Jie Tang

Understanding the physical mechanisms of compound hot-drought events (CHDEs) over the Yangtze River Basin (YRB) is essential for improving climate predictability. Using high-resolution observations and ERA5 reanalysis, this study conducted a three-dimensional comparative diagnosis of two spatially distinct CHDEs (August 2022 and 2019), deconstructing their circulation dynamics and thermodynamic budgets. Specifically, the 2022 basin-wide event was highly associated with La Niña and a negative Indian Ocean Dipole (NIOD). Anomalous latent heating in the tropical eastern Indian Ocean favored an extensive meridional Hadley circulation and a deep high-pressure belt, blocking southwest moisture transport. Thermodynamically, intense downward vertical motions produced severe descending adiabatic warming, which offset longwave radiational cooling and sustained anomalous heat accumulation throughout the deep troposphere. Conversely, the 2019 localized event occurred under a weak Central Pacific El Niño and a positive IOD. The anomalous tropical cooling weakened systematic subsidence and provided a favorable background for a Rossby wave train, featuring an offshore cyclone over the Western North Pacific that severed moisture pathways. Characterized by shallower vertical subsidence, the lack of a penetrative adiabatic heat source merely maintained a lower-level thermodynamic balance, confining extreme heat to the central–eastern YRB. Although superficially similar at the surface, these CHDEs are sustained by two distinct ocean–atmosphere interaction paradigms. Clarifying these dual paradigms provides a critical physical basis for improving sub-seasonal prediction.

An extreme winter icing event from 1 to 7 February 2024 in central-eastern China induced sequential hydrometeor phase transitions (freezing fog, freezing drizzle, intense freezing rain, and mixed-phase precipitation) at Hunan’s Gutaishan wind farm. To investigate the underlying physical mechanisms, this study utilized multisource observational data, ERA5 reanalysis, and turbine operational records. The combined influence of the South Branch Trough and the Western Pacific Subtropical High drove a prolonged convergence of southwesterly warm-moist advection with easterly cold air, maintaining a stable temperature inversion. During the freezing-fog stage, this cold-warm-cold inversion structure trapped near-surface moisture, leading to the accumulation of supercooled droplets that ultimately caused a shutdown of 50% of the operational turbines. The freezing-drizzle stage was governed by the warm-rain mechanism. Due to the absence of ice-phase hydrometeors in shallow clouds (cloud-top temperatures > -10 °C), purely liquid drizzle drops fell through the underlying cold layer to become supercooled, triggering a farm-wide shutdown. The intense freezing-rain stage followed the melting mechanism. Abundant ice-phase hydrometeors from deep clouds (cloud-top temperatures < -20 °C) melted completely within a pronounced warm layer (vertical temperature inversion strength of 10.0 °C km^− 1) and subsequently became supercooled in the underlying cold layer, accelerating blade icing. Finally, the mixed-phase stage was driven by a melting-refreezing mechanism. Mid-level dry-cold air intrusion weakened the warm layer, causing descending solid hydrometeors to undergo only partial melting. These hydrometeors then formed mixed-phase precipitation (coexisting ice pellets and trace supercooled rain) within the deep cold layer, maintaining the farm-wide shutdown.

This study analyzes the spatiotemporal evolution of ice accretion hazards in Northeast China during the early winter and assesses their potential risks to the power grid, based on the ERA5 reanalysis dataset from the European Centre for Medium-Range Weather Forecasts and observed grid icing failure data. Empirical Orthogonal Function (EOF) analysis reveals that the first mode (14.83% variance contribution) of cumulative freezing rain hours exhibits a spatially consistent increasing trend across the region, with a more pronounced increase in high-value areas such as southeastern Heilongjiang and central-eastern Jilin since 2000. Against this climatic background, high-resolution ice thickness inversion for the period 2010-2023 indicates a notable northward shift of high-risk icing areas after 2018, along with an expansion in both the intensity and spatial extent of ice accretion in Jilin and Heilongjiang. Independent validation using grid failure records from three typical icing disaster events demonstrates a high consistency between the inverted ice thickness and actual failure locations, with an accuracy exceeding 84%. Furthermore, return period assessment based on the Extreme Value Type-I distribution identifies southeastern Heilongjiang and central-eastern Jilin as core risk zones, where the estimated extreme ice thicknesses for 30-, 50-, and 100-year return periods increase progressively while maintaining a highly stable spatial pattern. This study provides critical quantitative support for the differentiated anti-icing design and disaster prevention strategy formulation of the power grid in Northeast China.

Heat waves, particularly humid heat waves that occur together with high temperatures and humidity, pose a severe hazard to human health in the context of global warming. In this work, daily observations from more 1500 sites are used to define dry and humid heat waves in a warm season (May to September) and assess their spatiotemporal characteristics during 1960–2015. Dry heat waves are identified with daily maximum temperatures, while humid heat waves are identified based on the wet bulb temperature, derived from both temperature and humidity. We compare dry and humid heat waves from various aspects based on multiple heat wave indices, including their frequency, duration, and intensity. Results suggest that the occurrence of both dry and humid heat wave days in China is higher in the southern than in the northern part of China, due to the higher air temperature and humidity therein. Compared to dry heat waves, humid heat waves are of higher amplitude but shorter duration. The long-term trend analysis shows that the occurrence of both dry and humid heat waves has increased overall over the last 50 years, with an especially rapid increase in the last 20 years, which may be related to China’s rapid warming since the late 1980s. The future projections with multiple global climate models indicate that China will experience more frequent, stronger, and longer-duration dry and humid heat waves in the future, under both intermediate and high-emission pathways.

The changes in clouds and precipitation are essential to understand the variation of water cycle under a changing climate and have not been well investigated on the Tibetan Plateau (TP). In this study, the long‐term variations and the associated mechanisms of total cloud amount (TC), low cloud amount (LC), the number of precipitation days (PN) and precipitation amount (PA), as well as the number of snow cover days (SN) and mean snow depth (SD) on the TP and its subregions of northeast (NE), central south (SC) and southeast (SE) are investigated with observational data in 1979–2016. The results indicate that TC has an overall decreasing trend, while LC has a significant increasing trend on the whole TP. PA in the NE has a significant increasing trend, and that in the SE has an insignificant decreasing trend. Light precipitation events tend to decrease and heavy precipitation events tend to increase. SN and SD have significant interannual decreasing trends. It is found that the atmospheric thermodynamic condition on the TP tends to become stable under a warming climate. The northward shifting of the westerly winds in association with the Hadley cell expanding in cold seasons and the strengthening South Asian high and the South Asian monsoon in warm seasons should be directly responsible for the generally decreasing trends in TC and related precipitation events on the south TP, and the increasing trends in LC and associated warm precipitation on the whole TP.

With the support of the Chinese National Antarctic Research Expedition, near-surface ozone (O₃) was continuously monitored at Zhongshan Station (ZOS) (69°22′12″ S, 76°21′49″ E, 18.5 m above sea level) in East Antarctica from 2008 to 2020. The seasonal and diurnal variability of near-surface O₃ at ZOS were investigated. O₃ enhancement events (OEEs) were frequently observed in the warm season (OEEs in January accounted for 23.0% of all OEEs). The OEEs at ZOS were related to the photochemical reaction processes under the influences of O₃ and solar radiation in the stratosphere and synoptic-scale air mass transport from coastal areas (Princess Elizabeth Land, Wilkes Land, and Queen Mary Land), as evidenced by the recorded wind speed, solar shortwave irradiance, and total column ozone data and the computed potential source contribution function and concentration-weighted trajectory models. The results computed by the tool Stratosphere-to-Troposphere Exchange Flux indicated that stratosphere-to-troposphere transport had no direct impact on OEEs at ZOS. Therefore, synoptic-scale air mass transport is the main cause of OEEs in Antarctica, which is consistent with previous studies. Unlike OEEs at inland Antarctic stations, which are mainly affected by air mass transport from inland plateaus, OEEs at ZOS, a coastal station, are mainly affected by air mass transport from coastal land in East Antarctica.