Strengthened Relationship between Eastern ENSO and Summer Precipitation over Northeastern China

This paper reveals a strengthened relationship between the spring eastern ENSO and summer precipitation over northeastern China (NEC) after the late 1990s. The relationship of the spring eastern ENSO with summer NEC precipitation is insignificant during 1983-97, whereas it becomes significantly positive during 1998-2012. In the earlier period, a zonal tripolar pattern in the middle to high latitudes of the North Asia-Pacific region and an anomalous anticyclone over Japan are the main factors responsible for NEC summer precipitation, although these atmospheric patterns have a weak correlation with the spring eastern ENSO. However, the atmospheric circulation that influences precipitation in NEC develops into the Siberian high and an anomalous cyclone over NEC after the late 1990s, which are strongly correlated with the spring eastern ENSO. The changes in associated atmospheric circulation partially contribute to the strengthening of the eastern ENSO-precipitation relationship. Additionally, the eastern ENSO signals persist from spring to summer via the tropical Indian Ocean (TIO) and a dramatic warming trend occurs in the TIO after the late 1990s. Observations and numerical simulations indicate that the circulation anomaly induced by warming in the TIO acts as a bridge linking the eastern ENSO and precipitation after the late 1990s. The northern Hadley and Ferrell cell anomalies associated with the TIO SST anomaly are much more significant and extend farther north to the midlatitudes, and the associated divergence anomalies centers shift from the tropical central Pacific to western Pacific; those further influence the NEC precipitation through modulation to the atmosphere circulation (e.g., geopotential height, horizontal wind, and moisture transport).