[1] The EISCAT radar in Tromsø (67 cgmLat) has been used to estimate statistics of electromagnetic (EM) energy transfer rates by utilizing calculated electric fields, conductivities and E-region neutral winds. It was found that the magnetospheric EM energy input is slightly larger in the evening than morning sector, but due to winds, the Joule heating rate has the largest values in the morning sector. The duskside subauroral region contains large northward electric fields and is a site of significant magnetospheric EM energy input and Joule heating. For quiet conditions (Kp: 0-2 + ), the neutral wind is the major source for Joule heating at all MLT except at the evening maximum of magnetospheric EM input. For medium (Kp: 3 À -4 + ) and high (Kp ≥ 5 À ) activity levels, winds increase Joule heating rates in the morning, but decrease them in the evening. The positive contribution of winds during the morning maximum is 30% and 20% for medium and high activity levels, respectively. The region where winds are a net load for the magnetospheric EM energy input is 17-20 MLT for medium and 13-18 MLT for high activity conditions. The median EM energy transfer to mechanical work made on winds is 20% at maximum. An event with a long-lasting high electric field showed that the ion drag acting on neutrals can decrease the Joule (ion-neutral collisional) heating by more than 50%.Citation: Aikio, A. T., L. Cai, and T. Nygrén (2012), Statistical distribution of height-integrated energy exchange rates in the ionosphere,

Abstract. We present a comprehensive study of a sequence of two substorms and multiple pseudobreakups using optical, magnetic and incoherent scatter radar measurements, energetic particles from two geosynchronous satellites and particle and field data from the Geotail spacecraft located at Xasm • -86 Re. Following conventional nomenclature, we classified as pseudobreakups those auroral breakups which did not exhibit significant poleward expansion (< 2 ø magnetic latitude).Auroral intensifications following substorm breakups were also observed, and were classified separately. Pseudobreakups were found not to differ from substorm breakups in longitudinal extent (from 1.3 to 6.1 hours of magnetic local time), or in duration (from 5 to 16 minutes). In general, the ionospheric currents producing ground magnetic disturbances were more intense during substorms than pseudobreakups. We found that pseudobreakups are associated with the same magnetospheric processes as substorm breakups which involve current wedge formation, midlatitude magnetic Pi2 pulsations and energetic particle injections at the geosynchronous altitude. Moreover, pseudobreakups are associated with magnetic reconnection in the near-Earth region, evidenced by the typical subsequent detection of a plasmoid at Geotail. This implies that the magnetotail volume influenced by a pseudobreakup is qui•e large in radial distance. We conclude that there is no definitive qualitative distinction between pseudobreakups and substorms but there is a continuum of states between the small pseudobreakups and large substorms.

Abstract. The four Cluster s/c passed over Northern Scandinavia on 6 February 2001 from south-east to north-west at a radial distance of about 4.4 R E in the post-midnight sector. When mapped along geomagnetic field lines, the separation of the spacecraft in the ionosphere was confined to within 110 km in latitude and 50 km in longitude. This constellation allowed us to study the temporal evolution of plasma with a time scale of a few minutes. Ground-based instrumentation used involved two all-sky cameras, magnetometers and the EISCAT radar. The main findings were as follows.Two auroral arcs were located close to the equatorward and poleward edge of a large-scale density cavity, respectively. These arcs showed a different kind of a temporal evolution. (1) As a response to a pseudo-breakup onset, both the up-and downward field-aligned current (FAC) sheets associated with the equatorward arc widened and the total amount of FAC doubled in a time scale of 1-2 min. (2) In the poleward arc, a density cavity formed in the ionosphere in the return (downward) current region. As a result of ionospheric feedback, a strongly enhanced ionospheric southward electric field developed in the region of decreased Pedersen conductance. Furthermore, the acceleration potential of ionospheric electrons, carrying the return current, increased from 200 to 1000 eV in 70 s, and the return current region widened in order to supply a constant amount of return current to the arc current circuit.Evidence of local acceleration of the electron population by dispersive Alfvén waves was obtained in the upward FAC region of the poleward arc. However, the downward accelerated suprathermal electrons must be further energised below Cluster in order to be able to produce the observed visible aurora.Correspondence to: A. T. Aikio (anita.aikio@oulu.fi) Both of the auroral arcs were associated with broad-band ULF/ELF (BBELF) waves, but they were highly localised in space and time. The most intense BBELF waves were confined typically to the return current regions adjacent to the visual arc, but in one case also to a weak upward FAC region. BBELF waves could appear/disappear between s/c crossings of the same arc separated by about 1 min.

Abstract. We report observations of a sequence of quiettime Earthward bursty bulk flows (BBFs) measured by the Cluster spacecraft in the near-tail plasma sheet (XGSM ∼ −12 to −14 R E ) in the evening sector, and by simultaneous highresolution measurements in the northern conjugate ionosphere by the EISCAT radars, a MIRACLE all-sky camera and magnetometers, as well as a meridian-scanning photometer (MSP) in the Scandinavian sector on 17 October 2005.The BBFs at Cluster show signatures that are consistent with the plasma "bubble" model Wolf, 1993, 1999), e.g. deflection and compression of the ambient plasma in front of the Earthward moving bubble, magnetic signatures of a flow shear region, and the proper flows inside the bubble. In addition, clear signatures of tailward return flows around the edges of the bubble can be identified. The duskside return flows are associated with significant decrease in plasma density, giving support to the recent suggestion by Walsh et al. (2009) of formation of a depleted wake. However, the same feature is not seen for the dawnside return flows, but rather an increase in density.In the ionosphere, EISCAT and optical measurements show that each of the studied BBFs is associated with an auroral streamer that starts from the vicinity of the polar cap boundary, intrudes equatorward, brakes at 68-70 • aacgm MLAT and drifts westward along the proton oval. Within the streamer itself and poleward of it, the ionospheric plasma flow has an equatorward component, which is the ionospheric manifestation of the Earthward BBF channel. A sharp velocity shear appears at the equatorward edge of a streamer. We suggest that each BBF creates a local velocity shear in the ionosphere, in which the plasma flow poleward of and inside the streamer is in the direction of the Correspondence to: T. Pitkänen (timo.pitkanen@oulu.fi) streamer and southeastward. A northwestward return flow is located on the equatorward side. The return flow is associated with decreased plasma densities both in the ionosphere and in the magnetosphere as measured by EISCAT and Cluster, respectively. In summary, we present the first simultaneous high-resolution observations of BBF return flows both in the plasma sheet and in the ionosphere, and those are in accordance with the bubble model. The results apply for the duskside return flows, but the manifestation of dawnside return flows in the ionosphere requires further studies.Finally, EISCAT measurements indicate increased nightside reconnection rate during the ∼35-min period of BBFs. We suggest that the observed temporal event of IMF rotation to a more southward direction produces enhanced open flux transport to the nightside magnetotail, and consequently, the nightside reconnection rate is increased.

The EISCAT (European Incoherent SCATer) Scientific Association has provided versatile incoherent scatter (IS) radar facilities on the mainland of northern Scandinavia (the EISCAT UHF and VHF radar systems) and on Svalbard (the electronically scanning radar ESR (EISCAT Svalbard Radar) for studies of the high-latitude ionised upper atmosphere (the ionosphere). The mainland radars were constructed about 30 years ago, based on technological solutions of that time. The science drivers of today, however, require a more flexible instrument, which allows measurements to be made from the troposphere to the topside ionosphere and gives the measured parameters in three dimensions, not just along a single radar beam. The possibility for continuous operation is also an essential feature. To facilitatefuture science work with a world-leading IS radar facility, planning of a new radar system started first with an EU-funded Design Study (2005-2009) and has continued with a follow-up EU FP7 EISCAT_3D Preparatory Phase project (2010-2014). The radar facility will be realised by using phased arrays, and a key aspect is the use of advanced software and data processing techniques. This type of software radar will act as a pathfinder for other facilities worldwide. The new radar facility will enable the EISCAT_3D science community to address new, significant science questions as well as to serve society, which is increasingly dependent on space-based technology and issues related to space weather. The location of the radar within the auroral oval and at the edge of the stratospheric polar vortex is also ideal for studies of the long-term variability in the atmosphere and global change. This paper is a summary of the EISCAT_3D science case, which was prepared as part of the EU-funded Preparatory Phase project for the new facility. Three science working groups, drawn from the EISCAT user community, participated in preparing this document. In addition to these working group members, who are listed as authors, thanks are due to many others in the EISCAT scientific community for useful contributions, discussions, and support.

[1] The spatial distribution of electric fields, conductances, and currents of steadily drifting medium-scale (15-50 km) arcs in the evening sector (20-23 magnetic local time (MLT)) is obtained from European Incoherent Scatter Radar (EISCAT) and optical groundbased measurements. The current systems of stable arcs residing in the northward convection electric field region show a consistent pattern: currents flow downward on the equatorward side of the arcs, then poleward, and upward from the arcs. In one event where the arcs are located in a region of convection reversals, the current pattern is more complicated. Most of the arcs are associated with an enhanced northward-directed electric field region on the equatorward side of the arc, colocated with downward field-aligned currents (FACs) and suppressed E and F region electron densities. The width of the region of the enhanced electric field is one to four times the width of the arc. In some cases, the electron density reduction is so pronounced that the region can be described as an auroral ionospheric density cavity. The electrostatic magnetosphere-ionosphere coupling model of arcs predicts that the width L of an arc is related to the ionospheric Pedersen conductance. This study shows that stable medium-scale arcs in the evening sector obey this equation. A value of K = 2 Â 10 À8 S m À2is obtained for 15-35 km wide arcs. It is argued that the large value of the field-aligned conductance cannot be interpreted in terms of the adiabatic theory. Possibly the high value of K results from nonadiabatic processes acting on the current-carrying electrons.

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Derivation of the auroral ionospheric currents from magnetic field measurements can produce drastically different results depending on the data and method used. We have cross tested several methods for obtaining instantaneous field‐aligned and horizontal currents from Swarm satellite and International Monitor for Auroral Geomagnetic Effects (IMAGE) ground magnetic field measurements. We found that Swarm can yield latitude profiles of the east‐west component of the divergence‐free current density at most at ∼200 km resolution, typically resolving the electrojets. The north‐south divergence‐free component, on the other hand, is not always well reproduced due to the small longitudinal distance between the side‐by‐side flying satellite pair. Swarm can yield the field‐aligned and curl‐free current density at a wider range of latitude resolutions (∼7.5–200 km) than the divergence‐free current density. While 7.5 km is suitable for comparison with auroras, 200 km typically resolves the Regions 1 and 2 field‐aligned currents. IMAGE can yield maps of the divergence‐free current density at ∼50 km resolution. Induced telluric currents should be accounted for in the derivation. Not accounting for them in the Swarm analysis, however, does not appear to introduce significant errors. Ionospheric conductances can be estimated by combining the total horizontal current density, consisting of the curl‐free and divergence‐free components, with the electric field measurements. Our results indicate that Swarm can only yield these at ∼200 km scale size when there is no significant dependence on longitude. However, combining the divergence‐free current from IMAGE with the curl‐free current and electric field from Swarm could yield conductance maps at ∼50 km resolution.