bluuebunny/crossref_metadata_2025_split huggingface dataset:
The difficulty for subducted oceanic crust to accumulate at the Earth's core‐mantle boundary
Authors: Li Mingming , McNamara Allen K. 
Published: April 2013

AbstractSeismic tomography has revealed two large low shear velocity provinces (LLSVPs) in the lowermost mantle beneath the central Pacific and Africa. The LLSVPs are further shown to be compositionally different from their surroundings. Among several hypotheses put forth in recent years to explain the cause of the LLSVPs, one postulates that they are thermochemical piles caused by accumulation of subducted oceanic crust at the core‐mantle boundary (CMB). Mineral physics experiments indicate that oceanic crust becomes denser than the surrounding mantle at lower mantle pressures. In addition, seismic observations provide evidence of subducted slabs arriving at the CMB. However, a major question pertains to whether subducted oceanic crust can survive viscous stirring associated with mantle plumes and accumulate into piles with the same spatial scale as LLSVPs. We perform a set of high‐resolution convection calculations to examine this hypothesis by investigating the interaction of thin oceanic crust (6 km) with mantle plumes. Our results show that as subducted oceanic crust is swept toward upwelling plume regions, the majority of it is viscously stirred into the surrounding mantle. Only a small amount of oceanic crust may accumulate at the base of plumes, but it is consistently entrained away into the plume at a rate equal to or greater than it is accumulated. We find that it is difficult for subducted oceanic crust to accumulate into large thermochemical piles at the CMB.
Probabilistic modeling of future volcanic eruptions at Mount Etna
Authors: Cappello Annalisa , Bilotta Giuseppe , Neri Marco , Negro Ciro Del 
Published: April 2013

AbstractThe statistical analysis of volcanic activity at Mt Etna was conducted with the twofold aim of (1) constructing a probability map for vent opening of future flank eruptions and (2) forecasting the expected number of eruptive events at the summit craters. The spatiotemporal map of new vent opening at Etna volcano is based on the analysis of spatial locations and frequency of flank eruptions starting from 1610. Thanks to the completeness and accuracy of historical data over the last four centuries, we examined in detail the spatial and temporal distribution of flank eruptions showing that effusive events follow a nonhomogenous Poisson process with space‐time varying intensities. After demonstrating the spatial nonhomogeneity and the temporal nonstationarity of flank eruptions at Etna, we calculated the recurrence rates (events expected per unit area per unit time) and produced different spatiotemporal probability maps of new vent opening in the next 1, 10 and 50 years. These probabilistic maps have an immediate use in evaluating the future timing and areas of Etna prone to volcanic hazards. Finally, the results of the analysis of the persistent summit activity during the last 110 years indicate that the hazard rate for eruptive events is not constant with time, differs for each summit crater of Mt Etna, highlighting a general increase in the eruptive frequency starting from the middle of last century and particularly from 1971, when the SE crater was formed.
Export of nutrients from the Arctic Ocean
Authors: Torres‐Valdés Sinhué , Tsubouchi Takamasa , Bacon Sheldon , Naveira‐Garabato Alberto C. , Sanders Richards , McLaughlin Fiona A. , Petrie Brian , Kattner Gerhard , Azetsu‐Scott Kumiko , Whitledge Terry E. 
Published: April 2013

AbstractThis study provides the first physically based mass‐balanced transport estimates of dissolved inorganic nutrients (nitrate, phosphate, and silicate) for the Arctic Ocean. Using an inverse model‐generated velocity field in combination with a quasi‐synoptic assemblage of hydrographic and hydrochemical data, we quantify nutrient transports across the main Arctic Ocean gateways: Davis Strait, Fram Strait, the Barents Sea Opening (BSO), and Bering Strait. We found that the major exports of all three nutrients occur via Davis Strait. Transports associated with the East Greenland Current are almost balanced by transports associated with the West Spitsbergen Current. The most important imports of nitrate and phosphate to the Arctic occur via the BSO, and the most important import of silicate occurs via Bering Strait. Oceanic budgets show that statistically robust net silicate and phosphate exports exist, while the net nitrate flux is zero, within the uncertainty limits. The Arctic Ocean is a net exporter of silicate (−15.7 ± 3.2 kmol s−1) and phosphate (−1.0 ± 0.3 kmol s−1; net ± 1 standard error) to the North Atlantic. The export of excess phosphate (relative to nitrate) from the Arctic, calculated at −1.1 ± 0.3 kmol s−1, is almost twice as large as previously estimated. Net transports of silicate and phosphate from the Arctic Ocean provide 12% and 90%, respectively, of the net southward fluxes estimated at 47°N in the North Atlantic. Additional sources of nutrients that may offset nutrient imbalances are explored, and the relevance and the pathway of nutrient transports to the North Atlantic are discussed.
Improved landslide‐tsunami prediction: Effects of block model parameters and slide model
Authors: Heller Valentin , Spinneken Johannes 
Published: April 2013

AbstractSubaerial landslide‐tsunamis and impulse waves are caused by mass movements impacting into a water body, and the hazards they pose have to be reliably assessed. Empirical equations developed with physical Froude model studies can be an efficient method for such predictions. The present study improves this methodology and addresses two significant shortcomings in detail for the first time: these are the effect of three commonly ignored block model parameters and whether the slide is represented by a rigid block or a deformable granular material. A total of 144 block slide tests were conducted in a wave flume under systematic variation of three important block model parameters, the slide Froude number, the relative slide thickness, and the relative slide mass. Empirical equations for the maximum wave amplitude, height, and period as well as their evolution with propagation distance are derived. For most wave parameters, remarkably small data scatter is achieved. The combined influence of the three block model parameters affects the wave amplitude and wave height by up to a factor of two. The newly derived equations for block slides are then related to published equations for granular slides. This comparison reveals that block slides do not necessarily generate larger waves than granular slides, as often argued in the technical literature. In fact, it is shown that they may also generate significant smaller waves. The new findings can readily be integrated in existing hazard assessment methodologies, and they explain a large part of the discrepancy between previously published data.
Analyzing the footprints of near‐surface aqueous turbulence: An image processing‐based approach
Authors: Schnieders J. , Garbe C. S. , Peirson W. L. , Smith G. B. , Zappa C. J. 
Published: April 2013

AbstractIn this contribution, a detailed investigation of surface thermal patterns on the water surface is presented, with wind speeds ranging from 1 to 7 m s  − 1 and various surface conditions. Distinct structures can be observed on the surface—small‐scale short‐lived structures termed fish scales and larger‐scale cold streaks that are consistent with the footprints of Langmuir circulations. The structure of the surface heat pattern depends strongly on wind‐induced stress. Consistent behavior regarding the spacing of cold streaks can be observed in a range of laboratory facilities when expressed as a function of water‐sided friction velocity, u * . This behavior systematically decreased until a point of saturation at u *  = 0.7 cm/s. We present a new image processing‐based approach to the analysis of the spacing of cold streaks based on a machine learning approach to classify the thermal footprints of near‐surface turbulence. Comparison is made with studies of Langmuir circulation and the following key points are found. Results suggest a saturation in the tangential stress, anticipating that similar behavior will be observed in the open ocean. A relation to Langmuir numbers shows that thermal footprints in infrared images are consistent with Langmuir circulations and depend strongly on wind wave conditions.
Increased CO2 outgassing in February‐May 2010 in the tropical Atlantic following the 2009 Pacific El Niño
Authors: Lefèvre Nathalie , Caniaux Guy , Janicot Serge , Gueye Abdou Karim 
Published: April 2013

AbstractThe fugacity of CO2 (fCO2) has been measured underway during the voyages of a merchant ship sailing from France to Brazil since 2008. High fCO2 values are observed in 2010, between approximately 8°S and 8°N, and are particularly pronounced in boreal spring. These high values are explained by the anomalous situation occurring in the tropical Atlantic in 2010 after the 2009 El Niño in the Pacific. The weakening of the trade winds during the El Niño event contributes to an increase of sea surface temperatures in the tropical Atlantic and a northward shift of the intertropical convergence zone. The anomalous position of the intertropical convergence zone is accompanied by reduced precipitation in boreal spring and hence a higher than usual sea surface salinity. The year 2010 is also characterized by a strong positive Atlantic multidecadal oscillation index and a negative North Atlantic oscillation index that contribute to the tropical Atlantic warming. Positive anomalies of both surface temperature and salinity cause an increase of surface CO2, leading to a stronger outgassing of CO2 in 2010 compared with 2009 and 2011. The main factor responsible for the CO2 anomalies is the Pacific El Niño teleconnection. The Atlantic multidecadal oscillation index also contributes in the northern hemisphere, and the role of the North Atlantic oscillation is negligible.
Investigation of the complex dynamics and structure of the 2010 Eyjafjallajökull volcanic ash cloud using multispectral images and numerical simulations
Authors: Spinetti C. , Barsotti S. , Neri A. , Buongiorno M. F. , Doumaz F. , Nannipieri L. 
Published: April 2013

AbstractWe investigated the structure and evolution of the 2010 Eyjafjallajökull volcanic cloud and its dispersal over Iceland and Europe integrating satellite multispectral images and numerical simulations. Data acquired by Medium Resolution Imaging Spectrometer (MERIS) and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) have been analyzed to quantify the cloud extent and composition. The VOL‐CALPUFF dispersal code was applied to reconstruct the transient and 3‐D evolution of the cloud. Source parameters estimated on the base of available a posteriori volcanological data sets have been used. Quantitative comparisons between satellite retrievals and modeling results were performed for two selected instants of time during the first and third eruptive phases on a regional scale. Sensitivity of the model to initial volcanological conditions has been analyzed at continental scale. Several complex non intuitive features of cloud dynamics have been highlighted and strengths and limitations of the adopted methods identified. The main findings are: the level of quantitative agreement between satellite observations and numerical results depends on ash cloud composition (particle sizes and concentration) with better agreement for smaller particles and higher concentrations; the agreement between observations and modeling outcomes also depends on the temporal stability of volcanological conditions and the complexity of the meteorological wind field; the irregular dispersion of ash, as reconstructed from satellite data and numerical modeling, can be well explained by the different response of particle sizes to strong vertical wind‐shear, and by resuspension processes acting at ground level; eruptive source conditions are the main source of uncertainty in modeling, especially during an ongoing crisis and at long‐range scales.
Impact of aerosol and thin cirrus on retrieving and validating XCO2 from GOSAT shortwave infrared measurements
Authors: Guerlet S. , Butz A. , Schepers D. , Basu S. , Hasekamp O. P. , Kuze A. , Yokota T. , Blavier J.‐F. , Deutscher N. M. , Griffith D. W. T. , Hase F. , Kyro E. , Morino I. , Sherlock V. , Sussmann R. , Galli A. , Aben I. 
Published: April 2013

Inadequate treatment of aerosol scattering can be a significant source of error when retrieving column‐averaged dry‐air mole fractions of CO2 (XCO2) from space‐based measurements of backscattered solar shortwave radiation. We have developed a retrieval algorithm, RemoTeC, that retrieves three aerosol parameters (amount, size, and height) simultaneously with XCO2. Here we evaluate the ability of RemoTeC to account for light path modifications by clouds, subvisual cirrus, and aerosols when retrieving XCO2 from Greenhouse Gases Observing Satellite (GOSAT) Thermal and Near‐infrared Sensor for carbon Observation (TANSO)‐Fourier Transform Spectrometer (FTS) measurements. We first evaluate a cloud filter based on measurements from the Cloud and Aerosol Imager and a cirrus filter that uses radiances measured by TANSO‐FTS in the 2 micron spectral region, with strong water absorption. For the cloud‐screened scenes, we then evaluate errors due to aerosols. We find that RemoTeC is well capable of accounting for scattering by aerosols for values of aerosol optical thickness at 750 nm up to 0.25. While no significant correlation of errors is found with albedo, correlations are found with retrieved aerosol parameters. To further improve the XCO2 accuracy, we propose and evaluate a bias correction scheme.Measurements from 12 ground‐based stations of the Total Carbon Column Observing Network (TCCON) are used as a reference in this study. We show that spatial colocation criteria may be relaxed using additional constraints based on modeled XCO2 gradients, to increase the size and diversity of validation data and provide a more robust evaluation of GOSAT retrievals. Global‐scale validation of satellite data remains challenging and would be improved by increasing TCCON coverage.
Toward improved corrections for radiation‐induced biases in radiosonde temperature observations
Authors: Sun Bomin , Reale Anthony , Schroeder Steven , Seidel Dian J. , Ballish Bradley 
Published: April 2013

AbstractRadiation‐induced biases in global operational radiosonde temperature data from May 2008 to August 2011 are examined by using spatially and temporally collocated Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) data as estimates of the truth. The data on average from most radiosonde types show a nighttime cold bias and a daytime warm bias relative to COSMIC. Most daytime biases increase with altitude and solar elevation angle (SEA). The global average biases in the 15–70 hPa layer are −0.05 ± 1.89 K standard deviation (~52,000 profiles) at night and 0.39 ± 1.80 K standard deviation (~64,500 profiles) in daytime (SEA > 7.5°). Daytime warm biases associated with clouds are smaller than those under clear conditions. Newer sondes (post‐2000) have smaller biases and appear to be less sensitive to effects of clouds. Biases at night show greater seasonal and zonal variations than those for daytime. In general, warm night biases are associated with warm climate regimes and less warm or cold night biases with cold climate regimes. Bias characteristics for 13 major radiosonde types are provided, as a basis for updating radiosonde corrections used in numerical weather predictions, for validating satellite retrievals, and for adjusting archived radiosonde data to create consistent climate records.
A comparison of tropospheric temperature changes over China revealed by multiple data sets
Authors: Zhang Lixia , Zhou Tianjun 
Published: April 2013

AbstractBased on four radiosonde data sets and three reanalysis data sets, the long‐term tropospheric temperature changes over China for the period 1958–2001, and the uncertainties are analyzed. The results from all data sets, except for HadAT2 and National Centers for Environmental Protection 20th Century Reanalysis data (NCEP‐20CR), show a significant warming trend in the lower troposphere temperature averaged over China during 1958–2001, but this trend decreases with height and is replaced by a cooling tendency at 500 hPa, reaching maximum cooling at 300 hPa. The year‐by‐year changes of temperature over China are largely in agreement among the radiosonde and the reanalysis data sets. The uncertainties of upper troposphere temperature changes are larger compared with those of the lower troposphere. The uncertainty was relatively small during 1970–1990 and large during 1958–1970 and from 1990 to the present. The trend uncertainty is large in the Northwest for the lower troposphere and in south China for the upper troposphere, with the largest trend uncertainty over Northwest China at 850 hPa and east to 100°E at 300 hPa. For the average temperature trend over China, the largest uncertainty peaks at 300 hPa for 1958–2001. The tropospheric temperature of China at 300 hPa, derived from HadAT2, warms up; this differs greatly from the other data sets. The warming trend is produced mainly by the stations over south China and is due to the choice of neighbor stations during construction. The temperature trend at 300 hPa in NCEP‐National Center for Atmospheric Research is cooler than the other data sets due to its abrupt cooling around the early 1990s. NCEP‐20CR can partly capture the cooling tendency at 300 hPa over North China but with weaker magnitude.
Links between mesopause temperatures and ground‐based VLF narrowband radio signals
Authors: Silber Israel , Price Colin , Rodger Craig J. , Haldoupis Christos 
Published: April 2013

AbstractThe Upper Mesosphere–Lower Thermosphere (UMLT) region of the atmosphere is known to vary on many temporal and spatial scales. However, this region of the atmosphere is very difficult to measure and monitor continuously. In this paper, we demonstrate an intriguing connection between mesopause temperatures and the intensity of very low frequencies (VLF) narrowband (NB) signals reflected off the lower ionosphere. The temperature data used are from the SABER instrument onboard the TIMED satellite, while the VLF data are obtained from various ground‐based receiving systems. The results of the analysis show a high anticorrelation between temperature and VLF amplitude. It is shown that the variability of the UMLT temperatures and VLF amplitudes can be explained by global seasonal solar irradiance changes (~72% of the variability), while the remaining variability has its origins from other sources (~28%). High‐resolution mesopause temperature estimates might be achieved in the future by combining VLF NB observations and calculated solar irradiance variability (as a function of hour, day, and location, i.e., latitude).
What is the effect of unresolved internal climate variability on climate sensitivity estimates?
Authors: Olson R. , Sriver R. , Chang W. , Haran M. , Urban N. M. , Keller K. 
Published: April 2013

AbstractMany studies have attempted to estimate the equilibrium climate sensitivity (CS) to the doubling of CO2concentrations. One common methodology is to compare versions of Earth models of intermediate complexity (EMICs) to spatially and/or temporally averaged historical observations. Despite the persistent efforts, CS remains uncertain. It is, thus far, unclear what is driving this uncertainty. Moreover, the effects of the internal climate variability on the CS estimates obtained using this method have not received thorough attention in the literature. Using a statistical approximator (“emulator”) of an EMIC, we show in an observation system simulation study that unresolved internal climate variability appears to be a key driver of CS uncertainty (as measured by the 68% credible interval). We first simulate many realizations of pseudo‒observations from an emulator at a “true” prescribed CS, and then reestimate the CS using the pseudo‒observations and an inverse parameter estimation method. We demonstrate that a single realization of the internal variability can result in a sizable discrepancy between the best CS estimate and the truth. Specifically, the average discrepancy is 0.84°C, with the feasible range up to several °C. The results open the possibility that recent climate sensitivity estimates from global observations and EMICs are systematically considerably lower or higher than the truth, since they are typically based on the same realization of climate variability. This possibility should be investigated in future work. We also find that estimation uncertainties increase at higher climate sensitivities, suggesting that a high CS might be difficult to detect.
Evaluation of volcanic aerosol impacts on atmospheric water vapor using CMIP3 and CMIP5 simulations
Authors: Li Jingwan , Sharma Ashish 
Published: April 2013

AbstractThe uncertainty in estimates of volcanic forcing and in the way general circulation models (GCMs) implement volcanic forcing affects the accuracy of the simulated atmospheric water vapor response to volcanic eruptions, which in turn influences the design of hydrologic infrastructure. This paper aims to investigate whether and to what extent the models can simulate the volcanic impacts on atmospheric water vapor. While a Kolmogorov‐Smirnov (K‐S) test on atmospheric water vapor from GCMs, reanalysis products, and observations all imply that volcanic aerosols have a statistically significant impact on atmospheric water vapor, and the areal extent of global atmospheric water vapor affected by volcanic eruptions is oversimulated by GCMs. Additionally, the spatial and temporal patterns of the volcano‐related water vapor variability are not well simulated by GCMs. Furthermore, the strong negative correlation between aerosol optical depth and water vapor residual is observed only in the equatorial Atlantic and Indian Oceans, and parts of the western Pacific Ocean rather than across the entire globe as simulated by volcanic forcing included Coupled Model Intercomparison Project Phase 3 (CMIP3) multimodel average (or over nearly the entire tropics by volcanic forcing included the BCC‐CSM1.1). Although the uncompleted removal of El Niño–Southern Oscillation signal may compromise the results, it is still safe, after performing the control run of K‐S test, to draw the conclusion that while volcanic forcing does exert a significant impact on atmospheric water vapor, the underlying relationship is considerably more complex than that evident in GCM simulations.