The relationship between spring (March to May) Arctic Oscillation (AO) and East Asian summer monsoon (EASM, May to July) on interannual timescale has a remarkable decadal variation in late 1990s, and their correlation coefficient abruptly turns from +0.77 during 1979–1997 to −0.62 during 1998–2007. In the following summer after a spring positive AO phase, the lower-troposphere over East Asia (EA) features a cyclonic anomaly before 1997 but an anticyclonic anomaly after 1997, which results from different simultaneous air–sea features imposed by spring AO and distinctive evolution from spring to summer. In pre-1997, the spring AO-associated signal is mainly memorized and persists over Pacific, because the spring AO-associated wave activity prefers the high-latitude propagation from North Atlantic to Pacific. In contrast, a subtropical wave train from North Atlantic Ocean to Indian Ocean (IO) is evidently enhanced in post-1997 epoch, and accordingly the IO plays a dominant role in memorizing and extending the influence of spring AO on EASM. This subtropical route of spring AO-EASM teleconnection is a new finding. The strengthening of the subtropical wave train in post-1997 epoch could be partly attributed to the strengthening signals of spring AO over North Atlantic Ocean.
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