El Niño-Southern Oscillation (ENSO) is the most significant global ocean–atmosphere coupled signal in the tropical Pacific Ocean, and it can affect the stratosphere. However, the ENSO-related dynamical processes that influence the ozone valley during summer are still not well understood and are under-investigated. In this study, we used the ERA5 and MERRA-2 reanalysis data from 1979 to 2021 combined with numerical simulations to analyze the mechanisms through which ENSO affects the ozone valley over the Tibetan Plateau in the upper troposphere and the lower stratosphere (UTLS) in summer. The results showed that the two cores of the ozone valley in UTLS were more evident in the summer following La Niña than in the summer following El Niño. At low latitudes, negative O₃ anomalies in UTLS were observed in the summer following El Niño and positive O₃ anomalies were observed in the summer following La Niña. At middle latitudes, negative O₃ anomalies in UTLS were found near 60°E in the summer following El Niño, while negative anomalies were found at 40°E and 120°E in the summer following La Niña. The analysis of the flow and vorticity fields suggested that the field anomalies can cause vertical motion, which in turn leads to the mixing of different ozone concentrations and affects the ozone valley in UTLS over the Tibetan Plateau. In particular, the warming of the Indian Ocean sea-surface temperature (SST) in the summer following El Niño enhances the South Asian High (SAH) through two-stage thermal adaptation, leading to ozone anomalies at low latitudes in the ozone-valley region. These conclusions were verified by a simulation using the WACCM4 model, the results of which were consistent with the original observations.

Sea fog significantly impacts marine activities, ecosystems, and radiation balance. We analyzed the decadal variation characteristics of sea fog frequency (SFF) over the northwestern Pacific and investigated the roles of the Pacific decadal oscillation (PDO) and sea surface temperature (SST) warming in driving these changes. The results show that SFF experienced a significant and sudden decadal increase around 1978 (up by 12.9%) and a prominent decadal decrease around 1999 (down by 7.8%). The sudden increase in SFF around 1978 was closely related to the PDO. A positive PDO phase induced unusual anticyclonic circulation and southerly winds over the northwestern Pacific, enhancing low-level atmospheric stability and moisture supply, thus facilitating sea fog formation. Nevertheless, the decrease in SFF around 1999 was related to SST warming in the north Pacific. The rise in sea temperatures weakened the SST front south of the foggy region, reducing the cooling and condensation of warm air necessary for sea fog formation. This study enhances the understanding of the decadal variability mechanism of SFF over the northwestern Pacific regulated by large-scale circulation systems and provides a reference for future sea fog forecasting work.

In this work, we studied the influence of spring (SP) and summer (SU) El Niño events on the landfalling tropical cyclones (TCs) in China. The results showed that compared to SU El Niño years, the average latitude of the landfalling TCs in SP El Niño years shifted significantly southward and that the average TC intensity was significantly stronger, especially in the post-landfall period. Additionally, more severe tropical storm-level TCs generated over the South China Sea made landfall in China. Meanwhile, in SP El Niño years, landfalling TCs in southern China had a greater landfall intensity, but landfalling TCs in eastern China were the opposite. These changes in TC intensity during the SP El Niño years could be attributed to more favorable dynamical and thermodynamical conditions, which are beneficial for maintaining TC intensity and duration after landfall. These results could have important implications for an in-depth understanding of TC activities, as well as TC disaster prevention and mitigation.

This study integrates the sea surface temperature, ozone and meteorological data of ERA5 to count the El Niño events since 1979 and has classified these events into eastern and central types in space as well as spring and summer types in time. The impacts of different types of El Niño events on the ozone valley of the Tibetan Plateau are discussed. The eastern (and spring) type of El Niño events are generally more intense and longer in duration than the central (and summer) type of El Niño events. Overall, in the summer of the following year after El Niño events, the total column ozone (TCO) anomalies near the Tibetan Plateau have a regular zonal distribution. At low latitudes, TCO exhibits negative anomalies, which become more negative approaching the equator. The TCO in the region north of 30° N mainly shows positive anomalies with the high-value region around 40° N. The responses of ozone to different types of El Niño events over the Tibetan Plateau are different, which is further validated by the WACCM4 simulation results. The greater intensity of the eastern (and spring) type of El Niño events caused stronger upward movement of the middle and upper atmosphere in the 20° N region in the subsequent summer as well as a stronger South Asian High. These have resulted in a wider range of negative TCO anomalies in the southern low-latitude region of the South Asian High. In addition, the growing intensity of El Niño extreme events over more than half a century warrants significant concern.

In the context of global warming, compound dry-hot events (CDHEs) are intensifying in Guangdong, yet CMIP6 projections remain uncertain. This study employs CMIP6 data and the Standardized Compound Event Indicator (SCEI) to quantify CDHEs severity, applying an observational constraint approach to reduce inter-model uncertainty. The results show that, after observational constraint, uncertainties decrease by about 63% and 77% in Period I and II under SSP126 and by about 57% and 59% under SSP585, greatly improving projection robustness. CDHE risk is highest in SSP585-Period II. Future dry-hot intensification in Guangdong generally increases from north to south, with western Guangdong most strongly affected. Although CDHEs weaken in other periods, western Guangdong shows persistent aggravation. Mechanism analyses indicate that SSP585-Period I is mainly linked to cold sea surface temperature (SST) anomalies in the South Atlantic and waters near Australia. After correction, dry-hot conditions show a marked weakening across Guangdong, although slight intensification persists over the Leizhou Peninsula. SSP585-Period II is primarily influenced by warm SST anomalies in the eastern Pacific and South Atlantic and cold anomalies in the North Pacific. The two SSP126 periods are associated with warm SST anomalies in the South Atlantic and waters near Australia and with cold anomalies in the South Atlantic, North Pacific, and North Atlantic, respectively. After correction, CDHEs generally weaken across Guangdong, although southern and south-central areas remain relatively severe. These findings indicate that historical key SST biases can strongly influence future CDHEs projections in Guangdong by modulating large-scale atmospheric circulation, including the Pacific-South American wave train, Indian Ocean SST anomalies, and the Western North Pacific Subtropical Anticyclone.