SM22B-01 INVITED
Observational Evidence for Continuous Versus Intermittent Reconnection at the Magnetopause
I will address the temporal behavior of magnetic reconnection at the low- and high-latitude magnetopause. Evidences for both continuous and intermittent reconnection at the magnetopause and their ionospheric signatures have been reported in the literature. Repeated detections of reconnection flows by multi-spacecraft during multiple magnetopause crossings, as well as the continuous observations of the proton aurora, have been taken as evidence for continuous reconnection. On the other hand, flux transfer events (FTEs) and their ionospheric signatures have often been interpreted as evidence for intermittent reconnection. One of the key questions is whether reconnection is dominantly continuous or intermittent during steady IMF conditions. I will discuss the possibility that some of the FTE signatures are caused not by intermittent reconnection, but by continuous reconnection with modulated reconnection rates instead.
SM22B-02
Anatomy of Diamagnetic Cusp Cavities - MHD Modeling
The Magnetospheric cusps are a key feature of the Earth's magnetosphere, as they offer the solar wind its most direct entry point to the magnetosphere. Regions of significantly depressed magnetic field accompanied by enhanced density and pressure have been identified in the vicinity of the cusps. These regions have been referred to as diamagnetic cavities or the stagnant exterior cusp. Many questions remain with regard to these cavities. In order to investigate these regions, we have implemented a high resolution local three dimensional MHD simulation with an initial configuration representing a cusp-like magnetic configuration. We present simulation results addressing the overall cusp structure and plasma properties in the vicinity of the cavities. Particularly, we address the influence of local and global parameter variations on the formation and evolution of these cusp cavities and plasma dynamics. We utilize specific magnetosheath parameters in order to compare properties of diamagnetic cavities to Cluster2 data of such events.
SM22B-03 INVITED
Magnetospheric Cusp During Northward and Southward IMF
The magnetospheric cusp is a region with direct connection to the dayside magnetopause and the ionosphere. Measurements of the particles and fields in this region contain a wealth of information about dayside reconnection as it drives the magnetosphere and about the ionospheric response. This presentation will outline the key observational signatures in the cusp and their association with the location of magnetic reconnection, its rate, and the plasma properties in the magnetosheath. The entry of magnetosheath plasma into the cusp and the subsequent distribution of magnetosheath and ionospheric plasma throughout the magnetosphere will also be described. Particular emphasis will be given to the distinction between the cusp under northward and southward IMF conditions and the signatures resulting from a temporally varying reconnection rate.
SM22B-04
Overlapping cusp ion structures under Northward IMF: signature of re-closed magnetic field lines?
On some occasions, Cluster data in the mid-altitude cusp reveal overlapping ion populations under Northward IMF. While the poleward part of the cusp exhibits the expected reverse dispersion due to lobe reconnection, its equatorward part shows a second high-energy ion population that coexists with the low energy tail of the dispersion. This second populations is either dispersionless or slightly dispersed with energies increasing with increasing latitude, indicative of sunward convection. The analysis of data from Cluster fleet and, for one event, of data from the EISCAT Svalbard Radar in conjunction with Cluster, reveals that the second population comes very likely from the opposite hemisphere and is on closed field lines. We interpret this overlap of closed-LLBL and cusp populations in terms of magnetic field lines being opened in one hemisphere by lobe reconnection and re- closed in the other.
SM22B-05
Cusp particle precipitation before and after an abrupt change of direction of the IMF
The polar cusp is a highly dynamic region responding very quickly to changes in the Interplanetary Magnetic Field (IMF) direction and solar wind dynamic pressure. The immediate effect of the rotation of the Interplanetary Magnetic Field (IMF) from southward to northward on cusp precipitation has been rarely observed by a polar orbiting satellite in the past. The four Cluster spacecraft observed such an event on 23 September 2004 as they were crossing the polar cusp within 2-16 minute from each other. Between the first three and the last spacecraft crossing the cusp, the IMF rotated from southward to northward with a dominant By (GSM) component. For the first time we can examine the changes in the particle precipitation immediately after such IMF change. The first two spacecraft observed a typical IMF-southward ion dispersion, while the last one observed both an IMF- Southward-like dispersion in the boundary layer and an IMF-northward dispersion in the cusp. After the IMF turning, the cusp is shown to have grown in size in both the poleward and equatorward directions. A three- dimensional magnetohydrodynamic (MHD) simulation is used to determine the locations of the sources of the ions and the topology of the magnetic field during the event. After the turning of the IMF northward, the simulation shows first a reconnection on the dawn northern lobes, poleward of the cusp, and then a second reconnection of the same field line on the dusk lobe in the southern hemisphere. We would then have a case of double lobe reconnection when the IMF is northward with a dominant By component (clock angle between 45 and 60 deg.).
SM22B-06 INVITED
Poleward drifting auroral forms and their relationship to the cusp
The response at ionosphreic altitudes to magnetic reconnection can be observed by a variety of instruments. All sky cameras, high frequency and incoherent scatter radars, and particle detectors on satellites monitor the particles, fields, and currents which are produced in response to reconnection at the magnetopause and which map down along the magnetospheric field to theionosphere. Ground-based observations, particularly in combination, are extremely useful in the study of magnetospheric dynamics driven by reconnection. Ionospheric observations can extend in two dimensions over large areas in the ionosphere, which maps out to vast regions of the magnetosphere. And when ionospheric proxies for mapped magnetospheric boundaries, low-altitude measurements reveal the motion of magnetospheric flux relative to magnetospheric boundaries, which is not possible to achieve with single-spacecraft measurements in the magnetosphere. A review of observations poleward drifting auroral forms and their relationship to the cusp will be presented. Future joint initiatives, combining both ground and space-based observations, will be discussed.
SM22B-07
Ground-Based and FAST Observations of Pc 1-2 Type ULF Waves in the Dayside Cusp Region
A closely-spaced search-coil ultra low frequency (ULF) magnetometer array installed in the northern hemisphere (Svalbard) observes Pc 1-2 type wave activity in the dayside cusp region. Perhaps the most commonly observed type of events is band-limited pulsations which typically occur from approximately 9 to 17 MLT over frequencies ranging from 0.2 to 0.4 Hz. Besides the band-limited features, some of the events display a variety of spectral structures such as increasing (or decreasing) tones, broad-band bursts, harmonic structures, etc. This study focuses on FAST observations of the events in conjunction with the ground-based magnetometer data. The FAST satellite, which overflew the regions where the magnetic footprints map down to the locations of the magnetometers, shows that the ion/electron energies and pitch angle distributions observed by the satellite during the wave events are consistent with Alfven wave produced aurora - Alfvenic aurora. This implies that the ULF wave events provide the energy to generate the Alfvenic aurora. We discuss the effects of the wave activity in the magnetospheric/ionospheric processes using the simultaneous observations of the ground-based magnetometer and FAST satellite along with the ground-based all-sky auroral imagers.
SM22B-08 INVITED
Open Questions: The Cusp and FTEs
The northern and southern cusps play an important role in the overall solar wind-magnetosphere-ionosphere interaction. Optical, radar, and ground magnetometer observations of transient events in the dayside auroral oval provide strong evidence for bursty reconnection on the dayside magnetopause occurring along extended reconnection lines during periods of southward and/or ecliptic IMF orientation. During periods of northward IMF orientation, the same ground-based observations provide evidence for reconnection on the magnetopause poleward of the cusps. Cluster observations in the cusp have confirmed the transition in reconnection locations from the dayside to the high-latitude magnetopause as a function of IMF orientation, while in situ observations of the dayside magnetopause indicate that bursty reconnection frequently generates transient events marked by symmetric bipolar magnetic field signatures normal to the nominal magnetopause and magnetic field strength enhancements. In this talk we review recent and invoke new results from analytical, two-dimensional hybrid, and three-dimensional MHD codes to describe the motion and fate of the newly-reconnected magnetic field lines within FTEs, with a view to predicting (1) the locations where events form, (2) the mechanism(s) by which they are generated, (3) their signatures on the dayside and flank magnetopause, (4) their antisunward motion, (5) their interaction with the cusps, and (6) their signatures in the dayside auroral oval, including their occurrence patterns as a function of season. We compare these predictions with observations, in particular the results of a statistical study of Interball-1 FTEs and new multipoint THEMIS observations of FTEs.