[1] We observed an isolated proton arc at the Athabasca station (MLAT: 62°N) in Canada on 5 September 2005, using a ground-based all-sky imager at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (Hb). This arc is similar to the detached proton arc recently observed by the IMAGE satellite . The arc appeared at 0500-0640 UT (2100-2240 MLT), coincident with strong Pc 1 geomagnetic pulsations in the frequency range of the electromagnetic ion cyclotron (EMIC) wave. The isolated arc did not change its structure and intensity during the late growth and expansive phases of a small substorm that occurred at 0550 UT. From particle data obtained by the NOAA 17 satellite, we found that the isolated arc was associated with the localized enhancement of ion precipitation fluxes at an energy range of 30-80 keV at L $ 4. Trapped ion flux enhancements (ring current ions) were also observed at two latitudinally separated regions. The localized ion precipitation was located at the outer boundary of the inner ring current ions. The DMSP F13 satellite observed signatures of an ionospheric plasma trough near the conjugate point of the arc in the Southern Hemisphere. The trough is considered to be connected to the plasmapause. These results indicate that the source region of the isolated arc was located near the plasmapause and in the ring current. We conclude that the observed isolated proton arc at subauroral latitudes was caused by the EMIC waves, which were generated near the plasmapause and resonantly scattered the ring current protons into the loss cone.
The SuperDARN Hokkaido HF radar, capable of measuring the subauroral ionospheric plasma convection especially during storms, has been in continuous operation since the beginning of December 2006. We report the first two‐dimensional observation of a dynamic variation of convection flow reversal in subauroral postmidnight sector during the storm main phase on 29 January 2007. The flow reversal region is extended over 20° in longitude and 5° in latitude, lasting for about 10–15 min, and the maximum flow speed is about 0.5–1.0 km/s. The flow reversal structure is reasonably reproduced by the ring current simulation coupled with the ionosphere, suggesting that it is produced by the region 2 field‐aligned current associated with the ring current enhancement during the storm main phase. The dynamic variation of the flow reversal structure is interpreted as a transient eastward extension of the elongated dusk convection cell to the postmidnight and equatorward of the dawn cell, associated with the variation of the ring current whose structure is controlled by the interplanetary magnetic field and solar wind dynamic pressure. It is suggested that the ring current variation is highly coupled with the interplanetary parameters and is much more complicated than ever thought.
A new digital all-sky imager experiment for optical auroral studies in conjunction with the Scandinavian twin auroral radar experiment Rev. ABSTRACTThe Optical Mesosphere Thermosphere Imagers (OMTIs) currently consist of eight all-sky cooled-CCD imagers and several interferometers and spectrometers. They are making routine observations of aurora and airglow in Japan, Australia, Indonesia, and Canada. Here we show recent results of OMTIs particularly from the two Canadian stations at Resolute Bay (RSB) and Athabasca (ATH). At RSB, we observe polar-cap plasma patches almost always during southward IMF periods. From two-dimensional cross-correlation analyses, we determine velocity vectors of the patches, which indicates the ionospheric convection vector, showing high correlation with the IMF-By and -Bz variations. At ATH, we often observe isolated proton arcs and Stable Auroral Red (SAR) arcs, which are located equatorward of the auroral oval. The appearance of the isolated proton arcs is highly correlated with the Pc 1 geomagnetic pulsations measured simultaneously at ATH, suggesting interactions between the electromagnetic ion cyclotron (EMIC) waves and protons in the vicinity of the plasmapause and the ring current. Similar interactions without waves are also suggested for the SAR arcs, which appear after the substorm expansion phase even without geomagnetic storms. These observations show promising capability to monitor magnetospheric processes from the ground stations, which would contribute to the future satellite projects, such as THEMIS, ERG, and Scope/Xscale.
Charged particle precipitation from Earth’s magnetosphere results in stunning displays of the aurora and energy transfer into the atmosphere. Some of this precipitation is caused by wave-particle interactions. In this study, we present an example of a wave-particle interaction between Electromagnetic Ion Cyclotron waves, and magnetospheric protons and electrons. This interaction resulted in a co-located isolated proton aurora and relativistic electron microbursts. While isolated proton aurora is widely believed to be caused by Electromagnetic Ion Cyclotron waves, this unique observation suggests that these waves can also scatter relativistic electron microbursts. Theoretically, nonlinear interactions between Electromagnetic Ion Cyclotron waves and electrons are necessary to produce the intense sub-second microburst precipitation. Lastly, detailed analysis of the auroral emissions suggests that no chorus waves were present during the event. This is in contrast to the most commonly associated driver of microbursts, whistler mode chorus waves, and supports other less commonly considered driving mechanisms.
In order to reach the new horizon of the space physics research, the Plasma Universe, via in-situ measurements in the Earth's magnetosphere, SCOPE will perform formation flying observations combined with high-time resolution electron measurements. The simultaneous multi-scale observations by SCOPE of various plasma dynamical phenomena will enable data-based study of the key space plasma processes from the cross-scale coupling point of view. Key physical processes to be studied are magnetic reconnection under various boundary conditions, shocks in space plasma, collisionless plasma mixing at the boundaries, and physics of current sheets embedded in complex magnetic geometries. The SCOPE formation is made up of 5 spacecraft and is put into the equatorial orbit with the apogee at 30Re (Re: earth radius). One of the spacecraft is a large mother ship which is equipped with a full suite of particle detectors including ultra-high time resolution electron detector. Among other 4 small spacecraft, one remains near (~10km) the mother ship and the spacecraft-pair will focus on the electron-scale physics. Others at the distance of 100~3000km (electron ~ ion spatial scales) from the mother ship will monitor plasma dynamics surrounding the mother-daughter pair. There is lively ongoing discussion on Japan-Europe international collaboration (ESA's Cross-Scale), which would certainly make better the coverage over the scales of interest and thus make the success of the mission, i.e., clarifying the multi-scale nature of the Plasma Universe, to be attained at an even higher level. THE SCIENCE OF THE SCOPE MISSION Magnetosphere as a Typical Piece of the Plasma Universe Large fraction of the Universe is filled by gas in plasma state. This implies that magnetic field would be playing significant roles in the gas dynamics of the Universe. There indeed are growing interests in the magnetic effects in astrophysical situations such as accretion disks. The Plasma Universe can be characterized by highenergy, large scale dynamic phenomena, and it is these active features mediated by the effects of the magnetic field that keep us fascinated. The Earth's magnetosphere can be regarded a typical piece of the Plasma Universe. The region is formed by the interaction between the solar wind and the planet's intrinsic magnetic field. Since the solar wind is super sonic, the bow shock is formed in the front side of the magnetosphere. The boundary that separates the shocked solar wind from the region occupied by the Earth's magnetic field (magnetosphere) is a velocity shear layer, a current layer, as well as a density gradient layer. That is, the boundary contains various source of free energy and is full of potential to behave dynamically. In the night side of the magnetosphere, the field lines are highly stretched along the sun-earth direction to form a current sheet across which the magnetic polarity reverses. The anti-parallel field lines are often subject to magnetic reconnection via which energy stored as the magnetic energy is released explosive...
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