1979—2016年间日长变化在年际、季节性、亚季节性及高频尺度上的大气激发  

Atmospheric Excitation of the Variation of Length of Day on Interannual,Seasonal,Sub-seasonal and High-frequency Timescales,1979—2016

作　　者：师思 周永宏[1,2,3] 许雪晴 SHI Si;ZHOU Yong-hong;XU Xue-qing(Key Laboratory of Planetary Sciences, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China;University of Chinese Academy of Sciences, Beijing 100049, China;Shanghai Key Laboratory of Space Navigation and Positioning Techniques, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030, China)

机构地区：[1]中国科学院上海天文台行星科学重点实验室,上海200030 [2]中国科学院大学,北京100049 [3]上海市空间导航与定位技术重点实验室,上海200030

出　　处：《天文学进展》2017年第4期448-461,共14页Progress In Astronomy

基　　金：国家自然科学基金(11373057;11773057;11673049;U1531128);上海市科学技术委员会资助课题(06DZ22101)

摘　　要：大气是日长变化最重要的激发源。基于欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)和美国环境预报中心/美国大气研究中心(National Centers for Environmental Prediction/National Center for Atmospheric Research,NCEP/NCAR)1979—2016年再分析气象数据集,计算大气激发函数(EAEF和NAEF),并与日长变化的观测值进行对比,综合分析大气对日长变化在年际、季节性、亚季节性和高频时间尺度上的激发贡献。鉴于ECMWF和NCEP/NCAR的风场顶层分别到达1 hPa和10 hPa,对NAEF计算地面-10 hPa风项,对EAEF分别计算地面-10 hPa和-1 hPa风项,以方便对比。研究结果表明,大气风项是日长变化在年际、季节性、亚季节性以及高频尺度上最主要的激发源。在季节性尺度上,EAEF和NAEF与日长变化观测值比较接近,但它们三者之间仍存在一定的差异。在亚季节性和4～20 d高频尺度上,大气激发分别可解释约88%和45%的日长变化。在年际尺度上,大气激发可以解释约65%的日长变化。EAEF对日长变化的解释率比NAEF高出2%～3%。1～10 hPa高层风场对日长的亚季节性及高频变化几乎无贡献,但对日长年际和季节性变化会产生影响。此外,还分析年际尺度上的日长变化和大气激发与南方涛动指数的相关性,揭示出2015—2016年厄尔尼诺事件在日长变化和大气激发中的信号。The atmosphere is the most important excitation source of the length of day(LOD)variation.We calculated the atmospheric excitation functions(wind term and pressure term)using meteorological reanalysis data sets(wind field and pressure field)from two international institutions,the European Centre for Medium-Range Weather Forecasts(ECMWF)and the National Centers for Environmental Prediction/National Center for Atmospheric Research(NCEP/NCAR)during the period of1979-2016.The contribution of atmospheric excitation to the interannual,annual,seasonal,intraseasonal and high-frequency LOD changes are comprehensively investigated,by comparing the atmospheric excitation functions(EAEF and NAEF)with the observed LOD change.Considering that the top layers of the ECMWF and NCEP/NCAR wind fields extend to1hPa and10hPa respectively,the NAEF wind term is computed by integrating from the Earth’s surface to10hPa,while the EAEF wind terms are integrated from the Earth’s surface to10hPa and1hPa separately.The atmospheric wind is shown to be the most effective process exciting the LOD change on interannual,seasonal,sub-seasonal and high-frequency timescales.On sub-seasonal and420d highfrequency timescales,about88%and45%of the observed LOD changes could be explained by the atmospheric excitation respectively.On interannual timescales,the explanation by the atmosphere is about65%.When compared with the NAEF,the EAEF explains2%~3%more of the LOD changes.The upper level wind field of1~10hPa has little effect on the subseasonal and high-frequency LOD changes,but contributes to the seasonal and interannual LOD variations.Moreover,we also investigate the correlations among the interannual LOD variation,atmospheric excitation,and southern oscillation index(SOI),and further reveals the lately2015-2016El Nino signal in the interannual LOD and atmospheric excitations.

关 键 词：日长变化 大气激发 南方涛动指数 

分 类 号：P183.3[天文地球—天文学]