Journal of Geophysical Research: Atmospheres最新文献

The Indian summer monsoon (ISM) is intricately linked to the El Niño-Southern Oscillation (ENSO) on interannual timescale. Although previous studies have explored ENSO's effects on the ISM, the reverse influence, particularly under global warming, remains unclear. This study examines the projected changes in the ISM's impacts on ENSO under the SSP5-8.5 emission scenario using 34 climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) that reasonably simulate the monsoon's effects on ENSO. A significant spread is found in the projections across the models, with approximately half of the models projecting an enhancing influence of ISM on ENSO, whereas the other half indicates a weakening effect. The intermodel spread is primarily associated with the projected changes in the strength of the feedback between precipitation and low-level circulation over the tropical northwest Pacific, which is crucial for generating ISM-induced anomalous circulation over the region. Models projecting an enhanced precipitation-circulation feedback simulate larger ISM-driven rainfall and circulation anomalies over the tropical northwest Pacific in a warmer climate, leading to more pronounced zonal wind anomalies near the equator along the southern side of the anomalous circulation and vice versa. As a result, the larger zonal wind anomalies caused by abnormal monsoons exert intensified effects on the subsequent ENSO evolution by significantly suppressing or amplifying the atmosphere-ocean coupling processes related to ENSO development.

Snowfall is an important component of the mass balance of ice sheets and glaciers in Antarctica. In coastal Victoria Land (VL), changes to snowfall can impact ice masses, landscapes, and coastal ecosystems. Coastal VL is characterized by strong gradients in snowfall rates between the polar desert of the McMurdo Dry Valleys and the high accumulation in northern VL. Extreme precipitation events significantly contribute to total precipitation, with the largest contribution in the Terra Nova Bay area. We present a comprehensive analysis of snowfall dynamics in this region, using a Lagrangian moisture source diagnostic to study moisture sources and Self-Organizing Maps (SOM) to link these to different synoptic weather types. The moisture for snowfall in VL originates from the Southern Ocean, with more local sources in the Ross Sea embayment in summer when sea ice is reduced. We show a strong division in moisture sources between northern and southern VL, with the north receiving precipitation from moisture sources to the west and southern VL from the east. Precipitation in northern VL results from meridional transport of marine air from lower latitudes, while precipitation in southern VL is related to cyclonic disturbances in the Ross Sea that bring moisture from the east. Extreme precipitation in northern VL occurs during blocking highs that intensify meridional transport. Such intrusions of marine air, sometimes in the form of atmospheric rivers, do not impact the more isolated western Ross Ice Shelf and southern VL further in the Ross Sea embayment.

Despite the relevancy of riming for precipitation formation, our observational knowledge of spatiotemporal scales of riming in clouds is poor. We use long-term cloud radar observations to statistically investigate the horizontal and vertical dimensions as well as the typical duration of riming events. We extend a recent retrieval for rime mass fraction into an algorithm that can separate the data into individual riming events and estimate the spatial dimensions using horizontal wind profiles. For 2,500 riming events, we find an average horizontal extent of the riming regions of 13 km and a duration of 18 min. Vertical profiles indicate that the majority of rime mass is built within the uppermost 250 m of the region where the radar can detect riming. Similar to previous studies, the riming events are almost exclusively detected between 0°C and −15°C. To further examine the correlation between riming and thermodynamic profiles, we derived liquid water content from radiosonde data. We find that strong riming usually starts close to the level where the liquid water path exceeds 0.2 kg m⁻². By defining a control group of nonriming events, we also find significantly enhanced liquid water below the −15°C isotherm for the riming cases. However, the existence of the 0.2 kg m⁻² level in ice clouds alone is not indicative of strong riming. We find this level to be four times more likely than strong riming events. We expect our multiyear statistical riming characteristics to be valuable for the future development of riming retrievals and model validation.

PM_2.5-bound antimony (Sb) may threaten human health and sustainable development, necessitating accurate source identification for its effective control. This study pioneered the application of Sb isotope signatures to trace PM_2.5-bound Sb sources, presenting the first isotopic fingerprints of Sb in urban PM_2.5. We selected two mega-cities with contrasting profiles: more developed Wuhan in central and less developed Guiyang in southwest China. Urban PM_2.5 in both cities exhibited an ε¹²³Sb value of 1.84 ± 0.79‱, with a distinct seasonal pattern, that is, heavier isotopes in spring/winter and lighter in summer/autumn. Isotopic source apportionment revealed waste incineration as the predominant anthropogenic Sb source in PM_2.5 for both cites at 34.0–39.1%, despite their massive economic and industrial differences. Brake wear emerged as the second major anthropogenic source, especially in Wuhan, where vehicle ownership is greater, accounting for 21.2%. Complementary analyses using enrichment factor, elemental ratios, positive matrix factorization modeling, and backward trajectory analysis corroborated the isotopic findings. This study offers a novel isotopic approach to identify PM_2.5-bound Sb sources, unveiling waste incineration and brake wear as major anthropogenic contributors from a new isotopic perspective.

Ammonia emissions from oceans are recognized as one of the most significant natural sources of ammonia globally; however, freshwater sources are rarely considered significant. The Great Lakes region, containing the largest network of freshwater lakes in the world, and a significant urbanized population exceeding 20 million, provides a unique opportunity to evaluate the potential for lacustrine (lake-associated) surfaces to contribute to regional ammonia levels. In this work, we combine an analysis of 20 years of water quality data from the Great Lakes region with the GEM-MACH (Global Environmental Multiscale (GEM)-Modelling Air quality and CHemistry (MACH)) chemical transport model to examine the influence of the Great Lakes on atmospheric ammonia. This analysis demonstrates that while regional ammonia levels are largely controlled by known terrestrial anthropogenic sources, lacustrine surfaces with an emission potential of only 200 increase summertime (July–September) monthly average ammonia (NH₃) levels by 5%–8% over the largest regional urban centers, with daily increases of up to 10%–20%. Supplemental water measurements collected from within 1 km offshore of the Greater Toronto Area were found to have an emission potential of 2000, suggesting that lacustrine emissions offshore of large urban areas could be significantly larger than those predicted by GEM-MACH. Our findings reveal that the Great Lakes may represent a regionally significant natural source of ammonia to the atmosphere.

Higher cloud top and stronger convection within Typhoon Lekima (2019) corresponds to lower brightness temperature (TB) from Fengyun-4A (FY-4A) Advanced Geostationary Radiation Imager (AGRI) observations. In this study, an effort is made to see if all-sky TB simulations from short-term model forecasts by a radiative transfer model could capture observed low-TB distributions. We employ a coupled ocean-atmosphere Weather Research and Forecasting (WRF) model at 3-km resolution and the European Center for Medium-Range Weather Forecasts (ECMWF) reanalysis v5 (ERA5) and the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) analysis as initial conditions. Horizontal structural distributions of all-sky TB simulations initialized by the NCEP GFS analysis better match AGRI observations than the ERA5 reanalysis, including the eyewall, moat and spiral rainband distributions of Typhoon Lekima. The cloud top pressure in most cloud areas near the center of Lekima is around 140 hPa, whereas in some rainbands far from the center is approximately 700 hPa. A high correlation in horizontal distributions of all-sky TB simulations with relative vorticity fields during the 24-hr period of WRF model forecasts suggests a potential relationship between dynamic and thermodynamic variables. The farther from the center of Lekima, the greater the proportion of high-wavenumber structures within both TB and relative vorticity fields. Within the radius of maximum wind speed, the azimuthal wavenumbers 0, 1, and 2 shown in TB and relative vorticity fields have greater comparability. High wavenumber structures in relative vorticity increase with radial distance in a way faster than those in TB.

Marine heatwaves (MHWs), defined as extreme sea surface temperature (SST) anomalies, significantly impact marine ecosystems and regional climate. While past research has focused on the regional driver, this study reveals a novel co-occurrence phenomenon between the northwest Pacific (NWP) and northwest Atlantic (NWA) during summer seasons (JJAS) from 1982 to 2022. We find significant correlations in MHW occurrence and intensity across these regions using three independent SST data sets. Concurrent high-pressure anomalies, reducing cloud cover and enhancing net shortwave radiation, are identified as the key driver of this co-occurrence. The Pacific decadal oscillation (PDO) emerges as the large-scale modulator. During negative PDO phases, tropical Pacific cooling weakens the meridional temperature gradient and westerlies around 30°N, inducing anomalous easterlies and subtropical high pressure. The Coriolis effect steers these easterly anomalies southward, generating anomalous southerlies and upper tropospheric convergence, ultimately triggering strong mid-latitude subsidence. This co-occurrence of high pressure and subsidence leads to reduced cloud cover, and amplified net shortwave radiation, driving rapid SST warming and the observed co-occurring MHWs in the NWP and NWA. Our North Pacific pacemaker experiment successfully replicates these PDO-induced features, including anomalous easterlies, high-pressure systems, and vertical motions in the subtropics, providing strong support for the proposed mechanisms. This study emphasizes the significant role of large-scale atmospheric-ocean teleconnections in shaping basin-scale MHW co-occurrence.

Shipping emissions are a major source of atmospheric pollutants globally. Accurate ship emission inventories are the key for developing pollution control strategies, but simulating the operating power of a ship under different navigational conditions is a challenge in ship emission estimation. Here, to improve the accuracy of the traditional power model and to establish framework for ship emissions in the port area, an improved load factor-based power model considering the impact of hull shape on the ship's resistance was proposed and applied to estimate the ship pollutant emissions. A series of data preprocessing methods were constructed based on automated identification system (AIS) high-precision measured data, including filling gaps and outliers, identifying vessel's operating mode with geofencing, and assigning fuel information by navigation area. The proposed power model and the AIS data preprocessing method were applied to estimate the ship pollutant emissions within Qingdao Port, China, in 2020. The total ship emissions were 1.27 × 10⁴, 6.33 × 10⁴, 1.91 × 10³, 1.76 × 10³, 3.11 × 10³, and 7.52 × 10³ tone for SO₂, NO_X, PM₁₀, PM_2.5, HC, and CO, respectively. As for emissions from ocean-going vessels, the proposed power model estimation was 3.9% lower than the propeller law power model and 2.4% higher than the admiralty law power model. We highlight that the proposed power model could be of large benefit in accurately evaluating regional ship emissions in the future, which can provide scientific assurance for ship emission inventory construction and green port development.

Unsteady land-sea breezes (LSBs) that result from time-varying surface temperature contrasts Δθ(t) are explored in the presence of a constant synoptic pressure forcing, M_g, oriented from sea to land (α = 0°) or land to sea (α = 180°). Large eddy simulations reveal the development of four distinctive regimes, depending on the joint interaction between M_g, α, and Δθ(t) in modulating the fine-scale dynamics. Time lags, computed as the shifts that maximize correlation coefficients of the velocity between the unsteady and the corresponding steady scenarios at Δθ = Δθ_max, are found to be significant and to extend 2 hr longer for α = 0° compared to α = 180°. These diurnal dynamics result in nonequilibrium conditions that are significantly affected by the flow history, and that behave differently over the two patches for the different α’s. Turbulence is found to be out of equilibrium with the mean flow, and the mean itself is found to be out of equilibrium with the thermal forcing. The sea surface heat flux is consistently more sensitive than its land counterpart to the time-varying external forcing Δθ(t), and more so for synoptic forcing from land to sea (α = 180°). Hence, although the land reaches equilibrium faster, the sea patch is found to exert a stronger control on the turbulence-mean flow equilibrium response. Finally, the vertical velocity profile at the shore and shore-normal velocity transects at the first grid level are shown to encode the multiscale regimes of the LSBs evolution and can thus be used to identify these regimes using k-means clustering.

The western North Pacific summer monsoon (WNPSM) is characterized by prominent northward propagation of intraseasonal oscillations (ISOs). However, the specific vorticity dynamics as an atmospheric precursor responsible for the northward propagation of ISOs remains unclear over the WNPSM. In this study, we utilized a multi-timescale vorticity diagnosis to identify the key dynamics of ISOs in WNPSM. Our findings indicate that both vortex tilting and vortex advection play important roles in vorticity generation and the subsequent development of new convection, ultimately leading to ISO propagation. Vortex tilting is primarily driven by the interaction between intraseasonal vertical velocity shear and background easterly wind shear, which is consistent with the ISOs during Indian summer monsoon (ISM). However, the impact of vortex tilting is confined near the equator in the eastern region of the WNPSM because of the decreased easterly wind shear from the Indian Ocean to the WNP. Meanwhile, vortex advection is the result of the transport of intraseasonal vorticity by the background southerly wind, which is significant over the region of tropical WNPSM. In summary, this differs from the tilting alone that controls northward-propagating ISOs during the ISM and is critical for advancing the unique framework for ISOs during the WNPSM.