bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field observations of wave‐induced streaming through a submerged seagrass (Posidonia oceanica) meadow
Authors: Luhar Mitul , Infantes Eduardo , Orfila Alejandro , Terrados Jorge , Nepf Heidi M. 
Published: April 2013

AbstractThis paper reports the findings of a 2 week field campaign designed to study wave‐induced flows within a meadow of Posidonia oceanica at water depth 9 m. Previous laboratory experiments suggest that waves induce a mean mass drift in the direction of wave propagation (“streaming”) through submerged canopies of vegetation. This paper provides the first field measurements of this wave‐induced streaming. During periods of high wave activity, streaming flows with magnitudes as high as 20% of the near‐bed oscillatory velocity were measured within the meadow. In addition to presenting field measurements of wave‐induced streaming, this paper also considers the damping of wave‐induced oscillatory flow within the seagrass meadow. Oscillatory velocities measured within the meadow were reduced by less than 30% relative to those above the meadow over the duration of the study. This is in agreement with previous laboratory and field measurements which show that oscillatory flows are damped less within submerged canopies compared to unidirectional flows. Existing analytical models underpredict the magnitude of the streaming flow and overpredict oscillatory velocity reductions. These discrepancies are thought to arise because the drag generated by flexible seagrasses moving with wave‐induced flow is not well described.
Annual maximum water levels from tide gauges: Contributing factors and geographic patterns
Authors: Merrifield Mark A. , Genz Ayesha S. , Kontoes Christopher P. , Marra John J. 
Published: April 2013

AbstractHourly time series from a quasi‐global set of 145 tide gauges are used to investigate annual maximum water levels at each station. High water levels are deconstructed into (1) a predicted tidal component, (2) a seasonal component, (3) a low‐frequency nontidal residual that accounts for sea level variability at time scales greater than a month but less than a year, and (4) a high‐frequency nontidal residual that captures variability particularly associated with storms at time scales greater than a month. The time‐averaged annual maximum water level correlates significantly with, and scales as 2.5 times, the water level standard deviation at the tide gauge stations. This relationship is used to estimate time‐averaged annual maximum water level on a nearly continuous global scale (excluding ice‐covered polar regions) by specifying variance maps of the tides from a tide model, the seasonal and low‐frequency residual components from satellite altimetry sea surface height, and the high‐frequency residual component from an atmospheric reanalysis product. The variance fields are combined to estimate time‐averaged annual maximum water levels that compare well with observed values at the tide gauge stations. Spatial patterns of annual maximum water levels and relative contributions from the tides and nontidal residual components are considered.
Structure and surface properties of eddies in the southeast Pacific Ocean
Authors: Holte James , Straneo Fiamma , Moffat Carlos , Weller Robert , Farrar J. Thomas 
Published: April 2013

AbstractA number of studies have posited that coastally generated eddies could cool the southeast Pacific Ocean (SEP) by advecting cool, upwelled waters offshore. We examine this mechanism by characterizing the upper‐ocean properties of mesoscale eddies in the SEP with a variety of observations and by estimating the surface‐layer eddy heat flux divergence with satellite data. Cyclonic and anticyclonic eddies observed during two cruises featured deep positive salinity anomalies along the 26.5 kg m−3isopycnal, indicating that the eddies had likely trapped and transported coastal waters offshore. The cyclonic eddies observed during the cruises were characterized by shoaling isopycnals in the upper 200 m and cool near‐surface temperature anomalies, whereas the upper‐ocean structure of anticyclonic eddies was more variable. Using a variety of large‐scale observations, including Argo float profiles, drifter records, and satellite sea surface temperature fields, we show that, relative to mean conditions, cyclonic eddies are associated with cooler surface temperatures and that anticyclonic eddies are associated with warmer surface temperatures. Within each data set, the mean eddy surface temperature anomalies are small and of approximately equal magnitude but opposite sign. Eddy statistics drawn from satellite altimetry data reveal that cyclonic and anticyclonic eddies occur with similar frequency and have similar average radii in the SEP. A satellite‐based estimate of the surface‐layer eddy heat flux divergence, while large in coastal regions, is small when averaged over the SEP, suggesting that eddies do not substantially contribute to cooling the surface layer of the SEP.
Mechanisms of aerosol‐forced AMOC variability in a state of the art climate model
Authors: Menary Matthew B. , Roberts Christopher D. , Palmer Matthew D. , Halloran Paul R. , Jackson Laura , Wood Richard A. , Müller Wolfgang A. , Matei Daniela , Lee Sang‐Ki 
Published: April 2013

AbstractMechanisms of sustained multidecadal changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) are investigated in a set of simulations with a new state‐of‐the‐art Earth system model. Anthropogenic aerosols have previously been highlighted as a potential mitigator of AMOC weakening. In this study, we explain the oceanic mechanisms behind how anthropogenic aerosols force a strengthening of the AMOC by up to 20% in our state‐of‐the‐art Earth system model. This strengthening is driven via atmospheric circulation changes which subsequently modulate the salinity budget of the North Atlantic subpolar gyre. Gradual salinification occurs via increased evaporation and decreased fluxes of ice through the Fram Straits. A component of the salinification is a positive feedback from the AMOC bringing more saline water northwards from the subtropical Atlantic. Salinification of the subpolar gyre results in increased deep convection and a strengthening of the AMOC. Following a reduction in aerosol concentrations, the AMOC rapidly weakens, approximately 3 times faster than in the case where anthropogenic aerosol concentrations had never been increased. Similarities and differences with available observational records and long term reanalysis products are also discussed.
CALIOP and AERONET aerosol optical depth comparisons: One size fits none
Authors: Omar A. H. , Winker D. M. , Tackett J. L. , Giles D. M. , Kar J. , Liu Z. , Vaughan M. A. , Powell K. A. , Trepte C. R. 
Published: April 2013

AbstractWe compare the aerosol optical depths (AOD) retrieved from backscatter measurements of the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) aboard the Cloud Aerosol Lidar Infrared Pathfinder Satellite Observations (CALIPSO) satellite with coincident Aerosol Robotic Network (AERONET) measurements. Overpass coincidence criteria of ±2 h and within a 40 km radius are satisfied at least once at 149 globally distributed AERONET sites from 2006 to 2010. Most data pairs (>80%) use AERONET measurements acquired ±30 min of the overpass. We examine the differences in AOD estimates between CALIOP and AERONET for various aerosol, environmental, and geographic conditions. Results show CALIOP AOD are lower than AERONET AOD especially at low optical depths as measured by AERONET (500 nm AOD < 0.1). Furthermore, the median relative AOD difference between the two measurements is 25% of the AERONET AOD for AOD > 0.1. Differences in AOD between CALIOP and AERONET are possibly due to cloud contamination, scene inhomogeneity, instrument view angle differences, CALIOP retrieval errors, and detection limits. Comparison of daytime to nighttime number of 5 km × 60 m (60 m in the vertical) features detected by CALIOP show that there are 20% more aerosol features at night. We find that CALIPSO and AERONET do not agree on the cloudiness of scenes. Of the scenes that meet the above coincidence criteria, CALIPSO finds clouds in more than 45% of the coincident atmospheric columns AERONET classifies as clear.
The role of groundwater in the Amazon water cycle: 3. Influence on terrestrial water storage computations and comparison with GRACE
Authors: Pokhrel Yadu N. , Fan Ying , Miguez‐Macho Gonzalo , Yeh Pat J.‐F. , Han Shin‐Chan 
Published: April 2013

AbstractWe explore the mechanisms whereby groundwater influences terrestrial water storage (TWS) in the Amazon using GRACE observations and two contrasting versions of the LEAF‐Hydro‐Flood hydrological model: one with and the other without an interactive groundwater. We find that, first, where the water table is shallow as in northwestern Amazonia and floodplains elsewhere, subsurface stores (vadose zone and groundwater) are nearly saturated year‐round, hence river and flooding dominate TWS variation; where the water table is deep as in southeastern Amazonia, the large subsurface storage capacity holds the infiltrated water longer before releasing it to streams, hence the subsurface storage dominates TWS variation. Second, over the whole Amazon, the subsurface water contribution far exceeds surface water contribution to total TWS variations. Based on LEAF‐Hydro‐Flood simulations, 71% of TWS change is from subsurface water, 24% from flood water, and 5% from water in river channels. Third, the subsurface store includes two competing terms, soil water in the vadose zone and groundwater below the water table. As the water table rises, the length of vadose zone is shortened and hence the change in groundwater store is accompanied by an opposite change in soil water store resulting in their opposite phase and contributions to total TWS. We conclude that the inclusion of a prognostic groundwater store and its interactions with the vadose zone, rivers, and floodplains in hydrological simulations enhances seasonal amplitudes and delays seasonal peaks of TWS anomaly, leading to an improved agreement with GRACE observations.
Validation of the diurnal cycles in atmospheric reanalyses over Antarctic sea ice
Authors: Tastula Esa‐Matti , Vihma Timo , Andreas Edgar L. , Galperin Boris 
Published: April 2013

AbstractThe diurnal cycles of near‐surface meteorological parameters over Antarctic sea ice in six widely used atmospheric reanalyses are validated against observations from Ice Station Weddell. The station drifted from February through May 1992 and provided the most extensive set of meteorological observations ever collected in the Antarctic sea ice zone. For the radiative and turbulent surface fluxes, both the amplitude and shape of the diurnal cycles vary considerably among different reanalyses. Near‐surface temperature, specific humidity, and wind speed in the reanalyses all feature small diurnal ranges, which, in most cases, fall within the uncertainties of the observed cycle. A skill score approach revealed the superiority of the ERA‐Interim reanalysis in reproducing the observed diurnal cycles. An explanation for the shortcomings in the reanalyses is their failure to capture the diurnal cycle in cloud cover fraction, which leads to errors in other quantities as well. Apart from the diurnal cycles, NCEP‐CFSR gave the best error statistics.
Microphysical implications of cloud‐precipitation covariance derived from satellite remote sensing
Authors: Lebsock Matthew , Morrison Hugh , Gettelman Andrew 
Published: April 2013

AbstractCovariance between cloud and precipitation water in shallow marine boundary layer clouds is assessed using collocated satellite observations from CloudSat and the moderate resolution imaging spectroradiometer (MODIS) at spatial scales typical of global models. An analytic construct is presented, which suggests that global models that do not take subgrid scale cloud‐precipitation covariance into account in their microphysical parameterizations may significantly underestimate grid mean microphysical process rates in warm clouds. The proposed framework indicates a mean bias in autoconversion rates of 129% when subgrid scale cloud water variability is neglected and bias in accretion rates of 60% when subgrid cloud‐precipitation covariability is neglected at a model grid resolution of 141 km. The bias in accretion rate is dependent on the significant correlation (ρ) found between cloud and precipitation, which in the global mean is found to be ρ = 0.44. The regional distribution of the process rate biases is largely governed by the spatial pattern of cloud water variance. Specific areas of low cloud water variance are found in the subtropical eastern ocean basins and the high latitudes, whereas much of the tropics display relatively larger cloud water variance. These regional distinctions in cloud water variance are associated with commensurate regionality in the process rate biases. The magnitude of the bias has a scale dependence that is governed by the spatial scaling behavior of the cloud and precipitation variances, which follow a power law scaling with exponent of 2/3 at scales below about 10 km and decreasing exponent above this length scale. While the parametric framework reduces biases in the accretion rate estimated from the grid‐mean values of cloud and precipitation water, it is shown that it still undercorrects the accretion rate because it neglects the fact that the precipitation fractional area is less than the cloud fractional area and is preferentially colocated with the highest cloud water concentrations. These results imply that (1) predicting the appropriate balance of autoconversion to accretion in global models requires not only the subgrid scale cloud water variability but also the subgrid scale covariability of cloud and precipitation water and (2) the ability of a global model to calculate the correct regional variation in process rates depends crucially on the fidelity of that model to predict or diagnose the spatial distribution of the variance in cloud water.
Influence of monsoon system on α‐HCH fate in Asia: A model study from 1948 to 2008
Authors: Xu Yue , Tian Chongguo , Zhang Gan , Ming Lili , Wang Yan , Chen Yingjun , Tang Jianhui , Li Jun , Luo Chunling 
Published: April 2013

AbstractThe Chinese Gridded Pesticide Emission and Residue Model was applied to simulate long‐term environmental fate of α‐hexachlorocyclohexane (HCH) in Asia spanning 1948 to 2008. The simulation identifies the southern Tibetan Plateau and the margin of the Asian monsoon regime from the northeast area of the Tibetan Plateau to the Northeast China as sink areas. This spatial pattern of sink distribution is closely related to the summer monsoon activities in Asia. Wet deposition associated with the summer monsoon (June to August) is responsible for at least half of the α‐HCH mass entering into the sink areas. After deposition, relatively low temperature and high soil organic matter in the sink areas are favorable for α‐HCH detention. Chinese and Indian sources are the major contributors to α‐HCH contamination over the monsoon margin and the Tibetan Plateau, driven by the East Asian summer monsoon and South Asian summer monsoon, respectively.
The precipitating cloud population of the Madden‐Julian Oscillation over the Indian and west Pacific Oceans
Authors: Barnes Hannah C. , Houze Robert A. 
Published: April 2013

AbstractThe variability of the precipitating cloud population of the Madden‐Julian Oscillation (MJO) is represented by statistics of echo features seen by the Tropical Rainfall Measuring Mission's Precipitation Radar over the central Indian and west Pacific Oceans. Echo features include isolated shallow echoes, deep convective cores, wide convective cores, and broad stratiform regions. Isolated shallow echoes are ever present but most numerous during suppressed MJO phases. Broad stratiform regions dominate variability in areal coverage and maximize during active phases. Deep convective and wide convective cores are more common and variable in number than broad stratiform regions. The magnitude of variability is similar in both regions. In the central Indian Ocean, active MJO phases have synchronous maximization of deep convective entities. In the west Pacific, broad stratiform regions maximize prior to wide convective cores. Reanalysis indicates that isolated shallow echoes are most numerous in dry mid‐tropospheric conditions and strong low‐level (1000–750 hPa) shear. Mid‐tropospheric moisture increases before deeper convective features increase in number, maximizes as deep convective features maximize, and decreases as wide convective cores and broad stratiform regions decline in population. Active‐stage deep and wide convective cores occur preferentially with moist mid‐tropospheric conditions and strong low‐level shear. Acute shear may favor downdraft momentum transport and consequently more robust gust‐front convective triggering. Broad stratiform regions maximize with a moist mid‐troposphere, strong low‐level shear, and moderate upper‐level (750–500 hPa) shear that is not so strong that the stratiform region disconnects from its convective moisture source.
Assimilation of microwave brightness temperature in a land data assimilation system with multi‐observation operators
Authors: Jia Binghao , Tian Xiangjun , Xie Zhenghui , Liu Jianguo , Shi Chunxiang 
Published: April 2013

AbstractA radiative transfer model (RTM) that provides a link between model states and satellite observations (e.g., brightness temperature) can act as an observation operator in land data assimilation to directly assimilate brightness temperatures. In this study, a microwave Land Data Assimilation System (LDAS) was developed with three RTMs (The radiative transfer model for bare field (QH), land emissivity model (LandEM), and Community Microwave Emission Model (CMEM)) as its multi‐observation operators (LDAS‐MO). Assimilation experiments using the Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR‐E) satellite brightness temperature data from July 2005 to December 2008 were then conducted to investigate the impact of the RTMs on the assimilated results over China. It was found that the assimilated volumetric soil‐water content using each of the three observation operators improved the estimation of soil moisture content in the top soil layer (0–10 cm), with reduced root mean square errors (RMSEs), and increased correlation coefficients with field observations (OBS) as compared to a control run with no assimilation for the absence of frozen or snow‐covered conditions. The assimilated soil moisture for the QH model, which was more sensitive to dry soil than the other models, produced closer correlations with OBS in arid and semi‐arid regions while smaller RMSEs were observed for LandEM. CMEM agreed most closely with OBS over the middle and lower reaches of the Yangtze River due to its better simulation of the brightness temperature over densely vegetated areas. To improve assimilation accuracy, a Bayesian model averaging (BMA) scheme for the LDAS‐MO was developed. The BMA scheme was found to significantly enhance assimilation capability producing the soil moisture analysis, showing the lowest RMSEs and highest correlations with OBS over all areas. It was demonstrated that the BMA scheme with LDAS‐MO has the potential to estimate soil moisture with high accuracy.
Characterizing and understanding radiation budget biases in CMIP3/CMIP5 GCMs, contemporary GCM, and reanalysis
Authors: Li J.‐L. F. , Waliser D. E. , Stephens G. , Lee Seungwon , L'Ecuyer T. , Kato Seiji , Loeb Norman , Ma Hsi‐Yen 
Published: April 2013

AbstractWe evaluate the annual mean radiative shortwave flux downward at the surface (RSDS) and reflected shortwave (RSUT) and radiative longwave flux upward at top of atmosphere (RLUT) from the twentieth century Coupled Model Intercomparison Project Phase 5 (CMIP5) and Phase 3 (CMIP3) simulations as well as from the NASA GEOS5 model and Modern‐Era Retrospective Analysis for Research and Applications analysis. The results show that a majority of the models have significant regional biases in the annual means of RSDS, RLUT, and RSUT, with biases from −30 to 30 W m−2. While the global average CMIP5 ensemble mean biases of RSDS, RLUT, and RSUT are reduced compared to CMIP3 by about 32% (e.g., −6.9 to 2.5 W m−2), 43%, and 56%, respectively. This reduction arises from a more complete cancellation of the pervasive negative biases over ocean and newly larger positive biases over land. In fact, based on these biases in the annual mean, Taylor diagram metrics, and RMSE, there is virtually no progress in the simulation fidelity of RSDS, RLUT, and RSUT fluxes from CMIP3 to CMIP5. A persistent systematic bias in CMIP3 and CMIP5 is the underestimation of RSUT and overestimation of RSDS and RLUT in the convectively active regions of the tropics. The amount of total ice and liquid atmospheric water content in these areas is also underestimated. We hypothesize that at least a part of these persistent biases stem from the common global climate model practice of ignoring the effects of precipitating and/or convective core ice and liquid in their radiation calculations.
Microphysical and radiative changes in cirrus clouds by geoengineering the stratosphere
Authors: Cirisan A. , Spichtinger P. , Luo B. P. , Weisenstein D. K. , Wernli H. , Lohmann U. , Peter T. 
Published: April 2013

AbstractIn the absence of tangible progress in reducing greenhouse gas emissions, the implementation of solar radiation management has been suggested as measure to stop global warming. Here we investigate the impacts on northern midlatitude cirrus from continuous SO2emissions of 2–10 Mt/a in the tropical stratosphere. Transport of geoengineering aerosols into the troposphere was calculated along trajectories based on ERA Interim reanalyses using ozone concentrations to quantify the degree of mixing of stratospheric and tropospheric air termed “troposphericity”. Modeled size distributions of the geoengineered H2SO4‐H2O droplets have been fed into a cirrus box model with spectral microphysics. The geoengineering is predicted to cause changes in ice number density by up to 50%, depending on troposphericity and cooling rate. We estimate the resulting cloud radiative effects from a radiation transfer model. Complex interplay between the few large stratospheric and many small tropospheric H2SO4‐H2O droplets gives rise to partly counteracting radiative effects: local increases in cloud radiative forcing up to +2 W/m2for low troposphericities and slow cooling rates, and decreases up to −7.5 W/m2for high troposphericities and fast cooling rates. The resulting mean impact on the northern midlatitudes by changes in cirrus is predicted to be low, namely <1% of the intended radiative forcing by the stratospheric aerosols. This suggests that stratospheric sulphate geoengineering is unlikely to have large microphysical effects on the mean cirrus radiative forcing. However, this study disregards feedbacks, such as temperature and humidity changes in the upper troposphere, which must be examined separately.