Mechanism for the formation of the high-altitude stagnant cusp: Cluster and SuperDARN observations

On 16 March 2002, Cluster moved from nightside to dayside, across the high-altitude northern cusp during an extended period of relatively steady positive IMF BY and BZ. Combined Cluster and SuperDARN data imply the existence of two reconnection sites: in the high- latitude northern hemisphere dusk and southern hemisphere dawn sectors. Within the cusp, Cluster encounters 3 distinct plasma regions. First, injections of magnetosheath-like plasma associated with dawnward and sunward convection suggest Cluster crosses newly- reconnected field lines related to the dusk reconnection site. Second, Cluster observes a Stagnant Exterior Cusp (SEC), characterized by nearly isotropic and stagnant plasma. Finally, Cluster crosses a region with significant antifield-aligned flows. We suggest the observed SEC may be located on newly re-closed field lines, reconnected first poleward of the northern hemisphere cusp and later reconnected again poleward of the southern hemisphere cusp. We discuss how the Cluster observations correspond to expectations of ’double reconnection’ model

The Earth: Plasma Sources, Losses, and Transport Processes

This paper reviews the state of knowledge concerning the source of magnetospheric plasma at Earth. Source of plasma, its acceleration and transport throughout the system, its consequences on system dynamics, and its loss are all discussed. Both observational and modeling advances since the last time this subject was covered in detail (Hultqvist et al., Magnetospheric Plasma Sources and Losses, 1999) are addressed

Space and ground-based investigations of dayside reconnection: Cluster, double star and SuperDARN observations

In this paper, we present an overview of several investigations that have exploited Cluster, Double Star and SuperDARN radar data in order to scrutinise the coupling of the solar wind, magnetosphere and ionosphere. The studies introduced have drawn upon simultaneous space- and ground-based data in order to overcome the inherent shortcomings of the in situ (space-based) and remotely-sensed (ground-based) measurement techniques. In particular, we shall highlight the results of studies that investigate the dynamics arising from magnetic reconnection at the dayside magnetopause and the resulting ionospheric responses

IMPALAS: Investigation of MagnetoPause Activity using Longitudinally-Aligned Satellites—a mission concept proposed for the ESA M3 2020/2022 launch

The dayside magnetopause is the primary site of energy transfer from the solar wind into the magnetosphere, and modulates the activity observed within the magnetosphere itself. Specific plasma processes operating on the magnetopause include magnetic reconnection, generation of boundary waves, propagation of pressure-pulse induced deformations of the boundary, formation of boundary layers and generation of Alfvén waves and field-aligned current systems connecting the boundary to the inner magnetosphere and ionosphere. However, many of the details of these processes are not fully understood. For example, magnetic reconnection occurs sporadically, producing flux transfer events, but how and where these arise, and their importance to the global dynamics of the magnetospheric system remain unresolved. Many of these phenomena involve propagation across the magnetopause surface. Measurements at widely-spaced (Δ ˜ 5 RE) intervals along the direction of dayside terrestrial field lines at the magnetopause would be decisive in resolving these issues. We describe a mission carrying a fields and plasmas payload (including magnetometer, ion and electron spectrometer and energetic particle telescopes) on three identical spacecraft in synchronized orbits. These provide the needed separations, with each spacecraft skimming the dayside magnetopause and continuously sampling this boundary for many hours. The orbits are phased such that (i) all three spacecraft maintain common longitude and thus sample along the same magnetopause field line; (ii) the three spacecraft reach local midday when northern European ground-based facilities also lie near local midday, enabling simultaneous sampling of magnetopause field lines and their footprints

Structure of field-aligned currents in the polar cusp: conjugated observations by Cluster, Double Star-2 and SuperDARN

Dayside field-aligned currents flowing along highly conductive field lines transmit magnetic stress caused by magnetopause reconnection, to the magnetosphere and the conjugated ionosphere. On 20 February 2005, Cluster at high altitude and Double Star-2 (TC-2) at mid altitude are situated in the vicinity of the northern cusp / mantle, with Cluster moving sunward and TC-2 anti-sunward. Their magnetic footprints come very close together at about 15:45 UT, just over the common field-of-view of SuperDARN radars. Based on this conjunction, we compare the transverse structure (form/elongation) of field-aligned current tubes at different altitudes, their intensity, their temporal dynamics, the associated particle carriers and their closure in the ionosphere. Cluster field-aligned currents are determined from the multi-satellite curlometer technique and compared to the currents determined from the single-satellite method based on the infinite current sheet hypothesis. This last method is also used to calculate currents from TC-2 magnetic data. The good comparison between drift velocity of injections calculated from the four-spacecraft timing technique and convection field measured by SuperDARN, allows to take into account the drift of the injection structures in the current calculation. Finally, fieldaligned currents deduced from magnetic measurements are also compared with electron and ion fluxes measured onboard Cluster and TC-2

Coordinated Cluster and Double Star observations of the dayside magnetosheath and magnetopause at different latitudes near noon

International audienceWe present results of a favorable conjunction where the equatorial spacecraft (TC-1) of the Double Star mission exits the dayside magnetopause near the equator, while Cluster is inbound, near the southern cusp. This configuration makes it possible to compare observations of the magnetopause, around the same magnetic local time but at different latitudes. In this paper, we report on the general properties of the magnetosheath plasma at the two latitudes: unlike predictions from gasdynamic modeling, the density is found lower near the nose of the magnetopause than further downstream. Then, we present three interesting events. First, an FTE is observed at TC-1 and not at Cluster; we discuss the implications this has on the evolution of FTEs and on the size of the reconnection site. Then, a structure observed at both spacecraft is interpreted as a bulge progressing along the magnetopause. It is not clear whether this bulge is actually the remnant of an FTE or a running pulse that makes Cluster sense the reconnection layer. In any case, a rotational discontinuity is observed within it. At last, a northward turning of the magnetosheath magnetic field is observed at TC-1 and a reverse FTE is subsequently seen at Cluster, suggesting that magnetic reconnection is very fast to set up following a change in the IMF orientation

Recent Cluster Results on Cusp and Magnetopause Boundary Phenomena

abstract SM21C-01 INVITEDInternational audienceThe combined data sets of Cluster and Double Star have provided extensive, multi-scale coverage of the Earth's magnetosphere. Since 2001 the Cluster orbit has preferentially sampled the high and mid altitude cusp regions during the spring seasons, and crossed both the high and low latitude, dayside magnetopause at other times. We present an overview of the most recent Cluster research on both the dayside and boundary layer phenomena based predominantly on multipoint studies. The Doublestar TC-1 spacecraft has also sampled either the subsolar region of the magnetopause, or southerly latitudes, at similar local times to cluster. We therefore also review coordinated CLUSTER-Double Star conjunctions for a number of dayside passes to investigate reconnection associated signatures observed at different locations. We Focus on both transient FTEs, arising from opened flux ropes during intermittant reconnection, and comparative boundary layer signatures during cusp and magnetopause transitions and investigate structure and dynamics of the magnetopause and FTE occurance on motion. Cluster provides good coordination with ionospheric instrumentation, particularly the EISCAT and SuperDARN radars and ground magnetomters and we also review investigations of the ground signatures of reconnection (FTEs and boundary layers) and other features of magnetospheric response. The spacecraft are conjugate simulataneously with both the ESR radar on Svalbard, and the Antarctic station at Zhongshan, when the ground stations lie under the cusp position, Cluster is passing out from the northern cusp and TC-1 is near the magnetopause