ENSO与中国夏季降水的联系：冬季QBO的调制作用

LINKAGE BETWEEN ENSO AND CHINA SUMMER RAINFALL: MODULATION BY QBO

关键词:  厄尔尼诺-南方涛动(ENSO)  平流层准两年振荡(QBO)  夏季降水异常  海温

Key words:  El Niño -Southern Oscillation (ENSO)  stratospheric Quasi-Biennial Oscillation (QBO)  summer precipitation  sea surface temperature (SST)

摘要:

使用NCEP/NCAR再分析资料、中国气象局台站降水资料和GPCC降水资料，系统研究了在冬季平流层准两年振荡(Quasi-Biennial Oscillation, QBO)调制下，厄尔尼诺-南方涛动(El Ni?o-Southern Oscillation, ENSO)不同阶段与中国夏季降水的可能联系。根据两者的位相和强度，可将它们的配置分为QBO西风/El Ni?o、QBO西风/La Nina、QBO东风/El Ni?o、QBO东风/La Nina。研究结果表明，在年际时间尺度上，ENSO和QBO无显著相关关系。冬季QBO西风位相时，El Ni?o发展年夏季，我国整体偏旱，而华南偏涝；衰减年夏季，华南、华东北部偏旱，东北、长江流域偏涝。La Nina发展年夏季，我国东部降水异常呈负-正-负的三极分布；衰减年夏季，东南沿海偏涝。冬季QBO东风位相时，El Ni?o发展年夏季，长江以北偏旱；衰减年夏季，我国东部降水异常呈负-正-负的三极分布。La Nina发展年夏季，江淮和华南南部偏旱；衰减年夏季，我国东部沿海偏涝。ENSO是影响我国夏季降水异常的重要因子，而QBO的调制作用在ENSO衰减年夏季更为显著。相比冬季QBO东(西)风位相，QBO西(东)风位相时El Ni?o (La Nina) 期间赤道西太平洋负(正)海温异常更强，衰减年夏季位于西太平洋的异常下沉(上升)运动和印度洋的异常上升(下沉)运动更强更深厚，西太平洋副热带高压范围更大(小)，南亚高压更偏东(西)。

Abstract:

By using the NCEP/NCAR reanalysis data, the China Meteorological Administration station precipitation data and Global Precipitation Climate Centre rainfall data, this work systematically studied a possible linkage between El Ni?o-Southern Oscillation (ENSO) in different periods and the summer precipitation in China as well as its modulation by the stratospheric Quasi-Biennial Oscillation (QBO). According to the phase and intensity of the ENSO and QBO, four configurations are investigated, including QBO westerly phase and El Ni?o, QBO westerly phase and La Nina, QBO easterly phase and El Ni?o, and QBO easterly phase and La Nina. The result shows that there is no significant correlation between ENSO and QBO on the interannual time scale. In the case of QBO westerly phase in winter, China is generally dry except that the south of China is anomalously wet during an El Ni?o developing summer; the south and the east of China are anomalously dry and more rainfall appears in the northeast of China and the middle and lower reaches of the Yangtze River during an El Ni?o decaying summer. In contrast, the precipitation anomalies in eastern China show a tripole pattern, i.e., a dry southern China, wet eastern and central China, and dry northern China during a La Nina developing summer accompanied by QBO westerly phase, while the coastal southeast China is anomalously wet during a La Nina decaying summer. In the case of QBO easterly phase in winter, north Yangtze River Valley is dry during an El Ni?o developing summer, but an anomalous tripole precipitation pattern forms during an El Ni?o decaying summer. The Yangtze-Huaihe valley region and coastal southern China are dry during a La Nina developing summer and QBO easterly phase. However, coastal eastern China is anomalously wet during a La Nina decaying summer and QBO easterly phase. ENSO is the major factor affecting China summer rainfall, but its effect is modulated by QBO, especially during an ENSO decaying summer. The positive (negative) sea surface temperature (SST) in the central and eastern equatorial Pacific are larger during El Ni?o (La Nina), and the anomalous sink (rise) branch is also deeper during an El Ni?o (La Nina) decaying summer when QBO is in its westerly (easterly) phase than in its easterly (westerly) phase. In addition, the 850 hPa anomalous high (low) in the northwestern Pacific is also stronger during an El Ni?o (La Nina) decaying summer when QBO is in its westerly (easterly) phase than in its easterly (westerly) phase. The Pacific subtropical high at 850hPa largely extends (shrinks) and South Asian High is located further eastward (westward) during an El Ni?o (La Nina) decaying summer when QBO is in its westerly (easterly) phase than in its easterly (westerly) phase.