Interdecadal Changes in the Boreal Summer Tropical-Extratropical Teleconnections Occurred Around Mid-to-late 1990s

This study investigates robust features of interdecadal changes in the Northern Hemisphere summer tropical-extratropical teleconnection that occurred around the mid-to-late 1990s by analyzing four different reanalysis data for atmospheric circulation and temperature, two precipitation reconstructions, and two sea surface temperature (SST) data during the satellite observation era of 1980-2023. For the last 44 years, there has been a significant increasing trend in anticyclonic circulation at lower and upper troposphere and 2m air temperature with wavenumber-5 Rossby wave structure in the Northern Hemisphere (NH) extratropics. The increase has been accompanied with the significant weakening and northward shift of jet stream over Eurasia and the North Pacific. It is further found that there has been a significant interdecadal shift occurred around the mid-to-late 1990s in the two distinct modes of tropical-extratropical teleconnection: Western Pacific-North America (WPNA) and circumglobal teleconnection (CGT) pattern. After the mid-to-late 1990s, the WPNA has played a more important role in modulating the extratropical atmospheric circulation and surface climate, which has preferentially occurred during the El Niño-Southern Oscillation (ENSO) decaying or transition summers such as 1998, 2010, and 2016. During these summers, severe heat waves occurred over many parts of the NH extratropics due to the combined effect of the increasing trend in the barotropic anticyclonic circulation and the significant WPNA across the NH. Although weakened, the CGT also contributed to hot summers over many parts of the NH extratropics, such as 1999, 2000, 2008, 2011, 2012, 2021, and 2022, when weak to moderate La Niña persisted.  This talk will also discuss the seasonal predictability and prediction for the two teleconnection modes in the state-of-the-art climate models.