bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evaluating and improving cloud phase in the Community Atmosphere Model version 5 using spaceborne lidar observations
Authors: Kay Jennifer E. , Bourdages Line , Miller Nathaniel B. , Morrison Ariel , Yettella Vineel , Chepfer Helene , Eaton Brian 
Published: April 2016

AbstractSpaceborne lidar observations from the Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite are used to evaluate cloud amount and cloud phase in the Community Atmosphere Model version 5 (CAM5), the atmospheric component of a widely used state‐of‐the‐art global coupled climate model (Community Earth System Model). By embedding a lidar simulator within CAM5, the idiosyncrasies of spaceborne lidar cloud detection and phase assignment are replicated. As a result, this study makes scale‐aware and definition‐aware comparisons between model‐simulated and observed cloud amount and cloud phase. In the global mean, CAM5 has insufficient liquid cloud and excessive ice cloud when compared to CALIPSO observations. Over the ice‐covered Arctic Ocean, CAM5 has insufficient liquid cloud in all seasons. Having important implications for projections of future sea level rise, a liquid cloud deficit contributes to a cold bias of 2–3°C for summer daily maximum near‐surface air temperatures at Summit, Greenland. Over the midlatitude storm tracks, CAM5 has excessive ice cloud and insufficient liquid cloud. Storm track cloud phase biases in CAM5 maximize over the Southern Ocean, which also has larger‐than‐observed seasonal variations in cloud phase. Physical parameter modifications reduce the Southern Ocean cloud phase and shortwave radiation biases in CAM5 and illustrate the power of the CALIPSO observations as an observational constraint. The results also highlight the importance of using a regime‐based, as opposed to a geographic‐based, model evaluation approach. More generally, the results demonstrate the importance and value of simulator‐enabled comparisons of cloud phase in models used for future climate projection.
Review on climate change on the Tibetan Plateau during the last half century
Authors: Kuang Xingxing , Jiao Jiu Jimmy 
Published: April 2016

AbstractThe Tibetan Plateau (TP) is undergoing significant warming since the 1950s. During the past two decades, extensive research has been conducted to investigate the climate change on the plateau. This review presents an overview of recent progress on climate change on the TP with the aim of providing a comprehensive understanding of changes in climate variables. Long‐term observation data from meteorological stations presented by the published literature were used to show the trends in various climate variables. The TP is overall getting warmer and wetter during the past decades. Temperature is significantly increased, especially since the 1980s. The overall warming rate ranges from 0.16 to 0.67°C decade−1 since the 1950s during different periods. The TP shows a uniform warming trend with the most significant warming in the northern part. Precipitation is slightly increased, and the spatial pattern of changes in precipitation is variable. The annual precipitation is increasing in most areas of the TP. Some subregions are becoming wetter, while some subregions are becoming drier. Pan evaporation, reference evapotranspiration, and potential evapotranspiration have been found to decrease since the 1960s. Actual evapotranspiration is significantly increased since the 1960s. Wind speed and sunshine duration increased up to the 1970s and then decreased significantly afterwards. Relative humidity fluctuated up and down to the end of the 1990s and appeared to decrease afterwards. Vapor pressure deficit shows an overall increasing trend since the 1970s. Causes of changes in the climate variables are presented, and future research directions are recommended.
Orbital evidence for more widespread carbonate‐bearing rocks on Mars
Authors: Wray James J. , Murchie Scott L. , Bishop Janice L. , Ehlmann Bethany L. , Milliken Ralph E. , Wilhelm Mary Beth , Seelos Kimberly D. , Chojnacki Matthew 
Published: April 2016

AbstractCarbonates are key minerals for understanding ancient Martian environments because they are indicators of potentially habitable, neutral‐to‐alkaline water and may be an important reservoir for paleoatmospheric CO2. Previous remote sensing studies have identified mostly Mg‐rich carbonates, both in Martian dust and in a Late Noachian rock unit circumferential to the Isidis basin. Here we report evidence for older Fe‐ and/or Ca‐rich carbonates exposed from the subsurface by impact craters and troughs. These carbonates are found in and around the Huygens basin northwest of Hellas, in western Noachis Terra between the Argyre basin and Valles Marineris, and in other isolated locations spread widely across the planet. In all cases they cooccur with or near phyllosilicates, and in Huygens basin specifically they occupy layered rocks exhumed from up to ~5 km depth. We discuss factors that might explain their observed regional distribution, arguments for why carbonates may be even more widespread in Noachian materials than presently appreciated and what could be gained by targeting these carbonates for further study with future orbital or landed missions to Mars.
Quantification of the bed load effects on turbulent open‐channel flows
Authors: Liu Detian , Liu Xiaofeng , Fu Xudong , Wang Guangqian 
Published: April 2016

AbstractWith a computational model combining large eddy simulation and a discrete element model, detailed quantification of the bed load effects on turbulent open‐channel flows is presented. The objective is the revelation of bed load particle impact on the mean flow properties and coherent structures. Two comparative numerical experiments with mobile and immobile beds are conducted. Mean properties (e.g., velocity and Reynolds stress profiles) show good agreement with experimental data. Comparing the mobile and immobile cases, the effective bed position is nearly the same, whereas the equivalent sand roughness is changed. The flow experiences higher bottom shear stress over immobile bed. To quantify impact on turbulent structures, a revised quadrant analysis is performed to calculate four key parameters of ejection and sweep events (duration, maximum shear stress, transported momentum, and period). Results show that the ejection and sweep events have comparable importance in the outer region. However, sweep becomes dominant in the near‐wall region. The motion of particles enhances the sweep dominance by breaking up the ejection structures and decreasing their occurrence ratio. The results also suggest that the ejection events are easier to be influenced by the particle motions because they originate from the near‐wall region. The duration, maximum shear stress, and transported momentum decrease close to the bed. The period remains relatively constant in the outer region but decreases near the bed. Visualization of the coherent structure reveals that the instantaneous particle motion has strong correlation with the bursting cycle events.
Extensive nitrogen loss from permeable sediments off North‐West Africa
Authors: Sokoll Sarah , Lavik Gaute , Sommer Stefan , Goldhammer Tobias , Kuypers Marcel M. M. , Holtappels Moritz 
Published: April 2016

AbstractThe upwelling area off North‐West Africa is characterized by high export production, high nitrate and low oxygen concentration in bottom waters. The underlying sediment consists of sands that cover most of the continental shelf. Due to their permeability sands allow for fast advective pore water transport and can exhibit high rates of nitrogen (N) loss via denitrification as reported for anthropogenically eutrophied regions. However, N loss from sands underlying naturally eutrophied waters is not well studied, and in particular, N loss from the North‐West African shelf is poorly constrained. During two research cruises in April/May 2010/2011, sediment was sampled along the North‐West African shelf and volumetric denitrification rates were measured in sediment layers down to 8 cm depth using slurry incubations with 15N‐labeled nitrate. Areal N loss was calculated by integrating volumetric rates down to the nitrate penetration depth derived from pore water profiles. Areal N loss was neither correlated with water depth nor with bottom water concentrations of nitrate and oxygen but was strongly dependent on sediment grain size and permeability. The derived empirical relation between benthic N loss and grains size suggests that pore water advection is an important regulating parameter for benthic denitrification in sands and further allowed extrapolating rates to an area of 53,000 km2 using detailed sediment maps. Denitrification from this region amounts to 995 kt yr−1 (average 3.6 mmol m−2 d−1) which is 4 times higher than previous estimates based on diffusive pore water transport. Sandy sediments cover 50–60% of the continental shelf and thus may contribute significantly to the global benthic N loss.
Daytime sensible heat flux estimation over heterogeneous surfaces using multitemporal land‐surface temperature observations
Authors: Castellví F. , Cammalleri C. , Ciraolo G. , Maltese A. , Rossi F. 
Published: April 2016

AbstractEquations based on surface renewal (SR) analysis to estimate the sensible heat flux (H) require as input the mean ramp amplitude and period observed in the ramp‐like pattern of the air temperature measured at high frequency. A SR‐based method to estimate sensible heat flux (HSR‐LST) requiring only low‐frequency measurements of the air temperature, horizontal mean wind speed, and land‐surface temperature as input was derived and tested under unstable conditions over a heterogeneous canopy (olive grove). HSR‐LST assumes that the mean ramp amplitude can be inferred from the difference between land‐surface temperature and mean air temperature through a linear relationship and that the ramp frequency is related to a wind shear scale characteristic of the canopy flow. The land‐surface temperature was retrieved by integrating in situ sensing measures of thermal infrared energy emitted by the surface. The performance of HSR‐LST was analyzed against flux tower measurements collected at two heights (close to and well above the canopy top). Crucial parameters involved in HSR‐LST, which define the above mentioned linear relationship, were explained using the canopy height and the land surface temperature observed at sunrise and sunset. Although the olive grove can behave as either an isothermal or anisothermal surface, HSR‐LST performed close to H measured using the eddy covariance and the Bowen ratio energy balance methods. Root mean square differences between HSR‐LST and measured H were of about 55 W m−2. Thus, by using multitemporal thermal acquisitions, HSR‐LST appears to bypass inconsistency between land surface temperature and the mean aerodynamic temperature. The one‐source bulk transfer formulation for estimating H performed reliable after calibration against the eddy covariance method. After calibration, the latter performed similar to the proposed SR‐LST method.
Linking snowfall and snow accumulation to generate spatial maps of SWE and snow depth
Authors: Broxton Patrick D. , Dawson Nicholas , Zeng Xubin 
Published: April 2016

AbstractIt is critically important but challenging to estimate the amount of snow on the ground over large areas due to its strong spatial variability. Point snow data are used to generate or improve (i.e., blend with) gridded estimates of snow water equivalent (SWE) by using various forms of interpolation; however, the interpolation methodologies often overlook the physical mechanisms for the snow being there in the first place. Using data from the Snow Telemetry and Cooperative Observer networks in the western United States, we show that four methods for the spatial interpolation of peak of winter snow water equivalent (SWE) and snow depth based on distance and elevation can result in large errors. These errors are reduced substantially by our new method, i.e., the spatial interpolation of these quantities normalized by accumulated snowfall from the current or previous water years. Our method results in significant improvement in SWE estimates over interpolation techniques that do not consider snowfall, regardless of the number of stations used for the interpolation. Furthermore, it can be used along with gridded precipitation and temperature data to produce daily maps of SWE over the western United States that are comparable to existing estimates (which are based on the assimilation of much more data). Our results also show that not honoring the constraint between SWE and snowfall when blending in situ data with gridded data can lead to the development and propagation of unrealistic errors.
Streamflow response to increasing precipitation extremes altered by forest management
Authors: Kelly Charlene N. , McGuire Kevin J. , Miniat Chelcy Ford , Vose James M. 
Published: April 2016

AbstractIncreases in extreme precipitation events of floods and droughts are expected to occur worldwide. The increase in extreme events will result in changes in streamflow that are expected to affect water availability for human consumption and aquatic ecosystem function. We present an analysis that may greatly improve current streamflow models by quantifying the impact of the interaction between forest management and precipitation. We use daily long‐term data from paired watersheds that have undergone forest harvest or species conversion. We find that interactive effects of climate change, represented by changes in observed precipitation trends, and forest management regime, significantly alter expected streamflow most often during extreme events, ranging from a decrease of 59% to an increase of 40% in streamflow, depending upon management. Our results suggest that vegetation might be managed to compensate for hydrologic responses due to climate change to help mitigate effects of extreme changes in precipitation.
Comparison of aerosol optical properties above clouds between POLDER and AeroCom models over the South East Atlantic Ocean during the fire season
Authors: Peers F. , Bellouin N. , Waquet F. , Ducos F. , Goloub P. , Mollard J. , Myhre G. , Skeie R. B. , Takemura T. , Tanré D. , Thieuleux F. , Zhang K. 
Published: April 2016

AbstractAerosol properties above clouds have been retrieved over the South East Atlantic Ocean during the fire season 2006 using satellite observations from POLDER (Polarization and Directionality of Earth Reflectances). From June to October, POLDER has observed a mean Above‐Cloud Aerosol Optical Thickness (ACAOT) of 0.28 and a mean Above‐Clouds Single Scattering Albedo (ACSSA) of 0.87 at 550 nm. These results have been used to evaluate the simulation of aerosols above clouds in five Aerosol Comparisons between Observations and Models (Goddard Chemistry Aerosol Radiation and Transport (GOCART), Hadley Centre Global Environmental Model 3 (HadGEM3), European Centre Hamburg Model 5‐Hamburg Aerosol Module 2 (ECHAM5‐HAM2), Oslo‐Chemical Transport Model 2 (OsloCTM2), and Spectral Radiation‐Transport Model for Aerosol Species (SPRINTARS)). Most models do not reproduce the observed large aerosol load episodes. The comparison highlights the importance of the injection height and the vertical transport parameterizations to simulate the large ACAOT observed by POLDER. Furthermore, POLDER ACSSA is best reproduced by models with a high imaginary part of black carbon refractive index, in accordance with recent recommendations.
Lidar surveys reveal eruptive volumes and rates at Etna, 2007–2010
Authors: Behncke Boris , Fornaciai Alessandro , Neri Marco , Favalli Massimiliano , Ganci Gaetana , Mazzarini Francesco 
Published: April 2016

AbstractThe quantification of eruptive activity represents one major challenge in volcanology. Digital comparison of lidar‐based elevation models of Etna (Italy) was made to quantify the volumes of volcanics emitted in 2007–2010. During this period, Etna produced several summit paroxysms followed by a flank eruption. We integrated the total volume difference resulting from the subtraction of the 2007 and 2010 digital elevation models with volumes of eruptive products based on field and aerial surveys to attribute volumes with hitherto unrealized precision to poorly constrained eruptions. The total erupted volume of 2007–2010 is >86 × 106 m3, most (~74 × 106 m3) of which is made up by the lava flows of the 2008–2009 flank eruption. The survey also reveals the high lava volume (5.73 × 106 m3) and average eruption rate (~400 m3 s−1) of the 10 May 2008 paroxysm, whose flow front stopped 6.2 km from the vent, not far from the town of Zafferana Etnea.
Three‐dimensional full‐kinetic simulation of the solar wind interaction with a vertical dipolar lunar magnetic anomaly
Authors: Deca Jan , Divin Andrey , Wang Xu , Lembège Bertrand , Markidis Stefano , Horányi Mihály , Lapenta Giovanni 
Published: April 2016

AbstractA detailed understanding of the solar wind interaction with lunar magnetic anomalies (LMAs) is essential to identify its implications for lunar exploration and to enhance our physical understanding of the particle dynamics in a magnetized plasma. We present the first three‐dimensional full‐kinetic electromagnetic simulation case study of the solar wind interaction with a vertical dipole, resembling a medium‐size LMA. In contrast to a horizontal dipole, we show that a vertical dipole twists its field lines and cannot form a minimagnetosphere. Instead, it creates a ring‐shaped weathering pattern and reflects up to 21% (four times more as compared to the horizontal case) of the incoming solar wind ions electrostatically through the normal electric field formed above the electron shielding region surrounding the cusp. This work delivers a vital piece to fully comprehend and interpret lunar observations, as we find the amount of reflected ions to be a tracer for the underlying field structure.
Decrease of aliphatic CHs from diatoms by in situ heating infrared microspectroscopy
Authors: Alipour Leila , Nakashima Satoru 
Published: April 2016

AbstractIn situ heating IR microspectroscopy at 260–300°C under air and N2 conditions has been conducted on diatom frustules to examine aliphatic CH losses during heating, simulating their changes with burial‐diagenesis. Assuming a reaction model made up of two first‐order kinetic relations, reaction rate constants k1 and k2 and activation energies (Ea) were evaluated for aliphatic CHs. The rate constants for loss of aliphatic CHs of diatom frustules under air and N2 flow are much larger, with much smaller activation energies (57–109 kJ/mol: air; 14–44 kJ/mol: N2), than those for conventional hydrocarbon generation reactions from kerogens (170–370 kJ/mol) studied at higher temperatures (350–450°C). The CH decrease rates are somewhat different from the amide I decrease (protein degradation) rates. The obtained results suggest that organic transformation reactions including degradation of aliphatic CHs inside the diatom silica frustules might be quite different from those of kerogens separated from the biological structures.
Determining groundwater Ra end‐member values for the estimation of the magnitude of submarine groundwater discharge using Ra isotope tracers
Authors: Cho Hyung‐Mi , Kim Guebuem 
Published: April 2016

AbstractRadium isotopes (228Ra and 226Ra) are excellent tracers of submarine groundwater discharge (SGD). To estimate SGD magnitudes, information on the end‐member values of Ra concentrations in groundwater is critical; however, the distribution characteristics of Ra in coastal aquifers are poorly understood. In this study, we show that Ra concentrations in coastal groundwater are primarily dependent on salinity based on the data (n > 500) obtained from global coastal aquifers, although previous end‐member calculations averaged all Ra concentrations without considering salinity. If we assume that SGD is composed mainly of seawater infiltrating the aquifer, previous estimates of SGD for the Atlantic Ocean and the global ocean were overestimated twofold to threefold. This may be similar for other applications using different Ra isotopes. Our study highlights that the end‐members of Ra isotopes in groundwater should be carefully considered when estimating SGD using Ra isotope mass balances in the ocean.
Solar cycle variations of thermospheric composition at the solstices
Authors: Qian Liying , Burns Alan G. , Solomon Stanley C. , Wang Wenbin , Zhang Yongliang 
Published: April 2016

AbstractWe examine the solar cycle variability of thermospheric composition (O/N2) at the solstices. Our observational and modeling studies show that the summer‐to‐winter latitudinal gradient of O/N2 is small at solar minimum but large at solar maximum; O/N2 is larger at solar maximum than at solar minimum on a global‐mean basis; there is a seasonal asymmetry in the solar cycle variability of O/N2, with large solar cycle variations in the winter hemisphere and small solar cycle variations in the summer hemisphere. Model analysis reveals that vertical winds decrease the temperature‐driven solar cycle variability in the vertical gradient of O/N2 in the summer hemisphere but increase it in the winter hemisphere; consequently, the vertical gradient of O/N2 does not change much in the summer hemisphere over a solar cycle, but it increases greatly from solar minimum to solar maximum in the winter hemisphere; this seasonal asymmetry in the solar cycle variability in the vertical gradient of O/N2 causes a seasonal asymmetry in the vertical advection of O/N2, with small solar cycle variability in the summer hemisphere and large variability in the winter hemisphere, which in turn drives the observed seasonal asymmetry in the solar cycle variability of O/N2. Since the equatorial ionization anomaly suppresses upwelling in the summer hemisphere and strengthens downwelling in the winter hemisphere through plasma‐neutral collisional heating and ion drag, locations and relative magnitudes of the equatorial ionization anomaly crests and their solar cycle variabilities can significantly impact the summer‐to‐winter gradients of O/N2 and their solar cycle variability.
Dayside cosmic noise absorption at the equatorward boundary of auroral oval as observed from Maitri, Antarctica (L = 5; CGM 62.45°S, 55.45°E)
Authors: Behera Jayanta K. , Sinha Ashwini K. , Vichare Geeta , Kozyreva Olga , Rawat Rahul , Dhar Ajay 
Published: April 2016

AbstractOn 02 April 2011, a couple of cosmic noise absorption (CNA) events were detected at Maitri, Antarctica (L = 5; CGM 63.14°S, 53.69°E) confining to nighttime and daytime. One of the two events that occurred during night hours was caused due to auroral substorm onset. The current study focuses on the later CNA event, which was recorded during daytime (10:00–13:00 magnetic local time (MLT), MLT = UT‐1, at Maitri, Antarctica). We refer to this CNA event as dayside CNA (DCNA) event. Absence of westward electrojet during DCNA confirms its dissimilarity from auroral substorm absorption events. A comparison has been made between the DCNA event of 02 April 2011 with that of 14 July 2011, a day with substorm activity when Maitri is in dayside but without DCNA event. The comparison has been made in the light of interplanetary conditions, imaging riometer data, ground magnetic signatures, GOES electron flux density, and associated pulsations. The study shows that stronger prolonged eastward interplanetary electric field favors the occurrence of DCNA event. It is concluded that DCNA event is due to the gradient curvature drift of trapped nonrelativistic electrons in the equatorial plane. Estimated energy of trapped electrons using azimuthal drift time for a set of ground stations within the auroral oval confirms the enhancement in electron fluxes in the same energy band as recorded by geostationary satellites GOES 13 and GOES 15. The reason for precipitation of electrons is expected to be the loss cone scattering caused by wave‐particle interaction triggered by ULF waves.