Journal of Geophysical Research: Atmospheres最新文献

The operation of geostationary (GEO) instruments such as the Tropospheric Emissions: Monitoring of Pollution (TEMPO) provides unprecedented hourly nitrogen dioxide (NO₂) observations compared to the once-daily data from a low-Earth orbit (LEO) platform like the TROPOspheric Monitoring Instrument (TROPOMI). This study investigates the performance and challenges of using TEMPO versus TROPOMI measurements to constrain anthropogenic nitrogen oxides (NO_x) emissions. The accuracy of TEMPO and TROPOMI NO₂ tropospheric columns are assessed using Pandora observations, finding a low bias of 9%–12.3% in TEMPO, and TROPOMI data during August 2023, while TEMPO midday and late afternoon observations are less of low bias. Top-down NO_x emissions derived by midday TEMPO and TROPOMI data are generally consistent over urban areas, being 5%–20% lower than bottom-up emissions provided by the 2021 GReenhouse gas And Air Pollutants Emissions System (GRA²PES), and align with 2023 GRA²PES emissions, demonstrating the reliability of using satellite data for timely updates of bottom-up inventories. However, assimilating additional morning/late afternoon TEMPO data leads to the poorest top-down NO_x emissions, likely resulting from larger negative measurement biases. NO_x emission inversions effectively mitigate NO_x overprediction, though the top-down NO_x emissions might be over-corrected in urban cores. NO_x emissions optimization also improves ozone forecasts by reducing the model's positive biases, especially when assimilating midday TEMPO data. Our study suggests that TEMPO midday observations provide better constraints on the magnitude and spatiotemporal variation of anthropogenic NO_x emissions than TROPOMI, while morning TEMPO v3 data should be used cautiously due to potential negative impact on NO_x emissions inversion.

Line-shaped contrails formed behind aircraft can evolve into broadly spread and long-living cirrus clouds under favorable conditions. These contrail-cirrus contribute significantly to the aviation-induced radiative forcing. While past modeling studies have examined contrail-cirrus across various atmospheric and aircraft-type dependent parameters, they have focused on conventional kerosene combustion. In this study, we investigate how the switch to an alternative propulsion system, such as hydrogen combustion, may alter contrail-cirrus properties using the large-eddy simulation (LES) model EULAG coupled with the Lagrangian Cloud Module (LCM), a particle-based microphysics module. Building on prior work that modeled hydrogen contrails during the vortex phase, we use those results to initialize the subsequent contrail-cirrus evolution. We explore a wide range of background meteorological conditions, including variations of ambient temperature, relative humidity with respect to ice, vertical wind shear, and updraft velocity, and assess two aircraft types. Key contrail properties, such as total ice crystal number and mass, are found to be most sensitive to the initial number of ice crystals and ambient temperature. We show that reducing the number of initially formed ice crystals substantially decreases contrail radiative impact. This is primarily due to a shorter contrail-cirrus lifetime, driven by the earlier onset and more efficient sedimentation of the fewer but larger ice crystals. Moreover, the relationship between radiative impact and initial ice crystal number is nonlinear, consistent with previous studies.

This study uses wind profiler data to examine the characteristics of the Sierra Barrier Jet (SBJ) over 23 cool seasons (October 2000–March 2023) and its influence on precipitation in Northern California. The analysis identifies 439 SBJ events, with a mean maximum wind speed of 25.6 $��{\text{ms}}^{�-�1�}�$ parallel to the Sierra, an average duration of 14.2 hr, and a typical altitude of maximum wind near 1.05 km. Previous studies show that many extreme cool-season precipitation events occur when landfalling atmospheric rivers (ARs) and SBJs coincide. During the study period, 220 ARs made landfall at San Francisco with 65% of them containing an SBJ. Alternatively, only 43% of SBJs occurred during a landfalling AR at San Francisco. Stronger SBJs also tended to coincide with higher IVT and stronger ARs, while weaker SBJs aligned with weaker ARs. ARs with higher IVT values also more frequently contained an SBJ. A precipitation analysis revealed that SBJ events accounted for up to 40% of the cool-season precipitation, with maxima from the coast north of San Francisco through the Central Valley and into the Mt. Shasta–Trinity Alps region. AR events similarly contributed up to 50%, with a similar spatial pattern. When SBJs and ARs occurred together, they produced more than 30% of the seasonal precipitation, with maxima across the coastal ranges and into the northern Central Valley. Zonal and meridional precipitation transects across Oroville (39.5°N, 121.6°W) further illustrates how SBJs and ARs enhanced precipitation over the northern Central Valley, the Sierra, and the Mt. Shasta–Trinity Alps region.

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.