bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermospheric atomic oxygen density estimates using the EISCAT Svalbard Radar
Authors: Vickers H. , Kosch M. J. , Sutton E. , Ogawa Y. , La Hoz C. 
Published: April 2013

AbstractCoupling between the ionized and neutral atmosphere through particle collisions allows an indirect study of the neutral atmosphere through measurements of ionospheric plasma parameters. We estimate the neutral density of the upper thermosphere above ~250 km with the European Incoherent Scatter Svalbard Radar (ESR) using the year‐long operations of the International Polar Year from March 2007 to February 2008. The simplified momentum equation for atomic oxygen ions is used for field‐aligned motion in the steady state, taking into account the opposing forces of plasma pressure gradients and gravity only. This restricts the technique to quiet geomagnetic periods, which applies to most of the International Polar Year during the recent very quiet solar minimum. The method works best in the height range ~300–400 km where our assumptions are satisfied. Differences between Mass Spectrometer and Incoherent Scatter and ESR estimates are found to vary with altitude, season, and magnetic disturbance, with the largest discrepancies during the winter months. A total of 9 out of 10 in situ passes by the CHAMP satellite above Svalbard at 350 km altitude agree with the ESR neutral density estimates to within the error bars of the measurements during quiet geomagnetic periods.
Universal time control of AKR: Earth is a spin‐modulated variable radio source
Authors: Morioka Akira , Miyoshi Yoshizumi , Kurita Satoshi , Kasaba Yasumasa , Angelopoulos Vassilis , Misawa Hiroaki , Kojima Hirotsugu , McFadden James P. 
Published: April 2013

AbstractAuroral kilometric radiation (AKR) is known to be transient emissions generated by rapidly accelerated electrons together with sudden auroral activation in the polar magnetosphere. In contrast, the characteristics and relationship with the auroral acceleration of rather continuous AKR emissions are not well understood. We examine the emission using long‐term data and report that the continuous AKR emission frequency changes with universal time (UT) as the Earth rotates, indicating that the Earth is a spin‐modulated variable radio source. The observed UT variation of AKR frequency means that the acceleration altitude changes periodically with planetary rotation. The observations indicate that the diurnal wobble of the tilted geomagnetic field in the solar wind flow alters the magnetosphere‐ionosphere (M‐I) coupling state in the polar magnetosphere, giving rise to periodic variation of auroral particle acceleration altitude. These observations of planetary radio wave properties provide insight into the physics of planetary particle acceleration.
Meridional electric fields in layer‐type and clump‐type plasma structures in midlatitude sporadic E region: Observations and plausible mechanisms
Authors: Chu Y.H. , Yang K.F. , Wang C.Y. , Su C.L. 
Published: April 2013

AbstractThe use of multibased line interferometry technique operated by a VHF coherent scatter radar with relatively broad radar beam pattern makes it possible to reveal zonal drift velocity of 3 m field‐aligned irregularities (FAIs) inside moving layer‐type or clump‐type plasma structures at kilometer scale. We present compelling evidences in this article showing that, no matter what types of the plasma structures, the apparent zonal drift velocity of the 3 m FAIs is always linearly dependent on the zonal trace velocity (or bulk velocity) of the kilometer‐scale plasma structure. This feature seems to imply that the bulk motion of the large‐scale plasma structure may significantly affect the observed 3 m FAI Doppler velocity, which should be removed to obtain true FAI drift velocity. In addition, there is an evident tendency for the 3 m FAIs in the layer‐type plasma structure to drift in the same zonal direction as the moving plasma structure. However, the correlation between the drift direction of the 3 m FAIs and the moving direction of the large‐scale plasma structure is indistinct for the clump‐type plasma structure. The meridional electric fields estimated from the true zonal FAI drift velocities for the layer‐type plasma structures moving in the west (east) direction point in the northward/upward (southward/downward) direction. Statistical results show that the mean value of the meridional electric field inside the layer‐type plasma structure is approximately 2.7–2.8 mV/m, about one order of magnitude larger than that for the clump‐type plasma structure. Mechanisms that are, respectively, responsible for the generations of the layer‐type and clump‐type plasma structures are discussed in this article. It is believed that neutral wind shear is very likely the main cause of the layer‐type plasma structure formation, while the clump‐type plasma structure may be associated with propagating gravity wave.
Geomagnetic and auroral activity driven by corotating interaction regions during the declining phase of Solar Cycle 23
Authors: Luan Xiaoli , Wang Wenbin , Lei Jiuhou , Burns Alan , Dou Xiankang , Xu Jiyao 
Published: April 2013

AbstractA superposed epoch analysis is performed to investigate the relative impact of the solar wind/interplanetary magnetic field (IMF) on geomagnetic activity, auroral hemispheric power, and auroral morphology during corotating interaction regions (CIRs) events between 2002 and 2007, when auroral images from Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Global Ultraviolet Imager were available. Four categories of CIRs have been compared. These were classified by the averaged IMF Bz and the time of maximum solar wind dynamic pressure around the CIR stream interface or onset time. It is found that during CIR events: (1) The peaks of auroral power and Kp were largely associated with dominant southward Bz, whereas auroral activity also became stronger with increases of solar wind speed, density, and dynamic pressure. (2) The percentage and absolute increases of auroral hemispheric power with solar wind speed were much greater under dominantly northward Bz conditions than under dominantly southward Bz conditions. (3) The enhancement of the auroral power and Kp with increasing solar wind speed followed the same pattern, for both dominantly southward and northward Bz conditions, regardless of the behavior of solar wind density and dynamic pressure. These results suggest that, during CIR events, southward Bz played the most critical role in determining geomagnetic and auroral activity, whereas solar wind speed was the next most important contributor. The solar wind dynamic pressure was the less important factor, as compared with Bz and solar wind speed. Relatively strong auroral precipitation energy flux (> ~3 mW/m2) occurred in a wider auroral oval region after the stream interface than before it for both dominantly northward and southward Bz conditions. These conditions enhanced the auroral hemispheric power after the stream interface. Intense auroral precipitation (> ~4 mW/m2) generally occurred widely at night under dominantly southward Bz conditions, but the location of this precipitation in the auroral oval was different when it was associated with different solar wind density and speed conditions.
VLF wave intensity in the plasmasphere due to tropospheric lightning
Authors: Colman J. J. , Starks M. J. 
Published: April 2013

AbstractA climatology of VLF (very low frequency) wave intensity from lightning in the plasmasphere is constructed. Starting from Optical Transient Detector/Lightning Imaging Sensor (OTD/LIS) lightning data representing 1995–2005, a climatology of strikes is assembled with 1° × 1° latitude‐longitude spatial resolution, averaged into 2 h bins for each month of the year. Assuming a linear relationship between optical flash rate and VLF power flux, and that the VLF amplitude drops off as one over distance, a proxy for VLF power is developed. A typical lightning spectrum is applied and the values are scaled by appropriate transionospheric absorptions for each time and place. These values are mapped along geomagnetic field lines in order to compare them to E‐field spectral densities measured by the DEMETER satellite between 2005 and 2009. An overview of the DEMETER survey mode data is presented which leads to the best scaling of the lightning VLF climatology in LEO (low earth orbit). The resulting data set represents a monthly, 2‐hour, solar minimum climatology of VLF wave intensity from lightning in LEO. Finally, the E‐field spectral densities are converted to Poynting flux, mapped to the plasmasphere, and converted to B‐field spectral densities. Good overall agreement is found with previous observations and estimates. This new climatology is expected to have a significant impact on calculations of pitch‐angle diffusion for relativistic electrons in the inner radiation belt.
Modeling ionospheric super‐fountain effect based on the coupled TIMEGCM‐SAMI3
Authors: Lu G. , Huba J. D. , Valladares Cesar 
Published: April 2013

AbstractRecently, efforts have been undertaken to develop a coupled thermosphere‐ionosphere‐plasmasphere model based on two well‐established models, namely, the Thermosphere‐Ionosphere‐Mesosphere General Circulation Model (TIMEGCM) developed at the National Center for Atmospheric Research and the SAMI3 ionosphere model developed at the Naval Research Laboratory. This paper presents the first results from the coupled model on the investigation of a prompt penetration electric field (PPEF) event that took place on 9 November 2004. The coupled model eliminates two major upper boundary limitations of the stand‐alone TIMEGCM, e.g., the upper boundary height and the prescribed O+ fluxes at the upper boundary. It is found that the F‐layer peak height is raised above 800 km in response to the large PPEF. The O+ fluxes in the top ionosphere vary drastically during the course of the PPEF, with strong upward and downward fluxes with a magnitude greater than 109 cm−2 s−1 in localized regions. For the first time, the coupled model allows us to simulate and visualize the super‐fountain effect on a global scale. Future model development is also envisaged, including the implementation of a more realistic magnetic field model and a fully two‐way coupling between neutrals and ions.
Anisotropic structures of oceanic slab and mantle wedge in a deep low‐frequency tremor zone beneath the Kii Peninsula, SW Japan
Authors: Saiga Atsushi , Kato Aitaro , Kurashimo Eiji , Iidaka Takashi , Okubo Makoto , Tsumura Noriko , Iwasaki Takaya , Sakai Shin'ichi , Hirata Naoshi 
Published: April 2013

AbstractAnisotropy is an important feature of elastic wave propagation in the Earth and can arise from a variety of ordered architectures such as fractures with preferential alignments or preferred crystal orientations. We studied the regional variations in shear wave anisotropy around a deep Low‐Frequency Earthquake (LFE) zone beneath the Kii Peninsula, SW Japan, using waveforms of local earthquakes observed by a dense linear array along the LFE zone. The fast directions of polarization are subparallel to the strike of the margin for both crustal and intraslab earthquakes. The delay time of the split shear waves in intraslab earthquakes is larger than that in crustal earthquakes and shows a down‐dip variation across the LFE zone. This indicates that anisotropy exists in the mantle wedge and in the lower crust and/or oceanic slab. We explain the observed delay time of 0.015–0.045 s by suggesting that the mantle wedge consists of a deformed, 1–15 km thick serpentine layer if the mantle wedge is completely serpentinized. In addition to high‐fluid pressures within the oceanic crust, the sheared serpentine layer may be a key factor driving LFEs in subduction zones.
Evolution of dike opening during the March 2011 Kamoamoa fissure eruption, Kīlauea Volcano, Hawai`i
Authors: Lundgren Paul , Poland Michael , Miklius Asta , Orr Tim , Yun Sang‐Ho , Fielding Eric , Liu Zhen , Tanaka Akiko , Szeliga Walter , Hensley Scott , Owen Susan 
Published: April 2013

AbstractThe 5–9 March 2011 Kamoamoa fissure eruption along the east rift zone of Kīlauea Volcano, Hawai`i, followed months of pronounced inflation at Kīlauea summit. We examine dike opening during and after the eruption using a comprehensive interferometric synthetic aperture radar (InSAR) data set in combination with continuous GPS data. We solve for distributed dike displacements using a whole Kīlauea model with dilating rift zones and possibly a deep décollement. Modeled surface dike opening increased from nearly 1.5 m to over 2.8 m from the first day to the end of the eruption, in agreement with field observations of surface fracturing. Surface dike opening ceased following the eruption, but subsurface opening in the dike continued into May 2011. Dike volumes increased from 15, to 16, to 21 million cubic meters (MCM) after the first day, eruption end, and 2 months following, respectively. Dike shape is distinctive, with a main limb plunging from the surface to 2–3 km depth in the up‐rift direction toward Kīlauea's summit, and a lesser projection extending in the down‐rift direction toward Pu`u `Ō`ō at 2 km depth. Volume losses beneath Kīlauea summit (1.7 MCM) and Pu`u `Ō`ō (5.6 MCM) crater, relative to dike plus erupted volume (18.3 MCM), yield a dike to source volume ratio of 2.5 that is in the range expected for compressible magma without requiring additional sources. Inflation of Kīlauea's summit in the months before the March 2011 eruption suggests that the Kamoamoa eruption resulted from overpressure of the volcano's magmatic system.
On robust and reliable automated baseline corrections for strong motion seismology
Authors: Melgar Diego , Bock Yehuda , Sanchez Dominga , Crowell Brendan W. 
Published: April 2013

AbstractComputation of displacements from strong motion inertial sensors is to date an open problem. Two distinct methodologies have been proposed to solve it. One involves baseline corrections determined from the inertial data themselves and the other a combination with other geophysical sensors such as GPS. Here we analyze a proposed automated baseline correction algorithm using only accelerometer data and compare it to the results from the real‐time combination of strong motion and GPS data. The analysis is performed on 48 collocated GPS and accelerometers in Japan that recorded the 2011 Mw 9.0 Tohoku‐oki earthquake. We study the time and frequency domain behavior of both methodologies. We find that the error incurred from automated baseline corrections that rely on seismic data alone is complex and can be large in both the time and frequency domains of interest in seismological and engineering applications. The GPS/accelerometer combination has no such problems and can adequately recover broadband strong motion displacements for this event. The problems and ambiguities with baseline corrections and the success of the GPS/accelerometer combination lead us to advocate for instrument collocations as opposed to automated baseline correction algorithms for accelerometers.
Observing Iceland's Eyjafjallajökull 2010 eruptions with the autonomous NASA Volcano Sensor Web
Authors: Davies Ashley Gerard , Chien Steve , Doubleday Joshua , Tran Daniel , Thordarson Thorvaldur , Gudmundsson Magnús T. , Höskuldsson Ármann , Jakobsdóttir Steinunn S. , Wright Robert , Mandl Daniel 
Published: April 2013

AbstractBetween 24 March and 5 June 2010, the Hyperion hyperspectral imager and Advanced Land Imager (ALI) on NASA's Earth Observing 1 (EO‐1) spacecraft obtained an unprecedented sequence of 50 observation pairs of the eruptions at Fimmvörðuháls and Eyjafjallajökull, Iceland. This high acquisition rate was possible only through the use of data flow streamlined by using the autonomously operating NASA Volcano Sensor Web (VSW). The VSW incorporates notifications of volcanic activity from multiple sources to retask EO‐1 and process Hyperion data to extract eruption parameters from high spatial and spectral resolution visible and short‐wavelength infrared data. Physical changes in eruption style and magnitude were charted as the eruptions ran their course. Rapid data downlink and automatic data‐processing algorithms generated a variety of products which are compared with estimates from ground‐based observations and post‐eruption in situ measurements. Estimates of effusion rate from heat loss measurements underestimate actual effusion rate (while still following broad eruption rate trends) but are closer to in situ estimates for effusive eruptions (Fimmvörðuháls) than explosive, ash‐rich eruptions (Eyjafjallajökull). During the later stages of the 2010 eruption, VSW‐generated products were rapidly delivered to end‐users in Iceland to aid in the assessment of risk and hazard. The success of the VSW led to Icelandic Meteorological Office (IMO) in situ sensors being incorporated into the VSW, and in May 2011 an IMO seismic alert autonomously triggered EO‐1 observations of a new eruption at Grímsvötn volcano. Finally, the VSW demonstrates an autonomy‐driven, multi‐asset, spacecraft retasking and data processing system that maximizes science return, a desirable capability for future NASA missions.
Evaluation of Wasatch fault segmentation and slip rates using Lake Bonneville shorelines
Authors: Jewell Paul W. , Bruhn Ronald L. 
Published: April 2013

ABSTRACTAnalysis of Lake Bonneville shorelines using lidar digital elevation data challenges accepted models of Wasatch fault deformation since the late Pleistocene. While footwall deformation of the Weber segment of the Wasatch fault is consistent with back‐rotation of the footwall block and greatest displacement rate toward the center of the segment, shorelines along the footwall of the Salt Lake City segment decrease in elevation toward the interior and are highest at the segment boundaries, an opposite pattern of footwall deformation than predicted for boundaries arresting or strongly inhibiting displacement during earthquakes. The spatial pattern of footwall rebound implies that some of the proposed persistent fault segment boundaries do not stop earthquake ruptures that originate on adjacent fault segments, nor constrain ruptures initiated within the Salt Lake City segment. Net vertical fault displacement at the boundary between the Salt Lake and Provo segments is 16–20 m over the past 16.3–18.5 ka, corresponding to a vertical displacement rate of 0.8–1.2 mm/yr, a net fault slip rate of 2.0–2.8 mm/yr, and horizontal extension rate of 1.8–2.6 mm/yr on the 25° west‐southwest dipping fault that forms the southern Salt Lake City segment boundary. Shoreline analysis suggests isostatic rebound caused by a drop in lake level was concentrated during a relatively short (~2000 year) time period following the Bonneville flood at ~16 ka. Lidar‐derived topography in conjunction with robust geomorphic datums improves our ability to map deformation associated with lithospheric flexure and faulting while demonstrating the limitation of lacustrine shorelines in this type of analysis.
Intraseasonal Kelvin wave in Makassar Strait
Authors: Pujiana K. , Gordon A. L. , Sprintall J. 
Published: April 2013

AbstractTime series observations during 2004–2006 reveal the presence of 60–90 days intraseasonal events that impact the transport and mixing environment within Makassar Strait. The observed velocity and temperature fluctuations within the pycnocline reveal the presence of Kelvin waves including vertical energy propagation, energy equipartition, and nondispersive relationship. Two current meters at 750 and 1500 m provide further evidence that the vertical structure of the downwelling Kelvin wave resembles that of the second baroclinic wave mode. The Kelvin waves derive their energy from the equatorial Indian Ocean winds, including those associated with the Madden‐Julian oscillations, and propagate from Lombok Strait to Makassar Strait along the 100‐m isobath. The northward propagating Kelvin waves within the pycnocline reduce the southward Makassar Strait throughflow by up to 2 Sv and induce a marked increase of vertical diffusivity.
Sea level and heat content changes in the western North Pacific
Authors: Moon Jae‐Hong , Tony Song Y. 
Published: April 2013

AbstractAltimetry‐observed sea level rise (SLR) over the western North Pacific (WNP), including the South China Sea, Yellow Sea, East China Sea, and East/Japan Sea, has a rate of ~5 mm/year over 1993–2010, which is about 1.5 times the rate of the global mean. Here we have examined sea level changes and related ocean heat content (OHC) in the WNP by comparing results from a non‐Boussinesq ocean general circulation model (mass‐conserved) with data sets from altimeters, the Gravity Recovery and Climate Experiment (GRACE), and in situ profiles. Our model reproduces the altimetry regional trends as well as their seasonal/interannual variations. Adding a GRACE‐estimated mass to the model result further explains the altimetry SLR in a way that mass‐induced effect contributes more in the midlatitudes than in the tropical WNP over the GRACE period. In addition, interannual variability and linear trend of regional sea levels are explained mainly by changes in the OHC due to heat convergence and divergence by ocean circulations, while seasonal variability is caused mainly by surface air‐sea fluxes. To understand the underline physics, a comparative experiment was carried out, showing that the recent strengthening trends of SLR and OHC in the tropical regions are significantly attributed to the heat and water mass redistribution in the upper ocean caused by the intensified easterly trade wind over the past two decades.
Water column iron dynamics in the subarctic North Pacific Ocean and the Bering Sea
Authors: Uchida Ren , Kuma Kenshi , Omata Aya , Ishikawa Satoko , Hioki Nanako , Ueno Hiromichi , Isoda Yutaka , Sakaoka Keiichiro , Kamei Yoshihiko , Takagi Shohgo 
Published: April 2013

AbstractWe measured water‐column iron concentrations from west to east along 47°N in the subarctic North Pacific, and in the Bering Sea. In the North Pacific dissolved Fe (D‐Fe) showed surface depletion, mid‐depth maxima at 1000–1500 m (west, 1.3–1.6 nM; east, 0.9–1.1 nM), and a gradual decrease with depth below 3500–4000 m depth (west, 1.1–1.4 nM; east, 0.6–0.7 nM). D‐Fe and total soluble Fe (T‐Fe) in deep water showed a decreasing trend eastward. The higher iron concentrations in western deep waters probably result from higher inputs of dissolved Fe through atmospheric deposition or lateral transport. In contrast, D‐Fe throughout the Bering Sea showed a consistent depth regime characterized by a rapid increase with depth to mid‐depths, a gradual increase with depth in intermediate water to a maximum of 1.6–1.7 nM at 1500–2250 m, and a gradual decrease with depth to 1.3–1.4 nM at 3700 m. Higher iron concentrations and deeper D‐Fe maxima in the Bering Sea are likely due to higher biological productivity and greater and deeper D‐Fe input from the decomposition of sinking particulate organic matter in deep water. We suggest that the higher concentrations and deeper input of D‐Fe as well as PO4 and humic‐type fluorescent dissolved organic matter in the Bering Sea probably results from the longer time for the accumulation of decomposition products resulting from iron supply from the organic‐rich downslope sediment along the steep continental slopes and slow replacement of the deep water in the Bering Sea Basin.