 3
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    A major solar eruptive event in July 2012: Defining extreme space weather scenarios (2013)
    Wiley
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    Publication Date: 2013-09-20
    Description: [1]  A key goal for space weather studies is to define severe and extreme conditions that might plausibly afflict human technology. On 23 July 2012 solar active region 1520 (~141°W heliographic longitude) gave rise to a powerful coronal mass ejection (CME) with an initial speed that was determined to be 2500±500 km/s. The eruption was directed away from Earth toward 125°W longitude. STEREO-A sensors detected the CME arrival only about 19 hours later and made in situ measurements of the solar wind and interplanetary magnetic field. In this paper we address the question of what would have happened if this powerful interplanetary event had been Earthward directed. Using a well-proven geomagnetic storm forecast model, we find that the 23-24 July event would certainly have produced a geomagnetic storm that was comparable to the largest events of the 20th Century (Dst ~ -500nT). Using plausible assumptions about seasonal and time-of-day orientation of the Earth's magnetic dipole, the most extreme modeled value of storm-time disturbance would have been Dst = -1182nT. This is considerably larger than estimates for the famous Carrington storm of 1859. This finding has far reaching implications because it demonstrates that extreme space weather conditions such as those during March of 1989 or September of 1859 can happen even during a modest solar activity cycle such as the one presently underway. We argue that this extreme event should immediately be employed by the space weather community to model severe space weather effects on technological systems such as the electric power grid.
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    Topics: Geosciences , Physics
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  • 4
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    Predicting the magnetic vectors within coronal mass ejections arriving at Earth: 1. Initial architecture (2015)
    Wiley
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    Publication Date: 2015-05-16
    Description: The process by which the Sun affects the terrestrial environment on short timescales is predominately driven by the amount of magnetic reconnection between the solar wind and Earth's magnetosphere. Reconnection occurs most efficiently when the solar wind magnetic field has a southward component. The most severe impacts are during the arrival of a coronal mass ejection (CME) when the magnetosphere is both compressed and magnetically connected to the heliospheric environment. Unfortunately, forecasting magnetic vectors within coronal mass ejections remains elusive. Here we report how, by combining a statistically robust helicity rule for a CME's solar origin with a simplified flux rope topology the magnetic vectors within the Earth-directed segment of aCME can be predicted. In order to test the validity of this proof-of-concept architecture for estimating the magnetic vectors within CMEs, a total of eight CME events (between 2010 and 2014) have been investigated. With a focus on the large false alarm of January 2014, this work highlights the importance of including the early evolutionary effects of a CME for forecasting purposes. The angular rotation in the predicted magnetic field closely follows the broad rotational structure seen within the in situ data. This time-varying field estimate is implemented into a process to quantitatively predict a time-varying Kp index that is described in detail in paper II. Future statistical work, quantifying the uncertainties in this process, may improve the more heuristic approach used by early forecasting systems.
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    Topics: Geosciences , Physics
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  • 5
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    Community-wide validation of geospace model local K-index predictions to support model transition to operations (2016)
    Wiley
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    Publication Date: 2016-06-09
    Description: 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 mid- 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- and mid-latitude domains. A summary of results is presented in this report, and an online tool for detailed analysis is available at the CCMC.
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  • 6
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    Modeling of coronal mass ejections that caused particularly large geomagnetic storms using ENLIL heliosphere cone model (2011)
    Wiley
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    Publication Date: 2011-06-16
    Description: In our previous paper we reported the results of modeling of 14 selected well-observed strong halo coronal mass ejection (CME) events using the WSA-ENLIL cone model combination. Cone model input parameters were obtained from white light coronagraph images of the CME events using the analytical method developed by Xie et al. (2004). This work verified that coronagraph input gives reasonably good results for the CME arrival time prediction. In contrast to Taktakishvili et al. (2009), where we started the analysis by looking for clear CME signatures in the data and then proceeded to model the interplanetary consequences at 1 AU, in the present paper we start by generating a list of observed geomagnetic storm events and then work our way back to remote solar observations and carry out the corresponding CME modeling. The approach used in this study is addressing space weather forecasting and operational needs. We analyzed 36 particularly strong geomagnetic storms, then tried to associate them with particular CMEs using SOHO/LASCO catalogue, and finally modeled these CMEs using WSA-ENLIL cone model. Recently, Pulkkinen et al. (2010) developed a novel method for automatic determination of cone model parameters. We employed both analytical and automatic methods to determine cone model input parameters. We examined the CME arrival times and magnitude of impact at 1 AU for both techniques. The results of the simulations are compared with the ACE satellite observations. This comparison demonstrated that WSA-ENLIL model combination with coronagraph input gives reasonably good results for the CME arrival times for this set of “geoeffective” CME events as well.
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    Topics: Geosciences , Physics
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  • 7
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    Geospace Environment Modeling 2008–2009 Challenge: Ground magnetic field perturbations (2011)
    Wiley
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    Publication Date: 2011-02-24
    Description: Acquiring quantitative metrics-based knowledge about the performance of various space physics modeling approaches is central for the space weather community. Quantification of the performance helps the users of the modeling products to better understand the capabilities of the models and to choose the approach that best suits their specific needs. Further, metrics-based analyses are important for addressing the differences between various modeling approaches and for measuring and guiding the progress in the field. In this paper, the metrics-based results of the ground magnetic field perturbation part of the Geospace Environment Modeling 2008–2009 Challenge are reported. Predictions made by 14 different models, including an ensemble model, are compared to geomagnetic observatory recordings from 12 different northern hemispheric locations. Five different metrics are used to quantify the model performances for four storm events. It is shown that the ranking of the models is strongly dependent on the type of metric used to evaluate the model performance. None of the models rank near or at the top systematically for all used metrics. Consequently, one cannot pick the absolute “winner”: the choice for the best model depends on the characteristics of the signal one is interested in. Model performances vary also from event to event. This is particularly clear for root-mean-square difference and utility metric-based analyses. Further, analyses indicate that for some of the models, increasing the global magnetohydrodynamic model spatial resolution and the inclusion of the ring current dynamics improve the models' capability to generate more realistic ground magnetic field fluctuations.
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    Topics: Geosciences , Physics
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  • 8
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    Generation of 100-year geomagnetically induced current scenarios (2012)
    Wiley
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    Publication Date: 2012-04-25
    Description: A series of 100-year extreme geoelectric field and geomagnetically induced current (GIC) scenarios are explored by taking into account the key geophysical factors associated with the geomagnetic induction process. More specifically, we derive explicit geoelectric field temporal profiles as a function of ground conductivity structures and geomagnetic latitudes. We also demonstrate how the extreme geoelectric field scenarios can be mapped into GIC. Generated statistics indicate 20 V/km and 5 V/km 100-year maximum 10-s geoelectric field amplitudes at high-latitude locations with poorly conducting and well-conducting ground structures, respectively. We show that there is an indication that geoelectric field magnitudes may experience a dramatic drop across a boundary at about 40°–60° of geomagnetic latitude. We identify this as a threshold at about 50° of geomagnetic latitude. The sub-threshold geoelectric field magnitudes are about an order of magnitude smaller than those at super-threshold geomagnetic latitudes. Further analyses are required to confirm the existence and location of the possible latitude threshold. The computed extreme GIC scenarios can be used in further engineering analyses that are needed to quantify the geomagnetic storm impact on conductor systems such as high-voltage power transmission systems. To facilitate further work on the topic, the digital data for generated geoelectric field scenarios are made publicly available.
    Print ISSN: 1539-4964
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    Topics: Geosciences , Physics
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  • 9
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    Geospace Environment Modeling 2008–2009 Challenge: Geosynchronous magnetic field (2011)
    Wiley
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    Publication Date: 2011-04-28
    Description: In this paper the metrics-based results of the inner magnetospheric magnetic field part of the 2008–2009 GEM Metrics Challenge are reported. The Metrics Challenge asked modelers to submit results for four geomagnetic storm events and five different types of observations that can be modeled by statistical or climatological or physics-based (e.g., MHD) models of the magnetosphere-ionosphere system. We present the results of 12 model settings that were run at the Community Coordinated Modeling Center and at the institutions of various modelers for these events. To measure the performance of each of the models against the observations, we use direct comparisons between the strength of the measured magnetic field (B), the sine of the elevation angle Θxz (τ), and the spectral power of fluctuations for both quantities. We find that model rankings vary widely by type of variable and skill score used. None of the models consistently performs best for all events. We find that empirical models perform well for weak storm events, and physics-based (magnetohydrodynamic) models are better for strong storm events. Within a series of runs of the same model we find that higher resolution may not always improve results unless more physics of the inner magnetosphere, such as the kinetic description of the ring current, is included.
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    Topics: Geosciences , Physics
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  • 10
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    Evaluating predictions of ICME arrival at Earth and Mars (2011)
    Wiley
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    Publication Date: 2011-09-02
    Description: We present a study of interplanetary coronal mass ejection (ICME) propagation to Earth and Mars. Because of the significant space weather hazard posed by ICMEs, understanding and predicting their arrival and impact at Mars is important for current and future robotic and manned missions to the planet. We compare running ENLILv2.6 with coronal mass ejection (CME) input parameters from both a manual and an automated method. We analyze shock events identified at Mars in Mars Global Surveyor data in 2001 and 2003, when Earth and Mars were separated by
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    Topics: Geosciences , Physics
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