Journal of Geophysical Research: Atmospheres最新文献

Using ensemble forecasts from the Global Ensemble Forecast System and controlled integrations with the Weather Research and Forecasting (WRF) model, we investigate how the North American stratospheric sub-vortex, closely linked to the 2019 sudden stratospheric warming (SSW), influences a large-scale precipitation event over the eastern United States in late January 2019 and further quantify its contribution to the precipitation anomalies of the event. This precipitation event is directly driven by a tropospheric cyclone and a downstream anticyclone, which jointly transport warm, moist air from the Gulf of Mexico into the eastern U.S. Through a series of WRF experiments, we indicate that a nudged run (NOBS), in which the stratospheric circulation is nudged toward the observed evolution represented by the ERA5 reanalysis data set, successfully captures the evolution of the tropospheric cyclone and anticyclone, whereas a parallel run (NCLM) nudged toward the ERA5 winter climatology fails to capture them. The NOBS run accurately simulates the sub-vortex over North America, which facilitates the southward invasion of cold air. Moreover, in the NOBS experiment, the well-captured stratospheric sub-vortex enhances downward coupling through the phase-locking mechanism, directly promoting the development of the tropospheric cyclone and indirectly influencing the downstream anticyclone. Our results indicate that the stratospheric anomalies contribute to approximately 37% of the total precipitation during the event. This finding underscores the importance of the sub-vortex's geometry in the lowermost stratosphere for driving this precipitation event and highlights the need to focus on polar vortex geometry to fully understand regional stratosphere-troposphere coupling.

Synchronous extreme heatwaves across Eurasia have become more frequent in recent decades, posing severe risks to ecosystems, society, and human health. Meanwhile, rapid Arctic Sea ice loss due to Arctic amplification has emerged as a crucial driver of extreme weather and climate events. However, its specific contribution to Eurasian synchronous heatwaves remains poorly understood. Using climate networks, atmospheric dynamic diagnostics, and numerical experiments, we revealed an interdecadal increase in the interannual relationship between Barents Sea ice and Europe-East Asian synchronous heatwaves after 2000. During 2000–2022, the persistent sea ice loss in the northern Barents Sea from late spring to summer, combined with strong land-atmosphere feedback over northwestern Europe, triggers and sustains a northwestern European anticyclone. This anticyclone disturbance, positioned north of the Eurasian subtropical jet, excites a northwest-southeastward propagating Rossby wave train in summer. Thus, another anticyclone is induced in the north of Tibetan Plateau. Together, these two anticyclones provide favorable atmospheric conditions for the occurrence of Europe-East Asian synchronous heatwaves. During 1979–1999, however, sea ice anomalies were primarily confined to the southern Barents Sea. The associated feedback processes and atmospheric circulation anomalies are too weak to excite and sustain a northwestern European anticyclone, thereby limiting the occurrence of such synchronous heatwaves in summer. These findings highlight the growing influence of Arctic Sea ice loss on midlatitude summer extremes and offer new insights into the mechanisms behind Europe-East Asian synchronous heatwaves in a warming climate.

The far-infrared (>16 μm) spectrum plays a crucial role in Earth's radiation budget but was rarely observed from space before 2024. Two Polar Radiant Energy in the Far Infrared Experiment (PREFIRE) satellites, PREFIRE2 (SAT-2) and PREFIRE1 (SAT-1), were launched in 2024. They measure spectrally resolved radiances from 5 to 53 μm at 0.84 μm spectral resolution. Deriving spectral outgoing longwave radiation (OLR) and tracking its changes relative to other polar climate factors are key focuses of the PREFIRE mission. We describe a set of algorithms developed to estimate spectral OLR from the PREFIRE L1B-calibrated radiances. Spectral angular distribution models were developed to invert spectral radiance to spectral flux. For the spectral region not covered by the PREFIRE measurements, a principal-component-based linear regression scheme is used to estimate the spectral flux. When the clear-sky spectral OLRs derived from the PREFIRE SAT-2 measurements are compared with counterparts derived from in situ measurements, the mean differences in broadband and far-IR OLR are 7.5 and 3.4 Wm⁻², respectively. The results are also evaluated against collocated broadband and other spectral satellite measurements. The difference (mean ± standard deviation) between the collocated PREFIRE SAT-2 and CERES broadband OLR is 2.8 ± 5.7 and 2.7 ± 6.5 Wm⁻² for clear-sky and cloudy-sky footprints, respectively. Similar agreements can be seen from the comparisons with spectral OLR derived from Atmospheric Infrared Sounder and Cross-track Infrared Sounder measurements. In general, spectral OLR derived from SAT-2 has better agreement with other collocated measurements than that from SAT-1, which can be attributed to the higher noisy performance of the SAT-1 instrument.

Anthropogenic activities, including anthropogenic climate change (ACC) and historical water and land management (HWLM), have intensified hydrological extremes in recent decades, with potential increases in flood risk. However, uncertainties in hydrological models and a lack of consideration for HWLM in climate models have limited the estimation and attribution of the changes in global-scale flood risks. Based on a multi-model ensemble of daily discharge simulations and projections from the latest Inter-Sectoral Impact Model Intercomparison Project (ISIMIP 3), our estimation shows that flood risks significantly increased (slightly decreased) in the north (south) of 50°N during 1971–2019 when considering the combined effects of ACC and HWLM. Under continuing global warming (from 1.5°C to 3°C), 59.6%–69.4% of the global land area would witness an increasing flood risk, with 71.9%–87.5% of basin-level risks attributable to anthropogenic activities, particularly in arid/tropical zones. Meanwhile, the flood risk in 38.8% of the global land area shows the anthropogenic signals before 2065. This increase is enlarged by greater flood magnitude and variability in the future, with flood magnitude being the dominant factor in most regions. We suggest that hydrological services and policymakers should implement adaptive strategies that consider anthropogenic increases in flood magnitude and variability, utilizing detected signals to guide global flood-risk mitigation.

Radiative convective equilibrium (RCE) critically constrains tropical climates, but its applicability to elevated terrains such as the Tibetan Plateau (TP) remains unknown. Based on 23 years (2001–2023) of multiple observational data sets, our study provides the first comprehensive observational assessment of RCE applicability over the TP. We find that the TP exhibits a pronounced annual-mean energy imbalance (−15.9 W/m²), characterized by strong seasonal asymmetry. Summers show intense positive energy imbalance (+56.0 W/m²) driven by latent heating from precipitation, while winters show extreme radiative cooling (−71.8 W/m²). Transitional months (April/September) alone achieve transient energy balance. The TP manifests four energy imbalance regimes, categorized by precipitation intensity and radiative cooling thresholds. These regimes transition seasonally, with Strong Precipitation-Weak Cooling dominating summer monsoonal regions and Weak Precipitation-Strong Cooling prevailing in winter and autumn. Daily near-RCE conditions occur transiently with only 5%–10% frequency across all spatiotemporal scales, contrasting sharply with tropical regions where equilibrium emerges through spatial aggregation. Analysis of extreme events reveals that intense latent heating drives a positive imbalance during summer heating events, which is compensated primarily by enhanced vertical dry static energy divergence. Persistent radiative cooling creates a sustained negative imbalance during winter cooling events, which is countered by vertical divergence of dry static energy flux and meridional cold air advection. These results challenge the direct application of tropical RCE paradigms to the TP region and highlight the need for a skewed RCE framework that explicitly incorporates the TP's unique thermal forcing effects.

Accurate representation of land use and urban morphological parameters (UMPs), particularly building height, road width, and roof width, is critical for urban climate/weather modeling. The Weather Research and Forecasting (WRF) coupled with the Single-Layer Urban Canopy Model (SLUCM) has been widely used; however, few studies have quantified urban modeling uncertainties associated with UMPs in Los Angeles, a key metropolitan area. This study assesses the impact of UMPs on WRF–SLUCM simulations in Los Angeles and quantifies UMP-induced uncertainties in 2-m air temperature (T₂), relative humidity (RH), wind speed and other outputs by integrating Polynomial Chaos Expansion, Sobol sensitivity analysis, and Monte Carlo methods. We apply urban Local Climate Zone (LCZ) land use data and find that incorporating accurate UMPs based on Los Angeles County improves wind speed simulations compared with default LCZ UMPs. Uncertainty analyses reveal strong sensitivities of urban meteorology to 50% UMP perturbation. The resulting average standard deviations of 2-m air temperature are 0.02 K (day) and 0.23 K (night), while those of urban canyon temperature are 0.51 K (day) and 1.03 K (night). Wind speed uncertainties are also notable, reaching 0.42 m/s (day) and 0.27 m/s (night). Among UMPs, building height has the strongest influence on urban T2, RH, and wind speed. Furthermore, uncertainties in urban meteorology propagate into heat stress estimates, where different indices show different spatial patterns of uncertainty. These findings underscore the importance of accurately representing UMPs in urban climate/weather simulations and their implications for assessing urban heat stress.

Surface momentum flux and drag coefficient are critical factors influencing the structure and intensity of tropical cyclones (TCs). However, due to limited measurements, the behavior of these quantities, particularly in TCs over the western North Pacific (WNP), is not fully understood. Here we analyze observations from dropsondes and radiosondes in 141 WNP TCs in 2009–2024. We find that over the deep and open South China Sea (SCS), the drag coefficient increases with wind speed until reaching 1.5 × 10⁻³ at a threshold wind speed of 30 m s⁻¹, then levels off or decreases above this wind speed. A quadrant analysis further reveals that the drag coefficient is significantly higher in the left-front storm quadrant than in the right-front and rear quadrants at wind speed around 30 m s⁻¹. Over the urban area, the drag coefficient is about 10² times higher than the open ocean and does not show significant variation with wind speed up to 25 m/s. These observations can inform the surface flux parameterizations used in TC modeling, prediction, and hazard assessment.

Airborne dust exerts myriad effects on climate, weather, human health and safety. In this study, 35-year records (1988–2022) of ground aerosol observations were analyzed to identify windblown dust events from 18 Interagency Monitoring of Protected Visual Environments (IMPROVE) stations over the western United States (US). Over 45% of dust events were recorded at two sites in the Chihuahuan Desert. The intensity of dust events, indicated by regional average concentration of PM₁₀ (particulate matter with diameter ≤ 10 μm) during these events, decreased by −0.24 μg/m³ per year compared to −0.10/m³ per year on non-dust days. However, the number and frequency of both severe dust events (24-hr PM₁₀ > 40 μg/m³) and moderate dust events (30 μg/m³ < PM₁₀ ≤ 40 μg/m³) have increased with moderate events increasing faster than severe events. The variability of dust event frequency was strongly associated with that of Pacific Decadal Oscillation (PDO) and El Niño Southern Oscillation (ENSO). The increasing wind speed has a stronger effect on the dust activity in the Northwest, whereas in the Southwest, the decreasing soil moisture has a larger impact on the increase in dust event frequency. This work provides the latest dust climatology, along with the underlying climate drivers and synoptic indicators that control the long-term variations of dust events over the western US.

Nitrogen oxides (NO_x) emissions are increasing rapidly in Sub-Saharan Africa, affecting local air quality. Outside South Africa, most hotspots are relatively small, posing a challenge for traditional top-down inversions. We tailor an existing top-down wind rotation and Gaussian plume fit inversion to suit the relatively small NO_x hotspots for most of Sub-Saharan Africa. We apply the customized inversion to 3 years (July 2018–December 2019 and January 2021–June 2022) of nitrogen dioxide (NO₂) observations from the Tropospheric Monitoring Instrument (TROPOMI) to derive annual NO_x emissions for 24 isolated hotspots (21 urban, three power plants) compared to at most 5 for Sub-Saharan Africa in past global studies. Annual hotspot emissions total 311.5 kt NO. Urban hotspot emissions range from <2 mol s⁻¹ for Antananarivo, Madagascar, to 27.7 ± 12.6 mol s⁻¹ for the megacity Lagos in Nigeria. Coal-fired power plant emissions are 2.7 ± 1.0 mol s⁻¹ for Hwange, Zimbabwe, and similar (∼70 mol s⁻¹) for Lethabo and combined Matimba and Medupi plumes in South Africa. Top-down estimates are 8%–20% less than Continuous Emissions Monitoring Systems emissions. We conduct a quasi-independent evaluation of urban top-down emissions by assessing improved agreement between the GEOS-Chem model and TROPOMI NO₂ after updating modeled emissions to match the top-down estimates. Annual urban inventory hotspot emissions decline by 43 kt NO and the model root mean squared error is more than halves from 1.2 × 10¹⁵ molecules cm⁻² to 0.48 × 10¹⁵ molecules cm⁻². Our top-down emissions exhibit large, up to six-fold, systematic differences with contemporary global and regional inventories.

An exceptionally heavy rainstorm (the “21·7” Predecessor Rain Event, 21·7PRE) affected Henan Province, China, from 17 to 22 July 2021, coinciding with Typhoon In-Fa (2021) over the western North Pacific. This study investigates how In-Fa remotely influenced the 21·7PRE by decomposing atmospheric fields using the multiscale window transform into basic-scale (>64 days), intraseasonal-scale (16–64 days), and synoptic-scale (<16 days) motions. A prominent mid-to-lower-tropospheric anticyclone, located approximately 880 km west of In-Fa, acted as intermediary circulation linking the typhoon and the rainfall event. The anticyclone channeled moisture into Henan, producing pronounced meridional moisture convergence and supplying ∼64% of the total moisture during the event. Meanwhile, intraseasonal-scale easterlies between In-Fa and the western Pacific subtropical high facilitated westward wave-energy propagation, which intensified an upper-level divergence zone over Henan Province. This upper-level divergence, together with local mesoscale cyclone activity, played a critical role in sustaining the extreme rainfall. These results indicate that Typhoon In-Fa exterted a substantial remote influence on the 21·7PRE through a synoptic-scale, cold-core anticyclonic anomaly that mediated wave-energy propagation and organized moisture transport. The findings highlight a dynamical pathway by which tropical cyclones can affect distant predecessor rain events beyond classical moisture-conveyor and subtropical-high paradigms.