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Published on January 17, 2008

Author: Marianna

Source: authorstream.com

Multi-Spacecraft Measurements of Magnetospheric Substorms and Their Implications for the Near-Earth Neutral Line Model:  Multi-Spacecraft Measurements of Magnetospheric Substorms and Their Implications for the Near-Earth Neutral Line Model D.N. Baker1, Nathan Farr1, T.I. Pulkkinen2, and M. Wiltberger3 1Laboratory for Atmospheric and Space Physics, University of Colorado, 2 Los Alamos National Laboratory, 3 NCAR/HAO Two Substorm Events: 11 August 2002:  1200 UT 1430 UT Goes 10 Polar Two Substorm Events: 11 August 2002 Cluster Cluster Polar Goes 10 X Y Z X Y Z Solar Wind Magnetic Field:  Solar Wind Magnetic Field AE:  AE Daily Summary of Electron Data:  Daily Summary of Electron Data Cluster: Magnetic Field and Models:  Start Growth Phase Expansion Phase Cluster: Magnetic Field and Models Growth Phase beginning at 1314 Expansion Phase beginning at 1422 POLAR:  Start Growth Phase Expansion Phase POLAR GOES-10:  Start Growth Phase Expansion Phase GOES-10 Cluster/GOES/POLAR Comparison:  Start Growth Phase Expansion Phase Cluster/GOES/POLAR Comparison Ground-Based: Tixie:  Start Growth Phase Expansion Phase Ground-Based: Tixie Electron Fluxes: Polar and Cluster:  Electron Fluxes: Polar and Cluster Expansion Phase Onsets Electron Flux (E > 40 keV) Cluster/RAPID Polar LANL Electron Data:  LANL Electron Data Cluster: Plasma Electrons/Field Data:  Cluster: Plasma Electrons/Field Data Cluster/PEACE Electrons: Electron beam observed at CL3 Beam occurs during traveling compression region (TCR) Timing of TCR suggests structure moving tailward ~ 780 km/s. TCR observation common at all spacecraft (yet only CL3 observes electron beam) Plasma/Energetic Electron Comparison:  Electron beam was observed by both PEACE and RAPID instruments. Beam was more distinctive in RAPID energy range Plasma/Energetic Electron Comparison RAPID: Streaming Electron Distributions:  11 August 2002, 14:22:32 UT RAPID: Streaming Electron Distributions RAPID: Bidirectional Electron Distributions:  11 August 2002, 14:22:44 UT RAPID: Bidirectional Electron Distributions Interpretation: Plasmoid (Flux Rope) Encounter:  Interpretation: Plasmoid (Flux Rope) Encounter POLAR S/C The NENL Connection:  The NENL Connection Summary and Conclusions:  Summary and Conclusions Multiple-spacecraft studies are key to understanding substorm timing and location Using the Cluster constellation along with radially-aligned ancillary spacecraft and ground data is shown to be very effective for understanding substorm processes Cluster provides a “microscopic” view while meso- and macro-scale views are provided by more widely separated platforms Cluster (plus POLAR, GEO) holds great promise for helping to resolve issues about substorm neutral line formation and motion LFM Model: Electric Field and Flow Vectors:  LFM Model: Electric Field and Flow Vectors Cluster/MHD comparison:  Cluster/MHD comparison Magnetic Y-component:  Start Growth Phase Expansion Phase Magnetic Y-component Magnetic X-component:  Start Growth Phase Expansion Phase Magnetic X-component Slide25:  The substorm research community has long sought the capability to view the magnetosphere-ionosphere system in a global way and concurrently to probe the microphysical details of key physical regions. This objective has been substantially realized with the combination of the CLUSTER constellation and global magnetospheric imaging missions. With the addition of ACE, POLAR, and various geostationary orbit spacecraft, there is an ability to apply both global and local observational principles. Many recent examples serve to illustrate the observational power of these new tools. Using tail crossing events in 2001-2005, CLUSTER has observed numerous clear substorm sequences of events in the mid-magnetotail region (X~19RE). In this paper we focus on a global substorm onset event on 11 August 2002. CLUSTER data reveal microphysical details while other spacecraft show the global, macroscopic context for a substorm expansion phase onset shortly after 1400 UT. We have used the Lyon-Fedder-Mobarry MHD simulation code to numerically model this specific event. The new observations and model comparisons lead to improved understandings of three-dimensional magnetospheric substorm processes. This event shows global features consistent with the present-day near-Earth neutral line (NENL) model of substorm dynamics, but the specific details reveal heretofore unappreciated aspects of magnetic reconnection and particle acceleration near the neutral line. GOES-8:  GOES-8 Start Growth Phase Expansion Phase Magnetic Z-component:  Start Growth Phase Expansion Phase Magnetic Z-component Competing Pictures : Substorm Onset:  Competing Pictures : Substorm Onset

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