The Impact of the Scandinavian Teleconnection Pattern on Late Autumn Rainfall in the Western Region of Southwest China

Based on rainfall datasets obtained from meteorological stations in China and the NCEP/NCAR reanalysis data, the simultaneous relationship between the Scandinavian teleconnection pattern (SCA) and late autumn precipitation over the western region of Southwest China (WSWC) during 1961-2012 is investigated. Results show that there is a significant negative correlation between the SCA index and the rainfall over WSWC. The negative correlation is asymmetric. During the positive SCA years, the rainfall in WSWC is less than that in normal years. However, during the negative SCA years, the relationship between the SCA index and the rainfall over WSWC is not significant. The negative rainfall anomaly over WSWC during positive SCA years is consistent with local anomalous descending motion in the lower and middle troposphere. The diagnostic analysis of the vertical motion equation indicates that the local descending motion is primarily maintained by anomalous cold temperature advection. The advection of anomalous temperature by mean westerlies contributes most to the anomalous cold temperature advection in WSWC. The downstream Rossby wave propagation triggered by the positive SCA pattern weakens the East Asian trough. Consequently, the eastern part of Southwest China becomes warmer. The climatological westerly wind brings anomalously cold air into the WSWC area, resulting in local descending motion and drought.