New auroral spectrometer using an acousto-optic tunable filter

This paper reports the performance and capability of a newly developed zenith spectrometer (for measurements of airglow and aurora) that uses an acousto-optic tunable filter (AOTF). The AOTF can scan the pass-band of the spectrometer between 450 and 700 nm with a bandwidth of 2-3 nm by changing the RF driver frequency from 180 to 100 MHz. The absolute sensitivity of the spectrometer is ～0.1-1.5 counts/Rayleigh/s per spectral step. The spectrometer is fully automated. The O I (557.7 nm) airglow line can be clearly identified in test observations of midlatitude airglow performed at Shigaraki Observatory, Japan. Based on an estimate of the signal-to-noise ratio, we conclude that the full auroral spectrum (450-700) nm can be measured by the AOTF spectrometer with a time resolution of ～100 s and a signal-to-noise ratio of ～100 for an auroral emission intensity of 10 kR. An example of the auroral spectra is shown for observations made at Syowa Station in Antarctica

Recent results of the Optical Mesosphere Thermosphere Imagers (OMTIs): 2014-2015

第6回極域科学シンポジウム[OS] 宙空圏11月16日（月）　国立極地研究所１階交流アトリウ

LF radio observation of storm-time energetic electron precipitation observed in the auroral and sub-auroral regions

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月26日（月）、27日（火） 国立極地研究所 2階ラウン

Fast flickering aurora within traveling current vortices

第6回極域科学シンポジウム[OS] 宙空圏11月16日（月）　国立極地研究所１階交流アトリウ

GPS Scintillations and TEC Variations in Association With a Polar Cap Arc

A unique example of a polar cap arc producing clear amplitude and phase scintillations in GPS L-band signals is presented using observations from an all-sky imager and a GPS receiver and a digital ionosonde at Resolute Bay and the SuperDARN Inuvik radar. During the southward interplanetary magnetic field (IMF) condition, the polar cap arc moved quickly from the dusk-side to the midnight auroral oval at a speed of ∼700 m/s, as revealed by all-sky 557.7 and 630.0 nm images. When it intersected the raypath of GPS signals, both amplitude and phase scintillations appeared, which is very different from previous results. Moreover, the scintillations were precisely determined through power spectral analysis. We propose that the strong total electron content (TEC) enhancement (∼6 TECU) and flow shears in association with the polar cap arc under the southward IMF condition were creating the scintillations. It provides evidence for the existence of polar cap arc scintillations that may be harmful for satellite applications even through L-band signals.publishedVersio

The geospace response to variable inputs from the lower atmosphere:a review of the progress made by Task Group 4 of CAWSES-II

The advent of new satellite missions, ground-based instrumentation networks, and the development of whole atmosphere models over the past decade resulted in a paradigm shift in understanding the variability of geospace, that is, the region of the atmosphere between the stratosphere and several thousand kilometers above ground where atmosphere-ionosphere-magnetosphere interactions occur. It has now been realized that conditions in geospace are linked strongly to terrestrial weather and climate below, contradicting previous textbook knowledge that the space weather of Earth's near space environment is driven by energy injections at high latitudes connected with magnetosphere-ionosphere coupling and solar radiation variation at extreme ultraviolet wavelengths alone. The primary mechanism through which energy and momentum are transferred from the lower atmosphere is through the generation, propagation, and dissipation of atmospheric waves over a wide range of spatial and temporal scales including electrodynamic coupling through dynamo processes and plasma bubble seeding. The main task of Task Group 4 of SCOSTEP's CAWSES-II program, 2009 to 2013, was to study the geospace response to waves generated by meteorological events, their interaction with the mean flow, and their impact on the ionosphere and their relation to competing thermospheric disturbances generated by energy inputs from above, such as auroral processes at high latitudes. This paper reviews the progress made during the CAWSES-II time period, emphasizing the role of gravity waves, planetary waves and tides, and their ionospheric impacts. Specific campaign contributions from Task Group 4 are highlighted, and future research directions are discussed

Simultaneous ground and satellite observations of an isolated proton arc at subauroral latitudes

We observed an isolated proton arc at the Athabasca station MLAT: 62◦N) in Canada on 5 September, 2005, using a ground-based allsky imager at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm (Hβ). This arc is similar to the detached proton arc observed recently by the IMAGE satellite [Immel et al., 2002]. The arc appeared at 0500-0700 UT (2100-2300 MLT) coincident with strong Pc 1 geomagnetic pulsations in the frequency range of the electromagnetic ion cyclotron (EMIC) wave. A small substorm took place at 0550 UT, while the isolated arc did not change its structure and intensity before and after the substorm onset. From particle data obtained by the NOAA 17 satellite, we found that the isolated arc was located in the localized (L ∼4) enhancement of ion precipitation fluxes at an energy range of 30-80 keV. 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 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 were driven by the EMIC waves, which were generated near the plasmapause and scattered the ring current protons resonantly into the loss cone

Statistical analysis of luminosity of polar cap patches

第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月26日（月）、27日（火） 国立極地研究所 2階ラウン