Journal of Geophysical Research: Atmospheres最新文献

Frequent droughts in the Sichuan Basin (SCB) have caused severe socioeconomic impacts and significantly altered the regional water cycle. However, the connection between these droughts and the atmospheric water cycle remains unclear. Here, we applied two process-based models—the Dynamic Recycling Model (DRM) and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model—to investigate the characteristics and mechanisms of atmospheric water cycles during SCB summer droughts from 1979 to 2022. The results show that the climatological mean precipitation recycling ratios for June, July, and August were 12.92%, 13.04%, and 12.63%, respectively, indicating the SCB's strong dependence on externally transported moisture. Most droughts are linked to deficits in external moisture transport. However, in the later stages of the most severe droughts (e.g., August 2006 and 2022), the drought evolves from preceding external moisture reduction into an internal-moisture-depletion regime. This shift is driven by extreme soil moisture depletion, which markedly intensifies land–atmosphere coupling and ultimately leads to the collapse of local moisture recycling. Moisture tracking further reveals that droughts with external deficits are associated with reduced oceanic inflow, while those with internal deficits exhibit reduced terrestrial moisture contributions despite sufficient oceanic supply, reflecting low efficiency in converting available moisture into rainfall. Large-scale circulation systems, especially the Western Pacific Subtropical High and mid-latitude westerlies, play a key role in shaping these drought-related anomalies by regulating moisture transport and precipitation efficiency, while land–atmosphere coupling further amplifies these anomalies. These findings provide new insights into summer drought dynamics in the SCB and inform improved drought prediction under a changing climate.

This study applies a simple two-box model to quantify the convective transport of trace gas species in the tropics. The model characterizes the interplay between convective transport and chemical reactions using two parameters: convective turnover time and the species' chemical lifetime. Using airborne measurements of 42 trace gases from the CONvective Transport of Active Species in the Tropics field campaign, we show that this model reproduces over 90% of the observed variability (R² > 0.9) in the observed ratio of upper troposphere (UT) to boundary layer mixing ratio—the UT fraction—across the 42 species, with the UT fraction serving as an indicator of convective venting efficiency. A key insight is that this efficiency is well captured by the ratio of chemical lifetime to turnover time. The turnover times derived from the box model are consistent with the mean transit time from the Transit Time Distribution framework of earlier studies. This physically intuitive box model provides an observation-based diagnostic for evaluating convective transport in global chemistry-climate models and for improving our understanding of chemistry-climate interactions.

Nitrogen stable isotopes (δ¹⁵N) of ice core nitrate (NO₃⁻) are often subject to diverse interpretations associated with changes in nitrogen oxide (NO_x) sourcing, atmospheric reactions, and/or post-depositional processes. Here, an ice core from Mont Blanc (French Alps) was analyzed to investigate the δ¹⁵N(NO₃⁻) record over the past 1,000 years. Atmospheric isotopic fractionation, including gas-particle partitioning, introduces a limited and quantifiable effect on δ¹⁵N(NO₃⁻)—up to 2.4 ‰ in extreme cases. Thus, the glacially-archived NO₃⁻ reliably reflects a record of Western European NO_x emissions by comparing δ¹⁵N and concentrations of NO₃⁻, and isotope–concentration mixing relationships (Keeling plot) with historical emission inventories. An increase in δ¹⁵N(NO₃⁻) in the 1800s reflects the dominance of NO_x emissions from coal combustion. During the 20th century, the δ¹⁵N(NO₃⁻) value substantially decreased, from (4.7 ± 1.5) ‰ in 1900 to (−1.9 ± 1.4) ‰ in 1990, and Keeling plot interpretation attributes this decrease to increasing oil combustion emissions. Between 1750 and 2016, the ice core's δ¹⁵N(NO₃⁻) record generally aligns with existing NO_x inventories for Western Europe. However, during the early 20th-century, low ice core δ¹⁵N(NO₃⁻) values suggest that the inventories may have underestimated NO_x emissions resulting from agriculture. Since 2000, the decreasing NO₃⁻ concentrations and δ¹⁵N(NO₃⁻) values highlight the success of mitigation policies in reducing fossil fuel-induced NO_x emissions, albeit with a delay of 20 years relative to emission inventories, that can be attributed to gas-particle partitioning and mis-quantification of NO_x sources. This work reaffirms the value of alpine ice cores for understanding aerosol sources.

Three large-scale (tens of kilometers in horizontal extent) multiple-stroke cloud-to-ground (CG) flashes were examined in detail. The flashes occurred in two summer thunderstorms in Florida and were bipolar in that some of the strokes (leader/return-stroke sequences) in a given flash transported to ground positive charge, while others transported negative charge. Positive strokes tended to have higher NLDN-reported peak currents and all terminated essentially on the ground surface, each time forming a new channel. Negative strokes tended to terminate on tall towers and all that did so produced characteristic wideband E-field signatures that exhibited oscillations after the initial peak. Additionally, we examined a negative flash composed of seven strokes all of which terminated on a tall tower. There were a total of three tall (451–497 m) towers involved, with one of them (497-m tall) being strike object for each of the four flashes examined here. The maximum GLM group energy for positive strokes was one to two orders of magnitude higher than for negative strokes. The oscillating E-field signatures are indicative of bouncing current waves that are manifestations of the transient response of a tall object to the lightning-caused excitation at or near its top (e.g., Rakov, 2001, https://doi.org/10.1109/15.974646); it is due to impedance discontinuities at the lightning attachment point and at the ground. The period of E-field oscillations can be linked to the tower height. The oscillations were detectable both in the ground wave and in the first skywave.

Despite the well-documented impact of spatial resolution on the model extreme precipitation intensity (EPI), it is unclear whether and how this might influence the relationship between EPI and meteorological conditions. In this study, we assess how this relationship is represented in the Energy Exascale Earth System Model (E3SM) at low (110 km), high (25 km), and ultra-high (3.25 km, SCREAM) resolutions, using the Stage IV and IMERG data as observational references. The convection-permitting SCREAM performs well in capturing the EPI variations with temperature and saturation deficit under a wide range of atmospheric saturation levels. When the near-surface atmosphere is close to saturation, observations show a continuous increase in EPI with temperature, a pattern qualitatively well reproduced by SCREAM, although its short simulation of 40 days limits the range of temperature variation needed for a quantitative scaling rate comparison. In contrast, E3SM at 110 and 25 km resolutions produces an increase of EPI with temperature, followed by an erroneous negative scaling at high temperatures, even in saturated conditions. These comparisons are robust across all sample regions covering the midlatitudes, tropics, high altitudes, and mountainous areas, revealing that unless the spatial resolution is high enough to resolve deep convection, model physics dominates over spatial resolution in improving the performance in capturing the emergent relationship between EPI and the environmental drivers. Among other factors, our analyses indicate that the biased EPI scaling with temperature in the low- and high-resolution E3SM simulations might be related to deficiencies in parameterizing the dependence of atmospheric convection on relative humidity.

The vapor pressure deficit (VPD), defined as the difference between saturated and actual water vapor pressure, is a key determinant of atmospheric evaporative demand and a critical regulator of terrestrial carbon cycles. Understanding how rising temperatures influence VPD dynamics is therefore crucial in the context of global warming. In this study, we reconstructed April–August VPD variability from 1864 to 2022 using a composite tree-ring stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope chronology derived from Chinese pine (Pinus tabuliformis) in Eastern China, a typical monsoon region. Our reconstruction shows that VPD from 1864 to 2022 has generally increased, and the drying trend is more significant since 1955. This accelerated VPD rise is attributed to both increasing temperature and decreasing precipitation, with temperature being the dominant driver. Future projections from the IPSL-CM6A-LR model, validated against our reconstruction, point to a marked and sustained increase in VPD across all four scenarios over the next century, thereby constituting a fundamental threat to regional ecosystems.

The Qinghai-Tibet Plateau (QTP) has experienced significant vegetation changes in recent decades, including shifts in land cover types (grassland expansion) and greening. Nevertheless, the feedback mechanisms between vegetation changes and regional climate, as well as its impact on the hydrological cycles, are yet to be adequately quantified. This study employs high-resolution vegetation data and RegCM5.0-CLM4.5 simulations to assess the impacts of vegetation change on the QTP. Through sensitivity experiments involving alterations in plant functional types and leaf area index (LAI), the effects on temperature and hydrological cycles are evaluated. The results indicate that from 2000 to 2020, notable increases in LAI were concentrated in the eastern QTP. When only bare land changed to grassland, there was significant warming on the plateau. When LAI also increased, temperature was influenced by both evaporation and albedo changes. As LAI further expanded, evaporative cooling dominated, temperature decreased, precipitation and total runoff increased, and the water cycle accelerated.

In recent years, the Indo-Gangetic Plain (IGP) has experienced recurring intense air pollution episodes during the post-monsoon season (October–November), posing significant health risks to millions of inhabitants. These pollution events coincide with agricultural waste burning, emitting large quantities of carbon monoxide (CO) into the troposphere. Using 18 years of Infrared Atmospheric Sounding Interferometer (IASI) measurements from the Metop satellites, we examined the interannual variability of CO concentrations over the IGP during the post-monsoon season from 2007 to 2024. We focused on three representative years with varying CO levels (2011, 2017, and 2024) to determine whether CO pollution events in the IGP were more influenced by fire intensity, represented by the Fire Radiative Power (FRP) from the Moderate Resolution Imaging Spectroradiometers, or by meteorological parameters, particularly average winds in the 0–2 km layer, provided by ERA5 reanalysis. The comparison of wind patterns and FRP showed that surface winds primarily drive CO pollution severity. Extreme CO concentrations were found in 2017 and 2024 which coincided with prolonged periods of weak surface winds. In contrast, 2011 exhibited moderate CO concentrations throughout the post-monsoon season due to stronger winds, despite higher FRP. Our findings highlight the influence of surface winds in conditioning extreme post-monsoon pollution episodes in the IGP and demonstrate the ability of IASI for long-term monitoring of regional air pollution caused by agricultural waste burning. However, these results rely on the accurate detection of fire activity, which remains challenging due to limitations in satellite observations and changes in agricultural practices.

Gas-particle partitioning is a crucial atmospheric process governing the cycle and fate of polycyclic aromatic hydrocarbons (PAHs). To clarify its mechanisms, we measured gaseous and particulate concentrations of PAHs in the East China Marginal Sea (ECMS) to develop an improved model integrating thermodynamic interactions between PAHs and distinct aerosol carbonaceous fractions. Aerosol samples were thermally divided into 6 carbonaceous fractions: OM₁ to OM₄ (organic matter), EC₁ and EC₂ (elemental carbon). A systematic surrogate method was employed to simulate the absorption/adsorption process of PAHs in each fraction, and a computational enumeration framework coupled with the Abraham solvation parameter model was implemented for model parameterization. Compared to conventional models, this model improved the prediction accuracy for logarithmic gas-particle partitioning coefficient (log K_P) by 34%. It also clarified that OM₃ exhibits the strongest absorption capacity, likely driven by polar-induced interactions between this fraction and PAHs, whereas PAH adsorption onto the EC₁ and EC₂ proceeded homogeneously. Additionally, the model identified adsorption onto elemental carbon as the dominant partitioning mechanism for 3- and 4-ring PAHs, while for 5-ring PAHs, the contribution of absorption into OM₃ becomes comparable to that of adsorption. The prediction deviations of log K_P for 3-ring PAHs by this model suggested that adsorption onto inorganic aerosol constituents may also influence their gas-particle partitioning. This study elucidated the interactions between PAHs and different carbonaceous fractions in aerosols and advanced mechanistic understanding of the gas-particle partitioning.

This study investigates effective radiative forcing (ERF) and atmospheric absorption due to aerosols over South Asia, focusing on changes in emissions from the pre-industrial period to the present day. Utilizing four global climate models (GCMs), CAM5, CAM6, ECHAM6, and NICAM-SPRINTARS, alongside a common regional emission inventory (SMoG-India-v1) and global Community Emissions Data System (CEDS) for emissions outside India, we assess the perturbations in shortwave (SW), longwave (LW), and net radiative fluxes resulting from aerosol emissions. Our analysis reveals a multi-model mean aerosol net ERF of −1.66 W/m² at the top of atmosphere (TOA), indicating significant cooling driven by a substantial negative SW ERF (−4.59 W/m²) dominated by aerosol-cloud interactions (ERF_ACI), partially offset by net positive LW ERF (+2.93 W/m²). At the surface, the net ERF indicates pronounced cooling of approximately −10.95 W/m², driven by both SW aerosol-radiation interaction (ERF_ARI; −8.31 W/m²) and SW ERF_ACI (−5.40 W/m²), with a positive LW ERF (+2.65 W/m²). Atmospheric absorption, the difference between ERF at TOA and the surface, shows a net absorption of +9.29 W/m², dominated by SW absorption from direct aerosol-radiation interactions (SW Atm.Abs._ARI), contributing +8.99 W/m², with LW absorption from aerosol-cloud interactions (LW Atm.Abs._ACI) adding +1.83 W/m². These findings highlight the dominant role of aerosol-cloud interactions in cooling at both TOA and the surface and the significant contribution of direct aerosol interactions to atmospheric absorption over the Indian region. This underscores the need to consider both aerosol effects in climate models to improve regional climate predictions and support effective mitigation and adaptation strategies.