bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simultaneous ground‐based optical and HF radar observations of the ionospheric footprint of the open/closed field line boundary along the geomagnetic meridian
Authors: Chen X.‐C. , Lorentzen D. A. , Moen J. I. , Oksavik K. , Baddeley L. J. 
Published: November 2015

AbstractPrevious studies have confirmed that the equatorward boundaries of OI 630.0 nm auroral emissions and broad Doppler spectral widths in Super Dual Auroral Radar Network (SuperDARN) data, the so‐called spectral width boundary (SWB), are good empirical proxies for the dayside open/closed field line boundary (OCB) in the ionosphere. However, both observational techniques are associated with mapping errors. SuperDARN uses a virtual height model for mapping, but it is not well known how the mapping error responds to a changing background ionosphere or transient reconnection events. Optical instruments, such as the meridian‐scanning photometers, have high spatial resolution near zenith, where the mapping error due to the assumed OI 630.0 nm auroral emission height becomes small by comparison. In this work, an adjusted method is introduced to identify the SWB, which does not require temporal smoothing across several scans. The difference in latitude between the SWB, as identified using this method, and the simultaneously observed OI 630.0 nm auroral emission boundary along a common line of sight is compared. Utilizing the OI 630.0 nm boundary as a reference location, we present two case studies observed at different levels of solar activity. In both instances the latitude offset of SWB from the reference location is discussed in relation to the background ionospheric electron density. The compared results indicate that the intake of high‐density solar extreme ultraviolet ionized plasma from subauroral latitudes causes a refraction of the HF radar beam path, which results in an overestimation of range mapping. The adjusted method would thus be a useful tool for identifying the OCB under changing ionospheric conditions in the cusp region.
Low‐latitude ionosphere response to super geomagnetic storm of 17/18 March 2015: Results from a chain of ground‐based observations over Indian sector
Authors:   Ramsingh, Sripathi S. , Sreekumar Sreeba , Banola S. , Emperumal K. , Tiwari P. , Kumar Burudu Suneel 
Published: November 2015

AbstractIn this paper, we present unique results of equatorial and low‐latitude ionosphere response to one of the major geomagnetic storms of the current solar cycle that occurred during 17–18 March 2015, where Dst reached its minimum of −228 nT. Here we utilized data from magnetometers, chain of ionosondes located at Tirunelveli (8.73°N, 77.70°E; geometry: 0.32°N), Hyderabad (17.36°N, 78.47°E; geometry 8.76°N), and Allahabad (25.45°N, 81.85°E; geometry 16.5°N) along with multistation GPS receivers over Indian sector. The observations showed a remarkable increase of h′F to as high as ~560 km over Tirunelveli (magnetic equator) with vertical drift of ~70 m/s at 13:30 UT due to direct penetration of storm time eastward electric fields which exactly coincided with the local time of pre‐reversal enhancement (PRE) and caused intense equatorial spread F irregularities in ionosondes and scintillations in GPS receivers at wide latitudes. Plasma irregularities are so intense that their signatures are seen in Allahabad/Lucknow. Storm time thermospheric meridional winds as estimated using two ionosondes suggest the equatorward surge of gravity waves with period of ~2 h. Suppression of anomaly crest on the subsequent day of the storm suggests the complex role of disturbance dynamo electric fields and disturbance wind effects. Our results also show an interesting feature of traveling ionospheric disturbances possibly associated with disturbance meridional wind surge during recovery phase. In addition, noteworthy observations are nighttime westward zonal drifts and PRE‐related total electron content enhancements at anomaly crests during main phase and counter electrojet signatures during recovery phase.
Sustained lobe reconnection in Saturn's magnetotail
Authors: Thomsen M. F. , Jackman C. M. , Mitchell D. G. , Hospodarsky G. , Kurth W. S. , Hansen K. C. 
Published: November 2015

AbstractThe degree to which solar wind driving may affect Saturn's magnetosphere is not yet fully understood. We present observations that suggest that under some conditions the solar wind does govern the character of the plasma sheet in Saturn's outer magnetosphere. On 16 September 2006, the Cassini spacecraft, at a radial distance of 37 Rs near local midnight, observed a sunward flowing ion population for ~5 h, which was accompanied by enhanced Saturn Kilometric Radiation emissions. We interpret this beam as the outflow from a long‐lasting episode of Dungey‐type reconnection, i.e., reconnection of previously open flux containing magnetosheath material. The beam occurred in the middle of a several‐day interval of SKR activity and enhanced lobe magnetic field strength, apparently caused by the arrival of a solar wind compression region with significantly higher than average dynamic pressure. The arrival of the high‐pressure solar wind also marked a change in the composition of the plasma‐sheet plasma, from water‐group‐dominated material clearly of inner‐magnetosphere origin to material dominated by light‐ion composition, consistent with captured magnetosheath plasma. This event suggests that under the influence of prolonged high solar wind dynamic pressure, the tail plasma sheet, which normally consists of inner‐magnetospheric plasma, is eroded away by ongoing reconnection that then involves open lobe field lines. This process removes open magnetic flux from the lobes and creates a more Earth‐like, Dungey‐style outer plasma sheet dominantly of solar wind origin. This behavior is potentially a recurrent phenomenon driven by repeating high‐pressure streams (corotating interaction regions) in the solar wind, which also drive geomagnetic storms at Earth.
Effects of Earth's rotation on the early differentiation of a terrestrial magma ocean
Authors: Maas Christian , Hansen Ulrich 
Published: November 2015

AbstractSimilar to other terrestrial planets like Moon and Mars, Earth experienced a magma ocean period about 4.5 billion years ago. On Earth differentiation processes in the magma ocean set the initial conditions for core formation and mantle evolution. During the magma ocean period Earth was rotating significantly faster than today. Further, the viscosity of the magma was low, thus that planetary rotation potentially played an important role for differentiation. However, nearly all previous studies neglect rotational effects. All in all, our results suggest that planetary rotation plays an important role for magma ocean crystallization. We employ a 3‐D numerical model to study crystal settling in a rotating and vigorously convecting early magma ocean. We show that crystal settling in a terrestrial magma ocean is crucially affected by latitude as well as by rotational strength and crystal density. Due to rotation an inhomogeneous accumulation of crystals during magma ocean solidification with a distinct crystal settling between pole and equator could occur. One could speculate that this may have potentially strong effects on the magma ocean solidification time and the early mantle composition. It could support the development of a basal magma ocean and the formation of anomalies at the core‐mantle boundary in the equatorial region, reaching back to the time of magma ocean solidification.
Near‐inertial ocean response to tropical cyclone forcing on the Australian North‐West Shelf
Authors: Rayson M. D. , Ivey G. N. , Jones N. L. , Lowe R. J. , Wake G. W. , McConochie J. D. 
Published: November 2015

AbstractThe Regional Ocean Modeling System (ROMS) was applied to the Australian North‐West Shelf (NWS) to hindcast the ocean response to four intense historical tropical cyclones (TCs). While the four cyclones had very different trajectories across the NWS, all passed within 150 km of a long‐term vertical mooring located on the continental shelf in 125 m depth. The observed ocean response at this relatively shallow, Southern Hemisphere shelf site was characterized by the development of a peak in the counter‐clockwise (CCW) near‐inertial kinetic energy, mixed layer deepening, and subsequent restratification. Strong near‐inertial isotherm oscillations were also observed following two of the cyclones. ROMS reproduced these features and also showed that the peak in the near‐inertial CCW kinetic energy was observed on the left side of each cyclone trajectory. The time rate of change of near‐inertial kinetic energy depended strongly on the storm Rossby number, i.e., defined based on the storm speed, the storm length scale, and the Coriolis frequency. The shallow water depth on the NWS resulted in first, a more rapid decay of near‐inertial oscillations than in the deep ocean, and second a generation efficiency (the ratio of near‐inertial power to the rate of wind work) of up to 10%, smaller than found for cyclones propagating across deeper water. The total energy put into near‐inertial motions is nevertheless large compared to the background tidal energy. The rapid decay of near‐inertial motions emphasizes the importance of frictional effects in characterizing the response to cyclone forcing in shallow seas.
DopSCAT: A mission concept for simultaneous measurements of marine winds and surface currents
Authors: Fois Franco , Hoogeboom Peter , Le Chevalier François , Stoffelen Ad , Mouche Alexis 
Published: November 2015

AbstractA radar scatterometer operates by transmitting a pulse of microwave energy toward the ocean's surface and measuring the normalized (per‐unit‐surface) radar backscatter coefficient (σ°). The primary application of scatterometry is the measurement of near‐surface ocean winds. By combining σ° measurements from different azimuth angles, the 10 m vector wind can be determined through a Geophysical Model Function (GMF), which relates wind and backscatter. This paper proposes a mission concept for the measurement of both oceanic winds and surface currents, which makes full use of earlier C‐band radar remote sensing experience. For the determination of ocean currents, in particular, the novel idea of using two chirps of opposite slope is introduced. The fundamental processing steps required to retrieve surface currents are given together with their associated accuracies. A detailed description of the mission proposal and comparisons between real and retrieved surface currents are presented. The proposed ocean Doppler scatterometer can be used to generate global surface ocean current maps with accuracies better than 0.2 m/s at a spatial resolution better than 25 km (i.e., 12.5 km spatial sampling) on a daily basis. These maps will allow gaining some insights on the upper ocean mesoscale dynamics. The work lies at a frontier, given that the present inability to measure ocean currents from space in a consistent and synoptic manner represents one of the greatest weaknesses in ocean remote sensing.
Enhanced sulfate formation by nitrogen dioxide: Implications from in situ observations at the SORPES station
Authors: Xie Yuning , Ding Aijun , Nie Wei , Mao Huiting , Qi Ximeng , Huang Xin , Xu Zheng , Kerminen Veli‐Matti , Petäjä Tuukka , Chi Xuguang , Virkkula Aki , Boy Michael , Xue Likun , Guo Jia , Sun Jianning , Yang Xiuqun , Kulmala Markku , Fu Congbin 
Published: November 2015

AbstractInvestigating sulfate formation processes is important not only for air pollution control but also for understanding the climate system. Although the mechanisms of secondary sulfate production have been widely studied, in situ observational evidence implicating an important role of NO2 in SO2 oxidation in the real atmosphere has been rare. In this study, we report two unique cases, from an intensive campaign conducted at the Station for Observing Regional Processes of the Earth System (SORPES) in East China, showing distinctly different mechanisms of sulfate formation by NO2 and related nitrogen chemistry. The first case occurred in an episode of mineral dust mixed with anthropogenic pollutants and especially high concentrations of NOx. It reveals that NO2 played an important role, not only in surface catalytic reactions of SO2 but also in dust‐induced photochemical heterogeneous reactions of NO2, which produced additional sources of OH radicals to promote new particle formation and growth. The second case was caused by aqueous oxidation of S(IV) by NO2 under foggy/cloudy conditions with high NH3 concentration. As a by‐product, the formed nitrite enhanced HONO formation and further promoted the gas‐phase formation of sulfate in the downwind area. This study highlights the effect of NOx in enhancing the atmospheric oxidizing capacity and indicates a potentially very important impact of increasing NOx on particulate pollution formation and regional climate change in East Asia.
On the evolution of a long‐lived mesoscale vortex over the Yangtze River Basin: Geometric features and interactions among systems of different scales
Authors: Fu Shen‐Ming , Li Wan‐Li , Ling Jian 
Published: November 2015

AbstractA long‐lived mesoscale vortex that caused extremely heavy rainfall events over the Yangtze River Basin was reproduced reasonably by the advanced Weather Research and Forecasting model. Using simulations, the three‐dimensional geometric features of the vortex, as well as the interactions between the vortex and its background circulations (BCs), were investigated. Results indicated that the geometry features of the vortex were closely related to vortex evolution, vortex‐related convection processes and precipitation, and vortex‐BC interactions. Growth in the horizontal size of the vortex favored its sustainment. The vortex tended to produce stronger convection processes and precipitation as its orientation became closer to the west‐east direction. The circulation budget revealed that the convergence‐related shrinking, the BC transport, and the effects caused by vortex movement were the dominant factors for vortex development. Divergence‐related stretching dominated vortex dissipation, and the transport effects associated with the BC and the eddy flows also accelerated this attenuation. The energy budget indicated that the vortex intensely interacted with its BCs during its lifetime. The BCs affected the vortex through downscaled energy cascade and mean transport; the eddy flow reacted to its BCs via upscaled energy cascade and eddy transport. Generally, the vortex had more dynamic than thermodynamic interactions with its BCs. BC effects were vital to the vortex evolution, whereas the variation in the BCs was predominantly determined by their own effects, although the reaction of the vortex‐related eddy flow cannot be ignored in the variation of the BC dynamical fields.
Meter‐scale spark X‐ray spectrum statistics
Authors: Carlson B. E. , Østgaard N. , Kochkin P. , Grondahl Ø. , Nisi R. , Weber K. , Scherrer Z. , LeCaptain K. 
Published: November 2015

AbstractX‐ray emission by sparks implies bremsstrahlung from a population of energetic electrons, but the details of this process remain a mystery. We present detailed statistical analysis of X‐ray spectra detected by multiple detectors during sparks produced by 1 MV negative high‐voltage pulses with 1 μs risetime. With over 900 shots, we statistically analyze the signals, assuming that the distribution of spark X‐ray fluence behaves as a power law and that the energy spectrum of X‐rays detectable after traversing ∼2 m of air and a thin aluminum shield is exponential. We then determine the parameters of those distributions by fitting cumulative distribution functions to the observations. The fit results match the observations very well if the mean of the exponential X‐ray energy distribution is 86 ± 7 keV and the spark X‐ray fluence power law distribution has index −1.29 ± 0.04 and spans at least 3 orders of magnitude in fluence.
Chemical apportionment of aerosol optical properties during the Asia‐Pacific Economic Cooperation summit in Beijing, China
Authors: Han Tingting , Xu Weiqi , Chen Chen , Liu Xingang , Wang Qingqing , Li Jie , Zhao Xiujuan , Du Wei , Wang Zifa , Sun Yele 
Published: November 2015

AbstractWe have investigated the chemical and optical properties of aerosol particles during the 2014 Asia‐Pacific Economic Cooperation (APEC) summit in Beijing, China, using the highly time‐resolved measurements by a high‐resolution aerosol mass spectrometer and a cavity attenuated phase shift extinction monitor. The average (±σ) extinction coefficient (bext) and absorption coefficient (bap) were 186.5 (±184.5) M m−1 and 23.3 (±21.9) M m−1 during APEC, which were decreased by 63% and 56%, respectively, compared to those before APEC primarily due to strict emission controls. The aerosol composition and size distributions showed substantial changes during APEC; as a response, the mass scattering efficiency (MSE) of PM1 was decreased from 4.7 m2 g−1 to 3.5 m2 g−1. Comparatively, the average single‐scattering albedo (SSA) remained relatively unchanged, illustrating the synchronous reductions of bext and bap during APEC. MSE and SSA were found to increase as function of the oxidation degree of organic aerosol (OA), indicating a change of aerosol optical properties during the aging processes. The empirical relationships between chemical composition and particle extinction were established using a multiple linear regression model. Our results showed the largest contribution of ammonium nitrate to particle extinction, accounting for 35.1% and 29.3% before and during APEC, respectively. This result highlights the important role of ammonium nitrate in the formation of severe haze pollution during this study period. We also observed very different optical properties of primary and secondary aerosol. Owing to emission controls in Beijing and surrounding regions and also partly the influences of meteorological changes, the average bext of secondary aerosol during APEC was decreased by 71% from 372.3 M m−1 to 108.5 M m−1, whereas that of primary aerosol mainly from cooking, traffic, and biomass burning emissions showed a smaller reduction from 136.7 M m−1 to 71.3 M m−1. As a result, the contribution of primary aerosol to particle extinction increased from 26.8% to 39.6%, elucidating an enhanced role of local primary sources in visibility deterioration during APEC. Further analysis of chemically resolved particle extinction showed that the extinction contributions of aerosol species varied greatly between different air masses but generally with ammonium nitrate, ammonium sulfate, and secondary OA being the three major contributors.
Numerical modeling of the ejecta distribution and formation of the Orientale basin on the Moon
Authors: Zhu Meng‐Hua , Wünnemann Kai , Potter Ross W. K. 
Published: November 2015

AbstractThe formation and structure of the Orientale basin on the Moon has been extensively studied in the past; however, estimates of its transient crater size, excavated volume and depth, and ejecta distribution remain uncertain. Here we present a new numerical model to reinvestigate the formation and structure of Orientale basin and better constrain impact parameters such as impactor size and velocity. Unlike previous models, the observed ejecta distribution and ejecta thickness were used as the primary constraints to estimate transient crater size—the best measure of impact energy. Models were also compared to basin morphology and morphometry, and subsurface structures derived from high‐resolution remote sensing observations and gravity data, respectively. The best fit model suggests a 100 km diameter impactor with a velocity of ~12 km s−1 formed the Orientale basin on a relatively “cold” Moon. In this impact scenario the transient crater diameter is ~400 km or 460 km depending on whether the crater is defined using the diameter of the excavation zone or the diameter of the growing cavity at the time of maximum crater volume, respectively. The volume of ejecta material is ~4.70 × 106 km3, in agreement with recent estimates of the Orientale ejecta blanket thickness from remote sensing studies. The model also confirms the remote sensing spectroscopic observations that no mantle material was excavated and deposited at Orientale's rim.
Geomorphic signal of active faulting at the northern edge of Lut Block: Insights on the kinematic scenario of Central Iran
Authors: Calzolari Gabriele , Della Seta Marta , Rossetti Federico , Nozaem Reza , Vignaroli Gianluca , Cosentino Domenico , Faccenna Claudio 
Published: November 2015

AbstractRecent works documented Neogene to Quaternary dextral strike‐slip tectonics along the Kuh‐e‐Sarhangi and Kuh‐e‐Faghan intraplate strike‐slip faults at the northern edge of the Lut Block of Central Iran, previously thought to be dominated by sinistral strike‐slip deformation. This work focuses on the evidence of Quaternary activity of one of these fault systems, in order to provide new spatiotemporal constraints on their role in the active regional kinematic scenario. Through geomorphological and structural investigation, integrated with optically stimulated luminescence dating of three generations of alluvial fans and fluvial terraces (at ~53, ~25, and ~6 ka), this study documents (i) the topographic inheritance of the long‐term (Myr) punctuated history of fault nucleation, propagation, and exhumation along the northern edge of Lut Block; (ii) the tectonic control on drainage network evolution, pediment formation, fluvial terraces, and alluvial fan architecture; (iii) the minimum Holocene age of Quaternary dextral strike‐slip faulting; and (iv) the evidence of Late Quaternary fault‐related uplift localized along the different fault strands. The documented spatial and temporal constraints on the active dextral strike‐slip tectonics at the northern edge of Lut Block provide new insights on the kinematic model for active faulting in Central Iran, which has been reinterpreted in an escape tectonic scenario.
Changes in paleostress and its magnitude related to seismic cycles in the Chelung‐pu Fault, Taiwan
Authors: Hashimoto Yoshitaka , Tobe Kota , Yeh En‐Chao , Lin Weiren , Song Sheng‐Rong 
Published: November 2015

AbstractPaleostress analysis was conducted through a multiple stress inversion method using slip data recoded for the core samples from the Taiwan Chelung‐pu Fault Drilling Project (TCDP). Two stress fields were obtained; one of these had horizontally plunging σ1, and the other has horizontally plunging σ2 or σ3 in the compressional stress direction of the Chi‐Chi earthquake. Stress magnitude for both the stress fields was constrained by stress polygons, which indicated larger SHmax for horizontally plunging σ1 than that in the case of horizontally plunging σ2 or σ3. These differences in stress orientations and stress magnitude suggest that the change in stress filed can be caused by stress drop and stress buildup associated with seismic cycles. The seismic cycles recoded in the core samples from TCDP could include many events at geological timescale and not only the 1999 Chi‐Chi earthquake.