bluuebunny/crossref_metadata_2025 huggingface dataset:
Bringing antiretroviral therapy (ART) closer to the end‐user through mobile clinics and home‐based ART: systematic review shows more evidence on the effectiveness and cost effectiveness is needed
Authors: Mdege Noreen Dadirai , Chindove Stanley
Published: April 2013

Background

Home‐based antiretroviral therapy (ART) and ART through mobile clinics can potentially increase access to ART for large numbers of people, including hard‐to‐reach populations. We reviewed literature on the effectiveness and cost implications of the home‐based ART and mobile clinic ART models.

Methods

We searched Medline, Embase, PsycInfo, CINAHL, Cochrane Library, Web of Knowledge and Current Controlled Trials Register for articles published up to March 2012. We included non‐randomised and randomised controlled clinical trials that recruited HIV/AIDS positive adults with or without prior exposure to ART.

Results

Six studies were included in the review, with only four effectiveness studies (all evaluating home‐based ART and none for mobile clinic ART) and four studies reporting on the cost implications. The evidence suggests home‐based ART is as effective as health facility‐based ART, including on clinical outcomes, viral load and CD4+ count. However, three of these studies were very small. Studies suggest health facility‐based ART is the most cost‐effective, followed by mobile‐clinic ART, with home‐based ART being the least cost‐effective.

Conclusions

Evidence on the effectiveness and cost implications of mobile clinic and home‐based ART is currently limited. Although the few available studies suggest home‐based ART can potentially be as effective as health facility‐based ART, there is need for more research before robust conclusions can be made. Results from the few available studies also suggest that health facility‐based ART is the most cost‐effective. Copyright © 2013 John Wiley & Sons, Ltd.
Challenges for exposure prediction in ecological risk assessment
Authors: Di Guardo Antonio , Hermens Joop LM
Published: April 2013

Evaluating organism exposure in the ecosystems is a difficult task and can be carried out measuring or predicting concentrations in the environment. Although current regulatory approaches favor a modeling approach, they either use a static representation of the environment and of the chemical discharge or a simplified dynamic approach (e.g., dealing with pesticides). Improving the ecological realism of exposure prediction offers a number of challenges. Some are related to the understanding of basic mechanisms such as bioavailability and the determination of internal exposure or the need to develop new paradigms for polar and ionized chemicals. Other issues are the need to provide monitoring data to understand the environmental fate of chemical mixtures, polar and ionized chemicals and metabolites, to understand the complexity of exposure in spatially and temporally variable environments. Exposure models require the development of suitable approaches to simulate the complexity of exposure in the ecosystems including the development of a variety of temporal and spatial scenarios and the integration of submodels (such as aquatic and terrestrial food webs). Finally, the integration of dynamic exposure and effect models is envisaged to fully carry out a more realistic ecological risk assessment. Integr Environ Assess Manag 2013;9:e4–e14. © 2013 SETAC
Proteomic profiling of halloysite clay nanotube exposure in intestinal cell co‐culture
Authors: Lai Xianyin , Agarwal Mangilal , Lvov Yuri M. , Pachpande Chetan , Varahramyan Kody , Witzmann Frank A.
Published: April 2013

Halloysite is aluminosilicate clay with a hollow tubular structure with nanoscale internal and external diameters. Assessment of halloysite biocompatibility has gained importance in view of its potential application in oral drug delivery. To investigate the effect of halloysite nanotubes on an in vitro model of the large intestine, Caco‐2/HT29‐MTX cells in monolayer co‐culture were exposed to nanotubes for toxicity tests and proteomic analysis. Results indicate that halloysite exhibits a high degree of biocompatibility characterized by an absence of cytotoxicity, in spite of elevated pro‐inflammatory cytokine release. Exposure‐specific changes in expression were observed among 4081 proteins analyzed. Bioinformatic analysis of differentially expressed protein profiles suggest that halloysite stimulates processes related to cell growth and proliferation, subtle responses to cell infection, irritation and injury, enhanced antioxidant capability, and an overall adaptive response to exposure. These potentially relevant functional effects warrant further investigation in in vivo models and suggest that chronic or bolus occupational exposure to halloysite nanotubes may have unintended outcomes. Copyright © 2013 John Wiley & Sons, Ltd.
Similarities and differences between sexes in regional loss of cortical and trabecular bone in the mid-femoral neck: The AGES-Reykjavik longitudinal study
Authors: Johannesdottir Fjola , Aspelund Thor , Reeve Jonathan , Poole Kenneth E , Sigurdsson Sigurdur , Harris Tamara B , Gudnason Vilmundur G , Sigurdsson Gunnar
Published: April 2013

The risk of hip fracture rises rapidly with age, and is notably higher in women. After falls and prior fragility fractures, the main clinically recognized risk factor for hip fracture is reduced bone density. To better understand the extent to which femoral neck density and structure change with age in each sex, we carried out a longitudinal study in subjects not treated with agents known to influence bone mineral density (BMD), to investigate changes in regional cortical thickness, as well as cortical and trabecular BMD at the mid-femoral neck. Segmental quantitative computed tomography (QCT) analysis was used to assess bone measurements in two anatomic subregions, the superolateral (superior) and inferomedial (inferior). A total of 400 older individuals (100 men and 300 women, aged 66–90 years) who were participants in the Age Gene/Environment Susceptibility-Reykjavik Study (AGES-Reykjavik), were studied. Participants had two QCT scans of the hip over a median follow-up of 5.1 years (mean baseline age 74 years). Changes in bone values during follow-up were estimated from mixed effects regression models. At baseline women had lower bone values in the superior region than men. At follow-up all bone values were lower in women, except cortical volumetric bone mineral density (vBMD) inferiorly. The relative losses in all bone values estimated in the superior region were substantially (about threefold) and significantly greater compared to those estimated in the inferior region in both sexes. Women lost cortical thickness and cortical vBMD more rapidly than men in both regions; and this was only weakly reflected in total femoral neck dual-energy X-ray absorptiometry (DXA)-like results. The higher rate of bone loss in women at critical locations may contribute materially to the greater femoral neck fracture incidence among women than men. © 2013 American Society for Bone and Mineral Research.
Theoretical characterization and design of small molecule donor material containing naphthodithiophene central unit for efficient organic solar cells
Authors: Duan Yu‐Ai , Geng Yun , Li Hai‐Bin , Jin Jun‐Ling , Wu Yong , Su Zhong‐Min
Published: April 2013

To seek for high‐performance small molecule donor materials used in heterojunction solar cell, six acceptor–donor–acceptor small molecules based on naphtho[2,3‐b:6,7‐b′]dithiophene (NDT) units with different acceptor units were designed and characterized using density functional theory and time‐dependent density functional theory. Their geometries, electronic structures, photophysical, and charge transport properties have been scrutinized comparing with the reported donor material NDT(TDPP)2 (TDPP = thiophene‐capped diketopyrrolopyrrole). The open circuit voltage (Voc), energetic driving force(ΔEL‐L), and exciton binding energy (Eb) were also provided to give an elementary understanding on their cell performance. The results reveal that the frontier molecular orbitals of 3–7 match well with the acceptor material PC61BM, and compounds 3–5 were found to exhibit the comparable performances to 1 and show promising potential in organic solar cells. In particular, comparing with 1, system 7 with naphthobisthiadiazole acceptor unit displays broader absorption spectrum, higher Voc, lower Eb, and similar carrier mobility. An in‐depth insight into the nature of the involved excited states based on transition density matrix and charge density difference indicates that all S1 states are mainly intramolecular charge transfer states with the charge transfer from central NDT unit to bilateral acceptor units, and also imply that the exciton of 7 can be dissociated easily due to its large extent of the charge transfer. In a word, 7 maybe superior to 1 and may act as a promising donor candidate for organic solar cell. © 2013 Wiley Periodicals, Inc.
IMSPeptider: A computational peptide collision cross‐section area calculator based on a novel molecular dynamics simulation protocol
Authors: de Carvalho Ranieri V. , Lopez‐Ferrer Daniel , Guimarães Katia S. , Lins Roberto D.
Published: April 2013

Introduction of ion mobility mass spectrometry (IMS/MS) into the proteomic workflow provides an orthogonal separation to the widely used LC‐MS platforms. IMS also provides structural information that could facilitate peptide identification. However, the lack of tools capable of predictive power in a high‐throughput fashion makes peptide global profiling quite challenging. To target this issue, a computational workflow was developed based on biophysical principles to predict the collision cross‐section area (CCS) of peptides as measured from IMS/MS experiments. Hosted on a web server, it allows the user to input a primary sequence (query) and retrieve information on peptide structure, sequence, and corresponding CCS. The current version is designed to identify peptide sequences up to 23 residues in length, in its higher charge state, based on a match of the molecule m/z and CCS. The protocol was validated against a 128‐sequences‐dataset and CCS predicted within 2.8% average error. © 2013 Wiley Periodicals, Inc.
A Model‐Based Approach to Predict Longitudinal HbA1c, Using Early Phase Glucose Data From Type 2 Diabetes Mellitus Patients After Anti‐Diabetic Treatment
Authors: Kjellsson Maria C. , Cosson Valérie F. , Mazer Norman A. , Frey Nicolas , Karlsson Mats O.
Published: April 2013

Predicting late phase outcomes from early‐phase findings can help inform decisions in drug development. If the measurements in early‐phase differ from those in late phase, forecasting is more challenging. In this paper, we present a model‐based approach for predicting glycosylated hemoglobin (HbA1c) in late phase using glucose and insulin concentrations from an early‐phase study, investigating an anti‐diabetic treatment. Two previously published models were used; an integrated glucose and insulin (IGI) model for meal tolerance tests and an integrated glucose‐red blood cell‐HbA1c (IGRH) model predicting the formation of HbA1c from the average glucose concentration (Cg,av). Output from the IGI model was used as input to the IGRH model. Parameters of the IGI model and drug effects were estimated using data from a phase1 study in 59 diabetic patients receiving various doses of a glucokinase activator. Cg,av values were simulated according to a Phase 2 study design and used in the IGRH model for predictions of HbA1c. The performance of the model‐based approach was assessed by comparing the predicted to the actual outcome of the Phase 2 study. We have shown that this approach well predicts the longitudinal HbA1c response in a 12‐week study using only information from a 1‐week study where glucose and insulin concentrations were measured.
Methamphetamine use can mimic testicular torsion
Authors: Doherty Michael H. , Gerscovich Eugenio O. , Corwin Michael T. , Wilkendorf Stephen R.
Published: April 2013

We report the case of a patient presenting with the classic clinical appearance of testicular torsion. Ultrasound showed testicular ischemia supporting the clinical diagnosis, but the lack of visualization of spermatic cord torsion was of concern. An attempt of clinical detorsion was considered unsuccessful and the patient was explored. No torsion was found. On postoperative review of the patient's medical history, we found methamphetamine use, with a positive urine test at the time of his emergent consultation for the scrotal pain episode. The use of amphetamines has been previously reported as the cause of ischemia of multiple organs, but we could not find previous reports of involvement of the testis mimicking torsion. © 2013 Wiley Periodicals, Inc. J Clin Ultrasound 41:461–463, 2013
A fatal complication of ultrasound‐guided abdominal paracentesis
Authors: Seidler Matthew , Sayegh Karl , Roy Anne , Mesurolle Benoît
Published: April 2013

Ultrasound‐guided abdominal paracentesis is a procedure that is frequently performed by radiologists for both diagnostic and therapeutic purposes. This procedure has been shown to be safe with few complications. We report the case of a patient who underwent an ultrasound‐guided therapeutic abdominal paracentesis for refractory ascites complicated by intraperitoneal hemorrhage leading to death. This case suggests that ultrasound‐guided paracentesis may need to become a more standardized procedure and that in the event of hemorrhage, alternative treatment options such as embolization or surgical intervention should be utilized when manual compression fails. © 2013 Wiley Periodicals, Inc. J Clin Ultrasound 41:457–460, 2013;
Monitoring of central retinal artery and vein with color doppler ultrasound during heart surgery as an alternative to transcranial doppler ultrasonography: A case report
Authors: Venturini Massimo , Zambon Massimo , Cristel Giulia , Agostini Giulia , Querques Giulia , Colombo Michele , Benussi Stefano , Landoni Giovanni , Zangrillo Alberto , Del Maschio Alessandro
Published: April 2013

Cardiac surgery can have severe neurologic complications. The noninvasive monitoring of intracranial circulation during heart surgery is usually performed with transcranial Doppler ultrasonography. We present the case of a 66‐year‐old man who underwent elective cardiac surgery for aortic valve replacement and coronary artery bypass graft, in whom monitoring was performed by simultaneously assessing blood flow velocity in the central retinal artery and vein. © 2013 Wiley Periodicals, Inc. J Clin Ultrasound 42:112–115, 2014
First observations of foreshock bubbles upstream of Earth's bow shock: Characteristics and comparisons to HFAs
Authors: Turner D. L. , Omidi N. , Sibeck D. G. , Angelopoulos V.
Published: April 2013

Using multipoint in situ observations upstream of Earth's bow shock from the THEMIS mission, we present the first observations of foreshock bubbles (FBs) and compare them to observations of hot flow anomalies (HFAs). FBs are recently conceptualized kinetic phenomena that can form under the commonplace condition of a rotational discontinuity in the interplanetary magnetic field interacting with backstreaming energetic ions in Earth's quasi‐parallel foreshock. FBs may have remained elusive until now due to their many observational similarities to HFAs and the lack of coordinated multipoint measurements. Here we introduce identification criteria for distinguishing between HFAs and FBs using in situ observations, and use them to analyze five example events that occurred on Bastille Day (14 July) and 11–12 August 2008. Three of these events satisfy the criteria for FBs and are inconsistent with multiple criteria for HFAs. The remaining two events are consistent with the traditional picture of HFAs. Furthermore, FBs involve two converging shocks, and using these events, we demonstrate their effectiveness at particle acceleration. Considering that their formation conditions are not extraordinary, FBs may be ubiquitous at collisionless, quasi‐parallel shocks in a variety of astrophysical settings.
Three‐dimensional failure envelopes and the brittle‐ductile transition
Authors: Schöpfer Martin P. J. , Childs Conrad , Manzocchi Tom
Published: April 2013

Rocks deformed at low confining pressure are brittle, meaning that after peak stress the strength decreases to a residual value determined by frictional sliding. The difference between the peak and residual value is the stress drop. At high confining pressure, however, no stress drop occurs. The transition pressure at which no loss in strength occurs is a possible definition of the brittle‐ductile transition. Here, we show, using numerical rock deformation, how this type of brittle‐ductile transition emerges from a simple model in which rock is idealized as an assemblage of cemented spherical unbreakable grains. Three‐dimensional failure and residual strength envelopes determined for this model material illustrate that the brittle‐ductile transition is a smoothly varying, mean stress‐dependent function in principal stress space. Neither the Mohr‐Coulomb nor the Drucker‐Prager failure criterion, which are the most commonly used empirical laws in rock and soil mechanics, respectively, adequately describes the dependence of peak strength and the brittle‐ductile transition on the intermediate stress (or Lode angle). A semi‐quantitative comparison between the modeled peak strength envelope with a selection of existing polyaxial rock data shows that the emergent intermediate stress dependence of strength in bonded particle models is comparable to that observed in rock. Deformation of particle models in which bond shear failure is inhibited illustrates that the non‐linear pressure dependence of strength (concave failure envelopes) is, at high mean stress, the result of microscopic shear failure, a result consistent with earlier two‐dimensional numerical multiple‐crack simulations.
Lithosphere structure and thickness beneath the North China Craton from joint inversion of ambient noise and surface wave tomography
Authors: Tang Youcai , Chen Y. John , Zhou Shiyong , Ning Jieyuan , Ding Zhifeng
Published: April 2013

We imaged detailed 3‐D crustal and uppermost mantle seismic structures in the North China Craton from inversion of Rayleigh wave phase velocity at periods of 6 to 143 s. The phase velocities were obtained from a combination of ambient noise and teleseismic surface wave tomography, and then the phase velocities were inverted to S‐wave velocities. The results show that both the Huabei Basin and Ordos Block have markedly rapid variations in both crustal velocities and the Moho depth. Huabei Basin has a thin (31–34 km) crust with low velocities while Ordos Block has a thick (~40 km) crust with high velocities. We also estimated the lithospheric thickness from the inverted S‐wave velocities using a simple S‐wave velocity/temperature relationship. Huabei Basin was imaged as a low S‐wave‐velocity anomaly in the uppermost mantle with very thin lithosphere (~65 km), while Ordos Block was revealed as a high S‐wave‐velocity anomaly with rather thick lithosphere (>120 km). These results indicated that Huabei Basin and Ordos Block have different thermal and/or chemical properties and had experienced different mantle processes and evolution histories since the Cenozoic. Furthermore, slow S‐wave velocities and very thin lithosphere (~65 km) were also found beneath Hetao and Weihe rifts bounding Ordos Block at north and south, respectively. However, Shanxi Rift—the boundary between Huabei Basin and Ordos Block—had a much thicker and higher velocity lithosphere than Hetao and Weihe rifts.
Emission ratios of anthropogenic volatile organic compounds in northern mid‐latitude megacities: Observations versus emission inventories in Los Angeles and Paris
Authors: Borbon Agnes , Gilman J. B. , Kuster W. C. , Grand N. , Chevaillier S. , Colomb A. , Dolgorouky C. , Gros V. , Lopez M. , Sarda‐Esteve R. , Holloway J. , Stutz J. , Petetin H. , McKeen S. , Beekmann M. , Warneke C. , Parrish D. D. , de Gouw J. A.
Published: April 2013

Ground‐based and airborne volatile organic compound (VOC) measurements in Los Angeles, California, and Paris, France, during the Research at the Nexus of Air Quality and Climate Change (CalNex) and Megacities: Emissions, Urban, Regional and Global Atmospheric Pollution and Climate Effects, and Integrated Tools for Assessment and Mitigation (MEGAPOLI) campaigns, respectively, are used to examine the spatial variability of the composition of anthropogenic VOC urban emissions and to evaluate regional emission inventories. Two independent methods that take into account the effect of chemistry were used to determine the emission ratios of anthropogenic VOCs (including anthropogenic isoprene and oxygenated VOCs) over carbon monoxide (CO) and acetylene. Emission ratios from both methods agree within ±20%, showing the reliability of our approach. Emission ratios for alkenes, alkanes, and benzene are fairly similar between Los Angeles and Paris, whereas the emission ratios for C7–C9 aromatics in Paris are higher than in Los Angeles and other French and European Union urban areas by a factor of 2–3. The results suggest that the emissions of gasoline‐powered vehicles still dominate the hydrocarbon distribution in northern mid‐latitude urban areas, which disagrees with emission inventories. However, regional characteristics like the gasoline composition could affect the composition of hydrocarbon emissions. The observed emission ratios show large discrepancies by a factor of 2–4 (alkanes and oxygenated VOC) with the ones derived from four reference emission databases. A bias in CO emissions was also evident for both megacities. Nevertheless, the difference between measurements and inventory in terms of the overall OH reactivity is, in general, lower than 40%, and the potential to form secondary organic aerosols (SOA) agrees within 30% when considering volatile organic emissions as the main SOA precursors.
The simulation of water vapor transport in East Asia using a regional air–sea coupled model
Authors: Yao Suxiang , Huang Qian , Zhang Yaocun , Zhou Xu
Published: April 2013

A regional air–sea coupled model (RegCM3‐POM) is used, and the ability of the model to simulate June, July, and August (JJA) moisture transport is verified. The coupled model (RegCM3‐POM) has better performances than the uncoupled model (RegCM3) in the simulation of the JJA mean water vapor characteristics from 1979 to 2002 and its interannual variations. The differences of water vapor between RegCM3‐POM and RegCM3 are mainly caused by different winds in the middle and low troposphere. The simulated circulation pattern of RegCM3‐POM is more similar to the Climate Forecast System Reanalysis (CFSR) data than that of the uncoupled model. The simulated geopotential height and the gradient of geopotential height in the coupled model are more accurate than those in the uncoupled model. The real‐time and lead–lag relationship between geopotential height and sea surface temperature (SST) in RegCM3‐POM is consistent with that between the height of CFSR data and HadISST (Hadley Center Sea Ice and Sea Surface Temperature data). Thus, the simulated water vapor in the lower troposphere and the vertically integrated moisture transport are more accurate in the coupled model than in RegCM3. In addition, the correlation coefficients between moisture transport and SST in RegCM3 are positive in South China Sea, corresponding to SST forcing; the correlation coefficients in RegCM3‐POM are negative, which is consistent with that between the vapor transport in CFSR data and HadISST. Thus, the air–sea coupled model represents more accurately than the uncoupled model the relationship between SST and moisture transport.
Statistical patterns in the location of natural lightning
Authors: Zoghzoghy F. G. , Cohen M. B. , Said R. K. , Inan U. S.
Published: April 2013

Lightning discharges are nature's way of neutralizing the electrical buildup in thunderclouds. Thus, if an individual discharge destroys a substantial fraction of the cloud charge, the probability of a subsequent flash is reduced until the cloud charge separation rebuilds. The temporal pattern of lightning activity in a localized region may thus inherently be a proxy measure of the corresponding timescales for charge separation and electric field buildup processes. We present a statistical technique to bring out this effect (as well as the subsequent recovery) using lightning geo‐location data, in this case with data from the National Lightning Detection Network (NLDN) and from the GLD360 Network. We use this statistical method to show that a lightning flash can remove an appreciable fraction of the built up charge, affecting the neighboring lightning activity for tens of seconds within a ∼ 10 km radius. We find that our results correlate with timescales of electric field buildup in storms and suggest that the proposed statistical tool could be used to study the electrification of storms on a global scale. We find that this flash suppression effect is a strong function of flash type, flash polarity, cloud‐to‐ground flash multiplicity, the geographic location of lightning, and is proportional to NLDN model‐derived peak stroke current. We characterize the spatial and temporal extent of the suppression effect as a function of these parameters and discuss various applications of our findings.
A novel approach to statistical downscaling considering nonstationarities: application to daily precipitation in the Mediterranean area
Authors: Hertig E. , Jacobeit J.
Published: April 2013

In the present study, nonstationarities in predictor–predictand relationships within the framework of statistical downscaling are investigated. In this context, a novel validation approach is introduced in which nonstationarities are explicitly taken into account. The method is based on results from running calibration periods. The (non)overlaps of the bootstrap confidence interval of the mean model performance (derived by averaging the performances of all calibration/verification periods) and the bootstrap confidence intervals of the individual model errors are used to identify (non)stationary model performance. The specified procedure is demonstrated for mean daily precipitation in the Mediterranean area using the bias to assess model skill. A combined circulation‐based and transfer function–based approach is employed as a downscaling technique. In this context, large‐scale seasonal atmospheric regimes, synoptic‐scale daily circulation patterns, and their within‐type characteristics, are related to daily station‐based precipitation. Results show that nonstationarities are due to varying predictors–precipitation relationships of specific circulation configurations. In this regard, frequency changes of circulation patterns can damp or increase the effects of nonstationary relationships. Within the scope of assessing future precipitation changes under increased greenhouse warming conditions, the identification and analysis of nonstationarities in the predictors–precipitation relationships leads to a substantiated selection of specific statistical downscaling models for the future assessments. Using RCP4.5 scenario assumptions, strong increases of daily precipitation become apparent over large parts of the western and northern Mediterranean regions in winter. In spring, summer, and autumn, decreases of precipitation until the end of the 21st century clearly dominate over the entire Mediterranean area.
Enhancing model‐based land surface temperature estimates using multiplatform microwave observations
Authors: Holmes Thomas R. H. , Crow Wade T. , Tugrul Yilmaz M. , Jackson Thomas J. , Basara Jeffrey B.
Published: April 2013

Land surface temperature plays an important role in surface processes and is a key input for physically based retrieval algorithms of soil moisture and evaporation. This study presents a framework for using independent estimates of land surface temperature from five microwave satellite sensors to improve the accuracy of land surface temperature output from a numerical weather prediction system in an off‐line (postprocessing) analysis. First, structural differences in timing and amplitude of the temperature signal were addressed. Then, satellite observations were assimilated into an auto‐regressive error model, formulated to estimate errors in the numerical weather prediction output. Errors in daily minimum and amplitude were treated separately. Results of this study provide new insights about potential added benefits of preprocessing and off‐line assimilation of microwave remote sensing‐based and model‐based temperature retrievals. It is shown that the satellite observations may be used to reduce errors in surface temperature, particularly for day‐time hours. Preprocessing is responsible for the bulk of this reduction in temperature error; data assimilation is shown to further reduce the random temperature error by a few tenths of a Kelvin, accounting for a 10% reduction in RMSE.
Effect of data coverage on the estimation of mean and variability of precipitation at global and regional scales
Authors: Wan Hui , Zhang Xuebin , Zwiers Francis W. , Shiogama Hideo
Published: April 2013

We use monthly precipitation simulated by a high‐resolution global climate model (the MIROC4h) to examine the effects of spatial and temporal coverage on the estimation of mean, trend, and variability of precipitation for large land regions and the global land area. We consider spatial and temporal coverage typical of publicly available precipitation data sets of in situ station observations. We find that the spatial coverage of these data sets is not sufficient for the estimation of total precipitation for the global and hemispheric land areas and for some large regions considered. Estimates of global and hemispheric total land precipitation tend to be biased to higher values due to undersampling in low precipitation regions. The existing station coverage may nevertheless provide reasonable estimates for the magnitude of trend and variability in global to regional land area mean precipitation. However, the incomplete spatial coverage of the observational records results in larger sampling errors in trend estimates, making it harder to detect statistically significant trends. Publicly available gridded precipitation data that are based on larger collection of stations (all of which are not publicly available) may provide a better alternative for the time being.
Probing molecular associations of field‐collected and laboratory‐generated SOA with nano‐DESI high‐resolution mass spectrometry
Authors: O'Brien Rachel E. , Nguyen Tran B. , Laskin Alexander , Laskin Julia , Hayes Patrick L. , Liu Shang , Jimenez Jose L. , Russell Lynn M. , Nizkorodov Sergey A. , Goldstein Allen H.
Published: April 2013

Aerosol samples from the 2010 CalNex field study in Bakersfield (BF) and Pasadena (LA) were analyzed using positive mode nanospray‐desorption electrospray ionization mass spectrometry. Secondary organic aerosol (SOA) produced in a photochemical chamber by photooxidation of diesel (DSL) fuel and isoprene (ISO) under humid, high‐NOx conditions, was analyzed for comparison. Three groups of organic compounds with zero, one, or two nitrogen atoms in their molecular formulas (0N, 1N, 2N) were compared in detail. The composition of ambient SOA exhibited greater overlap with DSL than with ISO. The overlap of the chamber experiments with the BF data was relatively consistent throughout the day while the overlap with LA data increased significantly in the noon to 6 P.M. sample, consistent with the SOA plume arriving from downtown Los Angeles. BF samples were more oxidized, contained more organic nitrogen, and had more overlap with the chamber data compared to LA samples. The addition of gaseous ammonia (NH3) to the DSL experiment was necessary to generate many of the 2N compounds observed in BF. This analysis demonstrates that DSL and ISO were important sources but cannot account for all of the observed ambient compounds indicating that other sources of organics were also likely important.
Modeling the transport and radiative forcing of Taklimakan dust over the Tibetan Plateau: A case study in the summer of 2006
Authors: Chen Siyu , Huang Jianping , Zhao Chun , Qian Yun , Leung L. Ruby , Yang Ben
Published: April 2013

The Weather Research and Forecasting model with chemistry (WRF‐Chem) is used to investigate an intense dust storm event during 26 to 30 July 2006 that originated over the Taklimakan Desert (TD) and transported to the northern slope of Tibetan Plateau (TP). The dust storm is initiated by the approach of a strong cold frontal system over the TD. In summer, the meridional transport of TD dust to the TP is favored by the thermal effect of the TP and the weakening of the East Asian westerly winds. During this dust storm, the transport of TD dust over the TP is further enhanced by the passage of the cold front. As a result, TD dust breaks through the planetary boundary layer and extends to the upper troposphere over the northern TP. TD dust flux arrived at the TP with a value of 6.6 Gg/day in this 5 day event but decays quickly during the southward migration over the TP due to dry deposition. The simulations show that TD dust cools the atmosphere near the surface and heats the atmosphere above with a maximum heating rate of 0.11 K day−1 at ~7 km over the TP. The event‐averaged net radiative forcings of TD dust over the TP are −3.97, 1.61, and −5.58 W m−2 at the top of the atmosphere (TOA), in the atmosphere, and at the surface, respectively. The promising performance of WRF‐Chem in simulating dust and its radiative forcing provides confidence for use in further investigation of climatic impact of TD dust over the TP.
On the lack of stratospheric dynamical variability in low‐top versions of the CMIP5 models
Authors: Charlton‐Perez Andrew J. , Baldwin Mark P. , Birner Thomas , Black Robert X. , Butler Amy H. , Calvo Natalia , Davis Nicholas A. , Gerber Edwin P. , Gillett Nathan , Hardiman Steven , Kim Junsu , Krüger Kirstin , Lee Yun‐Young , Manzini Elisa , McDaniel Brent A. , Polvani Lorenzo , Reichler Thomas , Shaw Tiffany A. , Sigmond Michael , Son Seok‐Woo , Toohey Matthew , Wilcox Laura , Yoden Shigeo , Christiansen Bo , Lott François , Shindell Drew , Yukimoto Seiji , Watanabe Shingo
Published: April 2013

We describe the main differences in simulations of stratospheric climate and variability by models within the fifth Coupled Model Intercomparison Project (CMIP5) that have a model top above the stratopause and relatively fine stratospheric vertical resolution (high‐top), and those that have a model top below the stratopause (low‐top). Although the simulation of mean stratospheric climate by the two model ensembles is similar, the low‐top model ensemble has very weak stratospheric variability on daily and interannual time scales. The frequency of major sudden stratospheric warming events is strongly underestimated by the low‐top models with less than half the frequency of events observed in the reanalysis data and high‐top models. The lack of stratospheric variability in the low‐top models affects their stratosphere‐troposphere coupling, resulting in short‐lived anomalies in the Northern Annular Mode, which do not produce long‐lasting tropospheric impacts, as seen in observations. The lack of stratospheric variability, however, does not appear to have any impact on the ability of the low‐top models to reproduce past stratospheric temperature trends. We find little improvement in the simulation of decadal variability for the high‐top models compared to the low‐top, which is likely related to the fact that neither ensemble produces a realistic dynamical response to volcanic eruptions.
Air‐mass origin as a diagnostic of tropospheric transport
Authors: Orbe Clara , Holzer Mark , Polvani Lorenzo M. , Waugh Darryn
Published: April 2013

We introduce rigorously defined air masses as a diagnostic of tropospheric transport. The fractional contribution from each air mass partitions air at any given point according to either where it was last in the planetary boundary layer or where it was last in contact with the stratosphere. The utility of these air‐mass fractions is demonstrated for the climate of a dynamical core circulation model and its response to specified heating. For an idealized warming typical of end‐of‐century projections, changes in air‐mass fractions are in the order of 10% and reveal the model's climate change in tropospheric transport: poleward‐shifted jets and surface‐intensified eddy kinetic energy lead to more efficient stirring of air out of the midlatitude boundary layer, suggesting that, in the future, there may be increased transport of black carbon and industrial pollutants to the Arctic upper troposphere. Correspondingly, air is less efficiently mixed away from the subtropical boundary layer. The air‐mass fraction that had last stratosphere contact at midlatitudes increases all the way to the surface, in part due to increased isentropic eddy transport across the tropopause. Correspondingly, the air‐mass fraction that had last stratosphere contact at high latitudes is reduced through decreased downwelling across the tropopause. A weakened Hadley circulation leads to decreased interhemispheric transport in the model's future climate.
Source attribution of carbon monoxide in India and surrounding regions during wintertime
Authors: Kumar Rajesh , Naja Manish , Pfister G. G. , Barth M. C. , Brasseur G. P.
Published: April 2013

This study presents a CO source contribution analysis for the atmosphere of South Asia during January–February 2008. The approach includes into the Weather Research and Forecasting Model with Chemistry 11 CO tracers, which track CO from different source types and regions. The comparison of model results with Measurement of Pollution in the Troposphere CO retrievals shows that the model reproduces the spatial, vertical, and temporal distributions of Measurement of Pollution in the Troposphere retrievals fairly well, but generally overestimates CO retrievals in the lower troposphere. CO mixing ratios averaged over the model domain at the surface, in the planetary boundary layer, and the free troposphere are estimated as 321 ± 291, 280 ± 208, and 125 ± 27 ppbv, respectively. Model results show that wintertime CO in the boundary layer and free troposphere over India is mostly due to anthropogenic emissions and to CO inflow. In the boundary layer, the contribution from anthropogenic sources dominates (40–90%), while in the free troposphere the main contribution is due to CO inflow from the lateral boundaries (50–90%). Over the Arabian Sea and the Bay of Bengal, 43–51% of surface CO mixing ratios come from the Indian subcontinent and 49–57% from regions outside of South Asia. The anthropogenic sources in the Indo‐Gangetic Plain region are found to contribute, on average, 42% and 76% to anthropogenic surface CO over the Arabian Sea and the Bay of Bengal, respectively. The anthropogenic emissions from western and southern India contribute 49% to anthropogenic surface CO over the Arabian Sea. Anthropogenic emissions contribute only up to 40% over Burma where biomass burning plays a more important role. Regional transport contributes significantly to total anthropogenic CO over southern India (41%), Burma (49%), and even exceeds the contribution from local sources in western India (58%).
Surface observations for monitoring urban fossil fuel CO2 emissions: Minimum site location requirements for the Los Angeles megacity
Authors: Kort Eric A. , Angevine Wayne M. , Duren Riley , Miller Charles E.
Published: April 2013

The contemporary global carbon cycle is dominated by perturbations from anthropogenic CO2 emissions. One approach to identify, quantify, and monitor anthropogenic emissions is to focus on intensely emitting urban areas. In this study, we compare the ability of different CO2 observing systems to constrain anthropogenic flux estimates in the Los Angeles megacity. We consider different observing system configurations based on existing observations and realistic near‐term extensions of the current ad hoc network. We use a high‐resolution regional model (Stochastic Time‐Inverted Lagrangian Transport‐Weather Research and Forecasting) to simulate different observations and observational network designs within and downwind of the Los Angeles (LA) basin. A Bayesian inverse method is employed to quantify the relative ability of each network to improve constraints on flux estimates. Ground‐based column CO2 observations provide useful complementary information to surface observations due to lower sensitivity to localized dynamics, but column CO2 observations from a single site do not appear to provide sensitivity to emissions from the entire LA megacity. Surface observations from remote, downwind sites contain weak, sporadic urban signals and are complicated by other source/sink impacts, limiting their usefulness for quantifying urban fluxes in LA. We find a network of eight optimally located in‐city surface observation sites provides the minimum sampling required for accurate monitoring of CO2 emissions in LA, and present a recommended baseline network design. We estimate that this network can distinguish fluxes on 8 week time scales and 10 km spatial scales to within ~12 g C m–2 d–1 (~10% of average peak fossil CO2 flux in the LA domain).
Summer rainfall variability over the Southeastern United States and its intensification in the 21st century as assessed by CMIP5 models
Authors: Li Laifang , Li Wenhong , Deng Yi
Published: April 2013

The variability of Southeastern (SE) United States (U.S.) summer precipitation in the current and future climate is analyzed using Coupled Model Intercomparison Project‐Phase 5 (CMIP5) models. By comparing simulated historical precipitation variability with observations, we categorize CMIP5 models into two groups: Group 1 (G1) models that simulate the summer precipitation variability reasonably well and Group 2 (G2) models that need further improvements. Our analysis suggests that the relatively higher skill of G1 models is attributable to their ability to accurately represent the dynamical linkage between SE U.S. summer precipitation variability and North Atlantic Subtropical High (NASH) western ridge position. In contrast, the inability of G2 models to represent such linkage leads to their biases in simulating SE U.S. summer precipitation variability. According to our analysis, the ensemble projection of CMIP5 models suggests that under the Representative Concentration Pathway (RCP) 4.5 scenario, SE U.S. summer precipitation variability will intensify and that this intensification is more pronounced among G1 models. Our analysis further suggests that this intensification is most likely due to the projected pattern shift of the NASH western ridge in a warming climate. Under the RCP4.5 scenario, the NASH western ridge will extend further westward leading to more frequent occurrences of the northwestward and southwestward ridge patterns that are respectively related to dry and wet summers in the SE U.S. Consequently, more frequent occurrence of summer precipitation extremes would be expected over the SE U.S. in the future.
Deuterium excess variations of rainfall events in a coastal area of South Australia and its relationship with synoptic weather systems and atmospheric moisture sources
Authors: Guan Huade , Zhang Xinping , Skrzypek Grzegorz , Sun Zhian , Xu Xiang
Published: April 2013

In this study, isotopic compositions of monthly (Global Network of Isotopes in Precipitation), event, and intraevent rain samples are used to examine the relationship between precipitation deuterium excess, the type of synoptic weather systems, and associated moisture directions in a coastal area of South Australia. The results indicate that both synoptic weather systems and associated atmospheric moisture sources influence deuterium excess values in precipitation. Rain events caused by frontal systems tend to have moisture sources from the Indian Ocean to the south of Australia. They usually have deuterium excess values of 15‰ to 25‰, depending on the moisture source direction. Rain events caused by synoptic low‐pressure and trough systems tend to have inland moisture sources, and have a deuterium excess of 10‰ to 15‰. In addition to weather systems and associated moisture sources, subcloud processes alter the deuterium excess in the resulting precipitation, which is an effect that is more significant during summer when it is warm and dry. Together, these factors contribute to the seasonal variability of deuterium excess in the study area. Deuterium excess of winter frontal precipitation, resulting from minimal subcloud evaporation, is useful to infer the moisture source direction. In other seasons, deuterium excess in precipitation is more likely altered by subcloud evaporation. Nevertheless, intraevent samples in the middle of a frontal event that has experienced minimal subcloud evaporation are useful to estimate cloud deuterium excess. The results also suggest that an abrupt change in dominant precipitation weather patterns occurs between January and February, characterized by a sudden decrease in δ18O and deuterium excess.
A 2000‐year dust storm record from Lake Sugan in the dust source area of arid China
Authors: Chen Fahu , Qiang Mingrui , Zhou Aifeng , Xiao Shun , Chen Jianhui , Sun Donghuai
Published: April 2013

Arid northwestern China is considered to be a major source of atmospheric dust supply to the Northern Hemisphere. However, dust storm evolution and dust emission processes in the past remain unclear due to the scarcity of geologic archives in this region. Hydrologically closed lakes in dust source areas act as a trap, providing the opportunity to trace the history of dust emission or eolian activity. Here we present the results of dust storm proxies and a dust storm history from Lake Sugan in the Qaidam Basin, a dust source area, on the northern Qinghai‐Tibetan Plateau. Grain size analyses of the materials deposited during modern dust storms and of the lake surface sediments demonstrate that the coarse component of the lake sediments was transported primarily by ambient winds when dust storms occurred. In combination with a sediment chronology generated by counting annual laminations, a 2000‐year dust storm history was reconstructed on the basis of changes in the coarse component and magnetic susceptibility of the lake sediments. Frequent and/or intensive dust storms occurred during the intervals AD 300–500, AD 1180–1240, and AD 1500–1700. The occurrence of dust storms largely coincided with the strengthening of the Siberian High with colder air masses from high latitudes, such as during the Little Ice Age, frequently encroaching into the dust source areas in northwestern China. Our results suggest that wind strength plays an important role in dust emissions in arid source areas. However, dust storms in the late 20th century are most likely associated with disturbance of the ground surface caused by petroleum exploitation in the Qaidam Basin.