Zhiyuan Hu

This study investigates the impact of climate change on the extreme 2020 Meiyu over the middle and lower reaches of the Yangtze River (middle‐lower Yangtze River (MLYR)) through global variable‐resolution ensemble subseasonal hindcasts. Results reveal that post‐1980 climate change enhanced the 2020 extreme Meiyu rainfall over the MLYR region by approximately 14.67% at monthly scale, while simultaneously decreasing light and moderate precipitation frequency but intensifying heavy and extreme precipitation occurrences. Climate change intensified the low‐pressure over northern China and southern China while weakening the Western Pacific subtropical high and the low‐pressure over the Indian Peninsula. The circulation pattern results in significant shear between northeasterly and northwesterly winds in the southern MLYR region, contrasting with the high‐pressure dominance in the northern MLYR region. This configuration suppressed convergence, vertical motion, and precipitation in the northern MLYR while enhancing these processes along its southern. Compared with frequently re‐initialized simulations, subseasonal hindcasts better preserve the continuous evolution of the Meiyu system and the consistency between precipitation and circulation responses, making them a more suitable framework for attribution of 2020 persistent rainfall Meiyu season. Overall, this study highlights the value of global variable‐resolution subseasonal simulations for attributing changes in Meiyu precipitation and its associated large‐scale circulation background under climate change. Future studies would benefit from improved subseasonal forecasting capabilities to enhance attribution reliability.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms by which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, during spring to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates PM_2.5 increases of predominantly 0–10 µg m⁻³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into “storage zone” that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by predominantly 0–10 µg m⁻³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates a PM_2.5 increase exceeding 10 ug/m³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into a "storage zone" that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by over 10 μg/m³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with the identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates a PM_2.5 increase exceeding 10 ug/m³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into a "storage zone" that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by over 10 μg/m³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with the identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates a PM_2.5 increase exceeding 10 ug/m³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into a "storage zone" that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by over 10 μg/m³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with the identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.

Lake-land thermal contrasts significantly modulate regional air quality, yet the coupling mechanisms which inland lakes regulate the diurnal evolution of PM_2.5 and its components remain poorly understood. This study conducts high-resolution (1 km) WRF-Chem simulations over Lake Chaohu and the adjacent megacity of Hefei, China, to elucidate these interactions. Results reveal a distinct diurnal reversal effect. During daytime, the lake presence facilitates a PM_2.5 increase exceeding 10 ug/m³ both over the lake and in surrounding urban areas by suppressed planetary boundary layer height, weakened vertical mixing, and reduced dry deposition velocities, which collectively transform the lake into a "storage zone" that prolongs PM_2.5 lifetimes. This accumulation is dominated by secondary PM_2.5, as the cooler and more humid lake air thermodynamically favors the ammonium nitrate formation. Furthermore, convergence zones where lake breezes meet background winds create localized stagnation traps that intensify shoreline pollution. At night, while the lake surface maintains higher PM_2.5 concentrations than surrounding land, its impact on the city reverses, exerting a purification effect with urban PM_2.5 decreasing by over 10 μg/m³ as land-breeze circulation enhances vertical mixing and facilitates primary pollutant dispersion. Sensitivity experiments reveal that failing to distinguish lake surfaces in emission inventories can significantly amplify daytime pollution. These findings emphasize that lakes act as complex dual regulators of urban air quality, with the identified mechanisms likely applicable to other urban-lake systems globally. This study highlights the necessity of high-resolution meteorological modeling and precise surface characterization for improved air quality forecasting in lake-adjacent megacities regions.

The PBLH affects the intensity of the surface turbulence and the state of pollutant dispersion. Current research on PBLH characteristics and their relationship with pollution in coastal megacities remains insufficient. Moreover, existing studies rarely evaluate the consistency of various boundary layer solution methods, making it difficult to identify deviations in single methods. So, we conducted enhanced observation experiments in Shenzhen, a megacity in China, between March and July 2023. The characteristics of the PBLH was analyzed by five months of observations from Micro-Pulse Lidar (MPL) and Microwave Radiometer (MWR). Five retrieval methods (Parcel, GRA, STD, WCT, and Theta) were applied for comparative assessment. The results shows that all methods captured similar diurnal patterns. During daytime, the PBLH ranged from 512 to 1345 m, with Theta yielding the highest and STD the lowest average values. At night, PBLH decreased overall, and method-dependent differences persisted. Under different pollution levels, this study also discussion the properties of PBLH using MPL and microwave radiometer. And aerosol optical depth (AOD) and PBLH showed a strong negative correlation, indicating aerosol-induced suppression of boundary layer growth. The study of boundary layer characteristics in coastal megacities can provide reference for atmospheric physics research in economically developed coastal areas.

Volcanic eruptions are responsible for ejecting huge quantities of ash and gases in the troposphere. Nyamuragira volcano has been a prodigious source of sulfur dioxide in the last decade, and its emissions may significantly affect regional weather. The impacts of volcanic aerosols from Nyamuragira’s 2006 eruption over Congo Basin on regional weather are investigated with a Weather Research and Forecast model coupled with chemistry (WRF-Chem). Two five-member ensemble experiments were performed: one without volcanic eruption and the other with volcanic eruption in the WRF-Chem model. The results show that volcanic aerosols cooled both the bottom of the atmosphere and the top of the atmosphere with the domain average value of -45.20 W m-2 and -30.76 W m-2 respectively and relatively warmed the atmosphere at 14.60 W m-2. Near-surface temperature was reduced remarkably in the aerosol layers aloft volcanic plume with a maximum decrease of 0.4 oC. The presence of volcanic aerosols reduced the wind speed in the lower atmosphere on average by 0.10 m s-1 but increased in the upper atmosphere on average by 0.15 m s-1. Further, the volcanic aerosols induced a decrease in precipitation by an average of 2.8 mm day-1 (25%) during the eruption. Although modeling volcanic aerosols radiative impact has challenges and presents large uncertainties, this study highlighted the capabilities of WRF-Chem to reproduce the dispersion of volcanic aerosol and its radiative feedback over Congo Basin.

Extreme precipitation plays an increasingly important role in shaping hydroclimatic risk under global warming, yet its long‐term contribution to total precipitation remains poorly understood. This study investigates the interdecadal changes in the Proportion of Extreme Precipitation to Total Precipitation (PEPTP) in South China from 1961 to 2024. Results show a significant increase in PEPTP since the early 1990s. The Indian Ocean capacitor effect dominate the earlier period, the post‐1992 phase is increasingly influenced by North Atlantic Zonal Dipole (NAZD). Notably, the Pacific Decadal Oscillation (PDO) modulates the NAZD–PEPTP relationship, with a significant positive correlation emerging during negative PDO phases. The recent enhancement of PEPTP coincides with a persistent negative PDO phase. These findings highlight the importance of multi‐oceanic modes and decadal variability in shaping extreme precipitation under climate change.