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148 results on '"Tam, S."'

1. First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite

Author

Kawai, K., Shiokawa, K., Otsuka, Y., Oyama, S., Kasaba, Y., Kasahara, Y., Tsuchiya, F., Kumamoto, A., Nakamura, S., Matsuoka, A., Imajo, S., Kazama, Y., Wang, S.‐Y., Tam, S. W. Y., Chang, T. F., Wang, B. J., Asamura, K., Kasahara, S., Yokota, S., Keika, K., Hori, T., Miyoshi, Y., Jun, C., Shoji, M., Shinohara, I., Kawai, K., Shiokawa, K., Otsuka, Y., Oyama, S., Kasaba, Y., Kasahara, Y., Tsuchiya, F., Kumamoto, A., Nakamura, S., Matsuoka, A., Imajo, S., Kazama, Y., Wang, S.‐Y., Tam, S. W. Y., Chang, T. F., Wang, B. J., Asamura, K., Kasahara, S., Yokota, S., Keika, K., Hori, T., Miyoshi, Y., Jun, C., Shoji, M., and Shinohara, I.

Abstract

Medium-scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all-sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm−3, respectively. The electric field variations projected to the ionosphere are mainly in the east-west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere.

Published
2022

2. Study of an Equatorward Detachment of Auroral Arc From the Oval Using Ground‐Space Observations and the BATS‐R‐US–CIMI Model

Author

Yadav, Sneha, Shiokawa, K., Oyama, S., Inaba, Y., Takahashi, N., Seki, K., Keika, K., Chang, Tzu‐Fang, Tam, S. W. Y., Wang, B.‐J., Kazama, Y., Wang, S.‐Y., Asamura, K., Kasahara, S., Yokota, S., Hori, T., Kasaba, Y., Tsuchiya, F., Kumamoto, A., Shoji, M., Kasahara, Y., Matsuoka, A., Matsuda, S., Jun, C.‐W., Imajo, S., Miyoshi, Y., Shinohara, I., Yadav, Sneha, Shiokawa, K., Oyama, S., Inaba, Y., Takahashi, N., Seki, K., Keika, K., Chang, Tzu‐Fang, Tam, S. W. Y., Wang, B.‐J., Kazama, Y., Wang, S.‐Y., Asamura, K., Kasahara, S., Yokota, S., Hori, T., Kasaba, Y., Tsuchiya, F., Kumamoto, A., Shoji, M., Kasahara, Y., Matsuoka, A., Matsuda, S., Jun, C.‐W., Imajo, S., Miyoshi, Y., and Shinohara, I.

Abstract

We present observations of an equatorward detachment of the auroral arc from the main oval and magnetically conjugate measurements made by the Arase satellite in the inner magnetosphere. The all-sky imager at Gakona (magnetic latitude = 63.6°N), Alaska, shows the detachment of the auroral arc in both red and green lines at local midnight (∼0130–0230 MLT) on 30 March 2017. The electron density derived from the Arase in-situ observations shows that this arc occurred outside the plasmapause. At the arc crossing, the electron flux of energies ∼0.1–2 keV is found to be locally enhanced at L∼4.3–4.5. We estimated auroral intensities for both red and green lines by using the Arase low-energy (0.1–19 keV) electron flux data. The peak latitude of the estimated intensity shows reasonably good correspondence with the observed intensity mapped at the ionospheric footprints of the Arase satellite. These findings indicate that the observed arc detachment at Gakona was associated with the localized enhancement of low-energy electrons (∼0.1–2 keV) at the inner edge of the electron plasma sheet. Further, we employ the simulation results of the Community Coordinated Modeling Center (CCMC), the BATS-R-US–CIMI 3-D MHD code to understand the conditions in the inner magnetosphere around the time of detachment. Although the simulation could not reproduce the lower-energy component responsible for the arc detachment, it successfully reproduced two earthward convection events at the lower radial distance (R) (R ≤ ∼4) around the time of arc detachment and the features of enhanced convection in similarity with the observations.

Published
2022

4. Substorm-Associated Ionospheric Flow Fluctuations During the 27 March 2017 Magnetic Storm: SuperDARN-Arase Conjunction

Author

Hori, T., Nishitani, N., Shepherd, S. G., Ruohoniemi, J. M., Connors, M., Teramoto, M., Nakano, S., Seki, K., Takahashi, N., Kasahara, S., Yokota, S., Mitani, T., Takashima, T., Higashio, N., Matsuoka, A., Asamura, K., Kazama, Y., Wang, S.-Y., Tam, S. W. Y., Chang, T.-F., Wang, B.-J., Miyoshi, Y., and Shinohara, I.

Subjects
ERG, Physics::Space Physics, substorm injection, SuperDARN, Physics::Atmospheric and Oceanic Physics, Physics::Geophysics, ULF wave, ring current electron, M‐I coupling
Abstract

Super Dual Auroral Radar Network (SuperDARN) observations show that ionospheric flow fluctuations of millihertz or lower‐frequency range with horizontal velocities of a few hundred meters per second appeared in the subauroral to midlatitude region during a magnetic storm on 27 March 2017. A set of the radars have provided the first ever observations that the fluctuations propagate azimuthally both westward and eastward simultaneously, showing bifurcated phase propagation associated with substorm expansion. Concurrent observations near the conjugate site in the inner magnetosphere made by the Arase satellite provide evidence that multiple drifting clouds of electrons in the near‐Earth equatorial plane were associated with the electric field fluctuations propagating eastward in the ionosphere. We interpret this event in terms of mesoscale pressure gradients carried by drifting ring current electrons that distort field lines one after another as they drift through the inner magnetosphere, causing eastward propagating ionospheric electric field fluctuations., ファイル公開：2019-03-28

Published
2018

5. Study of an Equatorward Detachment of Auroral Arc From the Oval Using Ground‐Space Observations and the BATS‐R‐US–CIMI Model

Author

Yadav, Sneha, Shiokawa, K., Oyama, S., Inaba, Y., Takahashi, N., Seki, K., Keika, K., Chang, Tzu‐Fang, Tam, S. W. Y., Wang, B.‐J., Kazama, Y., Wang, S.‐Y., Asamura, K., Kasahara, S., Yokota, S., Hori, T., Kasaba, Y., Tsuchiya, F., Kumamoto, A., Shoji, M., Kasahara, Y., Matsuoka, A., Matsuda, S., Jun, C.‐W., Imajo, S., Miyoshi, Y., and Shinohara, I.

Subjects
Physics::Space Physics
Abstract

We present observations of an equatorward detachment of the auroral arc from the main oval and magnetically conjugate measurements made by the Arase satellite in the inner magnetosphere. The all-sky imager at Gakona (magnetic latitude = 63.6°N), Alaska, shows the detachment of the auroral arc in both red and green lines at local midnight (∼0130–0230 MLT) on 30 March 2017. The electron density derived from the Arase in-situ observations shows that this arc occurred outside the plasmapause. At the arc crossing, the electron flux of energies ∼0.1–2 keV is found to be locally enhanced at L∼4.3–4.5. We estimated auroral intensities for both red and green lines by using the Arase low-energy (0.1–19 keV) electron flux data. The peak latitude of the estimated intensity shows reasonably good correspondence with the observed intensity mapped at the ionospheric footprints of the Arase satellite. These findings indicate that the observed arc detachment at Gakona was associated with the localized enhancement of low-energy electrons (∼0.1–2 keV) at the inner edge of the electron plasma sheet. Further, we employ the simulation results of the Community Coordinated Modeling Center (CCMC), the BATS-R-US–CIMI 3-D MHD code to understand the conditions in the inner magnetosphere around the time of detachment. Although the simulation could not reproduce the lower-energy component responsible for the arc detachment, it successfully reproduced two earthward convection events at the lower radial distance (R) (R ≤ ∼4) around the time of arc detachment and the features of enhanced convection in similarity with the observations.

Published
2021

6. First Simultaneous Observation of a Night Time Medium‐Scale Traveling Ionospheric Disturbance From the Ground and a Magnetospheric Satellite

Author

Kawai, K., Shiokawa, K., Otsuka, Y., Oyama, S., Kasaba, Y., Kasahara, Y., Tsuchiya, F., Kumamoto, A., Nakamura, S., Matsuoka, A., Imajo, S., Kazama, Y., Wang, S.‐Y., Tam, S. W. Y., Chang, T. F., Wang, B. J., Asamura, K., Kasahara, S., Yokota, S., Keika, K., Hori, T., Miyoshi, Y., Jun, C., Shoji, M., and Shinohara, I.

Subjects
Physics::Space Physics, Physics::Geophysics
Abstract

Medium-scale traveling ionospheric disturbances (MSTIDs) are a phenomenon widely and frequently observed over the ionosphere from high to low latitudes. Night time MSTIDs are caused generally by the polarization electric field in the ionosphere. However, propagation of this polarization electric field to the magnetosphere has not yet been identified. Here, we report the first observation of the polarization electric field and associated density variations of a night time MSTID in the magnetosphere. The MSTID event was observed by an all-sky airglow imager at Gakona (geographical latitude: 62.39°N, geographical longitude: 214.78°E, magnetic latitude: 63.20°N), Alaska. The Arase satellite passed over the MSTID in the inner magnetosphere at 0530–0800 UT (2030–2300 LT) on November 3, 2018. This MSTID, observed in 630 nm airglow images, was propagating westward with a horizontal wavelength of ∼165 km, a north–south phase front, and a phase velocity of ∼80 m/s. The Arase satellite footprint on the ionosphere crossed the MSTID in the direction nearly perpendicular to the MSTID phase fronts. The electric field and electron density observed by the Arase satellite showed periodic variation associated with the MSTID structure with amplitudes of ∼2 mV/m and ∼150 cm−3, respectively. The electric field variations projected to the ionosphere are mainly in the east-west direction and are consistent with the direction of the polarization electric field expected from MSTID growth by E × B drift. This observation indicates that the polarization electric field associated with the MSTID in the ionosphere is projected onto the magnetosphere, causing plasma density fluctuations in the magnetosphere.

Published
2021

7. Petrography and provenance of Laecanius Amphorae from Istria, northern Adriatic region, Croatia

Author

Tam´s Bezeczky and Maria A. Mange

Subjects
Archeology, Provenance, Heavy mineral, Mineralogy, Epidote, engineering.material, Petrography, Terra rossa, Clastic rock, Earth and Planetary Sciences (miscellaneous), engineering, Geology, Zircon, Hornblende
Abstract

Amphorae sherds from the Laecanius workshop of Roman Istria (10–5 B.C. and 78 A.D.), Croatia, were studied by integrating archaeological and geological techniques including fabric analysis, thin-section petrography, X-ray diffractometry (XRD), and heavy mineral analysis. The fabric of the sherds showed distinctive characteristics, permitting their classification and allocation into nine fabric groupss. Petrography revealed that quartz is the dominant clastic component, whereas carbonate is common as temper; XRD provided information on firing temperatures that ranged between 750 and 900°C. The sherds contain diverse heavy mineral suites with generally high epidote and garnet proportions; zircon is occasionally important. Garnet/epidote ratios and the presence of diagnostic species (pyroxene, hornblende) showed systematic variations that coincided with similar variations in fabric characteristics. Heavy mineral signatures of amphorae produced in other workshops proved essential in differentiating them from Laecanius sherds. A comparative heavy mineral analysis of terra rossa samples from the vicinity of the workshop indicated that terra rossa was the major source for the paste. Differences observed in the heavy mineral composition of the sherds and terra rossa were interpreted by the spatial heterogeneity of the latter and the mixing of the paste with sandy temper. Fresh Adriatic sponge spicules in the majority of Laecanius sherds and the temper-derived, generally immature heavy mineral assemblages suggest that sandy deposits from the Adriatic were used for the clastic temper.

Published
2006
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45. Variations in susceptibility to proteoglycan-induced arthritis and spondylitis among C3H substrains of mice: Evidence of genetically acquired resistance to autoimmune disease

Author

Glant, Tibor T., primary, B�rdos, Tam�s, additional, Vermes, Csaba, additional, Chandrasekaran, Raman, additional, Vald�z, Juan C., additional, Otto, Jeffrey M., additional, Gerard, David, additional, Velins, Sonja, additional, Lov�sz, Gy�rgy, additional, Zhang, Jian, additional, Mikecz, Katalin, additional, and Finnegan, Alison, additional

Published
2001
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