Journal of Geophysical Research: Atmospheres最新文献

This study investigates the development of an east Pacific easterly wave (EW) event in August 2019 and the effect of the Papagayo jet on its evolution. Convective-permitting numerical simulations were conducted. These included a control experiment and a Gap-Filled experiment with a closed mountain gap near the Gulf of Papagayo, to test the effect of a weaker Papagayo jet on this EW event. The initial disturbance developed into a mesoscale convective system in the Panama Bight and transitioned into an EW in the Papagayo jet exit region, both of which are reasonably captured in the control experiment. The weakened Papagayo jet in the Gap-Filled experiment reduces the meridional shear of the zonal wind and the associated barotropic energy extraction from the mean flow. This results in significantly weakened upward motion and vertical stretching near the center of the disturbance, thus weakening vorticity particularly at low levels below 700-hPa in the jet region. The weaker Papagayo jet and diminished low-level vorticity in the Gap-Filled experiment can further limit the subsequent EW vorticity intensity as it travels northwest along the Mexican coast. However, the Papagayo jet appears to have a limited impact on the horizontal vorticity structure and propagation of the EW disturbance. These results suggest that the broad-scale monsoonal westerlies south of the Papagayo jet may help maintain the low-level horizontal wind shear, even when the Papagayo jet is weakened, thereby contributing to the formation of the EW's tilted vorticity structure.

Soil salinity plays a critical role in regulating wetland evapotranspiration (ET)—including both soil evaporation and plant transpiration—by directly affecting water movement and indirectly altering plant physiology and ecosystem structure. However, common land surface models (LSMs) overlook salinity effects on ET, contributing to uncertainties in simulating land–atmosphere interactions and climate processes, particularly in the coastal regions. In this study, the Noah-MP LSM was enhanced to incorporate the effects of soil salinity. Using half-hourly meteorological forcing data and observed soil properties and salinity from the Dongtan coastal wetland in Shanghai (July–December 2023), we evaluated model performance before and after this improvement. Comparisons with in situ observations show that incorporating salinity significantly reduces the model's overestimation of latent heat flux—by up to 90 W/m² during the cold season—and decreases cumulative ET bias by as much as 130 mm, with the error rate reduced by approximately 33%. This improvement is largely attributed to salinity constraints on soil evaporation under sparse vegetation conditions. These findings highlight salinity as a key regulatory factor in wetland hydrothermal dynamics and offer a promising approach to improving LSM accuracy in coastal wetland environments.

Atmospheric rivers are episodic events that can advect relatively large quantities of moisture to Antarctica, contributing to both disproportionate precipitation and melting events. The Year of Polar Prediction, an international effort to improve weather prediction over the southern polar region, presents an opportunity to study the clouds and precipitation associated with winter atmospheric river events. This study uses enhanced surface, profile, and remote-sensing observations from the Antarctic Peninsula (AP) during a Targeted Observing Period around 16 May 2022, when an event occurred with local warming similar to a warm front. We compare regional atmospheric simulations with the polar-optimized version of the Weather Research and Forecasting Model to various in situ and remote-sensing observations. The study emphasizes data from three stations: Escudero, Vernadsky, and Rothera. Mixed-phase clouds were simulated at the three stations, with the precipitation being primarily rain at Escudero and primarily snow at Vernadsky and Rothera. The model produced reasonable simulations of the clouds and precipitation. Furthermore, modeled longwave cloud forcing at Escudero had small errors compared to observed values. A sensitivity test enhancing secondary ice production indicates mixed-phase cloud sensitivity to the Hallett-Mossop process, especially at Rothera.

Agricultural sector forms the backbone of India's socioeconomy. Despite consistent efforts to develop the irrigation network for increased agricultural production, approximately 60% of India's cropped area still remains rain fed, thereby functional to the strength of the Indian summer monsoon (ISM). The probability of a weak monsoon is strongly correlated with the occurrence of droughts during the ISM season. The possible influence of atmospheric drivers in initiating these droughts is observed through the dynamics of low-level jets (LLJ) over the northern Arabian Sea forming the core of LLJ during the ISM. Interestingly, since the past 72 years, from 1951 to 2022, the core of LLJ has become dry (increased saturation deficit by 17%) and weak (reduced wind speed by 5%). Additionally, the wind speed (saturation deficit) at the core shares close dependence (75%–80%) with the initiation of dry (wet) extremes exhibiting maximum correlation at a 2-day lag. Furthermore, we observed a 50% (40%) increase in the dry (wet) extremes driven by the lower-atmospheric dynamics of the LLJ core. Consequently, these dry (wet) extremes are characterized by a 6% (12%) enhancement in duration (intensity). Such conditions act as strong precursors for monsoon droughts.

Agricultural sector forms the backbone of India's socioeconomy. Despite consistent efforts to develop the irrigation network for increased agricultural production, approximately 60% of India's cropped area still remains rain fed, thereby functional to the strength of the Indian summer monsoon (ISM). The probability of a weak monsoon is strongly correlated with the occurrence of droughts during the ISM season. The possible influence of atmospheric drivers in initiating these droughts is observed through the dynamics of low-level jets (LLJ) over the northern Arabian Sea forming the core of LLJ during the ISM. Interestingly, since the past 72 years, from 1951 to 2022, the core of LLJ has become dry (increased saturation deficit by 17%) and weak (reduced wind speed by 5%). Additionally, the wind speed (saturation deficit) at the core shares close dependence (75%–80%) with the initiation of dry (wet) extremes exhibiting maximum correlation at a 2-day lag. Furthermore, we observed a 50% (40%) increase in the dry (wet) extremes driven by the lower-atmospheric dynamics of the LLJ core. Consequently, these dry (wet) extremes are characterized by a 6% (12%) enhancement in duration (intensity). Such conditions act as strong precursors for monsoon droughts.

A diverse array of sulfur-containing organic compounds (SOCs) was identified in seasonal snow samples collected from northwestern China, using high-performance liquid chromatography interfaced with an electrospray ionization high-resolution mass spectrometer (HPLC–ESI–HRMS). Hierarchical cluster analysis (HCA) of the HPLC–HRMS data set classified SOCs into distinct clusters based on their molecular characteristics. Substantial differences in SOC composition were observed between urban (U) and rural/remote (R) clusters. In ESI− mode, the SOCs in the U cluster exhibited higher unsaturation degrees, oxidation levels, and larger molecular sizes than the R cluster. These compounds were likely derived from anthropogenic sources, such as transportation and industry, whereas those in the R cluster exhibited signatures of mixed sources, including biomass burning, cooking-related emissions, and local biogenetic inputs. In ESI+ mode, SOCs were scarcely detected in the R cluster but were abundant in the U cluster. These compounds were predominantly reduced and unsaturated SOCs, with more than 85% (by intensity) containing one or no oxygen atoms in their elemental formulas. Tentative assignments for these species include sulfoxides, polycyclic aromatic S-heterocycles, thiols, and sulfides, likely originating from the use and production of heavy oils. Additionally, volatility estimates suggest that the SOCs identified in this study are more volatile than those found in other environmental media. The findings highlight the unique SOCs composition in snowpack of northwestern China, particularly those detected via positive ESI mode, offering new insights into the environmental, climatic, and biogeochemical roles of SOCs.

The Arctic has experienced rapid sea ice loss and a substantial surface albedo decline, altering its radiation budget. CMIP6 (Coupled Model Intercomparison Project Phase 6) models capture these trends but show considerable inter-model spread in the magnitude, distribution, and seasonality of Arctic surface albedo. Over land, spread in AMIP (Atmospheric Model Intercomparison Project) and CMIP6 is associated with snow cover variations, while over the ocean, where sea ice dominates, the sources are less clear. We compare CMIP6 simulations with observations from the Clouds and the Earth's Radiant Energy System (CERES) and develop a decomposition method to quantify contributions from sea ice albedo, concentration, and extent. Over the Arctic Ocean, all three factors contribute to inter-model spread in CMIP6. In AMIP, despite prescribed sea ice concentrations, we were surprised to find an inter-model spread in Arctic Ocean albedo similar to that in CMIP6, driven solely by sea ice albedo. Applying the decomposition to future projections shows that the largest decline occurs in the Central Arctic, driven primarily by reductions in sea ice extent. After 2045, sea ice extent emerges as the dominant driver, highlighting ice edge retreat as key to future albedo decline. These findings pinpoint key sources of inter-model spread in Arctic surface albedo and offer insights into quantifying shortwave (SW) radiative effect associated with sea ice responses in future projections.

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.

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.