NAO Signal in the Increased Interannual Variability of Spring Vegetation in Northeast Asia After the Early 2000s

Based on the leaf area index (LAI) and normalized difference vegetation index (NDVI) from 1982 to 2020, this study reveals a significant increase in the intensity of interannual variability (IIV) in spring (April–May) vegetation over Northeast Asia since the early 2000s. This change is closely linked to the notable increase in the IIV of April surface air temperatures over Northeast Asia from the former period (1986–2001) to the latter period (2002–2016). Further analysis also highlights a salient impact of the North Atlantic Oscillation (NAO) on the strengthened IIV in vegetation. During the latter period, there is a substantial increase in the IIV of the March NAO compared with the former period. This greater variability allows the positive NAO to significantly influence the net heat fluxes, thereby leading to a positive phase of the North Atlantic tripole (NAT) sea surface temperature (SST) pattern in March. Given the persistence of SSTs, the positive NAT SST pattern lasts to April, subsequently causing positive height anomalies over Northeast Asia through a wave train that originates from the North Atlantic and propagates downstream. This process consequently results in an increase in surface air temperature over Northeast Asia and hence the local vegetation. Thus, the increased IIV of the March NAO is conducive to enhancing the IIV in spring vegetation over Northeast Asia.