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  • Articles  (206)
  • Wiley  (174)
  • Nature Publishing Group (NPG)  (32)
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  • Articles  (206)
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  • 1
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    The vertical propagation of disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku Earthquake over Taiwan (2016)
    Wiley
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    Publication Date: 2016-02-05
    Description: In this paper, concurrent/co-located measurements of seismometers, infrasonic systems, magnetometers, HF-CW (high frequency - continuous wave) Doppler sounding systems, and GPS receivers are employed to detect disturbances triggered by seismic waves of the 11 March 2011 M9.0 Tohoku earthquake. No time delay between co-located infrasonic ( i.e. super long acoustic) waves and seismic waves indicates that the triggered acoustic and/or gravity waves in the atmosphere (or seismo-traveling atmospheric disturbances, STADs) near the Earth's surface can be immediately activated by vertical ground motions. The circle method is used to find the origin and compute the observed horizontal traveling speed of the triggered infrasonic waves. The speed of about 3.3 km/s computed from the arrival time versus the epicentral distance suggests that the infrasonic waves ( i.e. STADs) are mainly induced by the Rayleigh waves. The agreements in the travel time at various heights between the observation and theoretical calculation suggest that the STADs triggered by the vertical motion of ground surface caused by the Tohoku earthquake traveled vertically from the ground to the ionosphere with speed of the sound in the atmosphere over Taiwan.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Observations of global ionospheric responses to the 2009 stratospheric sudden warming event by FORMOSAT-3/COSMIC (2012)
    Wiley
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    Publication Date: 2012-06-29
    Description: The global ionospheric response to a stratospheric sudden warming (SSW) is studied using three-dimensional electron density maps derived from radio occultation observations of FORMOSAT-3/COSMIC during the 2009 SSW periods. Results show that the ionospheric electron density at EIA crests exhibit a morning/early afternoon increase followed by an afternoon decrease and an evening increase, indicative of a semidiurnal component during the SSW period, which is consistent with recent studies. The latitude-altitude electron density slice maps show that the SSW related modifications of the equatorial plasma fountain interact with the existing summer-to-winter neutral winds and resulting in a north–south asymmetry. The global ionospheric response shows a clear longitudinal dependence in the equatorial plasma fountain enhancement during morning/early afternoon, inferred from the duration of the equatorial ionization anomaly (EIA) enhancement. Following the enhancement, prominent global EIA reductions resulting from the equatorial plasma fountain weakening in the afternoon sector are seen. The ionospheric response to the 2009 SSW event is also compared with the usual seasonal variation during January–February 2007. Instead of showing the electron density increase in the northern hemisphere and decrease in the southern hemisphere as the usual seasonal variation does, the SSW period ionosphere shows prominent global electron density reductions in the afternoon period during the 2009 SSW event.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 3
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    Influence of Southwest Monsoon Flow and Typhoon Track on Taiwan Rainfall during Exit Phase: Modeling Study of Typhoon Morakot (2009) (2017)
    Wiley
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    Publication Date: 2017-09-06
    Description: This paper studies the dramatic decadal increase of Taiwan rainfall in the typhoon exit phase. The exit phase is defined as the time interval when a typhoon center leaves the Taiwan coast to 100 km away from the nearest coastline. Typhoons move across Taiwan through its northern (track N), central (track C), or southern (track S) part are selected for a statistical study. Taiwan hourly rainfall data of 21 surface gauge stations from the past 57 years are divided into two periods: 1960-1989 (P1) and 1987-2016 (P2). From P1 to P2, there are decadal increases of rainfall (~60%) and rainfall intensity (~30%, mm h -1 ) in the exit phase. There is also a decadal increase of the track-C typhoons. The southwest monsoon water vapor flux (SWF) in a local region southwest of Taiwan, as computed from the JRA-55 dataset, is substantially larger in the track-C typhoons than that in the track-N typhoons. Our analysis indicates that the increase of SWF leads to the increase of rainfall intensity. Moreover, both the enhanced SWF and the prolonged duration time contribute to the increased rainfall in the exit phase. Typhoon Morakot (2009), a track-C typhoon with extremely slow speed in the exit phase, produced the record-breaking rainfall. Model experiments and potential vorticity tendency diagnosis of Typhoon Morakot are used to understand the dynamics of increased duration time. The slowdown of typhoon motion is shown to be due to the asymmetric convection in the Taiwan Strait, which is produced by the interaction between typhoon circulation and southwest monsoon flow. The enhanced SWF and the prolonged duration time may explain the observed fact that the decadal rainfall increase is much larger than that of rainfall intensity in the exit phase.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
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  • 4
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    Superconductivity at 43 K in SmFeAsO1-xFx (2008)
    Nature Publishing Group (NPG)
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    Publication Date: 2008-05-27
    Description: Since the discovery of high-transition-temperature (high-T(c)) superconductivity in layered copper oxides, extensive effort has been devoted to exploring the origins of this phenomenon. A T(c) higher than 40 K (about the theoretical maximum predicted from Bardeen-Cooper-Schrieffer theory), however, has been obtained only in the copper oxide superconductors. The highest reported value for non-copper-oxide bulk superconductivity is T(c) = 39 K in MgB(2) (ref. 2). The layered rare-earth metal oxypnictides LnOFeAs (where Ln is La-Nd, Sm and Gd) are now attracting attention following the discovery of superconductivity at 26 K in the iron-based LaO(1-x)F(x)FeAs (ref. 3). Here we report the discovery of bulk superconductivity in the related compound SmFeAsO(1-x)F(x), which has a ZrCuSiAs-type structure. Resistivity and magnetization measurements reveal a transition temperature as high as 43 K. This provides a new material base for studying the origin of high-temperature superconductivity.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Chen, X H -- Wu, T -- Wu, G -- Liu, R H -- Chen, H -- Fang, D F -- England -- Nature. 2008 Jun 5;453(7196):761-2. doi: 10.1038/nature07045. Epub 2008 May 25.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China. chenxh@ustc.edu.cn〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18500328" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 5
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    A large iron isotope effect in SmFeAsO(1 - x)F(x) and Ba(1 - x)K(x)Fe(2)As(2) (2009)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2009-05-09
    Description: The recent discovery of superconductivity in oxypnictides with a critical transition temperature (T(C)) higher than the McMillan limit of 39 K (the theoretical maximum predicted by Bardeen-Cooper-Schrieffer theory) has generated great excitement. Theoretical calculations indicate that the electron-phonon interaction is not strong enough to give rise to such high transition temperatures, but strong ferromagnetic/antiferromagnetic fluctuations have been proposed to be responsible. Superconductivity and magnetism in pnictide superconductors, however, show a strong sensitivity to the crystal lattice, suggesting the possibility of unconventional electron-phonon coupling. Here we report the effect of oxygen and iron isotope substitution on T(C) and the spin-density wave (SDW) transition temperature (T(SDW)) in the SmFeAsO(1 - x)F(x) and Ba(1 - x)K(x)Fe(2)As(2) systems. The oxygen isotope effect on T(C) and T(SDW) is very small, while the iron isotope exponent alpha(C) = -dlnT(C)/dlnM is about 0.35 (0.5 corresponds to the full isotope effect). Surprisingly, the iron isotope exchange shows the same effect on T(SDW) as T(C). This indicates that electron-phonon interaction plays some role in the superconducting mechanism, but a simple electron-phonon coupling mechanism seems unlikely because a strong magnon-phonon coupling is included.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Liu, R H -- Wu, T -- Wu, G -- Chen, H -- Wang, X F -- Xie, Y L -- Ying, J J -- Yan, Y J -- Li, Q J -- Shi, B C -- Chu, W S -- Wu, Z Y -- Chen, X H -- England -- Nature. 2009 May 7;459(7243):64-7. doi: 10.1038/nature07981.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Hefei National Laboratory for Physical Sciences at Microscale and Department of Physics, University of Science and Technology of China, Hefei, Anhui 230026, China.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19424151" target="_blank"〉PubMed〈/a〉
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 6
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    Equatorial plasma bubble generation / inhibition during 2015 St. Patrick's Day storm (2017)
    Wiley
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    Publication Date: 2017-08-01
    Description: All sky camera observations carried out over Taiwan showed intense equatorial plasma bubbles (EPB) in 630.0 nm airglow images on consecutive nights of 13-16 March, 2015, but was absent in the following night of 17 March when St. Patrick's Day magnetic storm occurred. Rate of total electron content (TEC) index by using Global Positioning System (GPS) network data also confirmed the absence of irregularities on the night 17 March. The results however revealed strong irregularities over Indian sector on the same night. Flux tube integrated Rayleigh-Taylor instability growth rates computed using the prior (forecast) state of Thermosphere-Ionosphere Electrodynamics General Circulation Model output after assimilating the GPS-TEC measurements also agree with the observations, showing smaller values over Taiwan and larger values over India on the night of 17 March. The ionospheric response to the storm over Taiwan that resulted in the apparent inhibition of EPB is investigated in this study by using the data assimilation output. Results indicate that on the night of the magnetic storm, pre-reversal enhancement of zonal electric field over Taiwan was weaker when compared to that over India. Further analysis suggests that the absence of enhancement in the zonal electric field could be due to westward penetration electric field in response to rapid northward turning of interplanetary magnetic field that occurred during the dusk period over Taiwan.
    Print ISSN: 1539-4964
    Electronic ISSN: 1542-7390
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Global equatorial plasma bubble growth rates using ionosphere data assimilation (2017)
    Wiley
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    Publication Date: 2017-03-16
    Description: Flux tube integrated Rayleigh-Taylor instability growth rates computed using the results of ionosphere data assimilation are used for the first time to investigate global plasma bubble occurrence. The study is carried out by assimilating total electron content measurements using ground based global positioning system (GPS) receivers into thermosphere ionosphere electrodynamic general circulation model, and the growth rates are calculated using standalone model run without assimilation (control run) as well as using prior (or forecast) state output of the assimilation run. The growth rates are compared with rate of change of total electron content index (ROTI), estimated from global network of GPS receivers, as well as all sky airglow observations carried out over Taiwan on the nights of 16, and 17 March 2015. In contrast to the growth rates using the control run, results using data assimilation show remarkable agreement with the ROTI. Further, the all sky images reveal intense plasma bubbles over Taiwan on the night of 16 March, when the corresponding assimilated growth rate is also pronounced. Similarly, absence of plasma bubbles in the all sky images on the night of 17 March (St. Patrick's day storm) is supported by smaller growth rates predicted by the assimilation model. Significant improvements in the calculated growth rates could be achieved because of the accurate updating of zonal electric field in the data assimilation forecast. The results suggest that realistic estimate or prediction of plasma bubble occurrence could be feasible by taking advantage of the data assimilation approach adopted in this work.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 8
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    Modeling the ionospheric pre-reversal enhancement using coupled thermosphere-ionosphere data assimilation (2017)
    Wiley
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    Publication Date: 2017-02-05
    Description: We report that assimilating total electron content (TEC) into a coupled thermosphere-ionosphere model by using the ensemble Kalman filter results in improved specification and forecast of eastward pre-reversal enhancement (PRE) electric field (E-field). Through data assimilation, the ionospheric plasma density, thermospheric winds, temperature and compositions are adjusted simultaneously. The improvement of dusk-side PRE E-field calculation over the prior state is achieved primarily by intensification of eastward neutral wind. The improved E-field calculation promotes a stronger plasma fountain and deepens the equatorial trough. As a result, the horizontal gradients of Pedersen conductivity and eastward wind are increased due to greater zonal electron density gradient and smaller ion drag at dusk, respectively. Such modifications provide preferable conditions and obtain a strengthened PRE magnitude closer to the observation. The adjustment of PRE E-field is enabled through self-consistent thermosphere and ionosphere coupling processes captured in the model. This study suggests that the PRE E-field that is critical in driving the evening equatorial plasma instability could be better forecasted by assimilation of TECs in the 10 minutes cycling.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
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  • 9
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    Ionosphere Data Assimilation Modeling of 2015 St. Patrick's Day Geomagnetic Storm (2016)
    Wiley
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    Publication Date: 2016-11-12
    Description: The ionospheric plasma disturbances during a severe storm can affect human activities and systems, such as navigation and HF communication systems. Therefore, the forecast of ionospheric electron density is becoming an important topic recently. This study is conducted with the ionospheric assimilation model by assimilating the total electron content observations into the thermosphere-ionosphere coupling model with different high-latitude ionospheric convection models, Heelis and Weimer, and further to forecast the variations of ionospheric electron density during the 2015 St. Patrick's Day geomagnetic storm. The forecast capabilities of these two assimilation models are evaluated by the root-mean-square-error values in different regions to discuss its latitudinal effects. Results show the better forecast in the electron density at the low-latitude region during the storm main phase and the recovery phase. The well reproduced eastward electric field at the low-latitude region by the assimilation model reveals that the electric fields may be an important factor to have the contributions on the accuracy of ionospheric forecast.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 10
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    Ionospheric data assimilation with TIE-GCM and GPS-TEC during geomagnetic storm conditions (2016)
    Wiley
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    Publication Date: 2016-05-28
    Description: The main purpose of this paper is to investigate the effects of rapid assimilation-forecast cycling on the performance of ionospheric data assimilation during geomagnetic storm conditions. An ensemble Kalman filter software developed by the National Center for Atmospheric Research (NCAR), called Data Assimilation Research Testbed, is applied to assimilate ground-based GPS total electron content (TEC) observations into a theoretical numerical model of the thermosphere and ionosphere (NCAR Thermosphere-Ionosphere-Electrodynamics General Circulation Model) during the 26 September 2011 geomagnetic storm period. Effects of various assimilation-forecast cycle lengths: 60-, 30- and 10-minutes on the ionospheric forecast are examined by using the global root-mean-squared observation-minus-forecast (OmF) TEC residuals. Substantial reduction in the global OmF for the 10-minutes assimilation-forecast cycling suggests that a rapid cycling ionospheric data assimilation system can greatly improve the quality of the model forecast during geomagnetic storm conditions. Furthermore, updating the thermospheric state variables in the coupled thermosphere-ionosphere forecast model in the assimilation step is an important factor in improving the trajectory of model forecasting. The shorter assimilation-forecast cycling (10 minutes in this paper) helps to restrain unrealistic model error growth during the forecast step due to the imbalance among model state variables resulting from an inadequate state update, which in turn leads to a greater forecast accuracy.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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