bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms and predictability of multiyear ecosystem variability in the North Pacific
Authors: Chikamoto Megumi O. , Timmermann Axel , Chikamoto Yoshimitsu , Tokinaga Hiroki , Harada Naomi 
Published: November 2015

AbstractAleutian Low variations provide vorticity, buoyancy, and heat‐flux forcing to the North Pacific Ocean, which in turn cause changes in ocean circulation, mixed layer characteristics and sea ice coverage. In this process the white noise atmospheric characteristics are integrated dynamically and thermodynamically to generate red noise ocean spectra. Using the Community Earth System Model (version 1.0.3) we study the resulting biogeochemical and ecosystem responses in the North Pacific. We find that ocean dynamical variables have an impact on the tendencies of key nutrients and biological production, which leads to a further reddening of biogeochemical spectra resulting in potential predictability on time scales of 2–4 years. However, this low‐pass filtering does not apply to all biogeochemical variables and is regionally dependent. It is shown that phytoplankton biomass in the Central North Pacific adjusts to the much shorter‐term variability associated with changes in mixed layer depth, light availability, and zooplankton grazing, thus limiting the predictability of phytoplankton anomalies to about 1 year. In the eastern North Pacific the slow advection of anomalous nutrient concentrations leads to longer persistence of phytoplankton variability and increased potential predictability of up to 3 years.
Ammonia and nitrite oxidation in the Eastern Tropical North Pacific
Authors: Peng Xuefeng , Fuchsman Clara A. , Jayakumar Amal , Oleynik Sergey , Martens‐Habbena Willm , Devol Allan H. , Ward Bess B. 
Published: November 2015

AbstractNitrification plays a key role in the marine nitrogen (N) cycle, including in oceanic oxygen minimum zones (OMZs), which are hot spots for denitrification and anaerobic ammonia oxidation (anammox). Recent evidence suggests that nitrification links the source (remineralized organic matter) and sink (denitrification and anammox) of fixed N directly in the steep oxycline in the OMZs. We performed shipboard incubations with 15N tracers to characterize the depth distribution of nitrification in the Eastern Tropical North Pacific (ETNP). Additional experiments were conducted to investigate photoinhibition. Allylthiourea (ATU) was used to distinguish the contribution of archaeal and bacterial ammonia oxidation. The abundance of archaeal and β‐proteobacterial ammonia monooxygenase gene subunit A (amoA) was determined by quantitative polymerase chain reaction. The rates of ammonia and nitrite oxidation showed distinct subsurface maxima, with the latter slightly deeper than the former. The ammonia oxidation maximum coincided with the primary nitrite concentration maximum, archaeal amoA gene maximum, and the subsurface nitrous oxide maximum. Negligible rates of ammonia oxidation were found at anoxic depths, where high rates of nitrite oxidation were measured. Archaeal amoA gene abundance was generally 1 to 2 orders of magnitude higher than bacterial amoA gene abundance, and inhibition of ammonia‐oxidizing bacteria with 10 μM ATU did not affect ammonia oxidation rates, indicating the dominance of archaea in ammonia oxidation. These results depict highly dynamic activities of ammonia and nitrite oxidation in the oxycline of the ETNP OMZ.
Observations of wind stress direction during Typhoon Chaba (2010)
Authors: Potter Henry , Collins Clarence O. , Drennan William M. , Graber Hans C. 
Published: November 2015

AbstractDirect flux measurements of stress direction taken at the ocean surface during Typhoon Chaba (2010) over 3 days are examined for wind speeds between 12 and 26.5 m s−1. Results show stress deviated up to 35° from the wind direction and resided predominantly between the wind and peak wave directions in both bimodal and unimodal seas. Off‐wind stress angle was most pronounced in Chaba's wake where wind sea and swell created an apparent unimodal system with narrow directional spread. These conditions lasted 2 days during which the stress direction was midway between the wind and wave directions. The implications for tropical cyclone forecasting are discussed.
Kinetic Alfvén waves and particle response associated with a shock‐induced, global ULF perturbation of the terrestrial magnetosphere
Authors: Malaspina David M. , Claudepierre Seth G. , Takahashi Kazue , Jaynes Allison N. , Elkington Scot R. , Ergun Robert E. , Wygant John R. , Reeves Geoff D. , Kletzing Craig A. 
Published: November 2015

AbstractOn 2 October 2013, the arrival of an interplanetary shock compressed the Earth's magnetosphere and triggered a global ULF (ultra low frequency) oscillation. The Van Allen Probe B spacecraft observed this large‐amplitude ULF wave in situ with both magnetic and electric field data. Broadband waves up to approximately 100 Hz were observed in conjunction with, and modulated by, this ULF wave. Detailed analysis of fields and particle data reveals that these broadband waves are Doppler‐shifted kinetic Alfvén waves. This event suggests that magnetospheric compression by interplanetary shocks can induce abrupt generation of kinetic Alfvén waves over large portions of the inner magnetosphere, potentially driving previously unconsidered wave‐particle interactions throughout the inner magnetosphere during the initial response of the magnetosphere to shock impacts.
The competition of electron and ion heating during magnetic reconnection
Authors: Haggerty C. C. , Shay M. A. , Drake J. F. , Phan T. D. , McHugh C. T. 
Published: November 2015

AbstractThe physical processes that control the partition of released magnetic energy between electrons and ions during reconnection is explored through particle‐in‐cell simulations and analytical techniques. We demonstrate that the development of a large‐scale parallel electric field and its associated potential controls the relative heating of electrons and ions. The potential develops to restrain heated exhaust electrons and enhances their heating by confining electrons in the region where magnetic energy is released. Simultaneously, the potential slows ions entering the exhaust below the Alfvénic speed expected from the traditional counterstreaming picture of ion heating. Unexpectedly, the magnitude of the potential and therefore the relative partition of energy between electrons and ions is not a constant but rather depends on the upstream parameters and specifically the upstream electron normalized temperature (electron beta). These findings suggest that the fraction of magnetic energy converted into the total thermal energy may be independent of upstream parameters.
Acoustically induced slip in sheared granular layers: Application to dynamic earthquake triggering
Authors: Ferdowsi Behrooz , Griffa Michele , Guyer Robert A. , Johnson Paul A. , Marone Chris , Carmeliet Jan 
Published: November 2015

AbstractA fundamental mystery in earthquake physics is “how can an earthquake be triggered by distant seismic sources?” Here we use discrete element method simulations of a granular layer, during stick slip, that is subject to transient vibrational excitation to gain further insight into the physics of dynamic earthquake triggering. Using Coulomb friction law for grains interaction, we observe delayed triggering of slip in the granular gouge. We find that at a critical vibrational amplitude (strain) there is an abrupt transition from negligible time‐advanced slip (clock advance) to full clock advance; i.e., transient vibration and triggered slip are simultaneous. The critical strain is of order 10−6, similar to observations in the laboratory and in Earth. The transition is related to frictional weakening of the granular layer due to a dramatic decrease in coordination number and the weakening of the contact force network. Associated with this frictional weakening is a pronounced decrease in the elastic modulus of the layer. The study has important implications for mechanisms of triggered earthquakes and induced seismic events and points out the underlying processes in response of the fault gouge to dynamic transient stresses.
Observations of runup and energy flux on a low‐slope beach with high‐energy, long‐period ocean swell
Authors: Fiedler Julia W. , Brodie Katherine L. , McNinch Jesse E. , Guza Robert T. 
Published: November 2015

AbstractThe transformation of surface gravity waves from 11 m depth to runup was observed on the low‐sloped (1/80) Agate Beach, Oregon, with a cross‐shore transect of current meters, pressure sensors, and a scanning lidar. Offshore wave heights H0 ranged from calm (0.5 m) to energetic (>7 m). Runup, measured with pressure sensors and a scanning lidar, increases linearly with (H0L0)1/2, with L0 the deep‐water wavelength of the spectral peak. Runup saturation, in which runup oscillations plateau despite further increases in (H0L0)1/2, is not observed. Infragravity wave shoaling and nonlinear energy exchanges with short waves are included in an infragravity wave energy balance. This balance closes for high‐infragravity frequencies (0.025–0.04 Hz) but not lower frequencies (0.003–0.025 Hz), possibly owing to unmodeled infragravity energy losses of wave breaking and/or bottom friction. Dissipative processes limit, but do not entirely damp, increases in runup excursions in response to increased incident wave forcing.
Influence of sediment cohesion on deltaic shoreline dynamics and bulk sediment retention: A laboratory study
Authors: Straub Kyle M. , Li Qi , Benson W. Matthew 
Published: November 2015

AbstractWhile boundary and forcing conditions influence the average location of a shoreline in deltaic systems, internal morphodynamics can drive high‐magnitude deviations from the long‐term trend. Here we explore the role of sediment cohesion on these morphodynamics using physical experiments. Specifically, we explore the role of sediment cohesion on the scales of autogenic shoreline transgressions and regressions. Results indicate that sediment cohesion enhances the time and space scales associated with autogenic cycles of channel formation, elongation, and abandonment. In systems with high sediment cohesion, this cycle can drive shoreline transgressions that produce flooding surfaces in the resulting stratigraphy which could be confused with surfaces produced by increases in sea level rise or subsidence rates. Enhanced channelization resulting from sediment cohesion also increases the pumping of fine‐grained sediment into the marine realm, where it can bypass the delta foreset, thus decreasing total delta sediment retention rate.
Modeling aftershocks as a stretched exponential relaxation
Authors: Mignan A. 
Published: November 2015

AbstractThe decay rate of aftershocks has been modeled as a power law since the pioneering work of Omori in the late nineteenth century. Although other expressions have been proposed in recent decades to describe the temporal behavior of aftershocks, the number of model comparisons remains limited. After reviewing the aftershock models published from the late nineteenth century until today, I solely compare the power law, pure exponential and stretched exponential expressions defined in their simplest forms. By applying statistical methods recommended recently in applied mathematics, I show that all aftershock sequences tested in three regional earthquake catalogs (Southern and Northern California, Taiwan) and with three declustering techniques (nearest‐neighbor, second‐order moment, window methods) follow a stretched exponential instead of a power law. These results infer that aftershocks are due to a simple relaxation process, in accordance with most other relaxation processes observed in Nature.
Impact of the Atlantic meridional overturning circulation on the decadal variability of the Gulf Stream path and regional chlorophyll and nutrient concentrations
Authors: Sanchez‐Franks A. , Zhang R. 
Published: November 2015

AbstractIn this study, we show that the underlying physical driver for the decadal variability in the Gulf Stream (GS) path and the regional biogeochemical cycling is linked to the low frequency variability in the Atlantic meridional overturning circulation (AMOC). There is a significant anticorrelation between AMOC variations and the meridional shifts of the GS path at decadal time scale in both observations and two Earth system models (ESMs). The chlorophyll and nutrient concentrations in the GS region are found significantly correlated with the AMOC fingerprint and anticorrelated with the GS path at decadal time scale through coherent isopycnal changes in the GS front in the ESMs. Our results illustrate how changes in the large‐scale ocean circulation, such as AMOC, are teleconnected with regional decadal physical and biogeochemical variations near the North American east coast. Such linkages are useful for predicting future physical and biogeochemical variations in this region.
Tropical sources and sinks of carbonyl sulfide observed from space
Authors: Glatthor N. , Höpfner M. , Baker I. T. , Berry J. , Campbell J. E. , Kawa S. R. , Krysztofiak G. , Leyser A. , Sinnhuber B.‐M. , Stiller G. P. , Stinecipher J. , von Clarmann T. 
Published: November 2015

AbstractAccording to current budget estimations the seasonal variation of carbonyl sulfide (COS) is governed by oceanic release and vegetation uptake. Its assimilation by plants is assumed to be similar to the photosynthetic uptake of CO2 but, contrary to the latter process, to be irreversible. Therefore, COS has been suggested as cotracer of the carbon cycle. Observations of COS, however, are sparse, especially in tropical regions. We use the comprehensive data set of spaceborne measurements of the Michelson Interferometer for Passive Atmospheric Sounding to analyze its global distribution. Two major features are observed in the tropical upper troposphere around 250 hPa: enhanced amounts over the western Pacific and the Maritime Continent, peaking around 550 parts per trillion by volume (pptv) in boreal summer, and a seasonally varying depletion of COS extending from tropical South America to Africa. The large‐scale COS depletion, which in austral summer amounts up to −40 pptv as compared to the rest of the respective latitude band, has not been observed before and reveals the seasonality of COS uptake through tropical vegetation. The observations can only be reproduced by global models, when a large vegetation uptake and a corresponding increase in oceanic emissions as proposed in several recent publications are assumed.
Quantifying changes in climate variability and extremes: Pitfalls and their overcoming
Authors: Sippel Sebastian , Zscheischler Jakob , Heimann Martin , Otto Friederike E. L. , Peters Jonas , Mahecha Miguel D. 
Published: November 2015

AbstractHot temperature extremes have increased substantially in frequency and magnitude over past decades. A widely used approach to quantify this phenomenon is standardizing temperature data relative to the local mean and variability of a reference period. Here we demonstrate that this conventional procedure leads to exaggerated estimates of increasing temperature variability and extremes. For example, the occurrence of “two‐sigma extremes” would be overestimated by 48.2% compared to a given reference period of 30 years with time‐invariant simulated Gaussian data. This corresponds to an increase from a 2.0% to 2.9% probability of such events. We derive an analytical correction revealing that these artifacts prevail in recent studies. Our analyses lead to a revision of earlier reports: For instance, we show that there is no evidence for a recent increase in normalized temperature variability. In conclusion, we provide an analytical pathway to describe changes in variability and extremes in climate observations and model simulations.
Disruption of groundwater systems by earthquakes
Authors: Liao Xin , Wang Chi‐Yuen , Liu Chun‐Ping 
Published: November 2015

AbstractEarthquakes are known to enhance permeability at great distances, and this phenomenon may also disrupt groundwater systems by breaching the barrier between different reservoirs. Here we analyze the tidal response of water level in a deep (~4 km) well before and after the 2008 M7.9 Wenchuan earthquake to show that the earthquake not only changed the permeability but also altered the poroelastic properties of the groundwater system. Based on lithologic well logs and experimental data for rock properties, we interpret the change to reflect a coseismic breaching of aquitards bounding the aquifer, due perhaps to clearing of preexisting cracks and creation of new cracks, to depths of several kilometers. This may cause mixing of groundwater from previously isolated reservoirs and impact the safety of groundwater supplies and underground waste repositories. The method demonstrated here may hold promise for monitoring aquitard breaching by both natural and anthropogenic processes.
Spatially coherent trends of annual maximum daily precipitation in the United States
Authors: Sun Xun , Lall Upmanu 
Published: November 2015

AbstractA new multilevel, hierarchical Bayesian model is developed to simultaneously identify clusters of stations with similar temporal patterns, the trend associated with each cluster and for the individual stations within each cluster. An application to the annual maximum daily precipitation in the United States for a common 70 year (1941–2010) period across the HADEX2 sites is presented. The model identifies statistically homogeneous regions, spatially clustering the data into groups according to the intensity and the trend. Partial pooling of model parameters for each group is considered. Spatially consistent trends are detected in the Midwest and Northeast U.S., at the cluster and at the station level. The new approach can dramatically improve trend identification for precipitation extremes; e.g., all 14 stations in the Midwest report a significant trend as opposed to only 4 stations based on single site analysis. The method is generally applicable for improving trend identification over a heterogeneous region.
Ozone‐induced climate change propped up by the Southern Hemisphere oceanic front
Authors: Ogawa Fumiaki , Omrani Nour‐Eddine , Nishii Kazuaki , Nakamura Hisashi , Keenlyside Noel 
Published: November 2015

AbstractThe late twentieth century was marked by a significant summertime trend in the Southern Annular Mode (SAM), the dominant mode of tropospheric variability in the extratropical Southern Hemisphere (SH). This trend with poleward shifting tropospheric westerlies was attributed to downward propagation of stratospheric changes induced by ozone depletion. However, the role of the ocean in setting the SAM response to ozone depletion and its dynamical forcing remains unclear. Here we show, using idealized experiments with a state‐of‐the‐art atmospheric model and analysis of Intergovernmental Panel on Climate Change climate simulations, that frontal sea surface temperature gradients in the midlatitude SH are critical for translating the ozone‐induced stratospheric changes down to the surface. This happens through excitation of wave forcing, which controls the vertical connection of the tropospheric SAM with the stratosphere and shows the importance of internal tropospheric dynamics for stratosphere/troposphere coupling. Thus, improved simulation of oceanic fronts may reduce uncertainties in simulating SH ozone‐induced climate changes.
A submonthly database for detecting changes in vegetation‐atmosphere coupling
Authors: Zscheischler Jakob , Orth René , Seneviratne Sonia I. 
Published: November 2015

AbstractLand‐atmosphere coupling and changes in coupling regimes are important for making precise future climate predictions and understanding vegetation‐climate feedbacks. Here we introduce the Vegetation‐Atmosphere Coupling (VAC) index which identifies regions and times of concurrent strong anomalies in temperature and photosynthetic activity. The different classes of the index determine whether a location is currently in an energy‐limited or water‐limited regime, and its high temporal resolution allows to investigate how these regimes change over time at the regional scale. We show that the VAC index helps to distinguish different evaporative regimes. It can therefore provide indirect information about the local soil moisture state. We further demonstrate how the index can be used to understand processes leading to and occurring during extreme climate events, using the 2010 heat wave in Russia and the 2010 Amazon drought as examples.
A coupled ionosphere‐raytrace model for high‐power HF heating
Authors: Zawdie K. A. , Huba J. D. , Drob D. P. , Bernhardt P. A. 
Published: November 2015

AbstractThe first 3‐D model of artificial HF ionospheric heating to self‐consistently calculate the modification in heating location due to evolving ionospheric gradients has been developed. The model combines the ionosphere model SAMI3/ESF and the HF propagation code MoJo‐15. At each time step, the simulated path of the HF wave through the ionosphere is used to determine the HF heating location. These calculations have been used to explain the physical mechanism responsible for the snapback effect observed in an Arecibo HF heating experiment described by Bernhardt et al. (1988). The heater wave is refracted by the density cavity, which causes the heating location to drift in longitude. Eventually, the density cavity convects into the path of the refracted ray, such that only a small portion of the ray is above the threshold for HF heating and the heating location snaps back even though the ray itself is still refracted in longitude.
High‐resolution wind speed measurements using actively heated fiber optics
Authors: Sayde Chadi , Thomas Christoph K. , Wagner James , Selker John 
Published: November 2015

AbstractWe present a novel technique to simultaneously measure wind speed (U) at thousands of locations continuously in time based on measurement of velocity‐dependent heat transfer from a heated surface. Measuring temperature differences between paired passive and actively heated fiber‐optic (AHFO) cables with a distributed temperature sensing system allowed estimation ofUat over 2000 sections along the 230 m transect (resolution of 0.375 m and 5.5 s). The underlying concept is similar to that of a hot wire anemometer extended in space. The correlation coefficient betweenUmeasured by two colocated sonic anemometers and the AHFO were 0.91 during the day and 0.87 at night. The combination of classical passive and novel AHFO provides unprecedented dynamic observations of both air temperature and wind speed spanning 4 orders of magnitude in spatial scale (0.1–1000 m) while resolving individual turbulent motions, opening new opportunities for testing basic theories for near‐surface geophysical flows.