选取前期9、6和3个月欧亚大陆地表温度、东北半球500 h Pa高度场、热带印度洋海表面温度和西太平洋海表面温度作为预报因子,使用变形的典型相关分析(BP-CCA)方法,并选取各因子预报效果最好的时期作为关键时期,建立起各因子和青藏高原冬...选取前期9、6和3个月欧亚大陆地表温度、东北半球500 h Pa高度场、热带印度洋海表面温度和西太平洋海表面温度作为预报因子,使用变形的典型相关分析(BP-CCA)方法,并选取各因子预报效果最好的时期作为关键时期,建立起各因子和青藏高原冬季气温之间的统计降尺度模型。之后用交叉验证和集合典型相关分析(ECC)方法评估模型实际预报能力。进一步用独立样本检验来评估模型更长时间尺度的年际变化预测效果。结果表明,BP-CCA方法能很好地识别出不同因子影响青藏高原的空间模态。其中,温度积雪反照率的正反馈机制体现了欧亚大陆地表温度的可预报性;东北半球500 h Pa高度场环流型不利于高纬的冷空气入侵高原地区;热带印度洋海表面温度反映出典型的印度洋偶极子对高原气温的调控作用;西太平洋海表面温度通过控制副热带高压的位置,从而影响高原冬季气温。各因子预报场和观测场的相关系数在交叉检验和独立样本检验中分别约为0.5和0.3,均有一定的预报技巧。而利用ECC方法能综合各因子所提供的预报信息,从而得出更为可信和稳定的预报。展开更多
Classical monsoon dynamics considers the winter/spring snow amount on the Tibetan Plateau(TP)as a major factor driving the East Asian summer monsoon(EASM)for its direct influence on the land-sea thermal contrast.Actua...Classical monsoon dynamics considers the winter/spring snow amount on the Tibetan Plateau(TP)as a major factor driving the East Asian summer monsoon(EASM)for its direct influence on the land-sea thermal contrast.Actually,the TP snow increased and decreased after the late 1970s and 1990s,respectively,accompanying the two major interdecadal changes in the EASM.Although studies have explored the possible mechanisms of the EASM interdecadal variations,and change in TP snow is considered as one of the major drivers,few studies have illustrated the underlying mechanisms of the interdecadal changes in the winter TP snow.This study reveals a tripole pattern of change,with decreased winter precipitation over the TP and an increase to its north and south after the late 1990s.Further analyses through numerical experiments demonstrate that the tropical Pacific SST changes in the late 1990s can robustly affect the winter TP precipitation through regulating the Walker and regional Hadley circulation.The cooling over the tropical central-eastern Pacific can enhance the Walker circulation cell over the Pacific and induce ascending motion anomalies over the Indo-Pacific region.These anomalies further drive descending motion anomalies over the TP and ascending motion anomalies to the north through regulating the regional Hadley circulation.Therefore,the positive-negative-positive winter precipitation anomalies around the TP are formed.This study improves the previously poor understanding of TP climate variation at interdecadal timescales.展开更多
Previous studies have revealed a significantly negative correlation between prior winter snow cover over the Tibetan Plateau （TPSC） and tropical cyclone genesis frequency （TCF） over the western North Pacific （WNP...Previous studies have revealed a significantly negative correlation between prior winter snow cover over the Tibetan Plateau （TPSC） and tropical cyclone genesis frequency （TCF） over the western North Pacific （WNP） in the following typhoon season. This study revisited this relationship based on long-term observational data. The results showed that the interannual correlation between TCF over the WNP and TPSC experienced a shift in the early 1990s. This correlation is significant during only 1993-2012 and is considerably weak during 1976-1992. The possible reasons causing the shift were examined further, and the results demonstrated that the central Pacific （CP） E1 Nifio-Southern Oscillation （ENSO） has played a vital role in intensifying the interannual relationship between TCF over the WNP and TPSC since the early 1990s. During 1993-2012, TPSC was negatively related to CP ENSO. When TPSC was higher than （lower than） normal, CP ENSO was often in its cold （warm） phase. Such a combination remarkably enhances the relationship of TPSC with the zonal land-sea thermal difference and thus with the summer monsoon over the WNE Additionally, it enhances the modulation of TPSC on the dynamical environments controlling TCF. As a result, the linkage between TPSC and TCF was significantly strengthened in this period. In sharp contrast, due to the weak relationship between TPSC and ENSO followed by the weak modulation of TPSC on the summer monsoon over the WNP and the dynamical environment during 1976-1992, the linkage between TPSC and TCF was weak during this time period. The results from additional dynamical diagnostic analyses further showed that during 1993-2012 CP ENSO modulated the barotropic energy conversion of zonal winds over the WNP, contributing to the intensified relationship between TPSC and TCF. These results will improve seasonal forecasting of tropical cyclone activity over the WNP.展开更多
文摘选取前期9、6和3个月欧亚大陆地表温度、东北半球500 h Pa高度场、热带印度洋海表面温度和西太平洋海表面温度作为预报因子,使用变形的典型相关分析(BP-CCA)方法,并选取各因子预报效果最好的时期作为关键时期,建立起各因子和青藏高原冬季气温之间的统计降尺度模型。之后用交叉验证和集合典型相关分析(ECC)方法评估模型实际预报能力。进一步用独立样本检验来评估模型更长时间尺度的年际变化预测效果。结果表明,BP-CCA方法能很好地识别出不同因子影响青藏高原的空间模态。其中,温度积雪反照率的正反馈机制体现了欧亚大陆地表温度的可预报性;东北半球500 h Pa高度场环流型不利于高纬的冷空气入侵高原地区;热带印度洋海表面温度反映出典型的印度洋偶极子对高原气温的调控作用;西太平洋海表面温度通过控制副热带高压的位置,从而影响高原冬季气温。各因子预报场和观测场的相关系数在交叉检验和独立样本检验中分别约为0.5和0.3,均有一定的预报技巧。而利用ECC方法能综合各因子所提供的预报信息,从而得出更为可信和稳定的预报。
基金This study was jointly supported by the Second Tibetan Plateau Scientific Expedition and Research(STEP)program[grant number 2019QZKK0102]the National Natural Science Foundation of China[grant numbers 41675083 and 41991281].
文摘Classical monsoon dynamics considers the winter/spring snow amount on the Tibetan Plateau(TP)as a major factor driving the East Asian summer monsoon(EASM)for its direct influence on the land-sea thermal contrast.Actually,the TP snow increased and decreased after the late 1970s and 1990s,respectively,accompanying the two major interdecadal changes in the EASM.Although studies have explored the possible mechanisms of the EASM interdecadal variations,and change in TP snow is considered as one of the major drivers,few studies have illustrated the underlying mechanisms of the interdecadal changes in the winter TP snow.This study reveals a tripole pattern of change,with decreased winter precipitation over the TP and an increase to its north and south after the late 1990s.Further analyses through numerical experiments demonstrate that the tropical Pacific SST changes in the late 1990s can robustly affect the winter TP precipitation through regulating the Walker and regional Hadley circulation.The cooling over the tropical central-eastern Pacific can enhance the Walker circulation cell over the Pacific and induce ascending motion anomalies over the Indo-Pacific region.These anomalies further drive descending motion anomalies over the TP and ascending motion anomalies to the north through regulating the regional Hadley circulation.Therefore,the positive-negative-positive winter precipitation anomalies around the TP are formed.This study improves the previously poor understanding of TP climate variation at interdecadal timescales.
基金supported by the China Meteorological Administration Special Public Welfare Research Fund(Grant No.GYHY201406001)National Key Basic Research Program of China(Grant No.2012CB956003)+1 种基金the National Natural Science Foundation of China(Grant No.41375093)supported in part by the Youth Elite Project of the CMA
文摘Previous studies have revealed a significantly negative correlation between prior winter snow cover over the Tibetan Plateau （TPSC） and tropical cyclone genesis frequency （TCF） over the western North Pacific （WNP） in the following typhoon season. This study revisited this relationship based on long-term observational data. The results showed that the interannual correlation between TCF over the WNP and TPSC experienced a shift in the early 1990s. This correlation is significant during only 1993-2012 and is considerably weak during 1976-1992. The possible reasons causing the shift were examined further, and the results demonstrated that the central Pacific （CP） E1 Nifio-Southern Oscillation （ENSO） has played a vital role in intensifying the interannual relationship between TCF over the WNP and TPSC since the early 1990s. During 1993-2012, TPSC was negatively related to CP ENSO. When TPSC was higher than （lower than） normal, CP ENSO was often in its cold （warm） phase. Such a combination remarkably enhances the relationship of TPSC with the zonal land-sea thermal difference and thus with the summer monsoon over the WNE Additionally, it enhances the modulation of TPSC on the dynamical environments controlling TCF. As a result, the linkage between TPSC and TCF was significantly strengthened in this period. In sharp contrast, due to the weak relationship between TPSC and ENSO followed by the weak modulation of TPSC on the summer monsoon over the WNP and the dynamical environment during 1976-1992, the linkage between TPSC and TCF was weak during this time period. The results from additional dynamical diagnostic analyses further showed that during 1993-2012 CP ENSO modulated the barotropic energy conversion of zonal winds over the WNP, contributing to the intensified relationship between TPSC and TCF. These results will improve seasonal forecasting of tropical cyclone activity over the WNP.
