bluuebunny/crossref_metadata_2025_split huggingface dataset:
Middle‐ and low‐latitude ionosphere response to 2015 St. Patrick's Day geomagnetic storm
Authors: Nava B. , Rodríguez‐Zuluaga J. , Alazo‐Cuartas K. , Kashcheyev A. , Migoya‐Orué Y. , Radicella S.M. , Amory‐Mazaudier C. , Fleury R. 
Published: March 2016

AbstractThis paper presents a study of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earth's magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the Bz component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earth's magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models.
Statistics of ionospheric disturbances over the Antarctic Peninsula as derived from TEC measurements
Authors: Galushko V. G. , Paznukhov V. V. , Sopin A. A. , Yampolski Y. M. 
Published: March 2016

AbstractResults of ionospheric disturbances observations using multisite total electron content (TEC) measurements over the Antarctic Peninsula for the period from 2009 to 2012 are presented. Diurnal dependencies of the disturbance occurrence frequency, velocity, and direction of motion are established. Parameters of the disturbances are calculated using dynamic approach to the problem of ionospheric disturbances diagnostics which has been extended to allow for an arbitrary waveform of TEC perturbations. Specific data quality constraints are introduced to determine the presence of wavelike disturbances in the TEC records and to satisfy the required accuracy of parameter reconstruction. Statistical treatment of the results shows that during the daytime disturbances propagate predominantly in the northern and northeastern directions. In the evening and nocturnal hours the northwestern direction is prevailing, with the characteristic disturbance velocities ranging from 10 to 250 m/s. The most probable velocities are tens of meters per second, while the mean values are equal to about 100–130 m/s. In the daytime the velocities of the ionospheric disturbances are even higher. During the Antarctic winter time disturbances are usually observed at local noon time, in sharp contrast with the summer time, when they are present during the nights and mornings.
The effect of fracture density and stress state on the static and dynamic bulk moduli of Westerly granite
Authors: Blake O. O. , Faulkner D. R. 
Published: March 2016

AbstractElastic properties are key parameters during the deformation of rocks. They can be measured statically or dynamically, but the two measurements are often different. In this study, the static and dynamic bulk moduli (Kstatic and Kdynamic) were measured at varying effective stress for dry and fluid‐saturated Westerly granite with controlled fracture densities under isotropic and differential stress states. Isotropic fracturing of different densities was induced in samples by thermal treatment to 250, 450, 650, and 850°C. Results show that fluid saturation does not greatly affect static moduli but increases dynamic moduli. Under isotropic loading, high fracture density and/or low effective pressure results in a low Kstatic/Kdynamic ratio. For dry conditions Kstatic/Kdynamic approaches 1 at low fracture densities when the effective pressure is high, consistent with previous studies. Stress‐induced anisotropy exists under differential stress state that greatly affects Kstatic compared to Kdynamic. As a result, the Kstatic/Kdynamic ratio is higher than that for the isotropic stress state and approaches 1 with increasing axial loading. The effect of stress‐induced anisotropy increases with increasing fracture density. A key omission in previous studies comparing static and dynamic properties is that anisotropy has not been considered. The standard methods for measuring static elastic properties, such as Poisson's ratio, Young's and shear modulus, involve subjecting the sample to a differential stress state that promotes anisotropy. Our results show that stress‐induced anisotropy resulting from differential stress state is a major contributor to the difference between static and dynamic elasticity and is dominant with high fracture density.
An enhanced singular spectrum analysis method for constructing nonsecular model of GPS site movement
Authors: Wang Xiaoming , Cheng Yingyan , Wu Suqin , Zhang Kefei 
Published: March 2016

AbstractMany GPS time series contain offsets, sometimes nonsecular trends, and seasonal signals with time‐varying amplitudes due to several different types of geophysical phenomena. Therefore, the use of nonsecular models to depict the real geophysical movement of GPS sites is better than a linear model. In this study, an enhanced singular spectrum analysis (SSA) method for fitting GPS time series and predicting its coordinates is proposed. Simulation results show that the root‐mean‐square (RMS) of differences between the reconstructed and simulated signals is 1.7 mm; the RMS of the differences between the predicted coordinates and simulated signal is about 3 mm for the first half 1.5 years of testing period and decreases to 10 mm for the last half 1.5 years. Fitting results for three GPS time series are obtained using maximum likelihood estimation (MLE), which is used to fit the time series with a piecewise linear trend plus an annual/semiannual components, SSA, and state space model (SSM). Both SSA and SSM perform similarly and better than the MLE in extracting the nonsecular trend and annual/semiannual components from the GPS time series. The prediction results from SSA have higher coefficients with raw time series and lower power of annual/semiannual in their residuals than that from MLE for two case studies. The differences between the linear trend estimated by Plate Boundary Observatory and SSA nonsecular model for 16 GPS time series are all larger than 2 mm in up direction, which is not negligible for a high‐accuracy terrestrial reference frame construction.
Lithospheric flexure under the Hawaiian volcanic load: Internal stresses and a broken plate revealed by earthquakes
Authors: Klein Fred W. 
Published: March 2016

AbstractSeveral lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of Hawai`i, where the geometry of the lithosphere is circular with a central depression. The plate bends concave downward surrounding a stress‐free hole, rather than bending concave upward as with past assumptions. Earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of Mauna Loa and Mauna Kea where the load is greatest. The earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign. Focal mechanism P axes below the neutral plane display a striking radial pattern pointing to the stress center. Earthquakes above the neutral plane in the north part of the island have opposite stress patterns; T axes tend to be radial. The M6.2 Honomu and M6.7 Kiholo main shocks (both at 39 km depth) are below the neutral plane and show radial compression, and the M6.0 Kiholo aftershock above the neutral plane has tangential compression. Earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum. The hole is interpreted as the soft center where the lithospheric plate is broken. Kilauea's deep conduit is seismically active because it is in the ring of maximum bending. A simplified two‐dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial P axes below the neutral plane. A previous inversion of deep Hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model. For horizontal faults, the shear stress within the bending slab matches the slip in the deep Kilauea seismic zone and enhances outward slip of active flanks.
Do the Amazon and Orinoco freshwater plumes really matter for hurricane‐induced ocean surface cooling?
Authors: Hernandez O. , Jouanno J. , Durand F. 
Published: March 2016

ABSTRACTRecent studies suggested that the plume of low‐saline waters formed by the discharge of the Amazon and Orinoco rivers could favor Atlantic Tropical Cyclone (TC) intensification by weakening the cool wake and its impact on the hurricane growth potential. The main objective of this study is to quantify the effects of the Amazon‐Orinoco river discharges in modulating the amplitude of TC‐induced cooling in the western Tropical Atlantic. Our approach is based on the analysis of TC cool wake statistics obtained from an ocean regional numerical simulation with ¼º horizontal resolution over the 1998–2012 period, forced with realistic TC winds. In both model and observations, the amplitude of TC‐induced cooling in plume waters (0.3–0.4ºC) is reduced significantly by around 50–60% compared to the cooling in open ocean waters out of the plume (0.6–0.7ºC). A twin simulation without river runoff shows that TC‐induced cooling over the plume region (defined from the reference experiment) is almost unchanged (∼0.03ºC) despite strong differences in salinity stratification and the absence of barrier layers. This argues for a weaker than thought cooling inhibition effect of salinity stratification and barrier layers in this region. Indeed, results suggest that haline stratification and barrier layers caused by the river runoff may explain only ∼10% of the cooling difference between plume waters and open ocean waters. Instead, the analysis of the background oceanic conditions suggests that the regional distribution of the thermal stratification is the main factor controlling the amplitude of cooling in the plume region.
Turbulent production in an internal wave bottom boundary layer maintained by a vertically propagating seiche
Authors: Henderson Stephen M. 
Published: March 2016

AbstractInternal seiches, which supply the energy responsible for mixing many lakes, are often modeled as vertically standing waves. However, recent observations of vertical seiche propagation in a small lake are inconsistent with the standard, vertically standing model. To examine the processes responsible for such propagation, drag and turbulent production in the bottom boundary layer of a small lake are related to the energy supplied by a propagating seiche (period 10–24 h). Despite complex and fluctuating stratification, which often inhibited mixing within 0.4 m of the bed, bottom stress was well represented by a simple drag coefficient model (drag coefficient 1.5 × 10−3). The net supply of seiche energy to the boundary layer was estimated by fitting a model for internal wave vertical propagation to velocity profiles measured above the boundary layer (1–4.5 m above lakebed). Fitted reflection coefficients ranged from 0.3 at 1 cycle/d frequency to 0.7 at 2.4 cycles/d (cf. near‐unity coefficients of classical seiche theories). The net supply of seiche energy approximately balanced boundary layer turbulent production. Three of four peaks in production and energy flux occurred 0.8–2.2 days after strong oscillating winds, a delay comparable to the time required for seiche energy to propagate to the lakebed. A model based on the estimated drag coefficient predicted the observed frequency dependence of the seiche reflection coefficient. For flat‐bed regions in narrow lakes, the model predicts that reflection is controlled by the ratio of water velocity to vertical wave propagation speed, with sufficiently large ratios leading to weak reflection, and clear vertical seiche propagation.
Simulation of oil bioremediation in a tidally influenced beach: Spatiotemporal evolution of nutrient and dissolved oxygen
Authors: Geng Xiaolong , Pan Zhong , Boufadel Michel C. , Ozgokmen Tamay , Lee Kenneth , Zhao Lin 
Published: March 2016

AbstractNumerical experiments of oil bioremediation of tidally influenced beach were simulated using the model BIOMARUN. Nutrient and dissolved oxygen were assumed present in a solution applied on the exposed beach face, and the concentration of these amendments was tracked throughout the beach for up to 6 months. It was found that, in comparison to natural attenuation, bioremediation increased the removal efficiency by 76% and 65% for alkanes and aromatics, respectively. Increasing the nutrient concentration in the applied solution did not always enhance biodegradation as oxygen became limiting even when the beach was originally oxygen‐rich. Therefore, replenishment of oxygen to oil‐contaminated zone was also essential. Stimulation of oil biodegradation was more evident in the upper and midintertidal zone of the beach, and less in the lower intertidal zone. This was due to reduced nutrient and oxygen replenishment, as very little of the amendment solution reached that zone. It was found that under continual application, most of the oil biodegraded within 2 months, while it persisted for 6 months under natural conditions. While the difference in duration suggests minimal long‐term effects, there are situations where the beach would need to be cleaned for major ecological functions, such as temporary nesting or feeding for migratory birds. Biochemical retention time map (BRTM) showed that the duration of solution application was dependent upon the stimulated oil biodegradation rate. By contrast, the application rate of the amendment solution was dependent upon the subsurface extent of the oil‐contaminated zone. Delivery of nutrient and oxygen into coastal beach involved complex interaction among amendment solution, groundwater, and seawater. Therefore, approaches that ignore the hydrodynamics due to tide are unlikely to provide the optimal solutions for shoreline bioremediation.
Fram Strait and Greenland Sea transports, water masses, and water mass transformations 1999–2010 (and beyond)
Authors: Marnela Marika , Rudels Bert , Goszczko Ilona , Beszczynska‐Möller Agnieszka , Schauer Ursula 
Published: March 2016

AbstractThe exchanges between the Nordic Seas and the Arctic Ocean are important for the ocean circulation and climate. Transports are here estimated using summer hydrographic data from the Greenland Sea and the Fram Strait. Geostrophic transports are computed from hydrographic sections at 75°N in the Greenland Sea and at about 79°N in the Fram Strait. Geostrophic velocities are adjusted with summer velocities derived from Argo floats, and four conservation constraints are applied to a box closed by the two sections. The estimated net volume transports are 0.8 ± 1.5 Sv southward. Net freshwater transports through the Greenland Sea section are estimated at 54 ± 20 mSv and through the Fram Strait section at 66 ± 9 mSv. Heat loss in the area between the two sections is estimated at 9 ± 12 TW. Convection depths in the Greenland Sea are estimated from observations and vary between about 200 and 2000 dbar showing no trend. Water mass properties in the Greenland Sea are affected both by convection and lateral mixing. Vertical mixing is estimated from hydrography and based on it about 1 Sv of diluted Arctic Ocean waters are estimated to enter the Greenland Sea. The properties of Atlantic, intermediate, and deep waters are studied. Deep water properties are defined using water mass triangles and are subject to decadal changes.
Anatomy of the Antarctic Circumpolar Current volume transports through Drake Passage
Authors: Koenig Zoé , Provost Christine , Park Young‐Hyang , Ferrari Ramiro , Sennéchael Nathalie 
Published: March 2016

AbstractThe 20 year (October 1992 to August 2013) observation‐based volume transport time series of the Antarctic Circumpolar Current (ACC) through Drake Passage (DP) across the Jason altimeter track #104 is analyzed to better understand the ACC transport variability and its potential causes. The time series of three transport components (total (TT), barotropic (BT), and baroclinic (BC)) referenced to 3000 m present energetic intraseasonal fluctuations, with a salient spectral peak at 50 and 36 days, with the largest (least) variance being associated with the BT (BC) component. Low‐frequency variations are much less energetic with a significant variance limited to the annual and biannual timescales and show a nonstationary intermittent link with the Southern Annular Mode and the Nino 3.4 index for interannual timescales. The region around 57°S in the Yaghan Basin appears to be a strategic point for a practical monitoring of the ACC transport, as the whole‐track TT is significantly correlated with the local TT (r = 0.53) and BT (r = 0.69) around 57°S. These local BT (and TT) variations are associated with a well‐defined tripole pattern in altimetric sea level anomaly (SLA). There is evidence that the tripole pattern associated with BT is locally generated when the BC‐associated mesoscale SLAs, which have propagated eastward from an upstream area of DP, cross the Shackleton Fracture Zone to penetrate into the Yaghan Basin. Barotropic basin modes excited within the Yaghan Basin are discussed as a plausible mechanism for the observed energy‐containing intraseasonal spectral peaks found in the transport variability.
Observations of bubbles in natural seep flares at MC 118 and GC 600 using in situ quantitative imaging
Authors: Wang Binbin , Socolofsky Scott A. , Breier John A. , Seewald Jeffrey S. 
Published: March 2016

AbstractThis paper reports the results of quantitative imaging using a stereoscopic, high‐speed camera system at two natural gas seep sites in the northern Gulf of Mexico during the Gulf Integrated Spill Research G07 cruise in July 2014. The cruise was conducted on the E/V Nautilus using the ROV Hercules for in situ observation of the seeps as surrogates for the behavior of hydrocarbon bubbles in subsea blowouts. The seeps originated between 890 and 1190 m depth in Mississippi Canyon block 118 and Green Canyon block 600. The imaging system provided qualitative assessment of bubble behavior (e.g., breakup and coalescence) and verified the formation of clathrate hydrate skins on all bubbles above 1.3 m altitude. Quantitative image analysis yielded the bubble size distributions, rise velocity, total gas flux, and void fraction, with most measurements conducted from the seafloor to an altitude of 200 m. Bubble size distributions fit well to lognormal distributions, with median bubble sizes between 3 and 4.5 mm. Measurements of rise velocity fluctuated between two ranges: fast‐rising bubbles following helical‐type trajectories and bubbles rising about 40% slower following a zig‐zag pattern. Rise speed was uncorrelated with hydrate formation, and bubbles following both speeds were observed at both sites. Ship‐mounted multibeam sonar provided the flare rise heights, which corresponded closely with the boundary of the hydrate stability zone for the measured gas compositions. The evolution of bubble size with height agreed well with mass transfer rates predicted by equations for dirty bubbles.
Wildfires in a warmer climate: Emission fluxes, emission heights, and black carbon concentrations in 2090–2099
Authors: Veira A. , Lasslop G. , Kloster S. 
Published: March 2016

AbstractGlobal warming is expected to considerably impact wildfire activity and aerosol emission release in the future. Due to their complexity, the future interactions between climate change, wildfire activity, emission release, and atmospheric aerosol processes are still uncertain. Here we use the process‐based fire model SPITFIRE within the global vegetation model JSBACH to simulate wildfire activity for present‐day climate conditions and future Representative Concentration Pathways (RCPs). The modeled fire emission fluxes and fire radiative power serve as input for the aerosol‐climate model ECHAM6‐HAM2, which has been extended by a semiempirical plume height parametrization. Our results indicate a general increase in extratropical and a decrease in tropical wildfire activity at the end of the 21st century. Changes in emission fluxes are most pronounced for the strongest warming scenario RCP8.5 (+49% in the extratropics, −37% in the tropics). Tropospheric black carbon (BC) concentrations are similarly affected by changes in emission fluxes and changes in climate conditions with regional variations of up to −50% to +100%. In the Northern Hemispheric extratropics, we attribute a mean increase in aerosol optical thickness of +0.031±0.002 to changes in wildfire emissions. Due to the compensating effects of fire intensification and more stable atmospheric conditions, global mean emission heights change by at most 0.3 km with only minor influence on BC long‐range transport. The changes in wildfire emission fluxes for the RCP8.5 scenario, however, may largely compensate the projected reduction in anthropogenic BC emissions by the end of the 21st century.
How accurate are volcanic ash simulations of the 2010 Eyjafjallajökull eruption?
Authors: Dacre H. F. , Harvey N. J. , Webley P. W. , Morton D. 
Published: March 2016

AbstractIn the event of a volcanic eruption the decision to close airspace is based on forecast ash maps, produced using volcanic ash transport and dispersion models. In this paper we quantitatively evaluate the spatial skill of volcanic ash simulations using satellite retrievals of ash from the Eyjafjallajökull eruption during the period from 7 to 16 May 2010. We find that at the start of this period, 7–10 May, the model (FLEXible PARTicle) has excellent skill and can predict the spatial distribution of the satellite‐retrieved ash to within 0.5° × 0.5° latitude/longitude. However, on 10 May there is a decrease in the spatial accuracy of the model to 2.5°× 2.5° latitude/longitude, and between 11 and 12 May the simulated ash location errors grow rapidly. On 11 May ash is located close to a bifurcation point in the atmosphere, resulting in a rapid divergence in the modeled and satellite ash locations. In general, the model skill reduces as the residence time of ash increases. However, the error growth is not always steady. Rapid increases in error growth are linked to key points in the ash trajectories. Ensemble modeling using perturbed meteorological data would help to represent this uncertainty, and assimilation of satellite ash data would help to reduce uncertainty in volcanic ash forecasts.