Faculty Profiles - OTSUKA, Yuichi

Papers - OTSUKA, Yuichi

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Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations Reviewed Open Access

S. Suzuki, K. Shiokawa, A. Z. Liu, Y. Otsuka, T. Ogawa, T. Nakamura

ANNALES GEOPHYSICAE Vol. 27 ( 4 ) page： 1625 - 1629 2009

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

We present the characteristics of small-scale (< 100 km) gravity waves in the equatorial mesopause region derived from OH airglow imaging observations at Kototabang (100.3 degrees E, 0.2 degrees S), Indonesia, from 2002 to 2005. We adopted a method that could automatically detect gravity waves in the airglow images using two-dimensional cross power spectra of gravity waves. The propagation directions of the waves were likely controlled by zonal filtering due to stratospheric mean winds that show a quasi-biennial oscillation (QBO) and the presence of many wave sources in the troposphere.

DOI： 10.5194/angeo-27-1625-2009

Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below Reviewed Open Access

Tadahiko Ogawa, Yasunobu Miyoshi, Yuichi Otsuka, Takuji Nakamura, Kazuo Shiokawa

EARTH PLANETS AND SPACE Vol. 61 ( 4 ) page： 397 - 410 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

Using Global Positioning System (GPS) satellites. we have been conducting equatorial ionospheric scintillation observations at Kototabang, Indonesia since January 2003. Scintillations caused by equatorial plasma bubbles appear between 2000 and 0 100 LT in equinoctial months with a seasonal asymmetry, and their activity decreases with decreasing solar activity. A comparison between scintillation index (S-4) and Earth's brightness temperature variations suggests that file scintillation activity call be related to tropospheric disturbances over file Indian Ocean to the west of Kototabang. TO Understand better the reasons of day-to-day variability of S-4, we analyze S-4. T-bb and lower thermospheric neutral wind ((mu'(2)) over bar) data. The results show that S-4 fluctuates with periods of about 2.5, 5, 8, 14 and 25 days, possibly due to atmospheric waves from below and that similar periods are also found in the T-bb and (mu'(2)) over tilde variations. Using a general circulation model, we made numerical simulations to determine the behavior of neutral wind in the equatorial thermosphere. The results indicate the following: (1) 2- to 20-day waves dissipate rapidly above about an altitude of 125 km, and 0.5- to 3-hour waves become predominant above 100 km, (2) zonal winds above 200 km altitude are, on the whole, eastward during sunset-sunrise, (3) zonal wind patterns due to short-period (1-4 h) atmospheric gravity waves (AGWs) above 120 km altitude change day by day, exhibit wavy structures with scale lengths of about 30-1000 km and, as it whole, move eastward in about 100(-1) while changing patterns over time. These simulations suggest that the Rayleigh-Taylor instability responsible for plasma bubble generation call be seeded by AGWs with short periods of about 0.5-3 h, and that background conditions necessary for this instability are modulated by planetary-scale atmospheric waves propagating up to an altitude of about 120 km front below.

DOI： 10.1186/BF03353157

Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 'Halloween Storms' Reviewed Open Access

Y. Sahai, F. Becker-Guedes, P. R. Fagundes, A. J. de Abreu, R. de Jesus, V. G. Pillat, J. R. Abalde, C. R. Martinis, C. Brunini, M. Gende, C. -S. Huang, X. Pi, W. L. C. Lima, J. A. Bittencourt, Y. Otsuka

ANNALES GEOPHYSICAE Vol. 27 ( 12 ) page： 4463 - 4477 2009

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

The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation.
In this paper, we present ionospheric sounding observations during the period 29-31 October 2003 obtained at Palmas (a near equatorial location) and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly), Brazil, along with observations during the period 27-31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28-29 (geomagnetically quiet night) and 29-30 (geomagnetically disturbed night) October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS) are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1 degrees S) and map at the magnetic equator at an altitude of about 2500 km.

DOI： 10.5194/angeo-27-4463-2009

Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes Reviewed Open Access

K. Shiokawa, Y. Otsuka, T. Ogawa

EARTH PLANETS AND SPACE Vol. 61 ( 4 ) page： 479 - 491 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER HEIDELBERG

We review measurements of nighttime atmospheric/ionospheric wave in the upper atmosphere in Japan. Indonesia. and Australia. using all-sky airglow imagers of optical mesosphere thermosphere imagers (OMTIs). The imagers observe two-dimensional patterns of airglow emissions from oxygen (wavelength: 557.7 nm) and hydorxyl (OH) (near-infrared band) in the mesopause region (80-100 km) and from oxygen (630.0 nm) in the thermosphere/ionosphere (200-300 km). Several statistical studies were done to investigate propagation characteristics of small-scale (less than 100 km) gravity waves in the mesopause region and medium-scale traveling ionospheric disturbances (MSTIDs. similar to 100-1,000 km) in the thermosphere/ionosphere. Clear seasonal variations of occurrence and propagation directions were reported for these waves. The propagation directions in the mesopause region are controlled by wind filtering, ducting processes and relative location to the wave sources in the troposphere. On the other hand, systematic equatorward and westward motions were observed for all seasons for nighttime MSTIDs in the midlatitude ionosphere with geomagnetic conjugacy between the northern and Southern hemispheres. Ionospheric instabilities may play important role for the generation and propagation of these MSTIDs. We also give an example of simultaneous observation of quasi-periodic southward-moving waves in the mesopause and in the thermosphere at the geographic equator, From these results, we discuss mean wind acceleration by mesospheric gravity waves and penetration of gravity waves from the mesosphere to the thermosphere.

DOI： 10.1186/BF03353165

Relative effects of electric field and neutral wind on positive ionospheric storms Reviewed Open Access

N. Balan, H. Alleyne, Y. Otsuka, D.Vijaya Lekshmi, B. G. Fejer, I. McCrea

Earth, Planets and Space Vol. 61 ( 4 ) page： 439 - 445 2009

Language：English Publishing type：Research paper (international conference proceedings) Publisher：Springer Berlin

The paper studies the relative importance of penetrating eastward electric field (PEEF) and direct effects of equatorward neutral wind in leading to positive ionospheric storms at low-mid latitudes using observations and modeling. The observations show strong positive ionospheric storms in total electron content (TEC) and peak electron density (Nmax) at low-mid latitudes in Japan longitudes (≈125°E-145°E) during the first main phase (started at sunrise on 08 November) of a super double geomagnetic storm during 07-11 November 2004. The model results obtained using the Sheffield University Plasmashpere Ionosphere Model (SUPIM) show that the direct effects of storm-time equatorward neutral wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) can be the main driver of positive ionospheric storms at low-mid latitudes except in Nmax around the equator. The equatorward wind without PEEF can also result in stronger positive ionospheric storms than with PEEF. Though PEEF on its own is unlikely to cause positive ionospheric storms, it can lead to positive ionospheric storms in the presence of an equatorward wind. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS).

DOI： 10.1186/BF03353160

The Optical Mesosphere Thermosphere Imagers (OMTIs) for network measurements of aurora and airglow Reviewed

K. Shiokawa, K. Hosokawa, K. Sakaguchi, A. Ieda, Y. Otsuka, T. Ogawa, M. Connors

FUTURE PERSPECTIVES OF SPACE PLASMA AND PARTICLE INSTRUMENTATION AND INTERNATIONAL COLLABORATIONS Vol. 1144 page： 212 - + 2009

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AMER INST PHYSICS

The 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 I 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.

VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia Reviewed Open Access

Y. Otsuka, T. Ogawa, Effendy

EARTH PLANETS AND SPACE Vol. 61 ( 4 ) page： 431 - 437 2009

Language：English Publishing type：Research paper (scientific journal) Publisher：TERRA SCIENTIFIC PUBL CO

We report, for the first time, continuous observations of the nighttime F-region field-aligned irregularities (FAIs) over Indonesia. A VHF radar with operating frequency of 30.8 MHz and peak power of 20 kW has been operated at Kolotabang (0.20 degrees S, 100.32 degrees E; dip latitude 10.4 degrees S), Indonesia since February 2006. Five beams were allocated between +/- 54 degrees in azimuth around geographic South (126 degrees-234 degrees). From the Continuous observation from February 2006 to November 2007, we found that FAIs appeared frequently at pre-midnight between March and May and Lit post-midnight between May and August. The pre-midnight FAIs coincided well with GPS scintillation observed at the same site. Seasonal and local time variations of the pre-midnight FAI Occurrence are consistent with those of equatorial plasma bubbles reported in previous studies (e.g., Maruyama and Matuura, 1984). These results indicate that the pre-midnight FAIs could be associated with the equatorial plasma bubbles. On the other hand, seasonal and local time variations of the post-midnight FAIs were inconsistent with those of the plasma bubbles. The features of the post-midnight FAIs can be summarized as follows: (1) The post-midnight FAIs are not accompanied by GPS scintillations. (2) Most of the post-midnight FAI regions do not show propagation, but some of them propagate westward. (3) Echo intensity of the post-midnight FAIs was weaker than that of the pre-midnight FAIs. These features are similar to those of the FAI echoes that have been observed at mid-latitude (e.g., Fukao et, al., 1991). At Kototabang, Fukao et al. (2004) have firstly observed FAIs that resemble those Lit mid-latitude. The present paper reports statistical characteristics of the mid-latitude-type FAIs observed at Kototabang.

DOI： 10.1186/BF03353159

Zonal asymmetry of daytime 150-km echoes observed by Equatorial Atmosphere Radar in Indonesia Reviewed Open Access

T. Yokoyama, D. L. Hysell, A. K. Patra, Y. Otsuka, M. Yamamoto

ANNALES GEOPHYSICAE Vol. 27 ( 3 ) page： 967 - 974 2009

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

Multi-beam observations of the daytime ionospheric E-region irregularities and the so-called 150-km echoes with the 47-MHz Equatorial Atmosphere Radar (EAR) in West Sumatra, Indonesia (0.20 degrees S, 100.32 degrees E, 10.36 degrees S dip latitude) are presented. 150-km echoes have been frequently observed by the EAR, and their characteristics are basically the same as the equatorial ones, except for an intriguing zonal asymmetry; stronger echoes in lower altitudes in the east directions, and weaker echoes in higher altitudes in the west. The highest occurrence is seen at 5.7 degrees east with respect to the magnetic meridian, and the altitude gradually increases as viewing from the east to west. Arc structures which return backscatter echoes are proposed to explain the asymmetry. While the strength of radar echoes below 105 km is uniform within the wide coverage of azimuthal directions, the upper E-region (105-120 km) echoes also show a different type of zonal asymmetry, which should be generated by an essentially different mechanism from the lower E-region and 150-km echoes.

DOI： 10.5194/angeo-27-967-2009

New observational deployments for SEALION-Airglow measurements using all-sky imagers

Minoru Kubota, Mamoru Ishii, Takuya Tsugawa, Jyunpei Uemoto, Hidekatsu Jin, Yuichi Otsuka, Kazuo Shiokawa

Journal of the National Institute of Information and Communications Technology Vol. 56 ( 1-4 ) page： 299 - 307 2009

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

An airglow all-sky imager (ASI)-a new monitoring instrument-is scheduled to be set up in February 2010 at Chiang Mai, Thailand, as part of the framework of the Southeast Asia Low-latitude Ionospheric Network (SEALION) being developed in the Southeast Asian region by the National Institute of Information and Communications Technology (NICT). The ASI images airglow having an emission layer near the ionospheric F-layer in order to observe the two-dimensional structure and time evolution of such ionospheric disturbances as plasma bubbles. In Southeast Asia, the Solar-Terrestrial Environment Laboratory (STE) of Nagoya University has been conducting ASI-based observations at Kototabang, Indonesia, ever since 2002. This paper provides detailed insight into the formation, growth and propagation of plasma bubbles as derived from observational data recorded using ASI at Kototabang and using SEALION ionoson-des and GPS receivers. The functional requirements for another ASI to be installed and ASI-based observation schemes are then discussed based on that insight.

Nighttime medium-scale traveling ionospheric disturbances detected by network GPS receivers in Taiwan Reviewed Open Access

C. C. Lee, Y. A. Liou, Y. Otsuka, F. D. Chu, T. K. Yeh, K. Hoshinoo, K. Matunaga

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 113 ( A12 ) 2008.12

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

[1] The nighttime medium-scale traveling ionospheric disturbances (MSTIDs) are detected by the network GPS receivers in Taiwan for the first time. The two-dimensional mapping technique (a spatial resolution of 0.05 degrees x 0.05 degrees in latitude and longitude with 5 x 5 pixels smoothing) is applied on the data of TEC perturbations (TECp) and GPS phase fluctuations (Delta TEC/min). The results show that the MSTIDs move southwestward to latitude of 20.5 degrees N with a horizontal velocity between 100 and 160 m/s and a wavelength of about 500 km. The wavefronts of the MSTIDs are aligned along the northwest-southeast direction. Furthermore, the greater vertical bar Delta TEC/min vertical bar values are corresponding to the wave peak and trough of TECp. This coincidence indicates that the MSTIDs play an important role for the generation of F region irregularities in the low-latitude ionosphere.

DOI： 10.1029/2008JA013250

Northeastward motion of nighttime medium-scale traveling ionospheric disturbances at middle latitudes observed by an airglow imager Open Access

K. Shiokawa, Y. Otsuka, N. Nishitani, T. Ogawa, T. Tsugawa, T. Maruyama, S. E. Smirnov, V. V. Bychkov, B. M. Shevtso

Journal of Geophysical Research: Space Physics Vol. 113 ( A12 ) 2008.12

Nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed in 630-nm airglow images at middle latitudes are known to have a predominantly northwest-southeast phase surface and to move southwestward in the Northern Hemisphere of Earth. However, the mechanisms of MSTID generation and their systematic southwestward motion have not been clarified. In this paper, we report the "northeastward" motion of the MSTIDs observed at Paratunka, Far East Russia (52.97°N, 158.25°E), using an all-sky 630-nm airglow imager at 2000-2300 LT on 19 August 2007. The MSTIDs moved first southwestward but then back northeastward in the northern part of the images. The northeastward motion of the MSTIDs took place coincident with a F layer height decrease observed by an ionosonde at Paratunka. The F layer height decrease was also confirmed by an enhancement of the 630-nm airglow intensity, which seemed to propagate from northeast to southwest. This fact suggests that the F layer height decrease was caused by poleward wind enhancement rather than westward electric field. These observations imply that the F layer height decrease or the poleward thermospheric wind has some role in the northeastward turning of the MSTID propagation direction. Copyright 2008 by the American Geophysical Union.

DOI： 10.1029/2008JA013417

Statistical study of relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan Reviewed

Otsuka, Y., T. Tani, T. Tsugawa, and T. Ogawa

J. Atmos. Solar-Terr. Phys. Vol. 70 page： 2196-2202 2008.12

Statistical study of relationship between medium-scale traveling ionospheric disturbance and sporadic E layer activities in summer night over Japan Reviewed

Y. Otsuka, T. Tani, T. Tsugawa, T. Ogawa, A. Saito

JOURNAL OF ATMOSPHERIC AND SOLAR-TERRESTRIAL PHYSICS Vol. 70 ( 17 ) page： 2196 - 2202 2008.12

Language：English Publishing type：Research paper (scientific journal) Publisher：PERGAMON-ELSEVIER SCIENCE LTD

We investigate the relationship between medium-scale traveling ionospheric disturbance (MSTID) and sporadic E (E-s) layer activities in summer nights by analyzing total electron content (TEC) data obtained from a global positioning system (GPS) network in Japan and ionosonde data obtained at Kokubunji, Japan during May-August in 2001-2005. MSTID activity is defined as delta I/($) over bar, where delta I is standard deviation of the TEC perturbations over Kokubunji within 1 h, and 7 is the background TEC. By analyzing nighttime-averaged (19-02 LT) values of MSTID activity and E, layer parameters, we find that the MSTID activity is closely correlated with f(0)E(s) and f(0)E(s) -f(b)E(s). This result suggests that MSTID and the spatial structures of E, layer could be generated by an electro-dynamical coupling process between the Es layer and F region through polarization electric fields. Furthermore, we suggest that the appearance of the E, layer in the summer hemisphere could play an important role in generating MSTIDs in both hemispheres. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jastp.2008.07.008

Decay of 3-m-scale ionospheric irregularities associated with a plasma bubble observed with the Equatorial Atmosphere Radar Reviewed Open Access

Susumu Saito, Shoichiro Fukao, Mamoru Yamamoto, Yuichi Otsuka, Takashi Maruyama

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 113 ( A11 ) 2008.11

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

We investigated the decay processes of 3-m-scale ionospheric irregularities associated with plasma bubbles by multi-instrument observations. The observations were made using the Equatorial Atmosphere Radar (EAR), a 630-nm airglow imager, and ionosondes. The EAR's electronic beam steering capability allowed us to see the temporal evolution of 3-m-scale irregularities associated with plasma bubbles in two-dimensional views. Around midnight on 28 and 31 March 2006, the EAR detected plasma bubbles that drifted into its field of view. When their eastward drift motion slowed and they finally stopped moving eastward, the 3-m-scale irregularities decayed. These results suggest that instability driven by the eastward neutral wind kept the 3-m-scale irregularities in matured plasma bubbles, which are in the well-developed stage, active for several hours after sunset. The stagnated plasma bubbles drifted downward with the ambient westward electric field. This drift resulted in the backscatter echo patterns seen in the range-time-intensity (RTI) plots which look like those associated with mid-latitude plumes.

DOI： 10.1029/2008JA013118

F-3 layer during penetration electric field Reviewed Open Access

Balan, N, Thampi, SV, Lynn, K, Otsuka, Y, Alleyne, H, Watanabe, S, Abdu, MA, Fejer, BG

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 113 2008.9

Simultaneous appearance of isolated auroral arcs and Pc 1 geomagnetic pulsations at subauroral latitudes Reviewed Open Access

K. Sakaguchi, K. Shiokawa, Y. Miyoshi, Y. Otsuka, T. Ogawa, K. Asamura, M. Connors

JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS Vol. 113 ( A5 ) 2008.5

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

We have been conducting observations of aurora and geomagnetic pulsations at Athabasca, Canada, located at a subauroral latitude ( magnetic latitude: 62 degrees, L similar to 4.6), using an all-sky imager and an induction magnetometer. Isolated auroral arcs at wavelengths of 557.7 nm, 630.0 nm, and 486.1 nm ( H-beta) were often observed at latitudes separated equatorward from the main auroral oval. From a 1-year observation ( 4 September 2005 to 3 September 2006), we found 13 isolated arc events. All these isolated arcs occurred coincidentally with Pc 1 geomagnetic pulsations, although there were nine other Pc 1 events without isolated arcs in the field of view of the imager. The arcs were observed in both pre- and post-midnight sectors and tended to appear during the late recovery phase of geomagnetic storms. The isolated arcs had limited latitudinal and longitudinal widths of less than 230 km and 250 - 800 km, respectively. We found that as isolated arcs moved equatorward ( poleward), the frequencies of the simultaneous Pc 1 pulsations increased ( decreased). Using the Tsyganenko-02 magnetic field model, the observed Pc 1 frequencies were almost the same as the frequencies of He+ electromagnetic ion cyclotron ( EMIC) waves at the equatorial plane connected to observed isolated arcs. These results indicate that interactions of spatially localized EMIC waves with ring current ions cause high-energy ion precipitation and associated isolated auroras at subauroral latitudes. These results also imply that the dynamics and instabilities in the inner magnetosphere can be monitored as low-latitude auroral emissions away from the ordinary auroral oval.

DOI： 10.1029/2007JA012888

Daytime 150-km echoes observed with the Equatorial Atmosphere Radar in Indonesia: First results Reviewed Open Access

A. K. Patra, T. Yokoyama, Y. Otsuka, M. Yamamoto

GEOPHYSICAL RESEARCH LETTERS Vol. 35 ( 6 ) 2008.3

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

Results of the daytime 150-km echoes from 10.36 degrees S magnetic latitude observed using the Equatorial Atmosphere Radar (EAR), which are first of its kind from magnetic southern hemisphere, are presented. The echoing region of 145-165 km shows forenoon descent and afternoon ascent with signal intensity modulation with time resembling a necklace and the Doppler spectra are narrow, which are quite similar to those reported earlier from other locations. Westward and upward/southward irregularity drifts are found to be consistent with daytime background electric fields, providing a tool to investigate low latitude daytime electrodynamics. Detectability of these echoes suggests the absence of strong latitudinal dependence in contrast to the earlier belief, suggesting a possibility of their detection at mid-latitudes. Also the echoes show zonal anisotropy that is opposite to that observed over Pohnpei. The implications of these observations are discussed in the light of present understanding of 150-km echoing phenomenon.

DOI： 10.1029/2007GL033130

First three-dimensional simulation of the Perkins instability in the nighttime midlatitude ionosphere Reviewed

Tatsuhiro Yokoyama, Yuichi Otsuka, Tadahiko Ogawa, Mamoru Yamamoto, David L. Hysell

GEOPHYSICAL RESEARCH LETTERS Vol. 35 ( 3 ) 2008.2

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

A three-dimensional numerical simulation in the nighttime midlatitude ionosphere is developed for the first time and applied to the Perkins instability in the midlatitude F region. Growth of the Perkins instability is successfully reproduced under nighttime condition, and the numerical results basically agree with a linear theory and previous two-dimensional numerical studies. Northwest-southeast (NW-SE) alignment of density perturbations is generated from random seeding by applying a southeastward neutral wind. The perturbations are dominant at altitudes of 200 300 km where a steep density gradient exists, which is consistent with the altitude of 630-nm airglow emission that often shows NW-SE alignment. Further simulation in terms of the E-F coupling can be done in the near future.

DOI： 10.1029/2007GL032496

Optical and radio observations and AMIE/TIEGCM modeling of nighttime traveling ionospheric disturbances at midlatitudes during geomagnetic storms

K. Shiokawa, T. Tsugawa, T. Tsugawa, Y. Otsuka, T. Ogawa, G. Lu, A. Saito, M. Yamamoto

Geophysical Monograph Series Vol. 181 page： 271 - 281 2008

© 2008 by the American Geophysical Union. This paper summarizes our recent observations of storm-time traveling ionospheric disturbances (TIDs) over Japan. The storm-time TIDs, which are often referred as large-scale TIDs or traveling atmospheric disturbances, are generated at high-latitude auroral zone and propagate predominantly equatorward at midlatitudes as atmospheric waves in the thermosphere. The imaging measurements by airglow imagers and GPS networks give reliable wave parameters (wavelength, phase velocity, and amplitude) of TIDs. Comparison of imaging observations of TIDs between the northern and southern hemispheres revealed their nonconjugacy. Combinations of these imaging observations with vertical sounding measurements by ionosondes and radars provide a comprehensive description of TID structures at midlatitudes. Comparison between these observations and the assimilative mapping of the ionospheric electrodynamics technique with the thermosphere-ionosphere electrodynamics general circulation model results in several insights into the generation and propagation of TIDs at the high-latitude source region as well as limitations of the current global model.

DOI： 10.1029/181GM24

Discovery of anoumoulous stripes over the amazon by the PALSAR onboard ALOS satellite Reviewed

Masanobu Shimada, Yasushi Muraki, Yuichi Otsuka

International Geoscience and Remote Sensing Symposium (IGARSS) Vol. 2 ( 1 ) page： II387 - II390 2008

Language：English Publishing type：Research paper (international conference proceedings)

We discovered anomalous stripes over the large area of Amazon when the region was scanned by the radar (PALSAR) onboard ALOS satellite. The stripes appeared on the local midnight along the geomagnetic field line with a typical characteristic width of 600m. ©2008 IEEE.

DOI： 10.1109/IGARSS.2008.4779009

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