Faculty Profiles - OYAMA, Shin-ichiro

Papers - OYAMA, Shin-ichiro

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Tidal waves in the polar lower thermosphere observed using the EISCAT long run data set obtained in September 2005 Reviewed

Nozawa, S., Y. Ogawa, S. Oyama, H. Fujiwara, T. Tsuda, A. Brekke, C. M. Hall, Y. Murayama, S. Kawamura, H. Miyaoka, and R. Fujii

J. Geophy. Res. 2010.8

Links between a stratospheric sudden warming and thermal structures and dynamics in the high-latitude mesosphere, lower thermosphere, and ionosphere Reviewed Open Access

Kurihara, J., Y. Ogawa, S. Oyama, S. Nozawa , M. Tsutsumi , C. Hall , Y. Tomikawa , R. Fujii

Geophys. Res. Lett. 2010.7

Temperature enhancements and vertical winds in the lower thermosphere associated with auroral heating during the Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign Reviewed Open Access

Kurihara, J., S. Oyama, S. Nozawa, T. T. Tsuda, R. Fujii, Y. Ogawa, H. Miyaoka, N. Iwagami, T. Abe, K.-I. Oyama, M. Kosch, A. Aruliah, E. Griffin, and K. Kauristie

J. Geophys. Res. 2009.12

Ion heating in high-speed flow channel within the duskside cell of the polar-cap ion convection under large IMF-By condition Reviewed

Maeda, S., Y. Ogawa, K. Hosokawa, S. Nozawa, S. Oyama, T. Tsuda and A. Brekke

J. Geophysical Research 2009.11

Relations between proton auroras, intense electric field and ionospheric electron density depletion Reviewed Open Access

Fujii, R., Y. Iwata, S. Oyama, S. Nozawa, and Y. Ogawa

J. Geophysical Research page： 114, A09304, doi:10.1029/2009JA014319 2009.9

Spatial evolution of frictional heating and the predicted thermospheric-wind effects in the vicinity of an auroral arc measured with the Sondrestrom incoherent-scatter radar and the Reimei satellite Reviewed

Oyama, S., T. T. Tsuda, T. Sakanoi, Y. Obuchi, K. Asamura, M. Hirahara, A. Yamazaki, Y. Kasaba, R. Fujii, S. Nozawa, and B. J. Watkins

J. Geophysical Research Vol. 114 ( A07311 ) page： doi:10.1029/2009JA014091 2009.7

Acceleration mechanism of high-speed neutral wind observed in the polar lower thermosphere Reviewed Open Access

Tsuda, T. T., S. Nozawa, S. Oyama, T. Motoba, Y. Ogawa, H. Shinagawa, N. Nishitani, K. Hosokawa, N. Sato, M. Lester, and R. Fujii

J. Geophysical Research 2009.4

*Generation of the lower-thermospheric vertical wind estimated with the EISCAT KST radar at high latitudes during periods of moderate geomagnetic disturbance Reviewed Open Access

Oyama, S., B. J. Watkins, S. Maeda, H. Shinagawa, S. Nozawa, Y. Ogawa, A. Brekke, C. Lathuillere, and W. Kofman

Ann. Geophysicae Vol. 26 page： 1491-1505 2008.6

Excitation and diagnosis of cascading Langmuir waves in ionospheric plasmas at Gakona, Alaska, Reviewed

Burton, L. M., J. A. Cohen, R. Pradipta, A. Labno, M. C. Lee, O. Batishchev, D. L. Rokusek, S. P. Kuo, B. J. Watkins, and S. Oyama

Phys. Scr. 2008

Temporal evolution of pump beam self-focusing at the High-Frequency Active Auroral Research Program Reviewed Open Access

Kosch M. J., T. Pedersen, E. Mishin, M. Starks, E. Gerken-Kendall, D. Sentman, S. Oyama, B. Watkins

J. Geophysical Research 2007.8

Coordinated optical and radar observations of ionospheric pumping for a frequency pass through the second electron gyroharmonic at HAARP Reviewed Open Access

Kosch M. J., T. Pedersen, E. Mishin, S. Oyama, J. Hughes, A. Senior, B. Watkins, B. Bristow

J. Geophysical Research 2007.6

A two-dimensional simulation of thermospheric vertical winds in the vicinity of an auroral arc Reviewed Open Access

Shinagawa, H., and Oyama, S

Earth Planets and Space Vol. 58 ( 9 ) page： 58(9), 1173-1181 2006.9

Persistent enhancement of the HF pump-induced plasma line measured with a UHF diagnostic radar at HAARP Reviewed Open Access

Oyama, S., B. J. Watkins, F. T. Djuth, M. J. Kosch, P. Bernhardt, and C. J. Heinselman

J. Geophysical Research Vol. 111 ( A06309 ) page： 2005JA011363 2006.6

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

Plasma lines excited by a powerful, high-frequency (HF) radio wave are studied using
data obtained with an ultrahigh frequency (UHF) radar at HAARP (High Frequency
Active Auroral Research Program) from 3 to 5 February 2005. Of particular interest is
persistent enhancement of the radar backscatter power during HF on at several HF
frequencies. The persistent enhancement is induced with the HF frequency slightly lower
than foF2 by a few hundred kHz; by contrast the persistent enhancement does not
appear when the HF frequency is equal to and higher than foF2 or lower than foF2 by
more than 500 kHz. When persistent enhancements of the radar backscatter power
appear, two case studies show that the local plasma frequency at the reflection height of
the O-mode polarization wave is close to the second or third electron gyroharmonic
frequencies, but one case study shows that the local plasma frequency at the reflection
height is significantly different from the third electron gyroharmonic frequency.

DOI： 10.1029/2005JA011363

*Application of a new beam configuration to estimate lower thermospheric vertical velocities at high latitudes with mono-static incoherent scatter radars Reviewed Open Access

Oyama, S., B. J. Watkins, S. Maeda, and J. Watermann

Radio Science Vol. 40 ( RS4005 ) page： 2004RS003205 2005.7

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

We have developed a new beam configuration for monostatic incoherent scatter (IS)
radars at high latitudes in order to estimate the vertical component of the neutral wind
velocity in the lower thermosphere (from 100 to 120 km). This method has been applied to
experiments with the Sondrestrom IS radar, Greenland, on 5 and 8 March 2004. The
measurement and the analysis methods provide various temporal and altitudinal structures
of the vertical neutral wind velocity with amplitude of a few tens of meters per second at
3 km height resolution. This paper also demonstrates how to evaluate assumptions
adopted in calculations of the vertical neutral wind velocity using experimental data on
5 and 8 March 2004. Caution should be exercised in inferring effects of variations in
the thermospheric density or the ion-neutral collision frequency in association with
vertical thermospheric motions, in particular above 112 km.

DOI： 10.1029/2004RS003205

*Vertical ion motions observed with incoherent-scatter radars in the polar lower ionosphere Reviewed

Oyama, S., B. J. Watkins, S. Nozawa, S. Maeda, and M. Conde

J. Geophysical Research Vol. 110 ( A04302 ) page： 2004JA010705 2005.4

Summer-winter dependences of day-night differences in the ion temperature in the polar upper F region Reviewed

Oyama, S., C. Lathuillere, S. Maeda, and B. J. Watkins

Geophysical Research Letter Vol. 31 ( L05806 ) page： 2003GL018820 2004.3

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal)

The daily variation of ion temperature observed with the
European Incoherent Scatter (EISCAT) Tromsø UHF radar in
the upper F region (from 300 to 500 km) has been found to
be significantly dependent on season. Of particular interest
is the statistics that the ion temperature at local night is
higher than that at local daytime for near solar maximum
summer conditions; by contrast no differences for winter.
Using the ion energy equation estimates of the heat
exchange with electrons suggest these local time and
seasonal differences. A case study using summer-time
data from the Sondrestrom incoherent-scatter radar
(ISR) also shows local-time dependences similar to
that observed with the Tromsø ISR. The case study
using a summer-time data from the EISCAT Svalbard
radar (ESR) shows the opposite sense. These seasonal
characteristics of the ion temperature that depend on the
observation site suggest that the day-night difference of ion
temperature in the polar upper F region has complicated
magnetic-latitudinal dependences.

DOI： 10.1029/2003GL018820

The quasi 2-day wave observed in the polar mesosphere (2): Comparison of the characteristics observed at Tromso and Poker Flat Reviewed Open Access

Nozawa, S., H. Iwahashi, A. Brekke, C. M. Hall, C. Meek, A. Manson, S. Oyama, Y. Murayama, and R. Fujii

J. Geophysical Research page： 108 , 101029/2002JD003221 2003.12

Thermospheric and ionosphric dynamics in the auroral region Reviewed

Shinagawa, H., S. Oyama, S. Nozawa, S. C. Buchert, R. Fujii, and M. Ishii

Advances in Space Research Vol. 31 ( 4 ) page： 951-956 2003.9

Field-aligned ion motions in the polar E-F transition region: Mean characteristics Reviewed Open Access

Oyama, S., S. Nozawa, S. Maeda, Y. Murayama, R. Fujii, and H. Shinagawa

J. Geophysical Research page： 108(A8), 1334, doi:10.1029/2003JA009830 2003.8

The quasi 2-day wave observed in the polar mesosphere Reviewed Open Access

Nozawa, S., S. Imaida, A. Brekke, C. Hall, C. Meek, A. Manson, S. Oyama, K. Dobashi, and R. Fujii

J. Geophysical Research page： 108, 10.1029/2002JD002440 2003.1

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Papers - OYAMA, Shin-ichiro