Yihua Zheng

Simulation of the 23 July 2012 Extreme Space Weather Event: What if This Extremely Rare CME Was Earth Directed?

Extreme space weather events are known to cause adverse impacts on critical modern day technological infrastructure such as high-voltage electric power transmission grids. On 23 July 2012, NASAs Solar Terrestrial Relations Observatory-Ahead (STEREO-A) spacecraft observed in situ an extremely fast coronal mass ejection (CME) that traveled 0.96 astronomical units (∼1 AU) in about 19 h. Here we use the Space Weather Modeling Framework (SWMF) to perform a simulation of this rare CME. We consider STEREO-A in situ observations to represent the upstream L1 solar wind boundary conditions. The goal of this study is to examine what would have happened if this Rare-type CME was Earth-bound. Global SWMF-generated ground geomagnetic field perturbations are used to compute the simulated induced geoelectric field at specific ground-based active INTERMAGNET magnetometer sites. Simulation results show that while modeled global SYM-H index, a high-resolution equivalent of the Dst index, was comparable to previously observed severe geomagnetic storms such as the Halloween 2003 storm, the 23 July CME would have produced some of the largest geomagnetically induced electric fields, making it very geoeffective. These results have important practical applications for risk management of electrical power grids.

Viewing perspective in energetic neutral atom intensity

[1] Through interspacecraft comparison of energetic neutral oxygen (ENO) intensity from two different vantage points provided by IMAGE and Geotail, Lui et al. (2005) showed that viewing perspective plays a very important role in the observed ENO intensity level during a magnetic storm period. Motivated by the findings of Lui et al. (2005), we investigate how viewing perspective influences energetic neutral atom emissions from a modeling perspective. The main results of this paper are that (1) our simulation results, based upon O+ ion fluxes from the Comprehensive Ring Current Model and the subsequent ENO calculation, reproduce the total differential ENO intensity obtained from two spacecraft to a reasonable degree and (2) further analysis of our results indicates that pitch angle anisotropy in ring current ion flux, a crucial physical quantity in ring current dynamics, is one major contributor to the difference in energetic neutral atom intensity from different viewing perspectives.

The global context of the 14 November 2012 storm event

From 2 to 5 UT on 14 November 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ∼20–30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet.

The Linkage between the Ring Current and the Ionosphere System

The coupling between the ring current and the ionosphere is briefly reviewed and discussed. Given global energetic neutral atom (ENA) observations of the ring current, the three-dimensional current system driven by ring current plasma pressure (the region 2 system) is derived to illustrate where the ring current connects to the ionosphere. Special attention is given to how the ring current and ionospheric conductance set up the sub-auroral polarization streams (SAPS) through the closure of the region 2 current through the ionospheric trough region. Simultaneous ENA observations of the ring current and radar observations of the SAPS flow show that the onset of SAPS flow and equatorward motion is coincident with the injection and buildup of plasma pressure in the inner magnetosphere. The comprehensive ring current model is used to demonstrate how the SAPS can be generated by computing ring current pressure and allowing its pressure-driven currents to close through a model of ionospheric conductance including the trough region. The paper ends by discussing open questions and what is missing in our understanding of the generation of the large-scale electric fields of the inner magnetosphere and sub-auroral ionosphere.

Assessing predictive ability of three auroral precipitation models using DMSP energy flux

Our study statistically compares the total energy flux outputs of Newell et al.s (2010a) oval variation, assessment, tracking, intensity, and online nowcasting (OVATION) Prime model, Hardy et al.s (1991) Kp-based model, and a coupled Space Weather Modeling Framework ring current model to energy flux data obtained from 2198 Defense Meteorological Satellite Program (DMSP) satellite passes in the Northern Hemisphere. Our DMSP data set includes 28 days grouped into continuous 3 and 4 day periods between 2000 and 2008 and encompasses magnetic local times (MLTs) between 04:00 and 21:00. We obtain the most equatorward magnetic latitude coordinate, where a DMSP satellite energy flux measurement exceeds 0.4 erg/cm2/s, and use this point as a proxy for the equatorward boundary of the auroral oval in a particular MLT sector. We then calculate a prediction efficiency (PE) score by comparing the DMSP boundary coordinates to each model, using the same energy flux threshold to obtain a models boundary location. We find that the PE for the OVATION Prime model is 0.55, and the PE for the Hardy Kp model is 0.51. When we accomplish the same analysis using a higher energy flux threshold equal to 0.6 erg/cm2/s, the OVATION Prime models PE increases to 0.58, while the Hardy Kp models score drops to 0.41. Our results indicate that more complex modeling techniques, like those used in OVATION Prime, can more accurately model the auroral ovals equatorward boundary. However, Hardys discretized Kp model, despite its relative simplicity, is still a competitive and viable modeling option.

Research-Based Monitoring, Prediction, and Analysis Tools of the Spacecraft Charging Environment for Spacecraft Users

The Space Weather Research Center (http://swrc. gsfc.nasa.gov) at NASA Goddard, part of the Community Coordinated Modeling Center (http://ccmc.gsfc.nasa.gov), is committed to providing research-based forecasts and notifications to address NASAs space weather needs, in addition to its critical role in space weather education. It provides a host of services including spacecraft anomaly resolution, historical impact analysis, real-time monitoring and forecasting, tailored space weather alerts and products, and weekly summaries and reports. In this paper, we focus on how (near) real-time data (both in space and on ground), in combination with modeling capabilities and an innovative dissemination system called the integrated Space Weather Analysis system (http://iswa.gsfc.nasa.gov), enable monitoring, analyzing, and predicting the spacecraft charging environment for spacecraft users. Relevant tools and resources are discussed.