bluuebunny/crossref_metadata_2025_split huggingface dataset:
Observations and modeling of EMIC wave properties in the presence of multiple ion species as function of magnetic local time
Authors: Lee Justin H. , Angelopoulos Vassilis 
Published: October 2014

AbstractElectromagnetic ion cyclotron (EMIC) wave generation and propagation in Earth's magnetosphere depend on readily measurable hot (a few to tens of keV) plasma sheet ions, elusive plasmaspheric or ionospheric cold (sub‐eV to a few eV) ions, and partially heated warm ions (tens to hundreds of eV). Previous work has assumed all low‐energy ions are cold and not considered possible effects of warm ions. Using measurements by multiple Time History of Events and Macroscale Interactions during Substorms spacecraft, we analyze four typical EMIC wave events in the four magnetic local time sectors and consider the properties of both cold and warm ions supplied from previous statistical studies to interpret the wave observations using linear theory. As expected, we find that dusk EMIC waves grow due to the presence of drifting hot anisotropic protons and cold plasmaspheric ions with a dominant cold proton component. Near midnight, EMIC waves are less common because warm heavy ions that suppress wave growth are more abundant there. The waves can grow when cold, plume‐like density enhancements are present, however. Dawn EMIC waves, known for their peculiar properties, are generated away from the equator and change polarization during propagation through the warm plasma cloak. Noon EMIC waves can also be generated nonlocally and their properties modified during propagation by a plasmaspheric plume combined with low‐energy ions from solar and terrestrial sources. Accounting for multiple ion species, measured wave dispersion, and propagation characteristics can explain previously elusive EMIC wave properties and are therefore important for future studies of EMIC wave effects on energetic particle depletion.
Comparing foreshock characteristics and foreshock forecasting in observed and simulated earthquake catalogs
Authors: Ogata Yosihiko , Katsura Koichi 
Published: October 2014

AbstractIn this paper, we compare the empirical results regarding foreshocks obtained from the Japan data with results for synthetic catalogs in order to clarify whether or not the corresponding results are consistent with the description of the seismicity by a superposition of background activity and epidemic‐type aftershock sequence (ETAS) models. This question is important, because it is still controversially discussed whether the nucleation process of large earthquakes is driven by seismically cascading (ETAS type) or by aseismic accelerating processes. To explore the foreshock characteristics, we first applied the same clustering algorithms to real and synthetic catalogs and analyzed the temporal, spatial, and magnitude distributions of the selected foreshocks. Most properties are qualitatively the same in the real data and in synthetic catalogs. However, we find some quantitative differences particularly in the temporal acceleration, spatial convergence, and magnitude dependence, which also depend on the assumed synthetic catalogs. Furthermore, we calculated forecast scores based on a single‐link cluster algorithm which could be appropriate for real‐time applications. We find that the Japan Meteorological Agency catalog yields higher scores than all synthetic catalogs and that the ETAS models having the same magnitude sequence as the original catalog performs better (more close to the reality) than ETAS models with randomly picked magnitudes. We also find that the ETAS model that takes account of the triggering effect by small earthquakes below threshold magnitude performs more closely to the reality.
Comparison of decadal global water vapor changes derived from independent satellite time series
Authors: Mieruch S. , Schröder M. , Noël S. , Schulz J. 
Published: October 2014

AbstractWe analyze trends in total column water vapor (TCWV) retrieved from independent satellite observations and retrieval schemes. GOME‐SCIAMACHY (Global Ozone Monitoring Experiment‐SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY) measurements are carried out in the visible part of the solar spectrum and present a partly cloud‐corrected climatology that is available over land and ocean. The HOAPS (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite Data) product, provided by EUMETSAT's Satellite Application Facility on Climate Monitoring is based on passive microwave observations from the Special Sensor Microwave/Imager. It also includes the TCWV from cloudy pixels but is only available over oceans. The common observation time period is between 1996 and 2005. Due to the relatively short length of the period, the strong interannual variability with strong contributions from El Niño and La Niña events and the strong anomaly at the start of the common period, caused by the 1997/1998 El Niño, the observed trends should not be interpreted as long‐term climate trends. After subtraction of average seasonality from monthly gridded data, a linear model and a level shift model have been fitted to the HOAPS and GOME‐SCIAMACHY data, respectively. Autocorrelation and cross correlation of fit residuals are accounted for in assessing uncertainties in trends. The trends observed in both time series agree within uncertainty margins. This agreement holds true for spatial patterns, magnitudes, and global averages. The consistency increases confidence in the reliability of the trends because the methods, spectral range, and observation technique as well as the satellites and their orbits are completely independent of each other. The similarity of the trends in both data sets is an indication of sufficient stability in the observations for the time period of ≈ 10 years.
Cloud mask over snow‐/ice‐covered areas for the GCOM‐C1/SGLI cryosphere mission: Validations over Greenland
Authors: Chen Nan , Li Wei , Tanikawa Tomonori , Hori Masashiro , Aoki Teruo , Stamnes Knut 
Published: October 2014

AbstractCloud detection is a critically important first step required to derive many satellite data products. A novel cloud detection algorithm designed for the cryosphere mission of Global Climate Observation Mission First Climate satellite/Second Generation Global Imager (GCOM‐C1/SGLI) is presented. This reflectance‐based cloud detection scheme mainly utilizes only two short wavelength infrared channels with dynamic thresholds that depend on Sun‐satellite viewing geometry to perform accurate cloud detection over snow/ice surfaces in high latitude as well as high‐elevation regions. Profiles of atmospheric absorbing and scattering molecules as well as surface elevation are considered in the determination of the thresholds for the resulting snow/ice cloud mask (SCM) algorithm. Image‐based tests and statistical results have been used to validate the performance of the SCM over the Greenland plateau. Statistics using collocated Cloud‐Aerosol Lidar with Orthogonal Polarization and Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua observations over Greenland in 2007 show that over snow/ice surfaces the performance of the SCM is generally better than that of the MODIS cloud mask.
Evaluation of convection‐permitting model simulations of cloud populations associated with the Madden‐Julian Oscillation using data collected during the AMIE/DYNAMO field campaign
Authors: Hagos Samson , Feng Zhe , Burleyson Casey D. , Lim Kyo‐Sun Sunny , Long Charles N. , Wu Di , Thompson Greg 
Published: October 2014

AbstractRegional convection‐permitting model simulations of cloud populations observed during the 2011 Atmospheric Radiation Measurement (ARM) Madden‐Julian Oscillation Investigation Experiment/Dynamics of the Madden‐Julian Oscillation Experiment (AMIE/DYNAMO) field campaign are evaluated against ground‐based radar and ship‐based observations. Sensitivity of model simulated reflectivity, surface rain rate, and cold pool statistics to variations of raindrop breakup/self‐collection parameters in four state‐of‐the‐art two‐moment bulk microphysics schemes in the Weather Research and Forecasting (WRF) model is examined. The model simulations generally overestimate reflectivity from large and deep convective cells, and underestimate stratiform rain and the frequency of cold pools. In the sensitivity experiments, introduction of more aggressive raindrop breakup or decreasing the self‐collection efficiency increases the cold pool occurrence frequency in all of the simulations, and slightly reduces the reflectivity and precipitation statistics bias in some schemes but has little effect on the overall mean surface precipitation. Both the radar observations and model simulations of cloud populations show an approximate power law relationship between convective echo‐top height and equivalent convective cell radius.
Assessment of APCC multimodel ensemble prediction in seasonal climate forecasting: Retrospective (1983–2003) and real‐time forecasts (2008–2013)
Authors: Min Young‐Mi , Kryjov Vladimir N. , Oh Sang Myeong 
Published: October 2014

AbstractSince 2007, the Asia‐Pacific Economic Cooperation (APEC) Climate Center (APCC) has monthly issued multimodel ensemble (MME) seasonal predictions for 3 months, with 1 month lead time, and disseminated it to APEC member economies. This paper gives a comprehensive documentation of the current status of the APCC operational multimodel performance, with a large set of retrospective (1983–2003) and real‐time (2008–2013) predictions of temperature and precipitation. In order to investigate the enhancement in seasonal predictability that can be achieved by empirically weighted MME (using multiple regression) and calibrated MME (by correcting single‐model prediction using a stepwise pattern projection method) schemes, operationally implemented at the APCC, we compare them with a simple averaged MME (with equal weightings), for predicting seasonal mean temperature and precipitation 1 month ahead. The results indicate that the simple averaged MME consistently outperforms the multiple regression‐based MMEs, when considering all aspects of the predictions from operational prediction systems (i.e., in different variables, regions, and seasons) whereas the calibrated MME shows the capability to reduce errors and improve forecast skills in a large proportion of cases. The possible causes of the failure and success of the different MME methods implemented in the APCC operations are discussed.
Increasing the detectability of external influence on precipitation by correcting feature location in GCMs
Authors: Levy Adam A. L. , Jenkinson Mark , Ingram William , Lambert F. Hugo , Huntingford Chris , Allen Myles 
Published: October 2014

AbstractUnderstanding how precipitation varies as the climate changes is essential to determining the true impact of global warming. This is a difficult task not only due to the large internal variability observed in precipitation but also because of a limited historical record and large biases in simulations of precipitation by general circulation models (GCMs). Here we make use of a technique that spatially and seasonally transforms GCM fields to reduce location biases and investigate the potential of this bias correction to study historical changes. We use two versions of this bias correction—one that conserves intensities and another that conserves integrated precipitation over transformed areas. Focussing on multimodel ensemble means, we find that both versions reduce RMS error in the historical trend by approximately 11% relative to the Global Precipitation Climatology Project (GPCP) data set. By regressing GCMs' historical simulations of precipitation onto radiative forcings, we decompose these simulations into anthropogenic and natural time series. We then perform a simple detection and attribution study to investigate the impact of reducing location biases on detectability. A multiple ordinary least squares regression of GPCP onto the anthropogenic and natural time series, with the assumptions made, finds anthropogenic detectability only when spatial corrections are applied. The result is the same regardless of which form of conservation is used and without reducing the dimensionality of the fields beyond taking zonal means. While “detectability” is dependent both on the exact methodology and the confidence required, this nevertheless demonstrates the potential benefits of correcting location biases in GCMs when studying historical precipitation, especially in cases where a signal was previously undetectable.
A positive feedback between magmatism and mantle upwelling in terrestrial planets: Implications for the Moon
Authors: Ogawa Masaki 
Published: October 2014

AbstractA series of two‐dimensional numerical models of magmatism and mantle convection in small planetary bodies are presented to discuss how the small size of the Moon exerts control over its mantle evolution. Mantle convection is modeled by a solid‐state convection of internally heated materials with temperature‐dependent viscosity. Magmatism is modeled as upward permeable flow of basaltic magma generated by decompression melting of upwelling mantle materials. Migration of the generated magma causes compaction/expansion of the coexisting matrix. The volume change of matrix and the buoyancy of magma induced by magmatism enhance the upwelling flow and hence the magmatism itself, when the Rayleigh number exceeds a threshold that is around the critical Rayleigh number for the onset of thermal convection. This positive feedback makes magmatism vigorous and episodic and causes efficient cooling and stirring of the mantle in large planets like Venus and the Earth. In small planetary bodies where the Rayleigh number is lower than the threshold, however, magmatism occurs more continuously with a characteristic time of several hundred million years, cooling and convective stirring of the mantle caused by magmatism are less important, and a compositionally stratified structure develops in the mantle. These features of magmatism and mantle structure fit in with the observations on the Moon. The positive feedback is a key to understanding why the evolution of the lunar mantle is so different from that of lager planets like the Earth and Venus.
Hydrological response to multiple large distant earthquakes in the Mile well, China
Authors: Shi Zheming , Wang Guangcai 
Published: October 2014

AbstractGroundwater level changes of up to 0.716 m and temperature changes of up to 0.0708°C have been observed in the Mile well, Yunnan Province, China, in response to earthquakes with a seismic energy density exceeding 1 × 10−3 J⋅m−3 from 2004 to 2012. Sustained water level changes, however, only occurred in earthquakes with a surface wave magnitude Ms ≥ 8.0. Groundwater temperature and permeability changes also only occurred following such large earthquakes. This indicates that larger earthquakes (with Ms ≥ 8.0) are more effective at triggering hydrologic responses than smaller earthquakes. The amplitudes of changes in groundwater level and groundwater temperature were positively correlated, indicating that temperature changes are possibly caused by advection‐diffusion and mixing following groundwater inflows into the well. We used a tidal response as a proxy to investigate aquifer properties, showing that the changes in groundwater level and temperature correlate well with phase shift and tidal factor. Based on the aquifer parameters calculated from the tidal response using the M2 wave, we found that amplitudes of inferred changes in transmissivity and storage coefficient have a positive relationship with the groundwater level and temperature changes. The scale of transmissivity change was much larger than that of the storage coefficient. We interpret the co‐seismic changes in groundwater level and temperature in the Mile well to be due to changes of permeability in the aquifer due to unclogging of fractures induced by seismic waves.
Height changes over subglacial Lake Vostok, East Antarctica: Insights from GNSS observations
Authors: Richter Andreas , Popov Sergey V. , Fritsche Mathias , Lukin Valery V. , Matveev Alexey Yu. , Ekaykin Alexey A. , Lipenkov Vladimir Ya. , Fedorov Denis V. , Eberlein Lutz , Schröder Ludwig , Ewert Heiko , Horwath Martin , Dietrich Reinhard 
Published: October 2014

AbstractHeight changes of the ice surface above subglacial Lake Vostok, East Antarctica, reflect the integral effect of different processes within the subglacial environment and the ice sheet. Repeated GNSS (Global Navigation Satellite Systems) observations on 56 surface markers in the Lake Vostok region spanning 11 years and continuous GNSS observations at Vostok station over 5 years are used to determine the vertical firn particle movement. Vertical marker velocities are derived with an accuracy of 1 cm/yr or better. Repeated measurements of surface height profiles around Vostok station using kinematic GNSS observations on a snowmobile allow the quantification of surface height changes at 308 crossover points. The height change rate was determined at 1 ± 5 mm/yr, thus indicating a stable ice surface height over the last decade. It is concluded that both the local mass balance of the ice and the lake level of the entire lake have been stable throughout the observation period. The continuous GNSS observations demonstrate that the particle heights vary linearly with time. Nonlinear height changes do not exceed ±1 cm at Vostok station and constrain the magnitude of spatiotemporal lake‐level variations. ICESat laser altimetry data confirm that the amplitude of the surface deformations over the lake is restricted to a few centimeters. Assuming the ice sheet to be in steady state over the entire lake, estimates for the surface accumulation, on basal accretion/melt rates and on flux divergence, are derived.
Using dissolved organic matter age and composition to detect permafrost thaw in boreal watersheds of interior Alaska
Authors: O'Donnell Jonathan A. , Aiken George R. , Walvoord Michelle A. , Raymond Peter A. , Butler Kenna D. , Dornblaser Mark M. , Heckman Katherine 
Published: October 2014

AbstractRecent warming at high latitudes has accelerated permafrost thaw, which can modify soil carbon dynamics and watershed hydrology. The flux and composition of dissolved organic matter (DOM) from soils to rivers are sensitive to permafrost configuration and its impact on subsurface hydrology and groundwater discharge. Here, we evaluate the utility of DOM composition and age as a tool for detecting permafrost thaw in three rivers (Beaver, Birch, and Hess Creeks) within the discontinuous permafrost zone of interior Alaska. We observed strong temporal controls on Δ14C content of hydrophobic acid isolates (Δ14C‐HPOA) across all rivers, with the most enriched values occurring during spring snowmelt (75 ± 8‰) and most depleted during winter flow (−21 ± 8‰). Radiocarbon ages of winter flow samples ranged from 35 to 445 yr BP, closely tracking estimated median base flow travel times for this region (335 years). During spring snowmelt, young DOM was composed of highly aromatic, high molecular‐weight compounds, whereas older DOM of winter flow had lower aromaticity and molecular weight. We observed a significant correlation between Δ14C‐HPOA and UV absorbance coefficient at 254 nm (α254) across all study rivers. Using α254 as an optical indicator for Δ14C‐HPOA, we also observed a long‐term decline in α254 during maximum annual thaw depth over the last decade at the Hess Creek study site. These findings suggest a shift in watershed hydrology associated with increasing active layer thickness. Further development of DOM optical indicators may serve as a novel and inexpensive tool for detecting permafrost degradation in northern watersheds.
Controls on mixing‐dependent denitrification in hyporheic zones induced by riverbed dunes: A steady state modeling study
Authors: Hester Erich T. , Young Katie I. , Widdowson Mark A. 
Published: October 2014

AbstractThe hyporheic zone is known to attenuate contaminants originating from surface water, yet the ability of the hyporheic zone to attenuate contaminants in upwelling groundwater plumes as they exit to surface water is less understood. We used MODFLOW and SEAM3D to simulate hyporheic flow cells induced by riverbed dunes and upwelling groundwater together with mixing‐dependent denitrification of an upwelling nitrate (
) plume. Our base case modeled labile dissolved organic carbon (DOC) and dissolved oxygen (DO) advecting from surface water, and DO and
advecting from groundwater, typical of certain agricultural areas. We conducted sensitivity analyses that showed mixing‐dependent denitrification in the hyporheic zone increased with increasing hydraulic conductivity (K), decreasing lower boundary flux, and increasing DOC in surface water or
in groundwater. Surface water DOC, groundwater
, and K were the most sensitive parameters affecting mixing‐dependent denitrification. Nonmixing‐dependent denitrification also occurred when there was surface water
, and its magnitude was often greater than mixing‐dependent denitrification. Nevertheless, mixing‐dependent reactions provide functions that nonmixing‐dependent reactions cannot, with potential for hyporheic zones to attenuate upwelling
plumes, depending on geomorphic, hydraulic, and biogeochemical conditions. Stream and river restoration efforts may be able to increase mixing‐dependent reactions by promoting natural processes that promote bedform creation and augment labile carbon sources.
Organocatalysis in Enantioselective α‐Functionalization of 2‐Cyanoacetates
Authors: Díaz‐de‐Villegas María D. , Gálvez José A. , Badorrey Ramón , López‐Ram‐de‐Víu Pilar 
Published: October 2014

AbstractRecent progress in asymmetric organocatalysis has led to the development of several asymmetric transformations that employ various substrates. Among these, cyanoacetates have emerged as excellent nucleophiles in conjugate addition, alkylation, Mannich and α‐heterofunctionalization reactions. In this review we discuss the enantioselective functionalization of 2‐cyanoacetates through organocatalytic reactions.magnified image
N‐Imide Ylide‐Based Reactions: CH Functionalization, Nucleophilic Addition and Cycloaddition
Authors: Qiu Guanyinsheng , Kuang Yunyan , Wu Jie 
Published: October 2014

AbstractAs valuable building blocks for introducing nitrogen, N‐imide ylides represent an important class of reactive species and are synthons for the synthesis of nitrogen‐containing heterocycles that potentially have biological activities. During the past decades, tremendous efforts have been devoted to the tandem processes involving N‐imide ylides as well as their asymmetric applications. In particular, several types of N‐imide ylide‐based reactions have been established, such as CH functionalization, nucleophilic addition, and cycloaddition, etc. In this review, recent advances in N‐imide ylides chemistry are presented ordered according to the sequence of various reaction types.magnified image