Bibliography

Fast modulations of pulsating proton aurora related to subpacket structures of Pc1 geomagnetic pulsations at subauroral latitudes

To understand the role of electromagnetic ion cyclotron (EMIC) waves in determining the temporal features of pulsating proton aurora (PPA) via wave-particle interactions at subauroral latitudes, high-time-resolution (1/8 s) images of proton-induced N2+ emissions were recorded using a new electron multiplying charge-coupled device camera, along with related Pc1 pulsations on the ground. The observed Pc1 pulsations consisted of successive rising-tone elements with a spacing for each element of 100 s and subpacket structures, which manifest as amplitude modulations with a period of a few tens of seconds. In accordance with the temporal features of the Pc1 pulsations, the auroral intensity showed a similar repetition period of 100 s and an unpredicted fast modulation of a few tens of seconds. These results indicate that PPA is generated by pitch angle scattering, nonlinearly interacting with Pc1/EMIC waves at the magnetic equator.

Ozaki, M.; Shiokawa, K.; Miyoshi, Y.; Kataoka, R.; Yagitani, S.; Inoue, T.; Ebihara, Y.; Jun, C.-W; Nomura, R.; Sakaguchi, K.; Otsuka, Y.; Shoji, M.; Schofield, I.; Connors, M.; Jordanova, V.;

Published by: Geophysical Research Letters      Published on: 08/2016

YEAR: 2016     DOI: 10.1002/2016GL070008

fast modulation; Pc1 geomagnetic pulsations; pulsating proton aurora; subpacket structure; Van Allen Probes; wave-particle interactions

Equivalent Circuit Model for the Electric Field Sensitivity of a Magnetic Search Coil of Space Plasma

Magnetic search coils (MSCs) are sensitive to both magnetic and electric fields, but detecting electric fields is unnecessary for magnetic observations of plasma waves. However, it is important to evaluate both sensitivities for different geometries and electrostatic shields to avoid electric field pickup. An equivalent circuit model for the electric field sensitivity of an MSC in a collisionless isotropic cold plasma is developed here using electrical coupling through a sheath capacitance. That sensitivity is defined by a relationship between the MSC impedance and the sheath capacitance. To confirm the validity of the circuit model, the sensitivity to an electric field is measured by imposing an external electric field using charged parallel metallic plates in laboratory experiments. The coupling capacitance between the MSC and the charged plates is equivalent to the sheath capacitance in a space plasma. The measured results show good agreement with an approximate expression deduced from the equivalent circuit model.

Ozaki, Mitsunori; Yagitani, Satoshi; Takahashi, Ken; Imachi, Tomohiko; Koji, Hiroki; Higashi, Ryoichi;

Published by: IEEE Sensors Journal      Published on: 10/2014

YEAR: 2014     DOI: 10.1109/JSEN.2014.2365495

electric field sensitivity; Magnetic search coils; sheath impedance; space plasmas

Ground-based ELF/VLF chorus observations at subauroral latitudes-VLF-CHAIN Campaign

We report observations of very low frequency (VLF) and extremely low frequency (ELF) chorus waves taken during the ELF/VLF Campaign observation with High-resolution Aurora Imaging Network (VLF-CHAIN) of 17\textendash25 February 2012 at subauroral latitudes at Athabasca (L=4.3), Canada. ELF/VLF waves were measured continuously with a sampling rate of 100 kHz to monitor daily variations in ELF/VLF emissions and derive their detailed structures. We found quasiperiodic (QP) emissions whose repetition period changes rapidly within a period of 1 h without corresponding magnetic pulsations. QP emissions showed positive correlation between amplitude and frequency sweep rate, similarly to rising-tone elements. We found an event of nearly simultaneous enhancements of QP emissions and Pc1/electromagnetic ion cyclotron wave intensities, suggesting that the temperature anisotropy of electrons and ions developed simultaneously at the equatorial plane of the magnetosphere. We also found QP emissions whose intensity suddenly increased in association with storm sudden commencement without changing their frequency. Falling-tone ELF/VLF emissions were observed with their rate of frequency change varying from 0.7 to 0.05 kHz/s over 10 min. Bursty-patch emissions in the lower and upper frequency bands are often observed during magnetically disturbed periods. Clear systematic correlation between these various ELF/VLF emissions and cosmic noise absorption was not obtained throughout the campaign period. These observations indicate several previously unknown features of ELF/VLF emissions in subauroral latitudes and demonstrate the importance of continuous measurements for monitoring temporal variations in these emissions.

Shiokawa, Kazuo; Yokoyama, Yu; Ieda, Akimasa; Miyoshi, Yoshizumi; Nomura, Reiko; Lee, Sungeun; Sunagawa, Naoki; Miyashita, Yukinaga; Ozaki, Mitsunori; Ishizaka, Kazumasa; Yagitani, Satoshi; Kataoka, Ryuho; Tsuchiya, Fuminori; Schofield, Ian; Connors, Martin;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2014

YEAR: 2014     DOI: 10.1002/jgra.v119.910.1002/2014JA020161

Chorus; ELF/VLF; Radiation belts; subauroral latitudes; wave-particle interactions