bluuebunny/crossref_metadata_2025_split huggingface dataset:
Toward full exploitation of coherent and incoherent information in Sentinel‐1 TOPS data for retrieving surface displacement: Application to the 2016 Kumamoto (Japan) earthquake
Authors: Jiang Houjun , Feng Guangcai , Wang Teng , Bürgmann Roland 
Published: February 2017

AbstractSentinel‐1's continuous observation program over all major plate boundary regions makes it well suited for earthquake studies. However, decorrelation due to large displacement gradients and limited azimuth resolution of the Terrain Observation by Progressive Scan (TOPS) data challenge acquiring measurements in the near field of many earthquake ruptures and prevent measurements of displacements in the along‐track direction. Here we propose to fully exploit the coherent and incoherent information of TOPS data by using standard interferometric synthetic aperture radar (InSAR), split‐bandwidth interferometry in range and azimuth, swath/burst‐overlap interferometry, and amplitude cross correlation to map displacements in both the line‐of‐sight and the along‐track directions. Application to the 2016 Kumamoto earthquake sequence reveals the coseismic displacements from the far field to the near field. By adding near‐field constraints, the derived slip model reveals more shallow slip than obtained when only using far‐field data from InSAR, highlighting the importance of exploiting all coherent and incoherent information in TOPS data.
Temperature‐ and pressure‐dependent structural transformation of methane hydrates in salt environments
Authors: Shin Donghoon , Cha Minjun , Yang Youjeong , Choi Seunghyun , Woo Yesol , Lee Jong‐Won , Ahn Docheon , Im Junhyuck , Lee Yongjae , Han Oc Hee , Yoon Ji‐Ho 
Published: February 2017

AbstractUnderstanding the stability of volatile species and their compounds under various surface and subsurface conditions is of great importance in gaining insights into the formation and evolution of planetary and satellite bodies. We report the experimental results of the temperature‐ and pressure‐dependent structural transformation of methane hydrates in salt environments using in situ synchrotron X‐ray powder diffraction, solid‐state nuclear magnetic resonance, and Raman spectroscopy. We find that under pressurized and concentrated brine solutions methane hydrate forms a mixture of type I clathrate hydrate, ice, and hydrated salts. Under a low‐pressure condition, however, the methane hydrates are decomposed through a rapid sublimation of water molecules from the surface of hydrate crystals, while NaCl · 2H2O undergoes a phase transition into a crystal growth of NaCl via the migration of salt ions. In ambient pressure conditions, the methane hydrate is fully decomposed in brine solutions at temperatures above 252 K, the eutectic point of NaCl · 2H2O.
Combined effects of iron and copper from atmospheric dry deposition on ocean productivity
Authors: Wang F. J. , Chen Y. , Guo Z. G. , Gao H. W. , Mackey K. R. , Yao X. H. , Zhuang G. S. , Paytan A. 
Published: February 2017

AbstractAtmospheric deposition can provide nutrients and potential toxicants to marine ecosystem, hence affecting ocean net primary productivity (NPP). Nonetheless, the interactive effects of mixed aerosol components on phytoplankton have rarely been reported. Here we explored the combined effects of iron (Fe) and copper (Cu) on NPP over the East China Sea. In aerosol addition mesocosm experiments, phytoplankton growth was suppressed under high aerosol Cu but was increased when high Cu was accompanied by high Fe in aerosols. A time series of soluble aerosol Fe and Cu deposition was obtained and compared to regional chlorophyll a (Chl a) abundances from Moderate Resolution Imaging Spectroradiometer/Aqua. Strong positive correlations were observed between the dry flux ratios of soluble Fe/Cu and Chl a abundances in the large offshore area, whereas these variables were uncoupled in coastal regions where riverine input and upwelling dominated the biogeochemistry. Current work provides insight into the complex linkage between atmospheric deposition and marine productivity.
Large‐scale energy budget of impulsive magnetic reconnection: Theory and simulation
Authors: Kiehas S. A. , Volkonskaya N. N. , Semenov V. S. , Erkaev N. V. , Kubyshkin I. V. , Zaitsev I. V. 
Published: February 2017

AbstractWe evaluate the large‐scale energy budget of magnetic reconnection utilizing an analytical time‐dependent impulsive reconnection model and a numerical 2‐D MHD simulation. With the generalization to compressible plasma, we can investigate changes in the thermal, kinetic, and magnetic energies. We study these changes in three different regions: (a) the region defined by the outflowing plasma (outflow region, OR), (b) the region of compressed magnetic fields above/below the OR (traveling compression region, TCR), and (c) the region trailing the OR and TCR (wake). For incompressible plasma, we find that the decrease inside the OR is compensated by the increase in kinetic energy. However, for the general compressible case, the decrease in magnetic energy inside the OR is not sufficient to explain the increase in thermal and kinetic energy. Hence, energy from other regions needs to be considered. We find that the decrease in thermal and magnetic energy in the wake, together with the decrease in magnetic energy inside the OR, is sufficient to feed the increase in kinetic and thermal energies in the OR and the increase in magnetic and thermal energies inside the TCR. That way, the energy budget is balanced, but consequently, not all magnetic energy is converted into kinetic and thermal energies of the OR. Instead, a certain fraction gets transfered into the TCR. As an upper limit of the efficiency of reconnection (magnetic energy
kinetic energy) we find ηeff=1/2. A numerical simulation is used to include a finite thickness of the current sheet, which shows the importance of the pressure gradient inside the OR for the conversion of kinetic energy into thermal energy.
On the origin of the crescent‐shaped distributions observed by MMS at the magnetopause
Authors: Lapenta G. , Berchem J. , Zhou M. , Walker R. J. , El‐Alaoui M. , Goldstein M. L. , Paterson W. R. , Giles B. L. , Pollock C. J. , Russell C. T. , Strangeway R. J. , Ergun R. E. , Khotyaintsev Y. V. , Torbert R. B. , Burch J. L. 
Published: February 2017

AbstractMMS observations recently confirmed that crescent‐shaped electron velocity distributions in the plane perpendicular to the magnetic field occur in the electron diffusion region near reconnection sites at Earth's magnetopause. In this paper, we reexamine the origin of the crescent‐shaped distributions in the light of our new finding that ions and electrons are drifting in opposite directions when displayed in magnetopause boundary‐normal coordinates. Therefore, E × B drifts cannot cause the crescent shapes. We performed a high‐resolution multiscale simulation capturing subelectron skin‐depth scales. The results suggest that the crescent‐shaped distributions are caused by meandering orbits without necessarily requiring any additional processes found at the magnetopause such as the highly asymmetric magnetopause ambipolar electric field. We use an adiabatic Hamiltonian model of particle motion to confirm that conservation of canonical momentum in the presence of magnetic field gradients causes the formation of crescent shapes without invoking asymmetries or the presence of an E × B drift. An important consequence of this finding is that we expect crescent‐shaped distributions also to be observed in the magnetotail, a prediction that MMS will soon be able to test.
High‐latitude Pi2 pulsations associated with kink‐like neutral sheet oscillations
Authors: Wang G. Q. , Volwerk M. , Zhang T. L. , Schmid D. , Yoshikawa A. 
Published: February 2017

AbstractA kink‐like neutral sheet oscillation event observed by Cluster between 1436 and 1445 UT on 15 October 2004 has been investigated. The oscillations with periods between 40 and 60 s, observed at (−13.1, 8.7, −0.5) RE, are dominant in BX and BY. And they propagate mainly duskward with a velocity of (86, 147, 46) km/s. Their periods and velocity can be explained by the magnetic double‐gradient instability. These oscillations are accompanied by strong field‐aligned currents (FACs), which prefer to occur near the strongly tilted current sheet, and local maximum FAC tends to occur near the neutral sheet. The FACs show one‐to‐one correlated with a high‐latitude Pi2 pulsation event recorded by KTN and TIK stations with a delay time of ~60 and 90 s, respectively. Both the Pi2 and oscillations propagate westward with a comparative conjunctive speed. These findings suggest a strong relation between the FACs and Pi2, and we infer that the Pi2 is caused by the FACs. The periods of the FACs are modulated by the oscillations but not exactly equal, which is one possible reason that the period of the Pi2 caused by the FACs could be different from the oscillations. We speculate that a current circuit between the plasma sheet and ionosphere can be formed during strongly tilted current sheet, and successive tilted current sheet could generate quasiperiodic multiple FAC systems, which can generate high‐latitude Pi2 pulsations and control their periods.
MAVEN and the total electron content of the Martian ionosphere
Authors: Mendillo Michael , Narvaez Clara , Vogt Marissa F. , Mayyasi Majd , Mahaffy Paul , Benna Mehdi , Andersson Laila , Campbell Bruce , Němec Frantisek , Ma Ying Juan , Chaufray Jean‐Yves , Leblanc François , Gonzalez‐Galindo Francisco , Lopez‐Valverde Miguel Ángel , Forget François , Jakosky Bruce 
Published: February 2017

AbstractModel studies of the ionosphere of Mars under daytime conditions reveal that for solar zenith angles of 0°–40°, the shapes and magnitudes of the electron density profiles Ne(h) change by only small amounts. This suggests that midday observations made by MAVEN instruments along slanted orbit segments can be used to represent vertical profiles. The total electron content (TEC), defined as the height integral of Ne(h), is a measure of the cold plasma reservoir of the Martian ionosphere. During MAVEN's Deep‐Dip‐#2 campaign of April 2015, observations of total ion density by Neutral Gas and Ion Mass Spectrometer and electron density by Langmuir Probe and Waves from periapse (~130 km) to 400 km were used to form <TEC>topside—validated by independent diagnostics and models. Orbit‐by‐orbit changes in topside TEC were then used to assess the magnitudes of plasma escape associated with both large and small changes in the topside slope of Ne(h)—called an “ionopause episode.” The TEC changes due to these episodes, generalized to a global change, resulted in an escape flux of ~3–6 × 1024 ions/s, an escape rate consistent with prior observation by Phobos‐2, Mars Express, and MAVEN's own in situ studies.
A study on the evolution of plasma bubbles using the single station‐multisatellite and multistation‐single satellite techniques
Authors: Unnikrishnan K. , Sreekumar H. , Choudhary R. K. , Ashna V. M. , Ambili K. M. , Shreedevi P. R. , Rao P. B. 
Published: February 2017

AbstractThe characteristics of plasma bubble‐induced ionospheric irregularities were analyzed by estimating the drift velocity of plasma bubbles, their percentage of occurrence, seasonal/LT distributions, and east‐west spatial width using multifrequency Global Navigation Satellite Systems (GNSS) receiver systems at Trivandrum, Bangalore, Hyderabad, Delhi, and Hanle. Two techniques, namely, single station‐multisatellite and multistation‐single satellite observations, were used in the analysis by tracking two geostationary Indian satellites GSAT‐8 (PRN 127) and GSAT‐10 (PRN 128) for the year 2014. In addition, GNSS receiver data from a recently commissioned near‐equatorial station at Changanacherry, Kerala, were used to evaluate 15 plasma bubble events during the period of 29 October 2015 to 31 October 2016. Using, single station‐multisatellite technique, the distribution of drift velocity measurements from plasma bubble scintillations lies in the range of 120–140 m/s for Trivandrum, Changanacherry, and Hyderabad. For Bangalore, and Delhi, the most probable ranges of drift velocity were 120–160 m/s and 80–100 m/s, respectively. The highest probable value of east‐west width of plasma bubble evolution for Trivandrum and Changanacherry was within the range of 100–150 km. However, the same at Bangalore and Hyderabad was in the range of 150–200 km and 100–200 km for Delhi. The maximum probable LT of occurrence of plasma bubble is premidnight sector over the equator. The comparison of the characteristics of plasma bubble evolution over equatorial/low‐latitude Indian sector considering six stations by employing two unique techniques and an objective correlation method is the first time attempt.
Low‐latitude daytime F region irregularities observed in two geomagnetically quiet days by the Hainan coherent scatter phased array radar (HCOPAR)
Authors: Chen Gang , Jin Han , Yan Jingye , Zhang Shaodong , Li Guozhu , Yokoyama Tatsuhiro , Yang Guotao , Yan Chunxiao , Wu Chen , Wang Jin , Zhong Dingkun , Li Yaxian , Wang Zhihua 
Published: February 2017

AbstractHainan coherent scatter phased array radar (HCOPAR) located at low latitude of China has recorded the extremely rare daytime F region irregularities at noon of 22 July 2013 and 23 May 2016. The two field‐aligned irregularities (FAIs) appeared in the topside F2 layer and presented small Doppler velocities and narrow spectral widths. The fan sector maps show that the FAIs moved northward with almost no zonal speed. The irregularities emerged in the geomagnetically quiet condition and were irrelevant to the storm‐induced eastward electric field as other daytime cases. More than 2 h after the emergency of the daytime irregularities over Hainan, the Shaoyang digisonde situated ~870 km north to the HCOPAR recorded the spread‐F in ionospheric F1 layer. According to the echo altitudes, the spread‐F may connect the daytime bubbles via magnetic field line. The strong photoionization after sunrise made it difficult to generate the plasma bubbles in the sunlit ionosphere. Consequently, the two midday FAIs over Hainan may drift along the magnetic field lines from higher altitudes in the south and are most likely the remnant of previous night's bubbles.
The role of the convection electric field in filling the slot region between the inner and outer radiation belts
Authors: Califf S. , Li X. , Zhao H. , Kellerman A. , Sarris T. E. , Jaynes A. , Malaspina D. M. 
Published: February 2017

AbstractThe Van Allen Probes have reported frequent flux enhancements of 100s keV electrons in the slot region, with lower energy electrons exhibiting more dynamic behavior at lower L shells. Also, in situ electric field measurements from the Combined Release and Radiation Effects Satellite, Time History of Events and Macroscale Interactions during Substorms (THEMIS), and the Van Allen Probes have provided evidence for large‐scale electric fields at low L shells during active times. We study an event on 19 February 2014 where hundreds of keV electron fluxes were enhanced by orders of magnitude in the slot region and electric fields of 1–2 mV/m were observed below L = 3. Using a 2‐D guiding center particle tracer and a simple large‐scale convection electric field model, we demonstrate that the measured electric fields can account for energization of electrons up to at least 500 keV in the slot region through inward radial transport.
Evolution of a typical ion‐scale magnetic flux rope caused by thermal pressure enhancement
Authors: Teh W.‐L. , Nakamura T. K. M. , Nakamura R. , Baumjohann W. , Russell C. T. , Pollock C. , Lindqvist P.‐A. , Ergun R. E. , Burch J. L. , Torbert R. B. , Giles B. L. 
Published: February 2017

AbstractWith high time‐resolution field and plasma measurements by the Magnetospheric Multiscale spacecraft, interior fine structures of two ion‐scale magnetic flux ropes (~5 and ~11 ion inertial length radius) separated by ~14 s are resolved. These two ion‐scale flux ropes (FR1 and FR2) show non‐frozen‐in ion behavior and consist of a strong axial magnetic field at the reversal of the negative‐then‐positive bipolar field component. The negative bipolar field component of the FR2 is found to be depressed, where magnetic pressure and total pressure decrease, but ion and electron thermal pressures increase, a feature akin to a crater‐like flux rope. The pressure enhancement is due to the magnetosheath plasma feeding into the flux rope along the field lines. Magnetic field draping and energetic electrons are also observed in the trailing part of the FR2. The ratio of perpendicular and parallel currents indicates that the FR1 appears force‐free but the FR2 seems not. Moreover, the FR2 is time‐dependent as a result of a low correlation coefficient (CC = 0.75) for the derivation of the deHoffmann‐Teller frame using the direct measured electric fields, while the FR1 is in quasi‐steady conditions (CC = 0.94). It is concluded that the crater formation within the FR2 can be interpreted by the analytical flux rope simulation as the evolution of typical flux rope to crater‐like one due to the thermal pressure enhancement, which could be induced by the depression of transverse magnetic fields of the flux rope.
Electrical conductivity of hydrous andesitic melts pertinent to subduction zones
Authors: Guo Xuan , Li Bin , Ni Huaiwei , Mao Zhu 
Published: February 2017

AbstractAndesitic magmatism and rocks are widespread at convergent plate boundaries. Electrically conductive bodies beneath subduction zone arc volcanoes, such as the Uturuncu Volcano, Bolivia, may correspond to active reservoirs of H2O‐bearing andesitic magma. Laboratory measurements of electrical conductivity of hydrous andesitic melts are required to constrain the physicochemical conditions of these magma reservoirs in combination with magnetotelluric data. This experimental study investigates electrical conductivity of andesitic melts with 0.01–5.9 wt % of H2O at 1164–1573 K and 0.5–1.0 GPa in a piston cylinder apparatus using sweeping‐frequency impedance spectroscopy. Electrical conductivity of andesitic melt increases with increasing temperature and H2O concentration but decreases with pressure. Across the investigated range of H2O concentration, electrical conductivity varies by 1.2–2.4 log units, indicating stronger influence of H2O for andesitic melt than for rhyolitic and dacitic melts. Using the Nernst‐Einstein equation, the principal charge carrier is inferred to be Na in anhydrous melt but divalent cations in hydrous andesitic melts. The experimental data are regressed into a general electrical conductivity model for andesitic melt accounting for the pressure‐temperature‐H2O dependences altogether. Modeling results show that the conductive layer at >20 km depths beneath the surface of the Uturuncu Volcano could be interpreted by the presence of less than 20 vol % of H2O‐rich andesitic melt (with 6–9 wt % H2O).
Imaging Pacific lithosphere seismic discontinuities—Insights from SS precursor modeling
Authors: Tharimena Saikiran , Rychert Catherine , Harmon Nicholas , White Paul 
Published: February 2017

AbstractOceanic lithosphere provides an ideal location to decipher the nature of the lithosphere‐asthenosphere system which is vital to our understanding of plate tectonics. It is well established that oceanic lithosphere cools, thickens, and subsides as it ages according to the conductive cooling models. Yet this simple realization fails to explain various observations. For example, old oceanic lithosphere does not subside as predicted. Further, precise imaging of the lower boundary of the oceanic lithosphere has proven challenging. Here we use SS precursors to image the discontinuity structure across the Pacific Ocean using 24 years of teleseismic data. We image a sharp pervasive velocity discontinuity (3–15% drop over <21 km) at 30–80 km depth that increases in depth with age from the ridge to at least 36 ± 9 Myr along the 1100°C conductive cooling isotherm. Beneath seafloor >36 Myr, there is no age‐depth dependence, and we image the discontinuity at an average depth of 60 ± 1.5 km. The amplitude and sharpness of the boundary suggests that a compositional variation and/or layered carbonatitic melt may be required to explain our observations rather than temperature alone. The strength and pervasiveness of the boundary suggest that it is likely related to the lithosphere‐asthenosphere boundary. An additional deeper discontinuity at 80–120 km depth is imaged intermittently that in most cases likely represents a continuing negative velocity gradient in depth.
Nonheating methods for absolute paleointensity determination: Comparison and calibration using synthetic and natural magnetite‐bearing samples
Authors: Lerner Geoffrey A. , Smirnov Aleksey V. , Surovitckii Leonid V. , Piispa Elisa J. 
Published: February 2017

AbstractNonheating paleointensity methods utilize an anhysteretic remanent magnetization (ARM) or a saturation isothermal remanent magnetization to model the natural thermal remanent magnetization (TRM) to avoid heating‐induced alteration. We report the results of paleointensity experiments using the ARM, pseudo‐Thellier, and ratio of equivalent magnetization (REM) methods conducted to investigate their relative efficiency in recovering the true paleofield strength and to provide additional estimates of their calibration factors. The experiments on synthetic magnetite‐bearing samples representing single‐domain (SD) and pseudo‐single‐domain (PSD) magnetic states indicated that the correction factors for the ARM‐based methods depend on the magnetic grain size/domain state changing from ~6.3 (for SD grains) to ~4.1 (for ~1.5 µm PSD grains). The pseudo‐Thellier method yielded correct absolute paleointensity values when normalization by the TRM/ARM demagnetization slope was used. When applied to samples of lava flows and dikes from the ~32 kyr Lemptégy volcano (France), both the ARM and pseudo‐Thellier methods produced similar paleointensity estimates (28.0 ± 5.1 μT and 26.9 ± 4.7 μT, respectively) consistent with the available Thellier data for the 31–33 kyr time interval. The correction factors estimated from our synthetic samples for the REM (~3000) and for REMc (~1500) and REM′ (~1500) variants are consistent with the previously published estimates. However, all REM variants yielded unrealistically high estimates (>110 μT) of the paleofield strength from our natural samples. Our experimental results support ARM as a better proxy of TRM and suggest that the ARM‐based methods currently represent the best alternative to heating‐based absolute paleointensity method.