The geographical shift of global anthropogenic aerosols from the developed countries to the Asian continent since the 1980s could potentially perturb the regional and global climate due to ...aerosol‐cloud‐radiation interactions. We use an atmospheric general circulation model with different aerosol scenarios to investigate the radiative and microphysical effects of anthropogenic aerosols from different regions on the radiation budget, precipitation, and large‐scale circulations. An experiment contrasting anthropogenic aerosol scenarios in 1970 and 2010 shows that the altered cloud reflectivity and solar extinction by aerosols results in regional surface temperature cooling in East and South Asia, and warming in the US and Europe, respectively. These aerosol‐induced temperature changes are consistent with the relative temperature trends from 1980 to 2010 over different regions in the reanalysis data. A reduced meridional streamfunction and zonal winds over the tropics as well as a poleward shift of the jet stream suggest weakened and expanded tropical circulations, which are induced by the redistributed aerosols through a relaxing of the meridional temperature gradient. Consequently, precipitation is suppressed in the deep tropics and enhanced in the subtropics. Our assessments of the aerosol effects over the different regions suggest that the increasing Asian pollution accounts for the weakening of the tropics circulation, while the decreasing pollution in Europe and US tends to shift the circulation systems southward. Moreover, the aerosol indirect forcing is predominant over the total aerosol forcing in magnitude, while aerosol radiative and microphysical effects jointly shape the meridional energy distributions and modulate the circulation systems.
Key Points
The emission shift contributes to the “dimming” in Asia and “brightening” in the US and Europe
Atmospheric meridional circulations are weakened by the redistributed aerosols
Aerosol effects from different regions contribute distinctively to the circulation modification
Convective clouds produce a significant proportion of the global precipitation and play an important role in the energy and water cycles. We quantify changes of the convective cloud ice mass-weighted ...altitude centroid (Z
) as a function of aerosol optical thickness (AOT). Analyses are conducted in smoke, dust and polluted continental aerosol environments over South America, Central Africa and Southeast Asia, using the latest measurements from the CloudSat and CALIPSO satellites. We find aerosols can inhibit or invigorate convection, depending on aerosol type and concentration. On average, smoke tends to suppress convection and results in lower Z
than clean clouds. Polluted continental aerosol tends to invigorate convection and promote higher Z
. The dust aerosol effects are regionally dependent and their signs differ from place to place. Moreover, we find that the aerosol inhibition or invigoration effects do not vary monotonically with AOT and the variations depend strongly on aerosol type. Our observational findings indicate that aerosol type is one of the key factors in determining the aerosol effects on convective clouds.
Abstract Investigation of the major factors determining tropical upper-level cloud radiative effect (TUCRE) is crucial for understanding cloud feedback mechanisms. We examined the TUCRE inferred from ...the outputs of historical runs and AMIP runs from CMIP6 models employing a radiative-convective equilibrium (RCE). In this study, we incorporated the RCE model configurations of atmospheric dynamics and thermodynamics from the climate models, while simplifying the intricate systems. Using the RCE model, we adjusted the global mean surface temperature to achieve energy balance, considering variations in tropical cloud fraction, regional reflectivity, and emission temperature corresponding to each climate model. Subsequently, TUCRE was calculated as a unit of K/%, representing the change in global mean surface temperature (K) in response to an increment in the tropical upper-level clouds (%). Our RCE model simulation indicates that the major factors determining the TUCRE are the emission temperatures of tropical moist-cloudy and moist-clear regions, as well as the fraction of tropical upper-level clouds. The higher determination coefficients between TUCRE and both the emission temperature of tropical moist regions and the upper-level cloud fraction are attributable to their contribution to the trapping effect on the outgoing longwave radiations, which predominantly determines TUCRE. Consequently, the results of this study underscore the importance of accurately representing the upper-level cloud fraction and emission temperature in tropical moist regions to enhance the representation of TUCRE in climate models.
Polyadenosine diphosphate (ADP)—ribose polymerases (PARPs) are a family of enzymes that modulate diverse biological processes through covalent transfer of ADP-ribose from the oxidized form of ...nicotinamide adenine dinucleotide (NAD⁺) onto substrate proteins. Here we report a robust NAD⁺ analog—sensitive approach for PARPs, which allows PARP-specific ADP-ribosylation of substrates that is suitable for subsequent coppercatalyzed azide-alkyne cycloaddition reactions. Using this approach, we mapped hundreds of sites of ADP-ribosylation for PARPs 1, 2, and 3 across the proteome, as well as thousands of PARP-1—mediated ADP-ribosylation sites across the genome. We found that PARP-1 ADP-ribosylates and inhibits negative elongation factor (NELF), a protein complex that regulates promoter-proximal pausing by RNA polymerase II (Pol II). Depletion or inhibition of PARP-1 or mutation of the ADP-ribosylation sites on NELF-E promotes Pol II pausing, providing a clear functional link between PARP-1, ADP-ribosylation, and NELF. This analog-sensitive approach should be broadly applicable across the PARP family and has the potential to illuminate the ADP-ribosylated proteome and the molecular mechanisms used by individual PARPs to mediate their responses to cellular signals.
Extreme and persistent haze events frequently occur during wintertime China. While recent emissions reductions reduced annual mean fine particulate matter (PM2.5) concentrations over eastern China, ...their effectiveness on wintertime PM2.5 trend remains uncertain. We use observations and model simulations to quantify seasonal differences in PM2.5 trends and investigate the underlying chemical mechanisms driving such differences. We find a much slower decrease in observed wintertime PM2.5 (−3.2% yr−1) since 2014, in contrast to a drastic summertime decrease (−10.3% yr−1). Simulations show two previously underappreciated mechanisms buffering wintertime PM2.5 decrease, including an increase in oxidation capacity due to nitrogen oxides (NOx) reductions under wintertime volatile organic compound (VOC)‐limited chemistry, and an enhanced conversion of nitric acid to nitrate by ammonia due to sulfur dioxide reductions. Our findings suggest that control policies targeting VOC and deep NOx reductions are needed to improve wintertime PM2.5 air quality over China.
Plain Language Summary
Severe wintertime particulate matter (PM) pollution in China is an important environmental problem causing hundreds of thousands of deaths annually. Recent emissions reductions have gradually improved annual mean PM air quality in eastern China. However, our observational analysis unexpectedly shows a much weaker decrease in PM during winter compared with other seasons. State‐of‐the‐art model simulations suggest that the weakened wintertime PM decline is mainly attributed to the increase in wintertime atmospheric oxidation capacity and the enhanced conversion of nitric acid to nitrate by ammonia, which are induced by anthropogenic emission reductions. Our findings indicate that previous pollution control policies did not effectively mitigate severe wintertime PM pollution due to these unfavored chemical processes. Stricter control policies targeting oxidants and wintertime emission sources are imperative to counteract the buffering chemical mechanisms over China.
Key Points
We show a slower decrease in observed PM2.5 over China in winter (−3.2% yr−1) compared with summer (−10.3% yr−1) since 2014
Simulations show this is because wintertime NOx reductions under VOC‐limited chemistry cause an increase in secondary PM2.5 formation
Sulfur dioxide reductions also cause an enhanced conversion of nitric acid to particulate nitrate by ammonia
The large spread of model equilibrium climate sensitivity (ECS) is mainly caused by the differences in the simulated marine boundary layer cloud (MBLC) radiative feedback. We examine the variations ...of MBLC fraction in response to the changes of sea surface temperature (SST) at seasonal and centennial time scales for 27 climate models that participated in the Coupled Model Intercomparison Project phase 3 and phase 5. We find that the intermodel spread in the seasonal variation of MBLC fraction with SST is strongly correlated with the intermodel spread in the centennial MBLC fraction change per degree of SST warming and that both are well correlated with ECS. Seven models that are consistent with the observed seasonal variation of MBLC fraction with SST at a rate −1.28 ± 0.56%/K all have ECS higher than the multimodel mean of 3.3 K yielding an ensemble‐mean ECS of 3.9 K and a standard deviation of 0.45 K.
Key Points
Boundary cloud variations at seasonal and centennial scales are correlated
Boundary cloud seasonal response is correlated with sensitivity
Observations suggest a higher climate sensitivity than multimodel mean
Abstract
Classification is an essential method and has been developed widely in astronomy. However, planets still lack a universal classification framework, because the solar system planet sample is ...too small for statistical analysis. Fortunately, exoplanets supply large samples to help build up synthetic planetary populations then support a classification framework. In this study, we use synthetic populations to explore the diversity and evolution relations of planets. We detect six outstanding clusters in mass–radius space with the kernel density estimation and extract typical planets for each type. The first four types are gas-poor planets, and the last two are gas-rich. For an intermediate type, the light gas envelopes contribute to the observable radius but not the mass. Once the planet is massive enough (3.9
M
J
), its size shrinks with increasing mass due to self-gravity. Based on the evolution tracks and the gas envelopes’ properties, the environment is linked strongly to the gas properties, and it controls which type can form at a specific location. The system with gas giants will be different from those without, including total planet mass and the number of planets in the system. Giant planets shape the whole system by orbital resonance. Each type of planets’ period ratios are different, and gas giants have the most outstanding accumulation peak at 2:1 resonance. In the future, the patterns of observed planets’ retrieved interior structures can help to confirm the suggested classification. However, the structure degeneracy induces high uncertainty, such that the framework will still profit from additional theoretical constraints.
Abstract
A large spread in model estimates of the equilibrium climate sensitivity (ECS), defined as the global mean near-surface air-temperature increase following a doubling of atmospheric CO
2
...concentration, leaves us greatly disadvantaged in guiding policy-making for climate change adaptation and mitigation. In this study, we show that the projected ECS in the latest generation of climate models is highly related to seasonal variations of extratropical low-cloud fraction (LCF) in historical simulations. Marked reduction of extratropical LCF from winter to summer is found in models with ECS > 4.75 K, in accordance with the significant reduction of extratropical LCF under a warming climate in these models. In contrast, a pronounced seasonal cycle of extratropical LCF, as supported by satellite observations, is largely absent in models with ECS < 3.3 K. The distinct seasonality in extratropical LCF in climate models is ascribed to their different prevailing cloud regimes governing the extratropical LCF variability.
Atmospheric aerosols affect weather and global general circulation by modifying cloud and precipitation processes, but the magnitude of cloud adjustment by aerosols remains poorly quantified and ...represents the largest uncertainty in estimated forcing of climate change. Here we assess the effects of anthropogenic aerosols on the Pacific storm track, using a multiscale global aerosol–climate model (GCM). Simulations of two aerosol scenarios corresponding to the present day and preindustrial conditions reveal long-range transport of anthropogenic aerosols across the north Pacific and large resulting changes in the aerosol optical depth, cloud droplet number concentration, and cloud and ice water paths. Shortwave and longwave cloud radiative forcing at the top of atmosphere are changed by −2.5 and +1.3 W m ⁻², respectively, by emission changes from preindustrial to present day, and an increased cloud top height indicates invigorated midlatitude cyclones. The overall increased precipitation and poleward heat transport reflect intensification of the Pacific storm track by anthropogenic aerosols. Hence, this work provides, for the first time to the authors’ knowledge, a global perspective of the effects of Asian pollution outflows from GCMs. Furthermore, our results suggest that the multiscale modeling framework is essential in producing the aerosol invigoration effect of deep convective clouds on a global scale.
Abstract
Objective
To conduct a systematic scoping review of explainable artificial intelligence (XAI) models that use real-world electronic health record data, categorize these techniques according ...to different biomedical applications, identify gaps of current studies, and suggest future research directions.
Materials and Methods
We searched MEDLINE, IEEE Xplore, and the Association for Computing Machinery (ACM) Digital Library to identify relevant papers published between January 1, 2009 and May 1, 2019. We summarized these studies based on the year of publication, prediction tasks, machine learning algorithm, dataset(s) used to build the models, the scope, category, and evaluation of the XAI methods. We further assessed the reproducibility of the studies in terms of the availability of data and code and discussed open issues and challenges.
Results
Forty-two articles were included in this review. We reported the research trend and most-studied diseases. We grouped XAI methods into 5 categories: knowledge distillation and rule extraction (N = 13), intrinsically interpretable models (N = 9), data dimensionality reduction (N = 8), attention mechanism (N = 7), and feature interaction and importance (N = 5).
Discussion
XAI evaluation is an open issue that requires a deeper focus in the case of medical applications. We also discuss the importance of reproducibility of research work in this field, as well as the challenges and opportunities of XAI from 2 medical professionals’ point of view.
Conclusion
Based on our review, we found that XAI evaluation in medicine has not been adequately and formally practiced. Reproducibility remains a critical concern. Ample opportunities exist to advance XAI research in medicine.
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