Abstract. In this paper we present the first statistical study on auroral oval boundaries derived from small-and mediumscale field-aligned currents (FACs, < 150 km). The dynamics of both the equatorward and poleward boundaries is deduced from 10 years of CHAMP (CHAllenging Minisatellite Payload) magnetic field data (August 2000-August 2010). The approach for detecting the boundaries from FACs works well under dark conditions. For a given activity level the boundaries form well-defined ellipses around the magnetic pole. The latitudes of the equatorward and poleward boundaries both depend, but in different ways, on magnetic activity. With increasing magnetic activity the equatorward boundary expands everywhere, while the poleward boundary shows on average no dependence on activity around midnight, which seems to be stationary at a value of about 72 • Mlat. Functional relations between the latitudes of the boundaries and different magnetic activity indices have been tested. Best results for a linear dependence are derived for both boundaries with the dayside merging electric field. The other indices, like the auroral electrojet (AE) and disturbance storm time (Dst) index, also provide good linear relations but with some caveats. Toward high activity a saturation of equatorwards expansion seems to set in. The locations of the auroral boundaries are practically independent of the level of the solar EUV flux and show no dependence on season.

[1] The Investigation of Cusp Irregularities 2 sounding rocket was launched 5 December 2008 at 1035 UT. We present an overview of the associated solar wind and auroral conditions, and we look in detail at the relationship between poleward moving auroral forms (PMAFs) and the creation of polar cap patches using ground-based optical and radar data as well as in situ data from the rocket payload. The solar wind was found to be dominated by a stable interplanetary magnetic field (IMF) B z < 0 and by an IMF B y > 0 situation. The aurora was characterized by a series of PMAFs throughout the period of interest. Associated with each PMAF were polar cap patches seen to emerge from the most poleward location of the PMAFs. On the basis of the available data, we present a conceptual model explaining the creation of the polar cap patches under the given solar wind and ionospheric conditions.

[1] An isolated burst of 0.35 Hz electromagnetic ion cyclotron (EMIC) waves was observed at four sites on Svalbard from 0947 to 0954 UT 2 January 2011, roughly 1 h after local noon. This burst was associated with one of a series of~50 nT magnetic impulses observed at the northernmost stations of the IMAGE magnetometer array. Hankasalmi SuperDARN radar data showed a west-to-east (antisunward) propagating vortical ionospheric flow in a region of high spectral width~1-2 north of Svalbard, confirming that this magnetic impulse was the signature of a traveling convection vortex. Ground-based observations of the H a line at Longyearbyen indicated proton precipitation at the same time as the EMIC wave burst, and NOAA-19, which passed over the west coast of Svalbard between 0951 and 0952, observed a clear enhancement of ring current protons at the same latitude. Electron precipitation from this same satellite indicated that the EMIC burst was located on closed field lines, but near to the polar cap boundary. We believe these are the first simultaneous observations of EMIC waves and precipitating energetic protons so near to the boundary of the dayside magnetosphere. Although several spacecraft upstream of Earth observed a steady solar wind and predominantly radial interplanetary magnetic field orientation before and during this event, data from Geotail (near the morning bow shock) showed large reorientations of the interplanetary magnetic field and substantial decreases in ion density several minutes before it, and data from Cluster (near the afternoon bow shock) showed an outward excursion of the bow shock simultaneous with it. These upstream perturbations suggest that a spontaneous hot flow anomaly, a bow shock related instability, may have been responsible for triggering this event, but do not provide enough information to fully characterize that instability. , et al. (2013), Multi-instrument observations from Svalbard of a traveling convection vortex, electromagnetic ion cyclotron wave burst, and proton precipitation associated with a bow shock instability, J. Geophys.

[1] Ground based optical instruments are invaluable tools for studies of processes associated with the cusps and auroral morphology. In this work we present a method for obtaining the magnetic latitude of the open/closed field line boundary (OCB) from the cusp 6300 Å[OI] auroral red line using a meridian scanning photometer. The method which is based on a pre-defined reference cusp aurora produced by the GLOW model is examined with respect to uncertainties, and we describe how a set of equations describing the error is constructed. The method is applicable to data from optical instruments located at high latitude observation sites such as Svalbard and Antarctica. Equations describing both errors and the mapping altitude for transforming the OCB from instrument centered coordinates to magnetic latitude for instrumentation located in Svalbard (Longyearbyen) are presented. Further, by applying the GLOW model we present results illustrating the great variability in the altitude profile of the atomic oxygen 6300 Å[OI] red line emission in the cusp. A simple calculation showing how a poleward neutral wind will change the latitudinal shape of the cusp aurora is also performed.

We present ionospheric plasma conditions observed by the EISCAT radars in Tromsø and on Svalbard, covering 68°–81° geomagnetic latitude, during 6–8 September 2017. This is a period when X2.2 and X9.3 X‐ray flares occurred, two interplanetary coronal mass ejections (ICMEs) arrived at the Earth accompanied by enhancements of MeV‐range energetic particle flux in both the solar wind (SEP event) and inner magnetosphere, and an AL < −2,000 substorm took place. (1) Both X flares caused enhancement of ionospheric electron density for about 10 min. The X9.3 flare also increased temperatures of both electrons and ions over 69°–75° geomagnetic latitude until the X‐ray flux decreased below the level of X‐class flares. However, the temperature was not enhanced after the previous X2.2 flare in the prenoon sector. (2) At around 75° geomagnetic latitude, the prenoon ion upflow flux slightly increased the day after the X9.3 flare, which is also after the first ICME and a SEP event, while no outstanding enhancement was found at the time of these X flares. (3) The upflow velocity sometimes decreased when the interplanetary magnetic field (IMF) turned southward. (4) Before the first ICME arrival after the SEP event under weak IMF with Bz ~0 nT, a substorm‐like expansion of the auroral arc signature took place without local geomagnetic signature near local midnight, while no notable change was observed after the ICME arrival. (5) AL reached <−2,000 nT only after the arrival of the second ICME with strongly southward IMF. Causality connections between the solar/solar wind event and the ionospheric responses remain unclear.