Interdecadal change in the relationship between the NAO and summer rainfall in Northern Central Asia

Based on the Climate Research Unit (CRU) monthly rainfall data and the NationalCenters for Environment Prediction (NCEP)/National Center for Atmospheric Research (NCAR) reanalysis atmospheric circulation data during 1961–2020, we examine the interdecadal change in the relationship between the North Atlantic Oscillation (NAO) and summer rainfall in northern Central Asia (CA). Results show that the NAO negatively (positively) correlates with summer rainfall in northern CA during 1969–1989 (1990–2010), but it becomes obviously closer in the second period, indicating their relationship has experienced a significant interdecadal change over the past 60 years. The varying relationship between the NAO and summer rainfall in northern CA is caused by the interdecadal change in the NAO-related large-scale circulation anomalies. The positive NAOI is well related to the strengthening subtropical westerly jet over CA, an anomalous cyclone over west of CA and southerly wind prevailing over northern CA and convergences of water vapor occupying the whole northern CA, so the relationship between the NAO and summer rainfall in northern CA has become stronger during 1990–2010. Furthermore analysis suggests that the intensity of subtropical westerly jet over CA plays an important role in linking the NAO and summer rainfall in northern CA. In the first period, the atmospheric teleconnection pattern triggered by the NAO only has weak effects on the subtropical westerly jet over CA, but in the second period it can strongly modulate the change in the intensity of subtropical westerly jet over CA.