Faculty Profiles - SHIOKAWA, Kazuo

Space-time variability of polar cap patches: Direct evidence for internal plasma structuring Reviewed Open Access

Dahlgren H., Perry G. W., Semeter J. L., St-Maurice J. -P., Hosokawa K., Nicolls M. J., Greffen M., Shiokawa K., Heinselman C.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 9 ) 2012.9

Observed correlation between pulsating aurora and chorus waves at Syowa Station in Antarctica: a case study Reviewed Open Access

Ozaki, M, S. Yagitani, K. Ishizaka, K. Shiokawa, Y. Miyoshi, A. Kadokura, H. Yamagishi, R. Kataoka, A. Ieda, Y. Ebihara, N. Sato, I. Nagano

J. Geophys. Res. Vol. 117 ( A8 ) page： 8211 - 8211 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

A high correlation between a pulsating auroral patch and grouped chorus waves was observed on 17 April 2006 at Syowa Station in Antarctica. The spatial distribution of aurora-chorus correlation coefficients is evaluated in order to determine the source region. A pulsating patch at the highest-correlation pixel shows a one-to-one correspondence with the intensity variation of the grouped chorus waves, consisting of successive rising-tone elements with a duration and spacing of 2-3 s and 20-30 s, respectively. The generation region of the chorus waves is estimated from the latitude and longitude dependence of the equatorial electron gyrofrequencies using the IGRF geomagnetic field model. The extent of the estimated latitude and longitude is consistent with the spatial distribution of the high-correlation aurora-chorus region. The time difference between the chorus waves and the scattered electrons is also evaluated to discuss the validity of the source region. It shows that electrons reached the ionosphere sooner than the associated chorus waves by similar to 1 s, consistent with the theoretical value for conjugate pulsating aurora generated at the equator. These results support the hypothesis that pulsating aurora is caused by pitch angle scattering of high-energy electrons by whistler mode chorus waves, via a cyclotron resonance at the equator. These results are the first ground-based observations of high correlations between a spatially extended aurora and chorus waves.

DOI： 10.1029/2011JA017478

On post-midnight field-aligned irregularities observed with a 30.8-MHz radar at a low latitude: Comparison with F-layer altitude near the geomagnetic equator Reviewed

M. Nishioka, Y. Otsuka, K. Shiokawa, T. Tsugawa, Effendy, P. Supnithi, T. Nagatsuma, K. T. Murata

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 8 ) 2012.8

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We investigated the relationship between post-midnight F-region field aligned irregularities (FAIs) and F-layer altitude by analyzing data of a 30.8-MHz radar installed 5at Kototabang, Indonesia (0.2 degrees S, 100.3 degrees E; geomagnetic latitude 10.4 degrees S) and an ionosonde installed at Chumphon, Thailand (10.7 degrees N, 99.4 degrees E; geomagnetic latitude 3.3 degrees N). Chumphon is located near the geomagnetic equator on approximately the same meridian as Kototabang. Case studies show that the altitude of the F-layer rose at Chumphon a half hour before the post-midnight FAIs appeared at Kototabang. The Doppler velocity of the E-region FAIs observed simultaneously by the 30.8-MHz radar was downward, indicating that the F-layer uplift was not caused by the electric field. We also investigated seasonal variations of the post-midnight FAI occurrence and the F-layer altitude. Both the post-midnight FAIs and the uplift of the F-layer were frequently seen around midnight between May and August. The seasonal variation of the midnight F-layer uplift around the geomagnetic equator coincided with that of the post-midnight FAI occurrence at Kototabang. These results suggest that the uplift of the F-layer would play an important role in the generation of post-midnight FAIs. We evaluated the linear growth rate of the Rayleigh-Taylor instability based on the altitude of the F-layer observed at Chumphon. The result shows that the uplift of the F-layer can enhance the growth rate because gravity-driven eastward electric current increases. Therefore, we interpret that the observed FAIs were accompanied by plasma bubble, the growth rate of which was reinforced by the uplifted F-layer.

DOI： 10.1029/2012JA017692

Disappearance of equatorial plasma bubble after interaction with mid-latitude medium-scale traveling ionospheric disturbance Reviewed Open Access

Otsuka, Y, Shiokawa, K, Ogawa, T

GEOPHYSICAL RESEARCH LETTERS Vol. 39 ( 14 ) 2012.7

GPS total electron content variations associated with poleward moving Sun-aligned arcs Reviewed Open Access

Jayachandran P. T., Hosokawa K., Shiokawa K., Otsuka Y., Watson C., Mushini S. C., MacDougall J. W., Prikryl P., Chadwick R., Kelly T. D.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 5 ) 2012.5

Direct three-dimensional imaging of polar ionospheric structures with the Resolute Bay Incoherent Scatter Radar Reviewed Open Access

H. Dahlgren, J. L. Semeter, K. Hosokawa, M. J. Nicolls, T. W. Butler, M. G. Johnsen, K. Shiokawa, C. Heinselman

GEOPHYSICAL RESEARCH LETTERS Vol. 39 ( 5 ) 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Ionospheric plasma density structures in the dayside F-region of the polar cap are commonly occurring events, but adequate measurements of their formation and evolution have been sparse. With the advent of the advanced modular incoherent scatter radar RISR-N (Resolute Bay Incoherent Scatter Radar) it is now possible for the first time to study the temporal evolution of the plasma properties in the polar cap region in three dimensions, with a spatial resolution of tens of kilometers, from which the plasma rest frame can be experimentally established. We demonstrate the strength of the diagnostic with observations from an event of enhanced plasma density observed over Resolute Bay in December 2009. A colocated all-sky imager showed faint 630.0 and 557.7 nm emission corresponding to the plasma enhancements, and the structures could be traced back to a formation region in the open/closed field line boundary. This new plasma imaging technique will provide important information on the mechanisms controlling the structuring in the high latitude ionosphere. Citation: Dahlgren, H., J. L. Semeter, K. Hosokawa, M. J. Nicolls, T. W. Butler, M. G. Johnsen, K. Shiokawa, and C. Heinselman (2012), Direct three-dimensional imaging of polar ionospheric structures with the Resolute Bay Incoherent Scatter Radar, Geophys. Res. Lett., 39, L05104, doi:10.1029/2012GL050895.

DOI： 10.1029/2012GL050895

Electron and wave characteristics observed by the THEMIS satellites near the magnetic equator during a pulsating aurora Reviewed

A. Nakajima, K. Shiokawa, K. Sakaguchi, Y. Miyoshi, S. Lee, V. Angelopoulos, O. Le Contel, J. P. McFadden, J. W. Bonnell, K. -H. Fornacon, E. Donovan

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Based on conjugate ground and THEMIS satellite observations, we show electron spectra and wave characteristics near the magnetic equatorial plane during a pulsating aurora event on the high latitude side of the auroral oval. The pulsating aurora was observed by a 30-Hz sampled all-sky imager (ASI) at Gillam (56.4 degrees N, 265.4 degrees E), Canada, at similar to 0840-0910 UT on 8 January 2008. The auroral intensity pulsation at the possible THEMIS D (THD) footprints had frequency peaks at similar to 0.1-0.2 Hz. The footprint of THD was in the poleward part of the proton aurora observed by a meridian-scanning photometer. After auroral pulsation began at similar to 0842 UT, both THD and THEMIS E which was near THD in the mid-tail at 11.6-11.8 R-E, observed enhanced field-aligned electron fluxes at energies of 1-10 keV. However, the amplitudes of whistler mode waves and electrostatic cyclotron harmonics (ECH) waves observed by THD with the highest sampling rate of 8 kHz were not significant, showing a marked contrast to the recent report of clear correlation between whistler mode waves and auroral pulsations observed at 5-9 R-E. We suggest that the observed field-aligned electrons, which are probably caused by Fermi-type acceleration associated with earthward plasma flow in the mid-tail plasma sheet, are modulated by some wave processes to cause pulsating auroras.

DOI： 10.1029/2011JA017066

Polarization of Pc1/EMIC waves and related proton auroras observed at subauroral latitudes Reviewed Open Access

Nomura R., Shiokawa K., Sakaguchi K., Otsuka Y., Connors M.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 117 ( 2 ) 2012.2

Signatures of moving polar cap arcs in the F-region PolarDARN echoes Reviewed Open Access

A. V. Koustov, K. Hosokawa, N. Nishitani, K. Shiokawa, H. Liu

ANNALES GEOPHYSICAE Vol. 30 ( 3 ) page： 441 - 455 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：COPERNICUS GESELLSCHAFT MBH

Joint observations of the all-sky camera at Resolute Bay (Nunavut, Canada) and the Polar Dual Auroral Radar Network (PolarDARN) HF radars at Rankin Inlet and Inuvik (Canada) are considered to establish radar signatures of poleward moving polar cap arcs 'detaching' from the auroral oval. Common features of the events considered are enhanced power or echo occurrence in the wake of the arcs and enhanced spectral width of these echoes. When the arcs were oriented along some of the radar beams, velocity reversals at the arc location were observed with the directions of the arc-associated flows corresponding to a converging electric field. For the event of 9 December 2007, two arcs were poleward progressing almost along the central beams of the Inuvik radar at the speed close to the < B > E </B > x < B > B </B > drift of the bulk of the F-region plasma as inferred from HF Doppler velocities and from independent measurements by the Resolute Bay ionosonde. In global-scale convection maps inferred from all Super Dual Auroral Radar Network (SuperDARN) radar measurements, the polar cap arcs were often seen close to the reversal line of additional mesoscale convection cells located poleward of the normal cells related to the auroral oval.

DOI： 10.5194/angeo-30-441-2012

The Energization and Radiation in Geospace (ERG) Project Reviewed

Y. Miyoshi, T. Ono, T. Takashima, K. Asamura, M. Hirahara, Y. Kasaba, A. Matsuoka, H. Kojima, K. Shiokawa, K. Seki, M. Fujimoto, T. Nagatsuma, C. Z. Cheng, Y. Kazama, S. Kasahara, T. Mitani, H. Matsumoto, N. Higashio, A. Kumamoto, S. Yagitani, Y. Kasahara, K. Ishisaka, L. Blomberg, A. Fujimoto, Y. Katoh, Y. Ebihara, Y. Omura, M. Nose, T. Hori, Y. Miyashita, Y. -M. Tanaka, T. Segawa

DYNAMICS OF THE EARTH'S RADIATION BELTS AND INNER MAGNETOSPHERE Vol. 199 page： 103 - 116 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER GEOPHYSICAL UNION

The Energization and Radiation in Geospace (ERG) project for solar cycle 24 will explore how relativistic electrons in the radiation belts are generated during space stout's. This geospace exploration project consists of three research teams: the ERG satellite observation team, the ground-based network observation team, and the integrated data analysis/simulation team. Satellite observation will provide in situ measurements of features such as the plasma distribution function, electric and magnetic fields, and plasma waves, whereas remote sensing by ground-based observations using, for example, HF radars, magnetometers, optical instruments, and radio wave receivers will provide the global state of the geospace. Various kinds of data will be integrated and compared with numerical simulations for quantitative understanding. Such a synergetic approach is essential for comprehensive understanding of relativistic electron generation/loss processes through cross-energy and cross-regional coupling in which different plasma populations and regions are dynamically coupled with each other. In addition, the ERG satellite will utilize a new and innovative measurement technique for wave-particle interactions that can directly measure the energy exchange process between particles and plasma waves. In this paper, we briefly review some of the profound problems regarding relativistic electron accelerations and losses that will be solved by the ERG project, and we provide an overview of the project.

DOI： 10.1029/2012GM001304

Auroral Signatures of the Dynamic Plasma Sheet Reviewed Open Access

A. Keiling, K. Shiokawa, V. Uritsky, V. Sergeev, E. Zesta, L. Kepko, N. Ostgaard

AURORAL PHENOMENOLOGY AND MAGNETOSPHERIC PROCESSES: EARTH AND OTHER PLANETS Vol. 197 page： 317 - + 2012

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Understanding the physical connections of the coupled magnetosphere-ionosphere system will result in a more complete explanation of the aurora and will further the goal of being able to interpret the global auroral distributions as a dynamic map of the magnetosphere. Significant advances have been made in recent years toward this goal. In this chapter, we briefly review, while focusing on recent observations, selected auroral phenomena that are driven by magnetospheric processes. These include expansion of substorm aurora, plasma sheet waves and auroral modulations, ballooning instability and auroral beads, dipolarization/plasma injections and the auroral bulge, poleward boundary intensifications and auroral streamers, vortical flows and auroral spirals, and plasma flows prior to auroral onset. In addition, other auroral phenomena, such as auroral arcs, diffuse auroras, auroral asymmetry/conjugacy in the conjugate hemispheres, and auroral magneto spheric currents, are highlighted here but expanded in other chapters of this monograph for in-depth reviews.

DOI： 10.1029/2012GM001231

VHF radar observations of post-midnight f-region field-aligned irregularities over indonesia during solar minimum Reviewed

Y. Otsuka, K. Shiokawa, M. Nishioka, Effendy

Indian Journal of Radio and Space Physics Vol. 41 ( 2 ) page： 199 - 207 2012

Language：English Publishing type：Research paper (scientific journal)

A VHF backscatter radar with operating frequency 30.8 MHz has been operated at Kototabang (0.20°S, 100.32°E
dip latitude 10.4°S), Indonesia since February 2006. The F-region field-aligned irregularities (FAIs) observed by this radar from February 2006 to December 2010 during a solar minimum period have been analyzed and found that FAIs appeared frequently at the post-midnight sector between May and August every year from 2006 to 2010. Five-beam measurements by the radar revealed zonal propagation of the F-region FAIs. The present paper reports, for the first time, statistics of the zonal propagation velocity of the post-midnight FAIs. Between May and August, 46% (14%) of the post-midnight FAIs propagated westward (eastward), and zonal propagation was not discernible for 40% of the post-midnight FAIs. Average velocity was approximately 50 m s-1 westward. The post-midnight FAIs were likely associated with either plasma bubbles or medium-scale traveling ionospheric disturbances (MSTIDs).

High-latitude GPS TEC changes associated with a sudden magnetospheric compression Reviewed Open Access

P. T. Jayachandran, C. Watson, I. J. Rae, J. W. MacDougall, D. W. Danskin, R. Chadwick, T. D. Kelly, P. Prikryl, K. Meziane, K. Shiokawa

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 23 ) 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Using ionospheric total electron content (TEC) measured by Global Positioning System (GPS) receivers of the Canadian High Arctic Ionospheric Network (CHAIN) we provide clear evidence for a systematic and propagating temporary TEC enhancement produced by compression of the magnetosphere due to a sudden increase in solar wind dynamic pressure. The magnetospheric compression is evident in THEMIS/GOES satellite data. Application of a GPS triangulation technique revealed that the TEC changes propagated with a speed of 3-6 km/s in the antisunward direction near noon and similar to 8 km/s in the sunward direction in the pre-noon lower latitude sector. Characteristics of these TEC changes along with riometer absorption measurements seems to indicate that the TEC change is due to electron density enhancement in the F region and is possibly due to particle precipitation associated with sudden magnetospheric compression. Citation: Jayachandran, P. T., C. Watson, I. J. Rae, J. W. MacDougall, D. W. Danskin, R. Chadwick, T. D. Kelly, P. Prikryl, K. Meziane, and K. Shiokawa (2011), Highlatitude GPS TEC changes associated with a sudden magnetospheric compression, Geophys. Res. Lett., 38, L23104, doi: 10.1029/2011GL050041.

DOI： 10.1029/2011GL050041

Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging Reviewed Open Access

K. J. W. Lynn, Y. Otsuka, K. Shiokawa

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 23 ) 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Airglow observations of ionospheric electron density depletions made at Darwin, Australia have demonstrated that the tree-like structure of bubbles developed at the magnetic equator are mapped along magnetic field lines with considerable accuracy to the base of the ionosphere at higher latitudes. Ionosonde range-time displays made at Darwin and other equatorial sites in the Australian region show characteristic approaching and receding echoes which converge on a typical spread-F event. These off-angle echoes have often been referred to in the literature as satellite traces and associated with spread F with little recognition of their true significance. All four optical depletions previously reported in the literature as being seen at Darwin are found in this paper to be accompanied by such typical off-angle/spread F events. The zonal drift velocity of the moving reflectors can be measured from the speed at which such echoes approach and recede. Since digital ionosondes in equatorial sites have existed for many years, existing ionogram data, when suitably processed into range-time displays, may allow the occurrence of such events over several sunspot cycles to be found. A question remains as to whether all or only some of such equatorial range-time events correspond to electron density depletions. Citation: Lynn, K. J. W., Y. Otsuka, and K. Shiokawa (2011), Simultaneous observations at Darwin of equatorial bubbles by ionosonde-based range/time displays and airglow imaging, Geophys. Res. Lett., 38, L23101, doi:10.1029/2011GL049856.

DOI： 10.1029/2011GL049856

A statistical study of plasma sheet electrons carrying auroral upward field-aligned currents measured by Time History of Events and Macroscale Interactions during Substorms (THEMIS) Reviewed Open Access

Lee S., Shiokawa K., McFadden J. P., Nishimura Y.

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 2011.12

Long-term variations in tweek reflection height in the D and lower E regions of the ionosphere Reviewed Open Access

Hiroyo Ohya, Kazuo Shiokawa, Yoshizumi Miyoshi

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 ( 10 ) 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

We investigated, for the first time, long-term (1976-2010) variations in reflection heights of tweek atmospherics based on very low frequency (VLF) observations at Kagoshima, Japan. The results revealed the effects of the solar cycle on the nighttime lower ionosphere at low to middle latitudes. The tweek reflection heights on geomagnetically quiet days were analyzed every month over three solar cycles by using an automated spectral fitting procedure to estimate the cutoff frequency. The average and standard deviation of the reflection height were 95.9 km and +/-3.1 km, respectively. Typical periods of time variation for the reflection height were 13.3, 3.2, 1.3, 1.0, 0.6, and 0.5 years. The variations in tweek reflection heights did not show simple anticorrelation with solar activity. The correlation coefficient between tweek reflection height and sunspot number was 0.03 throughout the three solar cycles. Hilbert-Huang transform analysis successfully indicated the presence of 0.5-1.5 year and similar to 10 year variations as intrinsic mode functions (IMF). The decomposed IMF with the similar to 10 year variation had a positive correlation with sunspot numbers and a negative correlation with galactic cosmic rays (GCRs). We hypothesize that these variations in tweek reflection heights could be caused by coupling of several ionization effects at the D and lower E regions, effects such as geocorona, GCRs, particle precipitation, and variations in neutral density in the lower thermosphere. Among these processes, the geocorona and particle precipitation could show negative correlation, while the GCRs and neutral density could show positive correlation with solar activities.

DOI： 10.1029/2011JA016800

ジオスペース探査ERG計画(Technical Session,ICSANE 2011(International Conference on Space, Aeronautical and Navigational Electronics 2011))

小野高幸, 浅村和史, 三好由純, 高島健, 平原聖文, 小原隆博, 笠羽康正, 熊本篤志, 松岡彩子, 小嶋浩嗣, 塩川和夫, 関華奈子, 藤本正樹, 長妻努

電子情報通信学会技術研究報告. SANE, 宇宙・航行エレクトロニクス Vol. 111 ( 239 ) page： 57 - 61 2011.10

An empirical model of the quiet daily geomagnetic field variation Reviewed Open Access

Y. Yamazaki, K. Yumoto, M. G. Cardinal, B. J. Fraser, P. Hattori, Y. Kakinami, J. Y. Liu, K. J. W. Lynn, R. Marshall, D. McNamara, T. Nagatsuma, V. M. Nikiforov, R. E. Otadoy, M. Ruhimat, B. M. Shevtsov, K. Shiokawa, S. Abe, T. Uozumi, A. Yoshikawa

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 116 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp <= 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity.

DOI： 10.1029/2011JA016487

Ground-based multispectral high-speed imaging of flickering aurora Reviewed Open Access

Ryuho Kataoka, Yoshizumi Miyoshi, Takeshi Sakanoi, Ayumi Yaegashi, Yusuke Ebihara, Kazuo Shiokawa

GEOPHYSICAL RESEARCH LETTERS Vol. 38 ( 14 ) 2011.7

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

It has been suggested that dispersive Alfven waves (DAWs) are capable of accelerating electrons via Landau resonance, and the interference of DAWs plays an essential role to create flickering auroral patterns. Here we show evidence that the leading front of a typical interference pattern is more energetic than the trailing part, based on ground-based high-speed imaging observations at wavelengths of 670.5 nm and 844.6 nm, which are sensitive to relatively hard and soft electrons, respectively. The fine spatial resolution of 9.5 deg field-of-view at magnetic zenith and the 100 Hz sampling rate of electron multiplying charge-coupled device (EMCCD) enabled us to resolve the spatiotemporal variation of the flickering aurora. It is found that there is only 10 ms time delay with 0.5 km spatial shift on average in the obtained flickering patterns at two wavelengths. The time delay and spatial shift can be comprehensively explained by the traveling inhomogeneous interference pattern of DAWs, probably associated with the Landau damping and/or time-of-flight effect, which is only detectable using the highest resolved temporal and spatial observations of flickering aurora. Citation: Kataoka, R., Y. Miyoshi, T. Sakanoi, A. Yaegashi, Y. Ebihara, and K. Shiokawa (2011), Ground-based multispectral high-speed imaging of flickering aurora, Geophys. Res. Lett., 38, L14106, doi:10.1029/2011GL048317.

DOI： 10.1029/2011GL048317