Upstream Structures and Their Effects on the Magnetosphere

Kinetic processes within the Earth's foreshock generate a profusion of plasma and magnetic field structures with sizes and durations ranging from the microscale (e.g. SLAMs, solitons, and density holes) to the mesoscale (e.g. foreshock cavities or boundaries, hot flow anomalies, and bubbles). Swept into the bow shock by the solar wind flow, the perturbations associated with these features batter the magnetosphere, driving a wide variety of magnetospheric effects, including large amplitude magnetopause motion, bursty reconnection and the generation of flux transfer events, enhanced pulsation activity within the magnetosphere, diffusion and energization of radiation belt particles, enhanced particle precipitation resulting in dayside aurora and riometer absorption, and the generation of field-aligned currents and magnetic impulse events in high-latitude ground magnetometers. This talk reviews the ever growing menagery of structures observed upstream from the bow shock, examines their possible interrelationships, and considers their magnetospheric consequences

Concerning the Occurrence Pattern of Flux Transfer Events on the Dayside Magnetopause

We present an analytical model for the magnetic field perturbations associated with flux transfer events (FTEs) on the dayside magnetopause as a function of the shear between the magnetosheath and magnetospheric magnetic fields and the ratio of their strengths. We assume that the events are produced by component reconnection along subsolar reconnection lines with tilts that depend upon the orientation of the interplanetary magnetic field (IMF), and show that the amplitudes of the perturbations generated during southward IMF greatly exceed those during northward IMF As a result, even if the distributions of magnetic reconnection burst durations/event dimensions are identical during periods of northward and southward IMF orientation, events occurring for southward IMF orientations must predominate in surveys of dayside events. Two factors may restore the balance between events occurring for northward and southward IMF orientations on the flanks of the magnetosphere. Events generated on the dayside magnetopause during periods of southward IMF move poleward, while those generated during periods of northward IMF slip dawnward or duskward towards the flanks. Due to differing event and magnetospheric magnetic field orientations, events that produce weak signatures on the dayside magnetopause during intervals of northward IMF orientation may produce strong signatures on the flanks

THEMIS and Substorm Timing

The THEMIS mission represents the culmination of many years of planning directed towards understanding the processes that drive and trigger geomagnetic substorms. Following Akasofu's discovery of the substorm cycle, it became increasingly clear that timing questions provide the key to discriminating between proposed 'inside-out' and 'outside-in' models for substorms, triggered respectively by current disruption and magnetic reconnection. THEMIS observations provide a wealth of information that is currently being investigated to resolve this question. While observations in the magnetotail generally point towards reconnection. those on the ground point towards current disruption. This talk reviews the relevant observations and recent efforts at reconciliation

Correlative Studies with RBSP

The objectives of NASA's Living With a Star (LWS) Radiation Belt Storm Probe (RBSP) mission are: (1) Which physical processes produce radiation belt enhancement events? (2) What are the dominant mechanisms for relativistic electron loss? (3) How do ring current and other geomagnetic processes affect radiation belt behavior? Although a stand-alone mission, RBSP will benefit from correlative studies with observations made by other spacecraft and ground-based observatories. In this presentation, we describe the broad range of such studies as a function of RBSP mission phase, pointing to the unique contributions of both the RBSP mission and the other observatories

Active Missions and the VxOs with THEMIS as an Example

The Virtual Observatories (VxOs) provide a host of services to data producers and researchers. They help data producers to describe their data in standard Space Physics Archive Search and Extract (SPASE) terms that enable scientists to understand data products from a wide range of missions. They offer search interfaces based on specified criteria that help researchers discover conjunctions, prominent events, and intervals of interest. In this talk, we show how VMO services can be used with Time History of Events and Macroscale Interactions during Substorms (THEMIS) observations to identify magnetotail intervals marked by high speed flows, enhanced densities, or high temperatures. We present statistical surveys of when and where these phenomena occur. We then show how the VMO services can be used to identify events in which two or more THEMIS spacecraft observe specified features for more detailed analysis. We conclude by discussing the current limitations of VMO tools and outline plans for the future

Concerning the Motion and Orientation of Flux Transfer Events Produced by Component and Antiparallel Reconnection

We employ the Cooling et al. (2001) model to predict the location, orientation, motion, and signatures of flux transfer events (FTEs) generated at the solstices and equinoxes along extended subsolar component and high ]latitude antiparallel reconnection curves for typical solar wind plasma conditions and various interplanetary magnetic field (IMF) strengths and directions. In general, events generated by the two mechanisms maintain the strikingly different orientations they begin with as they move toward the terminator in opposite pairs of magnetopause quadrants. The curves along which events generated by component reconnection form bow toward the winter cusp. Events generated by antiparallel reconnection form on the equatorial magnetopause during intervals of strongly southward IMF orientation during the equinoxes, form in the winter hemisphere and only reach the dayside equatorial magnetopause during the solstices when the IMF strength is very large and the IMF points strongly southward, never reach the equatorial dayside magnetopause when the IMF has a substantial dawnward or duskward component, and never reach the equatorial flank magnetopause during intervals of northward and dawnward or duskward IMF orientation. Magnetosheath magnetic fields typically have strong components transverse to events generated by component reconnection but only weak components transverse to the axes of events generated by antiparallel reconnection. As a result, much stronger bipolar magnetic field signatures normal to the nominal magnetopause should accompany events generated by component reconnection. The results presented in this paper suggest that events generated by component reconnection predominate on the dayside equatorial and flank magnetopause for most solar wind conditions

Don't go with the Flow: An Invitation to Magnetosheath and Foreshock Studies

This talk reviews the predictions of gasdynamic, magnetohydrodynamic, and kinetic models for the magnetosheath and foreshock and compares these predictions with observations by the recent Cluster and THEMIS missions. Topics of interest include: the depletion layer, dawn/dusk asymmetries, the transmission of solar wind discontinuities, the formation of hot flow anomalies and cavities in the foreshock, and flows accelerated by field-line tension. We conclude by discussing opportunities for magnetosheath imaging

A statistical study of transient event motion at geosynchronous orbit

The geosynchronous GOES 5 and GOES 6 satellites frequently observe transient events marked by magnetic field strength increases and bipolar magnetic field signatures lasting several minutes. In this study we report a survey of 87 events observed simultaneously by both GOES spacecraft (for a total of 174 individual observations) from August to December 1984. Events detected in the prenoon sector outnumbered those in the postnoon sector by about a 3 to 1 ratio. The distribution of the events versus local time exhibited a significant prenoon peak like the distribution of magnetic impulse events observed in high-latitude ground magnetometers. A cross-correlation analysis of the two GOES data sets indicated lags that range from 0 to over 2 min, with the majority of the events moving antisunward. The short lags correspond to azimuthal speeds of hundreds of kilometers per second, greater than flow speeds in the magnetosheath, but less than fast mode waves. The short lags may indicate that the events move primarily latitudinally and/or that transient events are seldom localized, but rather occur over extended, if not global, regions. Investigations of event occurrence versus interplanetary magnetic field (IMF) Bz, event motion versus IMF By, and correspondence between upstream plasma data and the events all indicate that pressure pulses are the likely source of many of the events. About 27% of the events with simultaneous solar wind data were preceded by sharp reversals in one or more IMF components, and nearly all of this particular group of events occurred in the dawn sector. This suggests that the pressure pulses may be commonly generated in the foreshock/bow shock region, since the prenoon magnetopause lies generally behind the quasi-parallel bow shock where such pulses are thought to be triggered by IMF discontinuities. Finally, several events in the data set were also observed by the AMPTE/CCE. These are presented as case studies

A statistical study of the magnetic signatures of FTEs near the dayside magnetopause

During magnetopause crossings, the AMPTE CCE satellite frequently observed flux transfer events (FTEs) characterized by fluctuations in the magnetic field strength (B) and bipolar signatures in the field component (BN) normal to the nominal magnetopause. In this study, we survey 110 events observed from October to December 1984 and during January 1986. Nearly all events exhibited increases in B, and although the majority of events exhibited a symmetric bipolar signature in BN, a significant number (31 of 110) had asymmetric bipolar signatures in which the trailing pulse was dominant. Most of the asymmetric events were observed near the magnetic equator. This is consistent with an explanation in which FTEs form via merging along a single subsolar X line with strongly asymmetric signatures but that these signatures evolve into the familiar symmetric bipolar form with distance from the merging line

Opportunities for Cooperation: Themis and RBSP

This document outlines potential joint scientific studies involving the THEMIS and RBSP missions as a function of mission phase from the commissioning of RBSP in August 2012 through the end of its prime mission in the summer of 2014. It describes consensus recommendations for interspace craft separation, fast survey and burst mode strategies for THEMIS that will enable the two missions to achieve and exceed their common objectives. An appendix describes the need for careful intercalibration of THEMIS and RBSP particle observations