《Table 1.Definitions of eight BSISO phases using PC1 and PC2.》

  提示：宽带有限、当前游客访问压缩模式

本系列图表出处文件名：随高清版一同展现

《Factors Limiting the Forecast Skill of the Boreal Summer Intraseasonal Oscillation in a Subseasonal-to-Seasonal Model》

1. 获取 高清版本忘记账户？点击这里登录

1. 下载图表忘记账户？点击这里登录

To better evaluate the real-time forecast capability of the BSISO，we adopt the multi-variate（MV）EOF analysis proposed by Lee et al.（2013）to derive the real-time BSISO index from different lead forecasts.Our evaluation focuses on the spatial pattern and temporal evolution of the real-time BSISO index in the BCC S2S model output.As in Lee et al.（2013），we first remove the climatology（the first three harmonics）and the interannual variability（using the running mean of the last 120 days）from daily OLR and 850-hPa zonal wind（U850）fields in the Asian monsoon region（10?S–40?N，40?–160?E）.We then normalize and decompose the two anomaly fields，using the MV-EOF analysis.The first two modes（EOF1 and EOF2）can effectively represent the north-northeastward propagation of the 30–90-day BSISO.Using the time series（PC1 and PC2）of these two modes，we can then divide the BSISO lifecycle into eight phases（Wheeler and Hendon，2004；Lee et al.，2013），as in Table1.When（PC12+PC22）1/2>1.0，it is considered as an active BSISO event.The third and fourth EOF modes represent the northwestward-propagating signal with a shorter period of 10–30 days（Lee et al.，2013）.In our model assessments，the filtering and EOF analysis were carried out separately for each lead time.Jie et al.（2017）noted that the operational models generally show lower skills in predicting this 10–30-day mode.Our analysis also finds that the skill of the 10–30-day BSISO prediction of BCC S2S model is about nine days（not shown），similar to the range of weather forecasts.Therefore，only the 30–90-day BSISO mode is investigated in this study.