Journal of Geophysical Research: Atmospheres最新文献

The detection capability of the global infrasound International Monitoring System (IMS) deployed to monitor compliance with the Comprehensive Nuclear-Test-Ban Treaty is highly variable in space and time. Previous studies estimated the source energy of near-surface explosions from remote observations using empirical yield-scaling relations. However, these relations simplify the complexities of infrasound propagation. In order to reduce the variance in the predicted wave attenuation, massive numerical propagation simulations are carried out by exploring a wide range of realistic atmospheric scenarios. An analytical expression is proposed to model transmission losses at distances up to 4,000 km. This attenuation relation is validated using multi-year near- and far-field records of volcanic eruptions from Mount Etna, Italy, as a benchmark. An idealized explosive source model is combined with transmission loss and measured noise statistics to quantify the 90% probability detection threshold of the IMS network. This approach yields high-resolution detection capability simulation results with limited computational resources. Simulations predict that explosions equivalent to $��\sim �$500 t of TNT equivalent would be detected by at least two stations at any time of the year, with the detection capability being best during the solstice periods. Due to the high spatio-temporal variability of the winds in the ground-to-stratosphere levels, threshold variations can reach one order of magnitude from seasonal down to semi-diurnal scales.

Cold winters in Eurasia considerably affect transportation, agriculture, energy, and public health. This study utilizes 31 global climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) and 33 CMIP5 models to evaluate the historical surface air temperature, sea level pressure, 500-hPa geopotential height, 150-hPa meridional and zonal wind, and polar vortex indices during cold winters. Our research quantifies the advancements of CMIP6 over CMIP5. Additionally, future changes in these variables under three different Shared Socioeconomic Pathways (SSPs), that is, SSP 1–2.6, SSP 2–4.5, and SSP 5–8.5, are projected based on 20 out of the 31 CMIP6 models. The results indicate that the multimodel ensemble means from both CMIP5 and CMIP6 effectively capture the main features of the observed Eurasian cold winters and their associated factors with good simulation agreement. The CMIP6 ensemble mean outperforms its CMIP5 counterpart, and both ensemble means (CMIP5 and CMIP6) perform better than individual CMIP6 models. Among CMIP6 models, 500-hPa geopotential height achieves the highest simulation skill, whereas sea level pressure shows the lowest. Compared with same-institute models from CMIP5, CMIP6 models show overall improvements with sea level pressure simulation being notably advanced. Under the three SSPs, the occurrence probability of cold winters is projected to decrease as the area and intensity indices of the polar vortex decline. Moreover, surface temperature anomalies are projected to exhibit a “warm Arctic and cold Eurasia” pattern, and the anticyclonic anomalies at 500 hPa and 150 hPa are projected to be centered at high latitudes.

This study examines the individual and combined impacts of aerosol-radiation interactions (ARI) and aerosol-photolysis interactions (API) on regional air quality over India using the WRF-Chem model for May 2018. Model performance was validated against CERES, MERRA-2, and CPCB observations, demonstrating good agreement in simulating key meteorological variables and air pollutants. Results show that ARI increases mean PM_2.5 concentrations by approximately 3 μg/m³ (12.4%) across India by reducing surface shortwave radiation and enhancing atmospheric stability, which limits pollutant dispersion. In contrast, API reduces PM_2.5 by about 1.8 μg/m³ (7.2%) due to lower photolysis rates, which suppress secondary aerosol formation. When combined, ARI and API lead to a net PM_2.5 increase of around 2 μg/m³ (8.4%). Simultaneously, surface O₃ levels decrease under all scenarios: by 2.6 ppbv (4%) with ARI, 1.7 ppbv (2.6%) with API, and 1.2 ppbv (1.8%) when both effects are included. These results underscore the complex interplay between aerosols, atmospheric stability, and chemical processes. They highlight the need for integrated air quality strategies that account for both direct emissions and feedback effects from aerosol interactions, especially in regions with diverse emission sources like India.

The mechanism driving the lower thermospheric meridional circulation is analyzed using the high-resolution Whole Atmosphere Community Climate Model with thermosphere/ionosphere extension (WACCM-X). In the winter lower thermosphere, eastward forcing is dominant around z=120 km, consistent with equatorward circulation. Following previous studies, the vertical flux of the zonal momentum is examined for small-scale waves with zonal scales smaller than 2,000 km through the depth of the middle atmosphere. Wave decomposition analysis reveals that eastward waves with a wide range of phase speeds are generated around the polar vortex height. This result differs from the conventional understanding in gravity wave parameterizations, which states that eastward waves slower than the strong mesospheric wind cannot propagate to higher altitudes. Quasi-stationary and westward waves are also active in the mesosphere, some of which originate in the troposphere. However, these waves more often dissipate in the upper mesosphere at critical levels and easterly shear, which results in the dominance of eastward waves in the lower thermosphere. The horizontal and temporal variations of gravity wave activity in the lower thermosphere are associated with the structure of the mesospheric jet. These results suggest a possible method for diagnosing wave generation that could improve gravity wave parameterizations. In the summer hemisphere, westward forcing is expressed by the semidiurnal tide, as well as by filtered gravity waves. Thus, the driving mechanisms of the lower thermospheric circulation are the contribution of gravity waves, mainly generated in the mesosphere and selectively filtered in the upper mesosphere, and the semidiurnal tide.

In this study, we report the response of migrating diurnal tides (DW1) in the mesosphere and lower thermosphere (MLT) region to the Madden‒Julian oscillation (MJO). The DW1 amplitudes are decomposed from the neutral horizontal wind observed by four meteor radars in the equatorial region. The DW1 and zonal wind in the equatorial MLT region show consistent intraseasonal variations, implying that the upward propagating DW1 can affect the mesospheric zonal wind. By jointly analyzing the real-time multivariate MJO (RMM) indices and mesospheric DW1, we found that DW1 responds strongly to the MJO during both boreal winter (difference relative to seasonal means: ∼20%–25%) and summer (∼25%). The MJO convection affects the mesospheric DW1 by modulating the solar radiative absorption by water vapor and latent heat release in the troposphere. The seasonal difference in DW1–MJO response can be attributed to a slight weakening of the DW1 tidal heating sources during MJO phases 1–4 and a significant enhancement during phases 6–7 during summer, driven by the moisture transport from the Indian Ocean and Pacific to the East Asian continent. This finding provides an opportunity to the understanding of the coupling between the troposphere and the mesosphere through migrating tides.

Synoptic weather typing is a common technique for categorizing regional circulation patterns over a region. Defined and commonly used sets of synoptic weather types (SWTs) have the potential to simplify the analysis and interpretation of the regional circulation on the weather time and spatial scales and create a common language between the often segregated weather and climate research communities. However, circulation classifications are potentially complicated over Australia owing to its position in both the tropics and extratropics. Here we present a set of 30 SWTs over Australia by k means clustering the 850 hPa wind field in the ERA5 data set. We show that the Australian SWTs represent recognizable weather patterns over the continent throughout the year. Importantly, the SWTs capture features in the extratropics together with characteristics associated with the tropical monsoon. An initial analysis of the relationship of the SWTs with the modes of climate variability, high impact weather and renewable energy related variables showing the utility of the SWTs in a wide range of applications across disciplines within earth system sciences and beyond.

The Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument enables an unprecedented assessment of diurnal and community-scale variations in tropospheric nitrogen dioxide (NO₂) across North America. This study presents the first exploratory analysis of NO₂ patterns in eastern Canada, including Ontario, Quebec, and the Atlantic provinces, using TEMPO observations. We analyzed TEMPO data (V03) gridded at 0.02° × 0.02° from September 2023 to August 2024 and compared it with the Tropospheric Monitoring Instrument (TROPOMI) and surface-level measurements from Canadian national regulatory monitors. With the hourly resolution of TEMPO, we observed diurnal trends and hotspots that were not recognized by once-per-day TROPOMI measurements and pinpointed undermonitored areas. NO₂ in eastern Canada's eight major metropolitan areas, ports, and industrial cities similarly peaked in early morning and declined in later hours. Still, TEMPO detected variations in their hours of peaks and spikes, seasonal, and weekday-weekend distributions. In Atlantic Canada, correlations between TEMPO and TROPOMI column densities, as well as column-surface alignments, were lower (Spearman's ρ = 0.41–0.53) compared to the Quebec City-Windsor Corridor (Spearman's ρ = 0.81–0.90), primarily due to a wider dynamic range of pollution in the latter region. The two regions' TEMPO-TROPOMI mean absolute differences were 19.3% and 17.1%, respectively. Temporal variations (e.g., a later weekday morning peak in Ontario cities) and TEMPO's identification of additional undermonitored hotspots provide insights into air quality control planning. Our findings motivate future research using multiyear TEMPO data to investigate atmospheric NO₂ sources, transport, exposure, and associated population health impacts in Canada.

Entrainment-mixing processes between clouds and their environment significantly impact the microphysical, thermodynamical, and dynamical properties of clouds. However, quantitative observational analysis of different entrainment-mixing mechanisms between cumulus cores and edges remains lacking. This study provides the quantitative analysis of such mechanisms in cumulus cores versus edges using aircraft observations from the Rain in Cumulus Over the Ocean project. Results show that cores have larger liquid water content, larger cloud droplets, and smaller entrained droplet-free air parcels, consequently yielding a larger homogeneous mixing degree (ψ) and a smaller Damköhler number ($��D_a�$, the ratio of mixing time scale to droplet evaporation time scale). ψ is 0.13 higher and $��D_a�$ is 3.3 lower in the cores compared to the edges. Furthermore, core-edge differences in ψ are analyzed under varying environmental and cloud conditions. Smaller cloud width, weaker in-cloud vertical velocity, lower environmental relative humidity, and lower aerosol concentration all reduce ψ and enhance the core-edge ψ contrast. The results offer insights into the theoretical understanding and parameterizations of entrainment-mixing mechanisms in the cores and edges of cumulus clouds.

Tropical precipitation biases have persisted since the very first generations of climate models. These biases are highly sensitive to the region and/or season of interest, with commonalities in the east Pacific and Atlantic Ocean basins, possibly due to their similar observed climatological northern hemisphere intertropical convergence zone (ITCZ). However, the colloquial name “double ITCZ bias” comes from a time and/or zonal mean, and may be missing important information about errors at smaller time and space scales. In this study, we explore daily characteristics of the ITCZ in observations, reanalyses, and 25 Coupled Model Intercomparison Project 6 (CMIP6) models over the east Pacific Ocean. We devise and apply an algorithm that determines a region's dominant daily ITCZ configuration, its “ITCZ state,” based on the daily mean precipitation field. The five ITCZ states include: northern hemisphere (nITCZ), southern hemisphere (sITCZ), double (dITCZ), equatorial (eITCZ), and absent (aITCZ). We find that nearly all CMIP6 models gravely underestimate nITCZs and overestimate sITCZs during January through May, in contrast with what “double ITCZ bias” suggests. Surprisingly, all reanalyses also underestimate nITCZs and overestimate eITCZs. Errors in ITCZ state interannual variability are consistent with mean errors in reanalyses, while sITCZ interannual variability is far too low relative to the mean in most CMIP6 models. Lastly, all reanalyses and CMIP6 models overestimate precipitation rates in the southern hemisphere ITCZ band for dITCZs and sITCZs, suggestive of errors with atmospheric origins.

Compound climate extremes, where temperature and precipitation extremes occur together are increasing globally and pose growing risks to human and natural systems. India is already experiencing more frequent extreme weather events, underscoring the urgency of assessing how such events may evolve with continued warming. This study uses high-resolution, statistically downscaled, and bias-corrected CMIP6 climate projections from 30 different models to assess the future compound extremes such as Cold-Dry (CD), Cold-Wet (CW), Warm-Dry (WD), and Warm-Wet (WW) under 1.5°C and 2.0°C global warming levels for two future climate scenarios (SSP2-4.5 and SSP5-8.5) during the pre-monsoon season (March-June). The projections indicate that cold-related extremes (CD, CW) will become rare while warm-related extremes (WD, WW) will increase significantly across India, with the largest changes emerging by the mid-21st century across the West Central India (WCI), North East India (NEI), and Central North East India (CNEI). The occurrence of WD events has approximately doubled while WW events have increased nearly threefold across India during this season. Temperature increases, reinforced by land-atmosphere coupling and thermodynamic constraints such as higher vapor pressure deficit and greater moisture holding capacity, intensify wet and dry extremes, while circulation-driven precipitation changes play a lesser role. Population exposure to WD and WW events is projected to rise sharply, particularly in densely populated and climate-sensitive regions. These findings highlight the need for targeted, region-specific adaptation planning and risk-informed decision-making to manage the escalating risks from compound extremes in a warming climate.