Based on the monthly Extended Reconstructed Sea Surface Temperature dataset (ERSST v5) provided by the National Oceanic and Atmospheric Administration (NOAA), this study investigates how the longitudinal position of La Niña affects summer precipitation in Southeast China during its developing phase from 1950 to 2023. The underlying physical mechanisms are also explored. The results show that an eastward shift of the La Niña cold center tends to induce a meridional dipole precipitation anomaly pattern over Southeast China, characterized by increased rainfall over the Yangtze River Basin and decreased rainfall over South China. In contrast, no significant precipitation anomalies are observed in Southeast China when La Niña shifts westward. Further analysis reveals that the eastward-shifted La Niña events are often accompanied by positive Sea Surface Temperature Anomalies (SSTA) in the equatorial western Pacific, which strengthen the zonal SSTA gradient and enhance equatorial easterly wind anomalies. These changes are favorable for the development of an anomalous anticyclonic circulation near the South China Sea, which enhances moisture transport to the Yangtze River Basin while suppressing convection over South China via its subsiding branch. Conversely, westward-shifted La Niña events are featured by a weaker zonal SSTA gradient and negligible atmospheric circulation responses, thus exerting little influence on precipitation in Southeast China. This study highlights the crucial role of La Niña's longitudinal position in modulating summer rainfall patterns over China and provides new physical insights into the ENSO-precipitation relationship. These findings offer important implications for improving flood-season precipitation prediction.

Based on the monthly Sea Surface Temperature (SST) data from the Met Office Hadley Centre, the Global Precipitation Climatology Project monthly precipitation data, and the historical simulations from Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models, the present work investigates the seasonality of the SST-precipitation relationship over the tropical North Atlantic and possible role of ENSO (El Niño-Southern Oscillation). It is found that the relationship of SST anomalies in the tropical North Atlantic with local precipitation exhibits a remarkable seasonality. During spring and summer, there is a significant positive correlation between SST and precipitation in this region, indicating a strong local ocean-atmosphere coupling. In contrast, in autumn and winter, the ocean-atmosphere coupling weakens significantly, and almost no significant precipitation response to SST is detected. Further analysis reveals that this seasonality is mainly associated with the seasonal cycle of the background SST and local SST variability in the tropical North Atlantic. Despite cooler background SST in spring, the strong SST variability during this season makes SST easy to exceed the convection threshold and thus induces precipitation anomalies. In summer, the warm background SST favors the enhanced local ocean-atmosphere coupling. The relatively weak SST variability in autumn weakens the local precipitation response, despite a relatively warm SST background. The cooler background SST in winter results in a weak ocean-atmosphere coupling. ENSO has a significant influence on spring SST and precipitation anomalies in the tropical North Atlantic. As a result, the strong local SST anomalies in spring are more likely to actively trigger local convective responses under ENSO forcing. However, in other seasons, the impact of ENSO on SST anomaly in the tropical North Atlantic is relatively small, and thus there is almost no difference in local ocean-atmosphere coupling in the tropical North Atlantic with or without ENSO SST forcing. These findings emphasize the critical role of spring and summer tropical North Atlantic SST anomalies in local convection and associated climate impacts, which is important for short-term climate prediction related to the tropical North Atlantic SST.

The influences of active days of the Madden-Julian oscillation (MJO) over the Indian Ocean on summer precipitation days over the middle and lower reaches of the Yangtze River were investigated. Daily precipitation data collected at 753 stations, monthly sea surface temperature (SST) data from the Hadley Centre, daily mean reanalysis data from the National Centers for the Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR), and all-season real-time multivariate Madden-Julian Oscillation (RMM) index during 1980—2020 were used. The results show that the active days of MJO over the Indian Ocean have a statistically significant relationship with precipitation days over the middle and lower reaches of the Yangtze River, especially with the heavy precipitation days, since the MJO related circulation anomalies can continuously transport water vapor to eastern China. Further research indicates that the relationship between active days of MJO over the Indian Ocean and the precipitation days over the middle and lower reaches of the Yangtze River has experienced a decadal change with their relationship being significant since the 2000s. The decadal change of this relationship might be attributed to decreased variability in SST in the Indian Ocean. This decreased interannual variability of SST suggests weakened modulation effects on precipitation over the middle and lower reaches of the Yangtze River by the tropical Indian Ocean. In contrast, the MJO effects on the precipitation days over the middle and lower reaches of the Yangtze River turn to be significant after the 2000s due to less disturbances from the Indian Ocean SST.

Based on daily mean air temperature data from the first-generation global atmosphere reanalysis product (CRA) of China, the reconstructed monthly sea surface temperature data from National Oceanic and Atmospheric Administration (NOAA), and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) atmospheric circulation reanalysis data, the present study investigates influences of El Niño-Southern Oscillation (ENSO) on the early and late winter synoptic-scale air temperature variability over eastern China and possible mechanisms. It is revealed that the ENSO impacts differ remarkably between early and late winter. That is, the synoptic-scale air temperature response to ENSO over eastern China is weak in early winter but strong in late winter. In late winter, there is a significant positive correlation between ENSO and the synoptic temperature variability in the middle and lower reaches of the Yangtze river of eastern China. It suggests that the synoptic-scale air temperature variability and temperature fluctuation in late winters of El Niño (La Niña) years are usually stronger (weaker) than that in normal years. In late winter, ENSO can modulate the atmospheric baroclinicity by changing the meridional temperature gradient in the middle and high latitudes of Eurasia, which affects the synoptic-scale variation of atmospheric circulation in East Asia and subsequently affects the synoptic-scale air temperature variability over eastern China. Specifically, in late winters of El Niño years, the north-south temperature gradient is larger and the corresponding atmospheric baroclinicity is stronger, which could lead to more active meridional wind activities and more frequent cold air activities. Roughly opposite mechanisms apply during late winters of La Niña years. However, in early winter, ENSO has a weak influence on the meridional temperature gradient in the middle and high latitudes of Eurasia, and thus exhibits minor effects on the synoptic-scale temperature variability over eastern China. The results can enrich our understanding of the ENSO impact on air temperature variability in China, and provide references for improving seasonal prediction of wintertime air temperature over China.

This work investigates the spatial and temporal features of boreal autumn (August—October) East Siberian—Beaufort (EsCB) sea ice on decadal timescales during the period of 1950—2020 based on monthly Sea Surface Temperature (SST), Sea Ice Concentration (SIC) from the Hadley Center and atmospheric reanalysis dataset provided by the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The possible modulation effects of Atlantic Multidecadal Oscillation (AMO) on the EsCB sea ice are further elaborated. The EsCB sea displays the strongest decadal component of sea ice in the Arctic, accounting for more than 40% of the local total variance of SIC anomalies. Our further analyses show that the AMO exerts a prominent modulation on the EsCB sea ice. In the positive AMO phase, warm North Atlantic SST anomalies trigger poleward propagating atmospheric Rossby waves, favoring the establishment of an anomalous high over the central Arctic region. The corresponding adiabatic descending motion warms the lower troposphere and causes the EsCB sea ice to melt. The surface warming and EsCB sea ice melting can simultaneously give rise to an increase in local cloud amount and downward longwave radiation, which in turn increases the surface air temperature. This surface air temperature-cloud-longwave positive feedback is beneficial for the long-term maintenance of the decadal sea ice signal. The North Atlantic pacemaker experiments can realistically reproduce the observed physical process as shown above, which further supports our main conclusions.