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.

We used synthetic analysis, EOF decomposition, correlation coefficient analysis and causal analysis to investigate relationships between radiation flux and ENSO in the tropical Pacific in recent 170a. Our results indicate that SDLR increased significantly, by c.0.05 W / (M 2 * a), TOLR decreased slightly, by c.0.02 W / (M 2 * a), SDSR did not change significantly, and TISR increased slightly, by c.0.001 W / (M 2 * a). In the tropical western Pacific region, the average state of the tropospheric atmosphere rising and sinking intersecting area shifted eastward by 0.05 ° / a, and El Niño Modoki events increased. In the Middle East Pacific, especially Niño 3.4 with an ocean depth > 700 m, ocean heat content increased significantly, the maximum ILD region moved eastward, upward movement in the intersecting area was abnormally enhanced, the number of westerly wind bursts weakened, and the probability of El Niño Modoki occurrence increased. There was a correlation and causal relationship between marine heat content in zones Niño3 and Niño4, radiation flux, w and u, v anomalies near the intersecting zone. When the time series of the factor was ahead or behind, the lead lag correlation coefficient generally increased. The location of the ILD maximum only affected TOLR, and only SDLR can affect the longitudinal location of the ILD maximum. The longitudinal location of the ILD maximum and H niño3 , H niño3.4 interact as both cause and effect.