bluuebunny/crossref_metadata_2025_split huggingface dataset:
Changes in Anthropogenic PM and the Resulting Global Climate Effects Under the RCP4.5 and RCP8.5 Scenarios by 2050
Authors: Yang Dongdong , Zhang Hua , Li Jiangnan 
Published: December 2019

AbstractUsing an aerosolclimate model, we studied the temporal and spatial variations of anthropogenic PM(aerodynamic diameter2.5 m) and coarse particulate matter (CPM; aerodynamic diameter2.5m) under Representative Concentration Pathway (RCP) 4.5 and RCP8.5 scenarios from 2014 to 2050. The corresponding radiative forcing and climate responses were also explored. The PMburden decreases over most continents, especially East Asia. The CPM particles increase over northern Asia, North America, and central Africa, in contrast to decrease over most regions of East Asia and North Africa. Relative to 2014, the global annual mean effective radiative forcing due to changes in PMand CPM burden are 1.17 (1.10) and0.06 (0.07) W munder RCP4.5 (RCP8.5), respectively. The reduction in PMburden leads to apparent warming, especially over high latitudes of the Northern Hemisphere, with global annual mean surface air temperature increasing by 1.25 K under RCP4.5, and 1.22 K under RCP8.5. In contrast, changes in CPM result in apparent cooling over North America and northern Asia, with global annual mean changes in surface air temperature of 0.10 K for both scenarios. The Northern Hemisphere Hadley cell weakens and moves northward due to changes in PMafter 2014, whereas the corresponding circulation in the Southern Hemisphere is strengthened, with the Intertropical Convergence Zone shifting to 10°N. Global annual mean precipitation increases by 0.10 mm dayunder both scenarios. Generally, anthropogenic PMcontributes significantly to future changes in radiative forcing and climate.
Meridional Heat Transport During Atmospheric Rivers in High‐Resolution CESM Climate Projections
Authors: Shields Christine A. , Rosenbloom Nan , Bates Susan , Hannay Cecile , Hu Aixue , Payne Ashley E. , Rutz Jonathan J. , Truesdale John 
Published: December 2019

AbstractMeridional sensible and latent heat transport is evaluated for regions with landfalling atmospheric rivers using both MERRA‐2 reanalysis and fully coupled CESM1.3 high‐resolution climate projections. Western North America, the United Kingdom, and the Iberian Peninsula are chosen to represent the regions significantly impacted by atmospheric rivers (ARs). CESM1.3 historical simulations can accurately represent both sensible and latent regional meridional heat transports compared to MERRA‐2 both for the total period analyzed (1980–2016) and for days with atmospheric rivers only. Uncertainty in these calculations due to AR identification is assessed by applying available Tier 1 AR‐catalogs from Atmospheric Tracking Method Intercomparison Project (ARTMIP) to the MERRA‐2 analysis. CESM1.3 climate projections suggest that under global warming, latent heat transport increases across all regions in the mid‐latitudes where sensible heat decreases (increases) for western North America (Europe). Generally, changes to the meridional heat transport are forced by the upper‐level meridional wind component.
Future Reductions in Polar Cold Air Mass and Cold Air Outbreaks Revealed From Isentropic Analysis
Authors: Kanno Yuki , Iwasaki Toshiki 
Published: December 2019

AbstractThis study quantifies future changes in the polar cold air mass (PCAM) below a threshold potential temperature of 280 K and its horizontal fluxes, which are an indicator for the intensity of cold air outbreaks, by analyzing the outputs from five climate models from the Fifth Coupled Model Intercomparison Project. Under the business‐as‐usual scenario, the multimodel means of the wintertime total hemispheric PCAM decrease by 37% in the Northern Hemisphere and by 34% in the Southern Hemisphere by the end of the 21st century. The midlatitude equatorward PCAM fluxes are projected to decrease significantly by around 2050. This is primarily due to the reduction of the PCAM and to a lesser extent due to the weakening of the extratropical meridional circulation. Finally, intermodel differences in the total hemispheric PCAM reduction are shown to be linearly related to the climate sensitivity to the global mean surface air temperature.
Incidence of Alfvenic SC Pulse Onto the Conjugate Ionospheres
Authors: Pilipenko Vyacheslav A. , Fedorov Evgeniy N. , Xu Zhonghua , Hartinger Michael D. , Engebretson Mark J. , Edwards Thom R. 
Published: December 2019

AbstractA circuit analogy for magnetosphere‐ionosphere current systems has two extremes: the voltage generator (when the ground magnetic response is proportional to the ionospheric conductance) and the current generator (when the ground magnetic response practically does not depend on the ionospheric conductance). Nonsteady field‐aligned currents interact with the ionosphere in a different way depending on the ratio between the driver time scale
and the Alfven field line eigenperiod
. Sudden Commencement (SC) impulses at high latitudes correspond to the situation when
. This case of Alfven pulses propagating independently away from the equatorial plane is analytically examined with the magnetospheric plasma box model with thin asymmetric conjugate ionospheres. At high latitudes the amplitude ratio in conjugate ionospheres in general does not correspond directly to either the current or voltage regimes. Theoretical predictions are supported by examples of typical SC event observations at conjugate magnetometer sites in Greenland and Antarctica during summer and winter periods.
Analysis of the Beaufort Gyre Freshwater Content in 2003–2018
Authors: Proshutinsky A. , Krishfield R. , Toole J. M. , Timmermans M.‐L. , Williams W. , Zimmermann S. , Yamamoto‐Kawai M. , Armitage T. W. K. , Dukhovskoy D. , Golubeva E. , Manucharyan G. E. , Platov G. , Watanabe E. , Kikuchi T. , Nishino S. , Itoh M. , Kang S.‐H. , Cho K.‐H. , Tateyama K. , Zhao J. 
Published: December 2019

AbstractHydrographic data collected from research cruises, bottom‐anchored moorings, drifting Ice‐Tethered Profilers, and satellite altimetry in the Beaufort Gyre region of the Arctic Ocean document an increase of more than 6,400 km3 of liquid freshwater content from 2003 to 2018: a 40% growth relative to the climatology of the 1970s. This fresh water accumulation is shown to result from persistent anticyclonic atmospheric wind forcing (1997–2018) accompanied by sea ice melt, a wind‐forced redirection of Mackenzie River discharge from predominantly eastward to westward flow, and a contribution of low salinity waters of Pacific Ocean origin via Bering Strait. Despite significant uncertainties in the different observations, this study has demonstrated the synergistic value of having multiple diverse datasets to obtain a more comprehensive understanding of Beaufort Gyre freshwater content variability. For example, Beaufort Gyre Observational System (BGOS) surveys clearly show the interannual increase in freshwater content, but without satellite or Ice‐Tethered Profiler measurements, it is not possible to resolve the seasonal cycle of freshwater content, which in fact is larger than the year‐to‐year variability, or the more subtle interannual variations.
Experimental Assessments on Impacts of Salinity Anomalies on the Positive Indian Ocean Dipole
Authors: Kido Shoichiro , Tozuka Tomoki , Han Weiqing 
Published: December 2019

AbstractImpacts of salinity anomalies associated with the positive Indian Ocean Dipole (pIOD) are assessed through novel sensitivity experiments using a regional ocean model (Regional Ocean Model System) and detailed diagnostics of heat and momentum budget. During the pIOD, density stratification in the eastern equatorial Indian Ocean is enhanced due to anomalous surface freshening and subsurface saltening. This causes momentum inputs from the wind forcing to be more strongly trapped in the surface layer, and zonal and vertical current anomalies to be more confined to the upper layer. As a result, upward transports of cold water from below the thermocline to the surface layer are significantly suppressed, and the cooling in the eastern equatorial Indian Ocean is suppressed by as much as 1.0 °C. The above arguments are further corroborated by a set of sensitivity experiments using a linear continuously stratified ocean model, which can isolate the effect of stratification change caused by salinity anomalies associated with the pIOD in the Regional Ocean Model System simulation. Our results suggest that salinity does play an active role in the evolution of the pIOD, rather than being passively affected by large‐scale anomalous atmospheric and oceanic conditions.
The Subsurface Coherent Rock Content of the Moon as Revealed by Cold‐Spot Craters
Authors: Elder C. M. , Douglass B. , Ghent R. R. , Hayne P. O. , Williams J.‐P. , Bandfield J. L. , Costello E. 
Published: December 2019

AbstractA recently identified class of young lunar craters, cold‐spot craters, provides an optimal data set for probing the subsurface rock content on the Moon. Rocks, or lack of rocks, in crater ejecta have long been used as indicators of regolith thickness. However, the rockiness of crater ejecta depends on the subsurface rock content, crater excavation depth, and crater age. Cold‐spot craters are surrounded by a low thermal inertia signature that fades within 1 Myr, so any rocks in the proximal ejecta blanket have not yet been broken down or buried. Thus, the rock abundance in the proximal ejecta blankets of cold‐spot craters is affected only by the subsurface rock content of the target and the crater excavation depth, not the age of the crater. We show that an abrupt transition between fine‐grained regolith and underlying coherent rock cannot explain the observed rock abundance. Instead, we assume that the volume fraction of coherent rock (in contrast to fine‐grained regolith) increases exponentially in the lunar subsurface and use the observed Diviner rock abundance in cold‐spot crater ejecta to solve for the “e‐folding” depth over which the volume fraction of rock increases. In general, the subsurface rock content is higher in the maria than in the highlands consistent with more recent resurfacing of the maria. However, the highlands show a wider range of subsurface rock content values overall including some overlapping those of the maria. Some of this variability appears to be associated with the Orientale basin and possibly with several cryptomare deposits.
Phobos Surface Sputtering as Inferred From MAVEN Ion Observations
Authors: Nénon Q. , Poppe A. R. , Rahmati A. , Lee C. O. , McFadden J. P. , Fowler C. M. 
Published: December 2019

AbstractPhobos is bombarded by both protons and alpha particles from the solar wind and by Martian atomic and molecular oxygen ions. A numerical model of the distribution of planetary ions has previously proposed that these ions may dominate solar wind ions in sputtering the surface of Phobos when the moon is located downstream of Mars. This conclusion suggests a unique link between planetary atmospheric escape at Mars and the surface processing of its moon yet, remains to be confirmed with in situ ion measurements. In this article, a 4‐year‐long average of the ion environment that Phobos is exposed to is constructed from in situ ion observations conducted by the Mars Atmosphere and Volatile Evolution (MAVEN) mission. In turn, the flux of material sputtered from the surface of Phobos by this environment is computed. We confirm that planetary atomic oxygen ions dominate over solar wind ions in sputtering the surface of Phobos downstream of Mars during 20% of the moon's orbit. We also reveal that molecular oxygen ions sputter the surface of Phobos as much as or more than atomic oxygen ions in the Martian magnetotail. In addition to the long‐term average picture, the time variation of Phobos surface sputtered fluxes is investigated during the series of solar wind events that hit the Martian system in March 2015. We find that the flux of material liberated from Phobos' surface increased by a factor of 50 during this period.
Linear Inverse Modeling for Coupled Atmosphere‐Ocean Ensemble Climate Prediction
Authors: Perkins W. Andre , Hakim Greg 
Published: December 2019

AbstractPaleoclimate data assimilation (PDA) experiments reconstruct climate fields by objectively blending information from climate models and proxy observations. Due to high computational cost and relatively low forecast skill, most reconstruction experiments omit the prediction step, where a forecast is made from the previously reconstructed state to the next time proxy data is available. In order to enable this critical aspect of PDA, we propose an efficient method of generating forecast ensembles of coupled climate fields using a linear inverse model (LIM). We describe the general calibration of a LIM on multiple fields using a two‐step empirical orthogonal function field compression to efficiently represent the state. We find that a LIM calibrated on global climate model (GCM) data yields skillful forecasts, including for out‐of‐sample tests on data from a different GCM. The deterministic forecast skill tests for scalar indices show that the LIM outperforms damped persistence at leads up to 3 years and has skill up to 10 years for global average sea surface temperature. Analysis of 1‐year forecasts reveals that the LIM captures dynamic climate features with local and remote predictability related to teleconnections. The forecast ensemble characteristics of the LIM, which in part determine the weighting of information for PDA experiments, show that the LIM generally produces ensemble forecast errors that are 10% to 70% larger than ensemble variance for 1‐year forecasts on data representative of the last millennium. These results show that the LIM produces ensembles with reasonable calibration but also that LIMs for PDA may require some variance tuning to work optimally for data assimilation experiments.
Evaluation of the CABLEv2.3.4 Land Surface Model Coupled to NU‐WRFv3.9.1.1 in Simulating Temperature and Precipitation Means and Extremes Over CORDEX AustralAsia Within a WRF Physics Ensemble
Authors: Hirsch Annette L. , Kala Jatin , Carouge Claire C. , De Kauwe Martin G. , Di Virgilio Giovanni , Ukkola Anna M. , Evans Jason P. , Abramowitz Gab 
Published: December 2019

AbstractThe Community Atmosphere Biosphere Land Exchange (CABLE) model is a third‐generation land surface model (LSM). CABLE is commonly used as a stand‐alone LSM, coupled to the Australian Community Climate and Earth Systems Simulator global climate model and coupled to the Weather Research and Forecasting (WRF) model for regional applications. Here, we evaluate an updated version of CABLE within a WRF physics ensemble over the COordinated Regional Downscaling EXperiment (CORDEX) AustralAsia domain. The ensemble consists of different cumulus, radiation and planetary boundary layer (PBL) schemes. Simulations are carried out within the NASA Unified WRF modeling framework, NU‐WRF. Our analysis did not identify one configuration that consistently performed the best for all diagnostics and regions. Of the cumulus parameterizations the Grell‐Freitas cumulus scheme consistently overpredicted precipitation, while the new Tiedtke scheme was the best in simulating the timing of precipitation events. For the radiation schemes, the RRTMG radiation scheme had a general warm bias. For the PBL schemes, the YSU scheme had a warm bias, and the MYJ PBL scheme a cool bias. Results are strongly dependent on the region of interest, with the northern tropics and southwest Western Australia being more sensitive to the choice of physics options compared to southeastern Australia which showed less overall variation and overall better performance across the ensemble. Comparisons with simulations using the Unified Noah LSM showed that CABLE in NU‐WRF has a more realistic simulation of evapotranspiration when compared to GLEAM estimates.
Using a Down‐Looking Multifrequency ABS for Measuring Suspended Sediments in Rivers
Authors: Vergne Adrien , Le Coz Jérôme , Berni Céline , Pierrefeu Gilles 
Published: December 2019

AbstractIn the last decade, much progress has been made in continuously measuring suspended sediment concentration (SSC) in rivers using horizontal side‐looking Acoustic Doppler Current Profilers. However, these techniques do not provide information on the spatial variability of the suspension. In this study, we explore some new possibilities offered by the down‐looking deployment of a multifrequency acoustic backscatter system (ABS) in order to obtain information on the suspension throughout an entire river cross section. Two sites, with low and high levels of SSC, were investigated. The acoustic signal was processed using multifrequency inversion methods. Both water sample calibration data and modeling were used for retrieving the acoustic properties of the suspended particles. At the low SSC site (
30 mg/L), we successfully inverted the acoustic signal, except in some areas of high acoustic backscatter close to the surface that were probably generated by air microbubbles. At the high SSC site (
10 g/L), estimates of both fine and sand SSCs throughout the river cross section were successfully obtained, except in some areas close to the bottom where the acoustic signal was totally attenuated due to distance and high concentration of fine sediments. This work confirms the capacity of hydroacoustic technology for providing spatial information on river suspensions.
Predicting Shallow Groundwater Tables for Sloping Highland Aquifers
Authors: Alemie Tilashwork C. , Tilahun Seifu A. , Ochoa‐Tocachi Boris F. , Schmitter Petra , Buytaert Wouter , Parlange J‐Yves , Steenhuis Tammo S. 
Published: December 2019

AbstractWhile hydrological science has made great strides forward during the last 50 years with the advance of computing power and availability of satellite images, much is unknown about the sustainable development of water for irrigation, domestic use, and livestock consumption for millions of households in the developing world. Specifically, quantification of shallow underground water resources for irrigation in highland regions remains challenging. The objective is to better understand the hydrology of highland watersheds with sloping hillside aquifers. Therefore, we present a subsurface flow model for hillside aquifers with recharge that varied from day to day. Recharge to the aquifer was estimated by the Thornthwaite Mather procedure. A characteristic time was identified for travel time of water flowing from the upper part of the hillside to the river or well. Using the method of characteristics, we found that the height of shallow groundwater level can be predicted by determining the total recharge over the characteristic time divided by drainable porosity. We apply the model to farmer‐dug wells in the Ethiopian highlands using observed rainfall, potential evaporation, and a fitted travel time. We find that the model performs well with maximum water table heights being determined by the soil surface and minimum heights by the presence or absence of volcanic dikes downhill. Our application shows that unless the water is ponded behind a natural or artificial barrier, hillslope aquifers are unable to provide a continuous source of water during the long, dry season. This clearly limits any irrigation development in the highlands from shallow sloping groundwater.
The Dynamics of Suspended Sediment in a Typical Alpine Alluvial River Reach: Insight From a Seasonal Survey
Authors: Misset C. , Recking A. , Legout C. , Valsangkar N. , Bodereau N. , Zanker S. , Poirel A. , Borgniet L. 
Published: December 2019

AbstractThe transport of suspended sediment is associated with important social, economic, and environmental issues. It is still unclear, however, how suspended sediments eroded on hillslopes are transferred downstream through the river system. In this study, we aimed to investigate this process by applying a sediment budget approach to a typical 3.5‐km‐long Alpine braided reach. Using high‐frequency suspended load measurements combined with Monte Carlo simulations for uncertainty propagation, we observed a significant buffering behavior of the reach studied. Thirty‐two of the 48 events observed during the 2‐month campaign showed significant differences between upstream and downstream mass transported as suspension, despite the reach studied was short compared to the upstream drainage area (130 km2). These differences at the event scale varied widely within an envelope comprised between a net erosion equivalent to 74% of upstream suspended mass and a net deposition equivalent to 71%. Budgets were found to be controlled at a nearly instantaneous time scale by the liquid discharges and the suspended sediment concentrations in an opposite way: for low upstream concentrations, net erosion increased when the discharges increased, while above a certain concentration, net deposition increased when the concentrations increased. Moreover, coarse particles mobility in the reach (characterized via bedload transport measurements) appeared to have a strong influence on the availability of suspended particles as both quantities evolved concomitantly through time. These observations have important implications for our understanding and modeling of the transfer of suspended particles in gravel bedded streams.
Evaluation of SNODAS Snow Water Equivalent in Western Canada and Assimilation Into a Cold Region Hydrological Model
Authors: Lv Zhibang , Pomeroy John W. , Fang Xing 
Published: December 2019

AbstractSnow water equivalent (SWE) is one of the most hydrologically important physical properties of a snowpack. The U.S. National Weather Service's Snow Data Assimilation System (SNODAS) provides snow products at high spatial (~1 km2) and temporal (daily) resolution for the contiguous United States and southern Canada. This study evaluated the SNODAS SWE product in the boreal forest, prairie, and Canadian Rockies of western Canada against extensive snow survey measurements. SNODAS was found to work well in sheltered environments, to overestimate SWE under needle‐leaf forests, and to be unable to capture the spatial variation of SWE in windswept prairie and alpine environments. Results indicate that SNODAS SWE accuracy is strongly influenced by the missing blowing snow redistribution and canopy energetics and snow interception and sublimation processes in the mass balance calculations of the SNODAS model and by erroneous precipitation data forcing the model. To demonstrate how errors caused by missing processes can be corrected in areas with low assimilation frequency, SNODAS data were assimilated into a physically based hydrological model created using the modular Cold Region Hydrological Modelling (CRHM) platform that includes blowing and intercepted snow redistribution and subcanopy melt energetic processes. This approach decreased the overestimation of SWE compared to SNODAS from 135 to 79% in the study area and suggests that snow assimilation modeled SWE quality can be improved if snow redistribution, sublimation, and subcanopy melt processes are incorporated.