Journal of Geophysical Research: Atmospheres最新文献

El Niño–Southern Oscillation (ENSO) is a prominent climate phenomenon affecting precipitation patterns across much of the world. Regional ENSO-precipitation teleconnections are often asymmetric such that the precipitation response to El Niño is stronger or weaker than the response to La Niña. Better understanding of asymmetry in teleconnections can improve the predictability of climate extremes during ENSO events. In this study, we assess the capability of 50 state-of-the-art climate models and a reanalysis against observational data in simulating seasonal differences in asymmetric response of precipitation to ENSO. The analysis is performed across 46 sub-continental scale regions, using a precipitation composite technique for deriving the asymmetric component of precipitation response. Significant regional and seasonal diversity is found in the asymmetric response to ENSO, both in observations and models. Model performance in simulating the nature of teleconnections is higher than the performance in simulating the associated asymmetry. Model performance in capturing the regional diversity of asymmetry is highest in austral spring. The model biases in asymmetry are related to the inability of the models to accurately simulate the skewness of the heavy tailed local precipitation distributions and Niño3.4 SST distributions. In regions outside the Pacific and Indian Ocean basins, model bias in the skewness of local precipitation variability plays a larger role in model asymmetry bias. This analysis contributes to better understanding the fidelity of CMIP6 models in capturing asymmetry in teleconnections across different seasons and regions which are critical for making skillful projections of floods and droughts in a warming climate.

The efficiency of marine cloud brightening in cooling Earth's surface temperature is investigated using an ensemble of simulations with the Community Earth System Model version 2 (CESM2). We employ a susceptibility-based cloud seeding strategy, previously developed under the Community Climate System Model version 3 (CCSM3) to counteract the warming of CO₂ doubling, in which we target the regions of the ocean most easily brightened, to determine what area extent will be required to induce 1°C cooling under SSP2-4.5. The results indicate that cloud seeding over 5% of the ocean area is capable of achieving this goal in CESM2. Under this seeding scheme, cloud seeding is mainly deployed over lower latitudes which leads to a La Niña-like pattern of response which is a major unintended consequence. Potential mechanisms behind such side effects are presented and discussed. The simulations also reveal that the 5% cloud seeding scheme induces an overall reduction in global precipitation, with an increase over land and a decrease over the ocean.

Dimethyl sulphide (DMS) and methanethiol (MeSH) emissions from South Pacific surface seawater were determined in deck board Air-Sea Interface Tanks during the Sea2Cloud voyage in March 2020. The measured fluxes from water to headspace (F) varied with water mass type, with lowest fluxes observed with Subtropical and Subantarctic waters and highest fluxes from Frontal waters. Measured DMS fluxes were consistent with fluxes calculated using a two-layer model and seawater DMS concentrations. The MeSH:DMS flux ratio was 11%–18% across the three water mass types, confirming that MeSH may represent a significant unaccounted contribution to the atmospheric sulfur budget, with potentially important implications for marine aerosol formation and growth in models. Combining data from the ASITs and ambient surface seawater identified significant Spearman rank correlations for both dissolved DMS and MeSH with nanophytoplankton cell abundance (p_value < 0.012), suggesting an important role for this phytoplankton size class in determining regional DMS and MeSH emissions. Applying a nanophytoplankton-based parameterization to estimate DMS_w provided good agreement with a recent DMS climatology. Consequently, the observed relationship between DMS_w, MeSH_w and nanophytoplankton cell abundances may be applicable for modeling atmospheric fluxes.

The transport and delivery of low-abundance, bioactive trace elements to the surface ocean by aerosol mineral dust is a major planetary control over marine primary production and hence the global carbon cycle. Variations in the concentration of atmospheric dust have established links to global climate over geologic timescales and to regional biogeographic shifts over seasonal timescales. Constraining atmospheric dust variability is thus of high value to understanding oceanographic systems, especially vast, constitutively low-nutrient subtropical gyre ecosystems and high-nutrient/low-chlorophyll ecosystems where availability of the trace element iron is a dominant ecological control. Here we leverage the MERRA-2 reanalysis product to examine over four decades of surface-level atmospheric mineral dust concentrations in a domain of the subtropical North Pacific centered at Ocean Station ALOHA. This study region has been sampled regularly since the mid-1980s and was the site of the Hawaii Aerosol Time-Series (HATS) project in 2022–2023. Two unequal semi-annual periods of elevated dust evident in the long-term results are described and constrained. We look for evidence of shifts in total and seasonal atmospheric dust abundances or in the timing of the onset of the dominant spring/summer dusty period, finding year-to-year variations but little evidence for long-term trends. We observe significant but complex relationships between the Pacific Decadal Oscillation (PDO) index and both dust and precipitation. The 2022 calendar year was among the dustiest years for the study domain in the preceding two decades and, by contrast, 2023 exhibited a significant early spring lull in dust.

The number of cryptotephra (non-visible volcanic ash) records from northeastern North America is unique in the continent. The resulting tephrostratigraphic framework includes ash deposits sourced from volcanic arcs across the Northern Hemisphere and is an exceptional resource for correlating and dating paleoenvironmental records. It also provides an opportunity to explore more novel questions regarding the controls on ultra-distal tephra (volcanic ash >3,000 km from source) dispersal and deposition. Here, we examine temporal patterns in the tephrostratigraphy of northeastern North America to test the legitimacy of a previously noted change in ash deposition frequency at the Early Mid Holocene transition. We integrate five new cryptotephra records into the existing framework to improve its temporal and spatial extent and report further occurrences of widespread cryptotephra deposits including Mt. St. Helens We, Jala pumice, White River Ash east, Ruppert tephra, Mt. St. Helens Yn and Mazama Ash. Reexamination of the combined tephrostratigraphy using breakpoint analysis shows a significant increase in the frequency of ashfall after ca. 9,000 (7,860–9,650) cal yr BP (calendar years before C.E. 1950). We discuss this change in relation to volcanic and environmental controls of fine ash dispersal and preservation. We reject hypotheses relating to eruption frequency or depositional processes in favor of changing atmospheric transport patterns and tephra dispersal—possibly caused by the retreat of the Laurentide Ice Sheet. Our study is a novel example of how tephrostratigraphy can be used beyond traditional correlative and dating studies, in this case indicating large-scale changes in atmospheric circulation through time.

The diurnal variation in sea surface temperature (SST) plays a critical role in the simulation of oceanic and climate changes. Only increasing the air-sea coupling frequency from daily to hourly will result in a small SST diurnal amplitude. To accurately simulate this diurnal characteristic, a parameterization scheme for the diagnostic sublayer, which is shallower than the top model layer, and its temperature (sublayer temperature) was applied to models with coarse vertical resolution. In this study, we considered the effect of diurnal variation in SST on the performance of the second version of the Chinese Academy of Sciences Earth System Model (CAS-ESM2). Upon increasing the coupling frequency (EXP1), the diurnal variation in the global SST was reasonably reproduced with an underestimated amplitude. The observed amplitude was reasonably captured when applying sublayer temperature parameterization (EXP2). We compared these findings to a simulation of no diurnal variation in the SST by focusing on climatology, interannual variation, and ENSO asymmetry in a tropical Pacific region. In EXP1, the climatological mean state bias was not improved, but the discrepancy in the overestimation of interannual variability was largely improved. Compared with EXP1, in EXP2, the climatological cold tongue bias was reduced, and the skewness bias was less underestimated. Both diurnal coupling and the sublayer temperature should be considered to improve the performance of climate models.

Aerosols from sea spray and biomass burning play an important role in climate due to their considerable abundance in the atmosphere. The magnitude of their atmospheric impact depends on the chemical and physical properties of individual particles. The elemental composition of aerosol particles from Thailand, Southeast Asia, was analyzed using transmission electron microscopy (TEM) equipped with an energy dispersive X-ray spectrometer, with a special focus on sodium (Na) and potassium (K) as tracer elements for sea spray and biomass burning, respectively. Our analysis revealed that nearly all particles with aerodynamic diameters between 300 and 700 nm contained either Na or K, with approximately 74% of the particles containing both elements, that is, homogeneously mixed in the form of sulfate. While both Na and K were present in the same particles and K-rich particles were generally more abundant than Na-rich particles in all samples, higher Na fractions were observed when the particles were mainly transported from the ocean. The Na and K containing aerosol particles were often mixed with soot and organic particles. These results demonstrate the significant mixing of sea spray and biomass burning aerosols during their atmospheric transport. Such mixing can affect the hygroscopicity, viscosity, and optical properties of aerosols. This study highlights the significant mixing of natural aerosols from different sources at the individual particle level and suggests the need for accurate representation of aerosol properties in climate models.

With the significant increase in the abundance of greenhouse gases in the atmosphere over recent decades, more of the weak gaseous absorption bands are required to be incorporated in the gas optics model to improve the computational accuracy of radiation, and thus the warming effect of gases. Based on the latest HITRAN2020 spectroscopic data, a new 36-band correlated k-distribution (CKD) scheme is developed with high spectral band resolution for radiative transfer model. By considering errors of both radiative fluxes and atmospheric heating rates, optimizations are made to select the overlapping method and the number of k-distribution quadrature points in each band. The new CKD model exhibits a remarkable improvement in heating rates and radiative fluxes relative to the previous 17-band model when performing the identical radiative transfer calculations under 50 atmospheric profiles. The heating rate root-mean-square errors (RMSEs) of the 36-band model are 0.101 and 0.075 K d⁻¹ below 4 hPa for longwave and shortwave, respectively, when validated against the line-by-line benchmarks. The longwave irradiance RMSE is 0.47 W m⁻² at the top of atmosphere, and the shortwave RMSE is 2.15 W m⁻² at the surface. Furthermore, the cases simulating radiative forcing induced by varying gas concentrations demonstrate the ability of the 36-band model to study the warming effect of greenhouse gases.

This paper presents a study of the global medium-scale (scales620 km) gravity wave (GW) activity (in terms of zonal wind variance) and its seasonal, local time, and longitudinal variations by employing the enhanced-resolution ($��\sim �$50 km) whole atmosphere model (WAMT254) and space-based observations for geomagnetically quiet conditions. It is found that the GW hotspots produced by WAMT254 in the troposphere and stratosphere agree well with previously well-studied orographic and nonorographic sources. In the ionosphere-thermosphere (IT) region, GWs spread out forming latitudinal band-like hotspots. During solstices, a primary maximum in GW activity is observed in WAMT254 and GOCE over winter mid-high latitudes, likely associated with higher-order waves with primary sources in polar night jet, fronts, and polar vortex. During all the seasons, the enhancement of GWs around the geomagnetic poles as observed by GOCE (at $��\sim �$250 km) is well captured by simulations. WAMT254 GWs in the IT region also show dependence on local time due to their interaction with migrating tides leading to diurnal and semidiurnal variations. The GWs are more likely to propagate up from the MLT region during westward/weakly eastward phase of thermospheric tides, signifying the dominance of eastward GW momentum flux in the MLT. Additionally, as a novel finding, a wavenumber-4 signature in GW activity is predicted by WAMT254 between 6 and 12 local times in the tropics at $��\sim �$250 km, which propagates eastward with local time. This behavior is likely associated with the modulation of GWs by wave-4 signal of nonmigrating tides in the lower thermospheric zonal winds.

The roles of organosulfur compounds (OSCs), an important component in organic matter, in brown carbon (BrC) aerosol absorption is often overlooked. Here, the molecular composition of OSCs and its associations with methanol-soluble BrC (MS-BrC) absorption during a haze event in North China were revealed using a Fourier transform ion cyclotron resonance mass spectrometry analysis. By combining aggregated boosted tree model and partial least squares regression estimation, our results suggested that OSCs were mainly composed of potential aromatic structures, and the MS-BrC absorption was closely related to OSCs. Specifically, OSCs contribute a notable 26% of the total potential BrC molecular number and an upper limit of 10.4% of total MS-BrC absorption. Furthermore, we found that OSCs were mainly influenced by coal combustion, and the potential desulfurization reactions showed associations with the variations of MS-BrC absorption. Since the residential coal combustion (an important primary source of OSs) was the major energy in North China, our research underscores the potential of aromatic OSCs as tracers for assessing the impact of fossil fuel combustion on BrC and highlights the important atmospheric influences of OSCs (e.g., light absorption and health), which need more works to uncover the origins, fates, and environmental effects of OSCs.