Amplified contiguous United States summer rainfall variability induced by East Asian monsoon interdecadal change

The strength of the dominant variability of contiguous United States (CONUS) summer rainfall during 1960–2013 experiences an interdecadal change in the early 1990s. Before the early 1990s, the variation in CONUS summer rainfall is relatively small in amplitude (standard deviation: 0.64 mm day−1), whereas after it amplifies remarkably, with its standard deviation (1.31 mm day−1) roughly doubling. Observational diagnoses and simulation results show that enhanced East Asian subtropical monsoon variability plays a direct role in strengthening the CONUS summer rainfall dipole variability. Besides, a northward shift of the East Asian summer monsoon is also responsible for the amplification of the CONUS summer rainfall variability. This northward shift of the East Asian rain belt pushes the rainfall perturbation farther to the north, much closer to the subtropical East Asian upper-level westerly jet stream. As a result, the East Asian subtropical monsoon heating induces the upper-level Asia–North America teleconnection pattern more effectively, leading to the larger amplitude of CONUS summer rainfall variability.