Journal of Geophysical Research: Atmospheres最新文献

Land-atmosphere interactions play a critical role in the evolution and formation of low-level clouds. The different states of coupling between low-level clouds and the surface are uncertain, primarily over continental regions, where complex thermodynamics complicates their investigation. This study uses observations from the Atmospheric Radiation Measurement User Facility to explore cloud-surface coupling and perform a climatological analysis of this interaction in five countries across three continents. The results reveal consistent coupling thresholds and average percentages across the five sites, with coupled clouds accounting for 66% of the cases and decoupled clouds for 34%. Thermodynamic and dynamic evaluations show distinct differences between coupled and decoupled clouds. Coupled clouds are characterized by humid environments, in which vertical motions connect the surface and lower atmosphere to the cloud base, conditions that favor the formation of boundary layer clouds. Decoupled clouds prefer to occur in a drier and colder environment with vertical motions inside the boundary layer being detached from the cloud base, under which boundary layer clouds are hard to form. Coupled clouds peak during warmer hours and seasons, and vice versa for decoupled clouds. This study underscores the complexity of cloud-land-surface interactions and paves the way for further investigations into cloud formation and evolution under different atmospheric environments.

Investigating the spatial association and evolution of soil moisture (SM) droughts is crucial for mitigating their negative impacts on agriculture, the ecosystem, and the economy. Using complex network theory and random forest models, this study analyzed the spatial synchronization characteristics, regional drivers, and propagation patterns of weekly SM drought events across China from 1979 to 2019. Results revealed drought events displayed higher spatial synchronization in eastern Tibet, northern Shaanxi, and southeastern and northeastern China, with average degree centrality (DC) exceeding 250. The drivers of drought event synchronization exhibited regional heterogeneity: precipitation (P, 24.1%), potential evapotranspiration (PET, 15.2%), and atmospheric pressure (PRS, 10.8%) were dominant in western China; P, zonal wind speed at 10 m height (WIN_10v), and terrain gradient contributed more to DC simulation in the northeastern region, with an average contribution of 7.7%; river area (RiA) was the primary factor affecting drought synchrony in southern China, contributing 15.1%, which was 2.4–3 times higher than relative humidity (RHU) and WIN_10v. Drought propagation analysis identified source regions in western Xinjiang and northern Tibet while sink zones were concentrated in eastern Tibet, western Sichuan, northern Guizhou, northeastern Jiangxi, and southeastern Heilongjiang Provinces. Droughts originating from northern Tibet predominantly propagated along the south-southeast (SSE) direction, with a strength of 90 and distances ranging from 1,500 to 1,800 km. This study is valuable to enhance the understanding of the spatiotemporal patterns of SM droughts in China and highlight the potential of complex network approaches for agricultural drought monitoring and early warning.

This study uses a convection-permitting model simulation to describe the environmental conditions under which convective upscale growth occurs in central Argentina, particularly examining environmental parameters when deep convection initially forms that could differentiate the rate of initial upscale growth. Simulated mesoscale convective systems (MCSs) are separated into slow and rapid growth by the rate of spatial growth from convection initiation until reaching the MCS scale. A low-level jet (LLJ) is found more frequently near the deep convection that experiences rapid growth to an MCS, but its presence alone is not predictive of rapid growth. Using spatially-averaged parameters, we find that rapid growth to MCSs also occurs in environments that are significantly more thermodynamically favorable with greater low-level moisture and instability. Fewer significant differences are found in the kinematic environment with only the 0–2 km vertical wind shear magnitude being significantly larger for rapid growth MCSs compared to slow growth MCSs, potentially related to LLJs often peaking near this height. When focusing only on MCSs with the slowest and fastest growth rates, elevated-layer shear is significantly smaller for very rapid growth MCSs, suggesting elevated-layer shear may help discriminate between the upper and lower bounds of growth rate. Finally, when upscale growth occurs near the Sierras de Córdoba (SDC) with a LLJ present, rapid growth is also supported by favorable wind shear orientation. However, this does not hold for upscale growth occurring away from the SDC, highlighting the importance of interpreting shear direction relative to the orientation of features initiating deep convection.

Hole-punch clouds (HPCs) are circular or oval cloudless holes in thin supercooled cloud layers. They are believed to be generated by aircraft passing through supercooled cloud layers; however, the exact formation mechanisms remain poorly understood due to the scarcity of observations. In addition, basic HPC formation characteristics, such as expansion speed, are controversial. Using geostationary meteorological satellite Himawari-8 data and aircraft flight data of Flightradar24, this study clarifies HPC formation and development from 59 HPCs. Two growth stages of HPCs are identified: first, linear HPCs are formed. The length (L_major) and width (L_minor) of one of the long HPCs grew at rates of 43 m s⁻¹ and 3.8 m s⁻¹. This occurs within 10–20 min of an aircraft passing through supercooled clouds and their orientations consistent with tracks of aircraft. The upward expansion speed of the HPC was approximately 1.2 m s⁻¹. Second, these linear HPCs expand slowly and homogeneously for over an hour. The growth rate modes of L_major and L_minor of all HPCs were both 1–2 m s⁻¹. All observed HPCs initially appeared as lines, thus supporting that HPCs are generated by aircraft. Sub-grid-scale cloud-free areas or extremely thin supercooled cloud layers where aircraft passed would not generate HPCs. This is because not all aircraft that passed supercooled clouds generated HPCs.

A Moon-based radiometer enables disk-integrated measurements to capture planetary-scale variations in Earth's emitted radiation. However, existing studies have neither unraveled the influence of orbital dynamics on such radiation nor quantified how clouds modify these periodic signatures at the planetary scale, which leaves the underlying mechanisms driving disk-integrated radiation variations obscure and makes it difficult to isolate the authentic signals of the planetary system. In this study, outputs from NASA's Goddard Earth Observing System Version 5 (GEOS-5) model were mapped onto the Moon-based Earth observation geometry to simulate time-series data of disk-integrated radiation. The variability characteristics of this radiation were quantified via spherical harmonic decomposition, and the constructed spherical harmonic fingerprints effectively separate orbital dynamics and radiation signatures in disk-integrated observations. Results show that (a) Moon-based disk-integrated radiation variations are dominated by 1st- and 2nd-degree spherical harmonics, capturing large-scale radiative features while smoothing fine-scale fluctuations; (b) key cycles driven by Earth-Moon geometry include the synodic month, the sidereal month, and their semiperiodic counterparts, which are primarily governed by sectoral and zonal harmonic components, respectively; (c) clouds systematically reduce disk-integrated radiation but preserve orbital-driven periodicities, which averages out local cloud effects while retaining celestial motion signals. This study further discussed the potential of these observations to refine general circulation models (GCMs) via planetary-scale reality checks, as well as of bridging Earth system science and astrophysics by using Earth as a sample. In general, this study lays a foundation for interpreting disk-integrated radiation features in future missions.

The nitrogen stable isotope composition (δ¹⁵N) of atmospheric nitrate and nitrogen oxides (NO_x) is widely used to quantify their sources. However, the δ¹⁵N signatures from some important anthropogenic NO_x sources, for example, the coke and cement industries, are unknown, and reports on the signatures of δ¹⁵N(NO_x) from coal-fired power plants and other fossil fuel combustion related industrial processes are limited. Here, we report a comprehensive investigation of δ¹⁵N(NO_x) from various emission sources in Taiyuan, a megacity in Northern China where coal dominated the energy consumption before 2018. The different sources were investigated in 2023–2024, and the δ¹⁵N(NO_x) signatures for coal-fired and gas-fired power plants are (20.0 ± 2.3) ‰ and (−19.8 ± 0.8) ‰ (mean ± 1σ), respectively. While for residential gas furnaces, municipal solid waste incineration plants, coke industry, and cement industry, the δ¹⁵N(NO_x) signatures were measured as (−18.5 ± 0.8) ‰, (11.7 ± 2.4) ‰, (−10.9 ± 1.9) ‰, and (8.1 ± 2.3) ‰, respectively. Among them, the coke and cement industries have not been quantified before. In addition to these emission sources, we further collected ambient NO_x and found in Taiyuan the ambient δ¹⁵N(NO_x) values were significantly lower in winter ((−14.1 ± 4.2) ‰) than those in summer ((−4.2 ± 1.7) ‰). This is because in winter Taiyuan natural gas is the predominant NO_x emission source. That the winter δ¹⁵N(NO_x) was lower than that in summer appears to be opposite to previously reported seasonality of δ¹⁵N(NO₃⁻) values in Northern China which was suggested to be caused by seasonal δ¹⁵N(NO_x) differences, and this is likely because after the implementation of the coal-to-gas project and clean air policy in 2018, natural gas combustion became the dominant NO_x emission source in winter which is the heating season with extensive demand of fuel consumption.

African easterly waves (AEWs) are an important precursor or “seed” for Atlantic tropical cyclones (TCs), with 60%–80% of major hurricanes observed to originate from AEWs. However, climate model simulations indicate that AEWs are not necessary to maintain annual Atlantic TC frequency. Furthermore, small ensembles suggest that AEWs may impact the spatial distribution and landfall of Atlantic TCs. Here, we investigated the influence of AEWs on the spatial distribution of Atlantic TC tracks and landfall using 50-member ensembles of TC-permitting regional model simulations for five hurricane seasons characterized by different levels of TC activity. The control simulations are seasonal hindcasts in which AEWs were prescribed through the eastern lateral boundary condition using reanalysis. In the experiments, we suppressed AEWs by applying a 2–10 day filter to the eastern lateral boundary condition. In response to AEW suppression, we discovered statistically significant increases in Atlantic TC frequency (10%–26%) and landfall (16%–44%), a westward shift in TC genesis location and tracks with increased landfall over the Caribbean Islands, southwestern Gulf Coast, and southeastern US coast, and increases in mid-tropospheric relative humidity in the main development region. In addition, we evaluated TC genesis mechanisms in the absence of AEWs and found evidence that the intertropical convergence zone (ITCZ) intensified and extended northward, resulting in ITCZ wave-breaking that shed vortices which served as TC seeds. By uncovering the connections between TC seed types and the likelihood of TC landfall, this research can provide Atlantic coastal and island communities with useful information to prepare for TC impacts.

Accurate retrieval of satellite-derived aerosol optical depth (AOD) is critical for air quality forecasting, especially when AOD is assimilated into models. However, if retrieval errors in the satellite-derived AOD are not corrected or characterized, they can lead to false analysis increments and ultimately degrade the quality of data assimilation (DA). The issue also arises in the Geostationary Ocean Color Imager (GOCI)-II AOD product, which remains susceptible to cloud contamination. To address the issue, this study developed a cloud screening framework for GOCI-II AOD that combines two processes: (a) cloud removal using cloud type information from Himawari-8/9 Advanced Himawari Imager (AHI) and (b) a statistical cloud filtering based on AOD retrieval characteristics. Comparisons with Aerosol Robotic Network (AERONET) AOD demonstrated that the cloud screening framework effectively mitigated overestimation of GOCI-II AODs compared to AERONET AODs. Consequently, the cloud-screened GOCI-II AOD showed a better agreement with AERONET AOD, improving Pearson's correlation coefficient from 0.77 to 0.82 and decreasing root-mean-square error from 0.175 to 0.110. Despite these improvements, the normalized biases of the cloud-screened GOCI-II AOD against AERONET AOD still exhibited diurnal variations, with GOCI-II AODs being overestimated in coastal regions and underestimated in inland sites, under low-AOD conditions. Nonetheless, the enhanced consistency of the cloud-screened GOCI-II AOD with AERONET AOD and its more Gaussian-like error distribution supports the utility of the cloud screening framework in improving the quality of GOCI-II AOD for DA systems.

Mangrove ecosystems, located at the interface between land and sea, are characterized by periodic tidal inundation and salinity fluctuations, which exhibit complex land–atmosphere interactions influencing the water cycle. This study evaluated the Sigmoid Generalized Complementary (SGC) equation for estimating evaporation in a subtropical mangrove forest in the southern China, focusing on the effects of tidal inundation time fraction (TI) and salinity (SAL) on both evaporation and model parameters. Using a decade of eddy covariance and meteorological data, we found that the SGC equation accurately captured the diurnal and seasonal evaporation dynamics achieving high performance (R² = 0.94, RMSE = 11.98 W m⁻²; daily) with the best-fit parameters (α = 1.13, b = ∞). α is the atmospheric character parameter representing the atmospheric advection effect and b is the land surface parameter representing the surface moisture condition. Although TI had limited impact on the evaporation magnitude, it sufficiently affected parameter b which transitioned from land-like to open-water characteristics as inundation increased. Salinity did not significantly affect the SGC parameters but was negatively correlated with monthly evaporation, especially when exceeding about 15 PSU. Diurnally, evaporation was primarily controlled by net radiation rather than water level or salinity, and no water-energy decoupling was observed at the seasonal scale. These findings demonstrate the robustness and applicability of the SGC framework in intertidal environments, offer a new perspective for modeling evaporation in intertidal zones, and provide new insights into the interactions between hydrological drivers, salinity stress, and evaporation in mangroves.

In mid-winter 2024, extraordinary stratospheric warming occurred over the sub-Antarctic region with two distinctive warming maxima in mid-July to early August, followed by record negative anomalies in the southern annular mode (SAM) during late July to early August. However, the causality between these stratospheric and tropospheric extreme events remains unclear due to the rarity of such downward coupling during Southern Hemisphere (SH) winter—previous Antarctic stratospheric warmings and their associated downward coupling have largely occurred during SH spring. Here we provide insights into the dynamics and climate impacts of wintertime Antarctic vortex variability during 1979–2023 and compare the climatological behavior of wintertime SH stratosphere-troposphere coupling with that observed during mid-winter 2024. During 1979–2023, compared to the springtime stratospheric polar vortex variability in the SH, which is characterized by variations in vortex strength and breakdown timing and its robust signature in surface climate, wintertime variability in the SH stratospheric circulation is marked by expansion and contraction of the vortex with generally weak linkages to surface circulation. The 2024 mid-winter event mirrored many historical features of wintertime variability at stratospheric levels but had a much stronger signature in surface climate. It was unique with a record contraction of the vortex accompanied by record increases in polar stratospheric temperatures for July. These unusual stratospheric conditions atypically led to substantially higher-than-normal Antarctic ozone concentrations in July and August, delaying the development of the ozone hole, and record negative values in the SAM and extraordinary warmth over the Antarctic continent in early August 2024.