Journal of Geophysical Research: Atmospheres最新文献

Cloud radiative effects (CREs) play a critical role in Earth's energy balance and climate variability, yet the variability and specific contributions of distinct cloud types remain poorly understood. Using the Clouds and the Earth's Radiant Energy System FluxByCldTyp data set, this study investigates how temporal variations in total top-of-the-atmosphere CREs are influenced by changes in the physical properties and fractional coverages of 42 individual cloud types and their broader categories over a 19-year period. The analysis spans the tropical belt (25°S–25°N) and several convectively active regions, including the Tropical Western Pacific (TWP) and Africa. Our results show that variability in total CREs is primarily driven by changes in cloud fraction rather than microphysical properties. High clouds—particularly cirrostratus and deep convective clouds—exert strong negative correlations with shortwave CREs and strong positive correlations with longwave CREs, with correlation magnitudes reaching ±0.90 in the TWP. Low clouds, especially shallow cumulus, exhibit opposite correlations, partly due to obscuration by upper-level clouds. While properties like total cloud water path, optical depth, and particle size influence cloud type-mean CREs, their correlations with total CRE are relatively weak and largely due to co-variability with total cloud amount. These correlations are generally more distinct and stronger within regional domains than across the tropical mean. Additionally, strong interrelationships are found among cloud categories, with high and low clouds often varying inversely. These results underscore the importance of cloud type-specific contributions to radiative budget variability, providing observational benchmarks for climate model evaluation and cloud feedback studies.

The influence of surface aerosol injection on the stratocumulus-to-cumulus transition (SCT) is explored using large-eddy simulations. We examine how cloud-surface coupling (or the strength of the marine boundary layer (MBL) stratification that limits vertical turbulent mixing and convection) impacts the vertical transport of aerosols, and how injected aerosols influence cloud properties and associated cloud radiative effects during the SCT. By injecting aerosols at different stages of the SCT, noting that cloud is more decoupled from the surface over time due to entrainment warming, we find that cloud-surface coupling significantly affects aerosol vertical transport. However, injection timing (before drizzle if any) does not notably affect the SCT and the efficiency of marine cloud brightening, because aerosol number concentrations due to injections at different times rapidly converge before the transition onset. By varying the background aerosol concentration, we find that injected aerosols can significantly extend the persistence of stratocumulus decks by suppressing precipitation in clean environments but have little impact on stratocumulus breakup with higher background aerosol concentrations due to saturated aerosol effects. In clean MBLs, the SCT-delay-induced increase in cloud fraction dominates the overall cooling effects in response to aerosols, followed by Twomey effects. These cooling effects are slightly offset by decreased liquid water path (LWP) due to entrainment drying. In polluted MBLs, the Twomey effect is more dominant, followed by cloud fraction adjustments, and these coolings are also partly offset by LWP adjustments. All the simulations are made in relatively small domains in which injected aerosols are homogenized over a short time scale.

Aerosol liquid water content (ALWC) and pH significantly influence secondary inorganic aerosol (SIA) formation. However, the spatiotemporal variations in ALWC and aerosol pH, along with their impacts on SIA formation, remain poorly understood. Based on a-year-long field observations of aerosol chemical components, ALWC and aerosol pH for Lanzhou and Beijing were calculated using ISORROPIA II. Aerosol liquid water content in Lanzhou was highest in winter and lowest in summer (17.2 vs. 3.30 μg m⁻³), opposite to that of Beijing (10.6 vs. 22.9 μg m⁻³). Aerosol pH in both cities was highest in winter and lowest in summer (4.68 vs. 2.96 in Lanzhou, 5.34 vs. 2.88 in Beijing). Machine learning identified TNH₃ (NH₄⁺ + NH₃), SO₄²⁻, NO₃⁻, relative humidity (RH), and temperature as crucial factors influencing ALWC and aerosol pH in both cities, while Mg²⁺ and Cl⁻ were unique factors influencing pH in Lanzhou during summer and winter, respectively. During pollution periods, the effect of ALWC on enhancing heterogeneous and aqueous-phase reactions for SIA formation was more pronounced in Beijing than in Lanzhou, as elevated ALWC levels provided more reaction medium and facilitated solid-to-liquid phase transitions. Additionally, elevated pH notably enhanced aqueous-phase sulfate production via the O₃ oxidation pathway in winter in both cities and via the H₂O₂ oxidation pathway in summer in Beijing. This study highlights the heterogeneity of ALWC and pH, along with their distinct impacts on SIA formation, which should be considered in atmospheric models to improve predictions of secondary aerosol formation and better assess the associated environmental and climatic effects.

Land restoration projects are implemented across Africa to combat land degradation and climate change. By changing the vegetation cover, these projects can potentially impact cloud formation through changes in energy and water partitioning between the Earth's surface and the atmosphere. In West Africa, satellite observations have shown an increase in cloud formation over restored areas. However, even though the spatial arrangement of restored areas differs between regreening approaches, such as farmer-managed natural regeneration, area protection or reforestation, it is unknown how the spatial pattern of restoration projects impacts cloud formation. In this study, we use the Weather Research and Forecasting (WRF) mesoscale atmospheric model to determine how land restoration affects cloud formation for a case study at the border of the transnational W-Arly-Pendjari national park complex, with a sharp boundary between forest and grassland. First, we carry out a sensitivity analysis to determine the underlying mechanisms of cloud formation over forest regions, after which we run 27 land restoration scenarios with low (21%), intermediate (43%), and high (85%) forest cover and varying spatial clustering to assess the impact of land restoration patterns on cloud formation. The results highlight that an intermediate forest cover with higher clustering increases cloud formation due to stronger mesoscale circulation. A small scale heterogeneity in forest cover or a high forest cover, on the other hand, inhibits cloud formation. Because clouds play an important role in the Earth's water and energy balance, these results provide important insight into how projects can be designed to increase their climate benefits.

Studying aerosol liquid water content (ALWC) in high-humidity, high-organic-aerosol atmospheric environments is critically important for understanding how organic matter regulates climatic and environmental effects. Here, using field observations and model simulations, we explored ALWC at a subtropical coastal site in Shenzhen. We employed a multipath ALWC calculation framework for a comprehensive closure study of ALWC and quantified the contribution of organic matter to ALWC. Results showed average ALWC during the observation period was 8.8 μg m⁻³ nearly equivalent to the dry aerosol mass. Unexpectedly, organics—accounting for over 70% of the total mass concentration of PM_2.5—contributed an average of 42% ± 15% to ALWC, representing the highest contribution reported to date in similar studies. This demonstrated that neglecting the organic compounds significantly underestimate ALWC, as was further revealed consequently reducing aerosol extinction capacity by approximately 17.2%. Unlike previous assumptions, we found that organic contribution highly depends on their hygroscopicity (κ_org) not mass fraction or ambient humidity. Our study highlights the significant role of organics in regulating aerosols liquid water content urging their inclusion in air quality and climate simulation models with the implementation of carbon reduction strategies.

Aerosols over the Tibetan Plateau (TP) strongly influence regional climate and hydrological cycles. Here we investigate the size-resolved microphysical and optical properties of aerosols in an urban area of the northern TP using a tandem system of a differential mobility analyzer, a condensation particle counter, and a single particle soot photometer. Under the 2021 summer conditions, the average particle number size distribution follows a lognormal pattern, peaking at ∼70 nm. Refractory black carbon (rBC) aerosols constitute 17.7% of the total particle population in the 100–750 nm mobility diameter (D_mob) range, with their proportion rising to over 50% for D_mob > 500 nm. Most rBC particles are externally mixed, while only 12.2% are thickly coated with non-refractory materials. Externally mixed rBC particles show strong non-sphericity, with a dynamic shape factor increasing from 1.8 at 115 nm to 2.8 at 750 nm, consistent with aggregate structures. In contrast, thickly coated rBC particles are nearly spherical, with coating thickness increasing with size. The total rBC mass estimated from size-resolved measurements closely matches bulk rBC mass directly measured. rBC-free particles exhibit slight non-sphericity, with shape factor positively correlated with refractive index, likely due to dust contributions. Bulk scattering coefficients derived from size-resolved data match those estimated under the well-mixed spherical assumption. However, the later scheme—lacking observational constraints on morphology and mixing state—overestimates absorption by over a factor of three, thereby underestimating the single-scattering albedo. These results provide key constraints for improving aerosol radiative forcing estimates and advancing understanding of aerosol–climate interactions over the TP.

The Mediterranean Sea is a weak sink for the atmospheric CO₂ with the October-March extended winter season characterized by the occurrence of high CO₂ sink events. Here, we analyzed state-of-the-art ocean and atmospheric reanalyses and observational data sets to investigate the variability of the winter sink and its relation with synoptic atmospheric features crossing the region in the period 1999–2020. High CO₂ sink events are identified using classical extreme event approach with fixed threshold (95p) based on the CO₂ daily flux distribution. First, we showed that these events are driven by large-scale atmospheric configurations that produce stronger-than-average wind speed and colder-than-average 2 m and sea surface temperature patterns in the region. Second, a co-location analysis was applied to assess the probability to detect an extra-tropical cyclone at a fixed distance from the location of the events showing that the larger the event's magnitude, the higher the probability. In most of the cases, these cyclones originate within the Mediterranean region and are usually deeper, bigger in terms of size and characterized by a stronger circulation with respect to the systems that usually cross the region. By establishing a statistical relationship between high CO₂ sink events and synoptic atmospheric activity, we emphasize the potential influence of the cyclone activity on the carbon budget of the Mediterranean Sea.

Aerosol trace element (TE) transport serves as a critical driver of marine TE biogeochemical cycles and climate feedback systems. In the rapidly warming Arctic Ocean (AO), however, the contemporary distribution patterns and decadal variability of aerosol TE deposition remain poorly constrained, representing a critical gap in our understanding of current and future Arctic environmental changes. Here, we present extensive shipboard observations of 13 aerosol TEs across the AO during summer 2024. TE concentrations and the enrichment levels of these anthropogenic TEs rank among the lowest globally observed in the AO. The comparable or even elevated mineral- dominated TE concentrations and deposition fluxes (Al, Fe) in the Central AO than Peripheral AO challenge current dust models, potential influenced by sea ice/snow resuspension. Coal combustion (As, Se), non-exhaust vehicular emissions (Ni, Cr), and metallurgical activities (Zn) emerged as primary anthropogenic sources, with detectable anthropogenic imprint even in mineral-dominated TEs (e.g., Fe, Mn). Decadal comparisons with historical records revealed a near ten-fold reduction in Pb and Cd enrichment, contrasting with a near-doubling of V enrichment driven by intensified Arctic shipping. Moreover, the distinct aerosol Fe/Al fractionation between this study and historical observations likely arises from mixing inputs of anthropogenic Fe-rich particles and permafrost-derived Fe-depleted weathering products, which amplify uncertainties in Fe flux estimations derived from dust proxy approaches. This study provides advance understanding of aerosol TE dynamics in the warming Arctic and provide critical constraints for polar biogeochemical cycles.

The characteristics of Pekeris modes as well as Lamb modes are investigated using the new reanalysis data set JAWARA, which spans over 19 years and covers the entire middle atmosphere. Pekeris modes are a class of global normal modes whose energy is trapped in two height regions that is, around the stratopause and the surface, while the energy of Lamb mode is trapped only at the surface. Statistically significant spectral peaks corresponding to both Pekeris and Lamb modes are detected for seven normal modes. The vertical structures closely match theoretical expectations for most modes. Notably, the geopotential height amplitudes of the Pekeris modes are comparable to or greater than those of the Lamb modes in the mesosphere and lower thermosphere, suggesting an important role for Pekeris modes in the dynamics of this region. On the other hand, the Lamb modes are dominant in the stratosphere.

Organic aerosols (OAs) exhibit non-ideal behaviors that challenge conventional models assuming ideal equilibrium partitioning. This study integrates a unified kinetic framework into WRF-Chem model to handle non-ideal evolution of OAs with considering kinetic mass transfer process with multidirectional interactions (particle surface area, volume, molecular weight) governed by Fick's second law. Simulations in winter of the North China Plain (NCP) reveal that non-ideal treatment enhances condensation of organics species and water vapor, amplifies interactions between OA, aerosol liquid water content (ALWC), and secondary inorganic aerosols (SIA, pSO₄²⁻, pNO₃⁻ and pNH₄⁺). The revised framework reduces mean bias in OA and SIA predictions from normalized mean bias (NMB) of −18.4% to −2.9%, −33.4% to −23.0%, −2.0% to −0.3%, and −35.4% to −30.2%, respectively, achieves better performance in reproducing ALWC with better correlation (from 0.81 to 0.88), and improves PM_2.5 modeling accuracy (NMB from −18.0% to −9.5%) in “2 + 26” city cluster among the NCP. The framework enhances predictions without modifying chemical mechanisms and suggests a potential reductions in direct radiative forcing estimation (−0.77 W/m² among the NCP). The findings advocate urgent integrating non-ideal behavior of OA into air quality models to advance aerosol prediction.