Journal of Geophysical Research: Atmospheres最新文献

Low-level jets (LLJs), as dynamically significant narrow air currents in the lower troposphere, profoundly influence regional weather and anthropogenic activities. Motivated by persistent LLJs detected through Doppler LiDAR observations during March to April 2021, this study systematically characterizes these LLJs over Juehua Island (western Bohai Sea coast) by integrating high-resolution Weather Research and Forecasting Model simulations. Based on a 61-day simulation spanning March to April 2021, this study reveals a notable LLJ occurrence frequency of 25.3%, dominated by two distinct directional modes: southwesterly and northeasterly. The high frequency and pronounced directional dominance of LLJs in this region motivated a systematic investigation combining Empirical Orthogonal Function (EOF) analysis and sensitivity experiments. The LLJ-favorable synoptic patterns were extracted through EOF analysis of the sea-level pressure (SLP) field. The northwest-southeast SLP dipole pattern plays a dominant role, contributing 68% to LLJ formation. Southwesterly and northeasterly LLJs are favored by “high-southeast, low-northwest” and its opposite synoptic dipoles, respectively. Sensitivity experiments quantify the contribution of local geography at 21%, collectively accounted for by the Bohai Sea (16%) and the northwestern highlands (5%). Additionally, the Bohai Sea preferentially enhances southwest LLJs, which exhibit lower LLJ heights. In contrast, the northwestern highlands elevate LLJ heights and align LLJ directions with the terrain orientation, resulting in a more clustered wind direction distribution. This study quantified LLJ-favorable synoptic patterns, Bohai Sea and northwestern high terrain influences. These findings could provide valuable insights for regional LLJ forecasting.

Typhoon-induced Compound Flood (TCF), driven by the combined impact of extreme rainfall and increasing coastal water level (CWL), poses a substantial threat to urban safety. This study presents a framework for assessing the future compound flood hazard profiles in a coastal megacity in the Delta region of southern China. A coupled hydrology-hydrodynamic model is applied to simulate the flooding processes of 7 typhoon events. Scenarios are constructed using all possible pairwise combinations of three rainfall and three CWL conditions. These inputs are derived from statistical and dynamical downscaling of climate projections from the Coupled Model Intercomparison Project (CMIP6) ensemble under the SSP5-8.5 pathway. The results show that future CWL rise contributes more to future inundation than increasing rainfall, whereas rainfall contributions exhibit considerable uncertainties due to regional rainfall downscaling. Under extreme warming scenarios, future typhoons may produce increases of up to 230 mm in total rainfall and 28 mm per hour in rainfall intensity, which in turn increase the average urban inundation depth and area by 1.2 cm and 24.7 $��k�m^2�$, respectively. Given an average CWL of 170 cm and a maximum CWL of 440 cm in the future, the inundation depth and area could increase by up to 8.4 cm and 29 $��k�m^2�$, respectively. Within the 7 typhoons in this study, Hagupit (2014) exhibits the most notable compound effect, potentially expanding the medium-to-high risk area (inundation depth above 27 cm) by over 5%. This study demonstrates that climate change may intensify TCF, requiring flood-mitigating measures to consider rainfall-CWL interactions.

Employing the spaceborne observations from scatterometers (QuikSCAT and ASCAT), we quantify the contributions of different mechanisms to the Arctic MYI area changes over two decades (1999/2000–2017/2018). Specifically, the loss mechanisms (export, melt, deformation) and gain mechanism (replenishment) associated with MYI area variations are examined. On average, there was an annual (October-September) MYI area loss of 1,080.3 × 10³ km² due to export, melt, and deformation of 749.2 × 10³ km², 222.5 × 10³ km², and 108.6 × 10³ km², respectively. The substantial MYI depletion was largely offset by replenishment from the aging of first-year ice (FYI) at the end of the melt season, which on average amounted to 993.8 × 10³ km² in the Arctic Ocean. Therefore, a net annual MYI area loss of −86.5 × 10³ km² emerged in the Arctic. The consecutive occurrence of the anomalously low MYI replenishment from 2005 to 2007 was responsible for the dramatic decadal decline of MYI area between the QuikSCAT (P1:2000-2008) and ASCAT (P2: 2009–2018) periods from 3.29 × 10⁶ km² during P1 dropping a half to 1.61 × 10⁶ km² during P2. Moreover, the recently enhanced melt and deformation processes were favorable in maintaining the Arctic MYI at the low-level coverage during P2 relative to P1. The thermodynamic (melt and replenishment) and dynamic mechanisms (export) related to MYI variations are linked to Dipole Anomaly (DA), whereas North Atlantic Oscillation (NAO) acts to influence the thermodynamic mechanism (melt and replenishment). On the other hand, no significant connection is identified for Arctic Oscillation (AO) or Barents-Beaufort Oscillation (BBO).

This study investigates the interannual variability in the first occurrence dates of the first Madden Julian Oscillation (FMJO) and the first Boreal Summer Intraseasonal Oscillation (FBSISO) events over the Indian Ocean during 1940–2022. The FMJO typically occurs in November, whereas the FBSISO mainly occurs in early May. The FMJO onset exhibits substantially larger interannual variability. The timing of both phenomena is strongly influenced by the El Niño Southern Oscillation (ENSO), which modulates large scale atmospheric conditions, particularly through column moisture anomalies. The leading Empirical Orthogonal Function (EOF) mode of April column moisture anomalies displays a meridional dipolar pattern over the Indian Ocean. Its associated principal component (PC) time series shows a statistically significant correlation with the FBSISO onset date, indicating that a strong meridional moisture contrast with positive anomalies over the northern Indian Ocean favors an earlier FBSISO onset. The leading EOF mode of November column moisture anomalies exhibits a zonal dipolar pattern extending from the western equatorial Indian Ocean to the Maritime Continent, with a pronounced meridional contrast over the Maritime Continent. The corresponding PC is significantly correlated with the FMJO onset date, suggesting that a zonal moisture contrast with higher moisture over the western Pacific favors an earlier FMJO onset. These moisture anomalies are closely linked to ENSO conditions. Consequently, ENSO also modulates the onset timing of these events, although the onset dates show weaker correlations with ENSO than with monthly moisture anomalies. The physical mechanisms underlying the distinct responses of the FMJO and FBSISO to ENSO remain to be elucidated.

This study refines methane emission estimates for southeastern Australia's Gippsland region in 2019 through high-resolution atmospheric inverse modeling. Methane observations from three in situ monitoring sites were assimilated into a Bayesian four-dimensional variational inversion framework coupled with the Community Multiscale Air Quality model, employing prior emissions from the Open Methane Database (2024). Posterior results revealed increased emissions in the eastern region, particularly near gas infrastructure and wastewater facilities, suggesting that these sources may be underrepresented in prior inventories. In contrast, a consistent decline in methane emissions was observed across all months in the central-western part of the domain, where coal mining and power generation are concentrated. This decline is likely linked to the predominance of brown coal in the region, which emits substantially less methane than black coal, a distinction not clearly captured in the study inventory, potentially leading to overestimated emissions. Additionally, the most significant reduction in the entire studied domain occurred in February 2019, with emissions decreasing by approximately 30% relative to prior estimates. Sensitivity analyses and comparisons with the Emissions Database for Global Atmospheric Research inventory support the robustness of these findings. While total emissions across data sets were broadly similar, differences in spatial distribution led to notable variations in posterior outcomes. These results highlight the importance of incorporating local knowledge into emission inventories and the need for more detailed classification of emission sources, particularly coal type, to improve methane emission estimates at regional scales.

Peripheral subsidence of Northwest Pacific typhoons can trigger extreme surface ozone episodes, yet the relative contributions of local chemistry and vertical transport remain poorly constrained. Here we measured 30-min aerodynamic gradient fluxes of NO_x, O₃, and CO at 118 and 168 m on Canton Tower (Pearl River Delta) during 2 September typhoons in 2021 and 2022. Surface O₃ climbed by >50% in both events. In September 2021, moderate subsidence created hot, stagnant conditions that accelerated local photochemical ozone production, yielding upward O₃ flux. In September 2022, stronger, long-lived subsidence instead injected ozone-rich air from aloft, causing downward O₃ flux despite favorable chemistry. This flux evidence demonstrates that subsidence intensity toggles the balance between local production and vertical transport of ozone, informing forecasts of coastal extreme-ozone risk.

In this study, we use the Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere-ionosphere eXtension (SD-WACCM-X) to investigate how the migrating solar semidiurnal tide (SW2) in the mesosphere and lower thermosphere (MLT) responds to the strength of Arctic and Antarctic Stratospheric Polar Vortices (SPVs). SW2 shows a substantial response to both SPVs, though the Antarctic influence is weaker. During boreal winter, 50% of SW2 variability is linked to Arctic SPV strength, while 34% during austral spring is associated with Antarctic SPV. Classical tidal theory Hough modes (HMs) of SW2 point to a clear relationship between the HMs and Arctic SPV with the most significant change occurring in the first antisymmetric (2,3) HM. However, only the second symmetric (2,4) HM responds significantly to the Antarctic SPV. These distinctive differences in HMs arise from dynamic changes in the stratosphere and MLT. Stratospheric ozone contributes only 6%–10% to the (2,2) HM during weak state of Arctic SPV and shows no significant influence under Antarctic SPV variability. As such, HM variabilities are primarily caused by changes in background neutral winds during weak and strong Arctic and Antarctic SPVs rather than changes in stratospheric ozone heating. In addition, the zonal momentum budget of each HM of SW2 is analyzed. The classical term (Coriolis + pressure gradient forcing) exhibits the largest variations with the strength of the Arctic and Antarctic SPVs, followed by the advection term.

Compound-specific stable carbon isotope ratios (δ¹³C) were measured for low molecular weight aliphatic (C₂–C₆) dicarboxylic acids, phthalic acid, glyoxylic acid and glyoxal in Arctic aerosols collected at Alert (82.5°N) in late winter to early summer. Between dark winter in late February/early March to completely sunlit conditions in May the δ¹³C of many organic acids increased: (a) oxalic acid (C₂) from −23‰ to −5‰, (b) malonic acid (C₃, a precursor of C₂) from −28‰ to −17‰, and (c) glyoxylic acid (ωC₂, −18‰ to −10‰), also a precursor of C₂. In contrast, glyoxal, another precursor of oxalic acid and succinic acid, showed a wide variation from dark to light and no clear seasonal trend. Concentrations of C₂, ωC₂ and C₃ declined when their δ¹³C increased in April to May. The enrichment of ¹³C occurred during the preferential breaking of ¹²C–¹²C over ¹²C–¹³C bond in oxalic and other acids as solar radiation increased during polar sunrise. Photochemically driven variations in the isotopic enrichment of ¹³C of C₂ and related compounds that are a minor fraction of aerosol total carbon (TC), nevertheless they are the main source of variation in the δ¹³C values of TC during polar sunrise in the Arctic because the weakness of ¹²C–¹²C bond compared to ¹²C–¹³C bond is more pronounced for carboxylic acids than other species contributing to TC. This study on ¹³C signature of these species allows to gain information on their poorly known atmospheric budget in spite of the fact that they are ubiquitous in the atmosphere.

This study performs global variable resolution (VR) experiments using the Model for Prediction Across Scale-Atmosphere (MPAS-A) to simulate 3 years of July over the Tibetan Plateau (TP) at grid resolutions of 60, 60–10, and 60–3 km, transitioning from convective-permitting to quasi-hydrostatic scales. The re-initialization approach is used to constrain the background fields under the same parameterizations. The features analyzed here include mean spatial distribution, diurnal cycle, and evolution of every precipitation event. At coarser resolutions, MPAS-A misrepresents precipitation duration, with excessive rainfall persistence due to overly strong instability and weak intensity. Finer resolutions (especially 3 km) markedly improve sub-daily precipitation over the TP by resolving event durations, reducing the drizzle-like overestimation of long-duration rainfall at 60 km. These gains stem from sharper capture of onset-time forcing peaks (surface heating and moisture convergence) and faster instability removal, together with a weaker, non-linear dependence on moisture convergence and an enhanced representation of cessation. Overall, ∼10 km yields robust improvements with fewer artifacts, while 3 km offers the strongest sub-daily benefits but demands additional high-resolution observations for validation.

Based on seven reanalysis data sets and three atmospheric river (AR) detection algorithms, we investigate the dominant interdecadal modes of East Asian (EA) summer atmospheric rivers (ARs) from 1940 to 2024. The first mode exhibits a monopole pattern characterized by coherent AR enhancement, associated with a low-level anomalous anticyclone and an intensified western North Pacific subtropical high (WNPSH). The anomalous anticyclone is maintained by the meridional wave train induced from the western tropical Pacific under the anomalous Indo-West Pacific Walker circulation triggered by the negative sea surface temperature anomalies (SSTAs) over the southern Indian Ocean (IO), which is closely linked to the IO Basin mode. The second mode presents a zonal dipole pattern featured by opposite AR anomalies, corresponding to a pair of low-level anomalous cyclonic and anticyclonic circulations and the northeastward WNPSH retreat. The dipole circulation is mainly sustained by the meridional wave train excited from the Maritime Continent (MC) when cold tropical eastern Pacific SSTAs and warm MC SSTAs generate an anomalous Pacific Walker circulation, accompanied by the combined effect of a wave train from the mid-latitudes. The second mode is significantly modulated by the Pacific Decadal Oscillation. Particularly, the dominant EA AR mode varied from the monopole to dipole modes around 1977/1978 due to changes in oceanic forcing from the Indian to the Pacific Ocean, leading to a shift in EA AR frequency from an increasing trend to a relatively stable state.