The interdecadal variability of precipitation over sub-Saharan Africa (SSA) and central North China (CNC) is examined and compared in this study. Previous studies have found that the two regions have similar interdeca...The interdecadal variability of precipitation over sub-Saharan Africa (SSA) and central North China (CNC) is examined and compared in this study. Previous studies have found that the two regions have similar interdecadal dry–wet evolution in the past 100 years. The results show obvious decadal precipitation fluctuations in the two regions. In CNC, a persistent negative precipitation anomaly is detected from the early 1970s to the 2000s. In SSA, a negative precipitation anomaly is apparent since the late 1970s, while a distinct upward trend is found since the 1990s although the precipitation anomaly is still negative. Significant correlation is found between the decadal precipitation anomalies in SSA and the SST modes (Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO)), as well as the North Atlantic Oscillation (NAO), while in CNC the decadal precipitation is influenced by the NAO and PDO. The EOF results show that the total explained variance of the first four EOFs in SSA is smaller than that of CNC. The fourth and third modes in SSA are significantly associated with the AMO and PDO respectively, while the first, third, and fourth modes are significantly associated with the NAO. The first mode in CNC is significantly associated with the NAO. The first mode of the precipitation anomaly in SSA fluctuates out of phase with that in CNC, while in-phase changes are apparent among the third and the fourth modes.展开更多
LOCATED between easternSichuan Province and west-ern Hubel Province,theThree Gorges of the Yangtze River—the Qutang,Wu and Xilinggorges-are known for their dan-gerous shoals and rapids and theirmagnificent scenery an...LOCATED between easternSichuan Province and west-ern Hubel Province,theThree Gorges of the Yangtze River—the Qutang,Wu and Xilinggorges-are known for their dan-gerous shoals and rapids and theirmagnificent scenery and rich folk-lore.Qutang. the first gorge,startsfrom Baidi Hill in Fengjie County,Sichuan Province.Baidi Hill is sur-rounded on three sides by water.South and north of the hill,MountChijia and Mount Baiyan riseabruptly out of the water.Themighty Yangtze River rolls rapidlyeastward along the narrow gorge.In the past there was a large rocknamed Yanyudui(Yingyushi in an-clent times)submerged at the mouthof Qutang Gorge.A folk song goes:“The Yingyu Rock is as big as aturtle and is a challenge to naviga-tors.”In 1958,the rock was re-moved,opening the waterway tosmooth navigation.The toweringcliffs on both sides of the river hidethe sun,filling tourists with awe andwonder.展开更多
A new analog error correction （AEC） scheme based on the moving North Pacific index （MNPI） is designed in this study. This scheme shows obvious improvement in the prediction skill of the operational coupled general...A new analog error correction （AEC） scheme based on the moving North Pacific index （MNPI） is designed in this study. This scheme shows obvious improvement in the prediction skill of the operational coupled general circulation model （CGCM） of the National Climate Center of China for the rainy season rainfall （RSR） anomaly pattern correlation coefficient （ACC） over the mid-to-lower reaches of the Yangtze River （MLRYR）. A comparative analysis indicates that the effectiveness of the new scheme using the MNPI is better than the system error correction scheme using the North Pacific index （NPI）. A Euclidean distance- weighted mean rather than a traditional arithmetic mean, is applied to the integration of the analog year＇s prediction error fields. By using the MNPI AEC scheme, independent sample hindcasts of RSR during the period 2003-2009 are then evaluated. The results show that the new scheme exhibited a higher forecast skill during 2003-2009, with an average ACC of 0.47; while the ACC for the NPI case was only 0.19. Furthermore, the forecast skill of the RSR over the MLRYR is examined. In the MNPI case, empirical orthogonal function （EOF） was used in the degree compression of the prediction error fields from the CCCM, whereas the AEC scheme was applied only to its first several EOF components for which the accumulative explained variance accounted for 80% of the total variance. This further improved the ACC of the independent sample hindcasts to 0.55 during the 7-yr period.展开更多
为了减小噪声对光纤陀螺(FOG)寻北的影响,提高寻北精度,提出了将粒子滤波这种非线性滤波方法应用于光纤陀螺四位置寻北的方案。根据四位置寻北模型建立光纤陀螺寻北系统的非线性状态空间模型,将基于系统重采样和在重采样后引入马尔可夫...为了减小噪声对光纤陀螺(FOG)寻北的影响,提高寻北精度,提出了将粒子滤波这种非线性滤波方法应用于光纤陀螺四位置寻北的方案。根据四位置寻北模型建立光纤陀螺寻北系统的非线性状态空间模型,将基于系统重采样和在重采样后引入马尔可夫链蒙特卡罗(Markov chain monte carlo,MCMC)移动的粒子滤波器分别应用于光纤陀螺寻北系统的非线性滤波。使用一个零偏稳定性为0.05°/h的闭环光纤陀螺进行实验,实验结果表明,这2种粒子滤波器均能够有效地提高光纤陀螺的寻北精度。基于系统重采样的粒子滤波器有随时间发散的趋势,这是由于在选定粒子数目较少的情况下,重采样导致粒子多样性丧失的结果;而在重采样后引入MCMC移动的粒子滤波器有很好的收敛性能。重复实验结果表明,使用基于MCMC移动的粒子滤波器可以达到更好的寻北性能。展开更多
基金the Chinese Academy of SciencesThe World Academy of Sciences(CAS-TWAS)for financial support+1 种基金provided by the National Key R&D Program of China [grant number 2016YFA0600404]the National Natural Science Foundation of China [grant number41530532]
文摘The interdecadal variability of precipitation over sub-Saharan Africa (SSA) and central North China (CNC) is examined and compared in this study. Previous studies have found that the two regions have similar interdecadal dry–wet evolution in the past 100 years. The results show obvious decadal precipitation fluctuations in the two regions. In CNC, a persistent negative precipitation anomaly is detected from the early 1970s to the 2000s. In SSA, a negative precipitation anomaly is apparent since the late 1970s, while a distinct upward trend is found since the 1990s although the precipitation anomaly is still negative. Significant correlation is found between the decadal precipitation anomalies in SSA and the SST modes (Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO)), as well as the North Atlantic Oscillation (NAO), while in CNC the decadal precipitation is influenced by the NAO and PDO. The EOF results show that the total explained variance of the first four EOFs in SSA is smaller than that of CNC. The fourth and third modes in SSA are significantly associated with the AMO and PDO respectively, while the first, third, and fourth modes are significantly associated with the NAO. The first mode in CNC is significantly associated with the NAO. The first mode of the precipitation anomaly in SSA fluctuates out of phase with that in CNC, while in-phase changes are apparent among the third and the fourth modes.
文摘LOCATED between easternSichuan Province and west-ern Hubel Province,theThree Gorges of the Yangtze River—the Qutang,Wu and Xilinggorges-are known for their dan-gerous shoals and rapids and theirmagnificent scenery and rich folk-lore.Qutang. the first gorge,startsfrom Baidi Hill in Fengjie County,Sichuan Province.Baidi Hill is sur-rounded on three sides by water.South and north of the hill,MountChijia and Mount Baiyan riseabruptly out of the water.Themighty Yangtze River rolls rapidlyeastward along the narrow gorge.In the past there was a large rocknamed Yanyudui(Yingyushi in an-clent times)submerged at the mouthof Qutang Gorge.A folk song goes:“The Yingyu Rock is as big as aturtle and is a challenge to naviga-tors.”In 1958,the rock was re-moved,opening the waterway tosmooth navigation.The toweringcliffs on both sides of the river hidethe sun,filling tourists with awe andwonder.
基金Supported by the National(Key)Basic Research and Development(973)Program of China(2013CB430204)National Natural Science Foundation of China(41305100 and 41105055)China Meteorological Administration Special Public Welfare Research Fund(GYHY201306021)
文摘A new analog error correction （AEC） scheme based on the moving North Pacific index （MNPI） is designed in this study. This scheme shows obvious improvement in the prediction skill of the operational coupled general circulation model （CGCM） of the National Climate Center of China for the rainy season rainfall （RSR） anomaly pattern correlation coefficient （ACC） over the mid-to-lower reaches of the Yangtze River （MLRYR）. A comparative analysis indicates that the effectiveness of the new scheme using the MNPI is better than the system error correction scheme using the North Pacific index （NPI）. A Euclidean distance- weighted mean rather than a traditional arithmetic mean, is applied to the integration of the analog year＇s prediction error fields. By using the MNPI AEC scheme, independent sample hindcasts of RSR during the period 2003-2009 are then evaluated. The results show that the new scheme exhibited a higher forecast skill during 2003-2009, with an average ACC of 0.47; while the ACC for the NPI case was only 0.19. Furthermore, the forecast skill of the RSR over the MLRYR is examined. In the MNPI case, empirical orthogonal function （EOF） was used in the degree compression of the prediction error fields from the CCCM, whereas the AEC scheme was applied only to its first several EOF components for which the accumulative explained variance accounted for 80% of the total variance. This further improved the ACC of the independent sample hindcasts to 0.55 during the 7-yr period.
文摘为了减小噪声对光纤陀螺(FOG)寻北的影响,提高寻北精度,提出了将粒子滤波这种非线性滤波方法应用于光纤陀螺四位置寻北的方案。根据四位置寻北模型建立光纤陀螺寻北系统的非线性状态空间模型,将基于系统重采样和在重采样后引入马尔可夫链蒙特卡罗(Markov chain monte carlo,MCMC)移动的粒子滤波器分别应用于光纤陀螺寻北系统的非线性滤波。使用一个零偏稳定性为0.05°/h的闭环光纤陀螺进行实验,实验结果表明,这2种粒子滤波器均能够有效地提高光纤陀螺的寻北精度。基于系统重采样的粒子滤波器有随时间发散的趋势,这是由于在选定粒子数目较少的情况下,重采样导致粒子多样性丧失的结果;而在重采样后引入MCMC移动的粒子滤波器有很好的收敛性能。重复实验结果表明,使用基于MCMC移动的粒子滤波器可以达到更好的寻北性能。
