Journal of Geophysical Research: Atmospheres最新文献

This study examines the cross-seasonal influence of the Arctic Oscillation (AO) on winter El Niño, using atmospheric and oceanic reanalysis data sets. It has been revealed that the linkage between positive AO and subsequent El Niño is closest during spring, indicating the seasonal dependent and selective impact of AO on ENSO. Composition analyses illustrate that positive spring AO is often associated with a dipole circulation anomaly over the North Pacific. The corresponding cyclonic circulation anomaly in the subtropical North Pacific initiates the Pacific Meridional Mode (PMM), which persists and evolves through the wind-evaporation-SST (WES) feedback from, triggering the westerly anomalies in the tropical western Pacific and subsequently triggering the onset of El Niño. Further clustering analysis reveals that the positive spring AO events exhibit two distinct spatial patterns: Type1 with prominent positive SLP anomaly over the midlatitude North Pacific and Type2 with the positive SLP anomaly over the North Atlantic. Both types can trigger El Niño by stimulating the subtropical cyclone anomaly in the North Pacific but through different mechanisms. In Type1 events, high-pressure anomalies in the midlatitude North Pacific trigger southward-propagating atmospheric waves, generating the cyclone anomalies in the subtropical North Pacific. Although in Type2 events, the AO-related circulation anomalies in the North Atlantic stimulate teleconnection wave trains that cross the Eurasian continent and propagate southward to the subtropical North Pacific, inducing the cyclone anomalies. However, Type1 events occur more frequently and are more closely linked to El Niño, highlighting the significant role of air-sea coupling processes in the North Pacific in triggering El Niño.

Lake surface conditions are critical for representing lake-atmosphere interactions in numerical weather prediction. The Community Land Model's 1-D lake component (CLM-lake) is part of NOAA's High-Resolution Rapid Refresh (HRRR) 3-km weather/earth-system model, which assumes that virtually all the two thousand lakes represented in CONUS have distinct (for each lake) but spatially uniform depth. To test the sensitivity of CLM-lake to bathymetry, we ran CLM-lake as a stand-alone model for all of 2019 with two bathymetry data sets for 23 selected lakes: the first had default (uniform within each lake) bathymetry while the second used a new, spatially varying bathymetry. We validated simulated lake surface temperature (LST) with both remote and in situ observations to evaluate the skill of both runs and also intercompared modeled ice cover and evaporation. Though model skill varied considerably from lake to lake, using the new bathymetry resulted in marginal improvement over the default. The more important finding is the influence bathymetry has on modeled LST (i.e., differences between model simulations) where lake-wide LST deviated as much as 10°C between simulations and individual grid cells experienced even greater departures. This demonstrates the sensitivity of surface conditions in atmospheric models to lake bathymetry. The new bathymetry also improved lake depths over the (often too deep) previous value assumed for unknown-depth lakes. These results have significant implications for numerical weather prediction, especially in regions near large lakes where lake surface conditions often influence the state of the atmosphere via thermal regulation and lake effect precipitation.

Stable boundary layers (SBLs) commonly form during the Arctic polar night, but their correct representation poses a major challenge for numerical weather prediction (NWP) systems. To enable detailed model verification, we performed measurements of the lower atmospheric boundary layer with airborne fiber-optic distributed sensing (FODS), a tethered sonde and ground-based eddy-covariance (EC) measurements during contrasting synoptic forcings in a fjord-valley system in Svalbard. The FODS-derived temperature variances and static stability profiles are used to investigate the spatial and temporal evolution of different inversion types. The strong gradients of the inversions are accompanied by an increased temperature variance, which is related to enhanced buoyancy fluctuations. The observed vertical temperature and wind speed profiles are compared to two configurations of the HARMONIE-AROME system with different horizontal resolutions at 2.5 and 0.5 km. The higher-resolution model captures cold pool and low level jet formation during weak synoptic forcing, resulting in a well-represented vertical temperature profile, while the coarser model exhibits a warm bias in near-surface temperatures of up to 8 K due to underestimated inversion strength. During changing background flow, the higher-resolution model is more sensitive to misrepresented fjord-scale wind directions and performs less well. The results indicate the importance of the ratio between nominal horizontal model resolution and valley width to represent SBL features. Our results underline the substantial benefit of spatially resolving FODS measurements for model verification studies as well as the importance of model and topography resolution for accurate representation of SBLs in complex terrain.

Pollutant emissions in China have significantly decreased over the past decade and are expected to continue declining in the future. Aerosols, as important pollutants and short-lived climate forcing agents, have significant but currently unclear climate impacts in East Asia as their concentrations decrease until mid-century. Here, we employ a well-developed regional climate model RegCM4 combined with future pollutant emission inventories, which are more representative of China to investigate changes in the concentrations and climate effects of major anthropogenic aerosols in East Asia under six different emission reduction scenarios (1.5°C goals, Neutral-goals, 2°C -goals, NDC-goals, Current-goals, and Baseline). By the 2060s, aerosol surface concentrations under these scenarios are projected to decrease by 89%, 87%, 84%, 73%, 65%, and 21%, respectively, compared with those in 2010–2020. Aerosol climate effect changes are associated with its loadings but not in a linear manner. The average effective radiative forcing at the surface in East Asia induced by aerosol-radiation-cloud interactions will diminish by 24% ± 13% by the 2030s and 35% ± 13% by the 2060s. These alternations caused by aerosol reductions lead to increases in near-surface temperatures and precipitations. Specifically, aerosol-induced temperature and precipitation responses in East Asia are estimated to change by −78% to −20% and −69% to 77%, respectively, under goals with different emission scenarios in the 2060s compared to 2010–2020. Therefore, the significant climate effects resulting from substantial reductions in anthropogenic aerosols need to be fully considered in the pathway toward carbon neutrality.

Atmospheric surface pressure provides valuable information on the vertical dynamical structure of the atmosphere. Previous studies have reported that among the waves observed in surface pressure, semidiurnal tides (SDTs) are significantly affected by the stratospheric Quasi-Biennial Oscillation (QBO). Using historical surface-pressure observations and the Earth-system model MRI-ESM2.0, this study confirms that SDTs and the QBO are synchronized, such that SDT amplitude increases or decreases, respectively, at a rate of ∼1 Pa per 20 ms⁻¹ during westerly or easterly phases of the QBO at 30 hPa. Our numerical simulations and a linear analytical model support the QBO-SDT relationship being dynamically forced by background zonal winds rather than by anomalous ozone radiative heating. We also find that the QBO-SDT relationship was notably disturbed by the volcanic eruptions of Mount Agung in 1963 and Mount Pinatubo in 1991, during which increased shortwave radiative absorption caused by stratospheric aerosol enhanced the SDT amplitude. Short-lived El Nino events also occurred, moistening the upper troposphere to provide extra solar heating when volcanic aerosol was transported to higher latitudes. The influence of volcanic eruptions and El Nino events overlap with the QBO frequency band, jointly working as “noise” in QBO-SDT synchronization.

Cities in South and Southeast Asia are developing rapidly without routine, up-to-date knowledge of air pollutant precursor emissions. This data deficit can potentially be addressed for nitrogen oxides (NO_x) by deriving city NO_x emissions from satellite observations of nitrogen dioxide (NO₂) sampled under windy conditions. NO₂ plumes of isolated cities are aligned along a consistent wind-rotated direction and a best-fit Gaussian is applied to estimate emissions. This approach currently relies on non-standardized choice of upwind, downwind, and across-wind distances from the city center, resulting in fits that often fail or yield non-physical parameters. Here, we propose an automated approach that defines many combinations of distances yielding 54 distinct sampling boxes that we test with TROPOspheric Monitoring Instrument (TROPOMI) NO₂ observations over 19 isolated cities in South and Southeast Asia. Our approach is efficient, uses open-source software, is adaptable to many cities, standardizes and eliminates sensitivity to sampling box choice, increases success of deriving emissions from 40% to 60% with one sampling box to 100% (all 19 cities) with 54, and yields emissions consistent with the current manual approach. We estimate that the annual emissions range from 15 ± 5 mol s⁻¹ for Bangalore (India) to 125 ± 41 mol s⁻¹ for Dhaka (Bangladesh). With enhanced success of deriving top-down emissions, we find support from comparison to past studies and inventory estimates that top-down emissions may be biased, as the method does not adequately account for spatial and seasonal variability in NO_x photochemistry. Further methodological development is needed for enhanced accuracy and use to derive sub-annual emissions.

Every spring, biomass burning (BB) plumes from the Indochina Peninsula (ICP) are transported downstream by specific synoptic weather processes, potentially influencing regional weather through radiative effects of BB aerosols. However, the favorable weather patterns for transport toward inland China and how they interact with BB aerosols are not fully understood. In this study, we identified three predominant synoptic weather processes associated with evident BB plume transport toward southern China over the past 20 years. The first two—the low pressure over the continent and the cold frontal passage—account for more than 76% of all the events. In low-pressure events accompanied by surface warming, a cyclonic system hovers over southern China, with southerly winds favoring the northward movement of BB plumes throughout the lower troposphere. The second type is caused by a frontal passage lasting only 1–2 days, which lifts BB plumes to above 700 hPa and transports them downstream. To further explore aerosol feedback on different weather patterns, we conducted WRF-Chem simulations and found an average of 2°C cooling near the surface, along with 1.5°C warming in the lower troposphere over the southern coast of East Asia. Consequently, the more stable atmosphere suppresses the low-pressure system but enhances the cold frontal system. Meanwhile, anomalous circulations from aerosol radiative effects align with those during the frontal passage, boosting plume transport with a 45% (20%) rise in CO (BC) along the transport belt toward inland southern China. This work highlights the importance of considering the interactions between wildfire pollutants and different weather processes.

Severe haze pollution has long been an environmental problem, which is complicated and poorly understood in the Sichuan Basin (SCB). In this study, a field observation was carried out to investigate the factors driving haze formation in urban Chengdu, a typical megacity in the SCB. It was found that the accumulation of biomass burning organic aerosol (BBOA) played an important role in haze formation in urban Chengdu. The average mass fraction of BBOA in PM_2.5 increased from ∼1% during clear days to ∼10% during severe haze episodes. A method combining backward trajectory analysis with fire spot distribution was used to evaluate the effects of regional transport of biomass burning (BB) emissions. The results showed that BBOA concentration increased by ∼3 times and PM_2.5 concentration increased by ∼54% when BB emissions were transported from adjacent areas to urban Chengdu. Moreover, the parameter f₆₀ (the ratio of the integrated signal at m/z 60 to the total signal in the organic component mass spectrum), which indicated the impacts of BB emissions, was reassessed to be 0.54% instead of the widely used value 0.3% previously. Our results uncovered the importance of BB emissions on haze formation in urban areas in the SCB and provided new insights into pollutant mitigation strategies in the region.

Australia has a large operational weather radar network spanning multiple climatic regimes. However, data from this network is not commonly used to obtain heavy rainfall event characteristics. Drawing on the methodology presented in Bowden et al. (2024, https://doi.org/10.1029/2023jd039253), areal radar variables are used to identify and characterize rainfall events at 15 Australian radar sites over an 11-year period. Rainfall events over all sites are grouped into three clusters based on their characteristics—stratiform (low rainfall intensities and small contributions from convective areas), convective (localized with high rainfall intensities and strong contributions from convective areas), and persistent (long-lasting, moderately intense, extensive events). Further, the top 100 events by accumulation and intensity were identified for each site. Stratiform cluster events are most common in the cool season, convective cluster events are most common in the warm season, and persistent cluster events exhibit strong regional variation in seasonal occurrence over Australia. Convective cluster events are most common at tropical and subtropical sites, and stratiform cluster events are most common at mid-latitude sites. Persistent cluster rainfall events occur least frequently, but make significant contributions to rainfall totals around Australia. Furthermore, almost all high accumulation rainfall events belong to the persistent cluster, and most high intensity events belong to the convective cluster. Examination of rainfall event environments with reanalysis data shows that persistent cluster events and high accumulation events both occur in environments with strong positive column moisture anomalies and mid-level ascent, consistent with past findings on Australian heavy rainfall environments.

The thawing of carbon-rich northern high-latitude permafrost might unleash irreversible changes in the Earth's climate system. Previous studies have suggested that solar radiation modification (SRM) can significantly slow the degradation of permafrost, potentially restoring its extent and soil carbon stocks to levels comparable to those under equivalent global warming caused by greenhouse gas increases alone. However, this study identifies that the efficacy of SRM in mitigating permafrost degradation is contingent upon the warming trajectory and the timing of SRM intervention. Employing SRM to keep global warming at a maximum of 1.5°C can substantially reduce permafrost degradation; however, simulations suggest that by 2300, approximately half of the permafrost area reduction and one-third of the carbon losses expected under the high-emissions SSP5-8.5 scenario would still take place. By employing SRM to achieve a return to 1.5°C warming stabilization levels after a temperature overshoot, it is possible to effectively restore the permafrost area. However, the lost permafrost carbon cannot be regained. Additionally, the soil carbon within permafrost regions displays contrasting trends between the phases of overshoot and subsequent stabilization. Our simulations show that achieving the 1.5°C warming target after a 4°C temperature overshoot could necessitate up to 7% increase in SRM application due to permafrost carbon release. Moreover, perturbed parameter ensemble simulations indicate that the key parameter influencing the uncertainty of soil carbon losses in permafrost regions under 1.5°C warming and overshoot scenarios is distinct from that under the SSP5-8.5 scenario.