天文学进展2017，Vol.35Issue(4)：448-461,14.DOI:10.3969/j.issn.1000-8349.2017.04.05
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
摘要
Abstract
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 inter-national 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 of 1979—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 (E AE F and N AE F ) with the observed LOD change. Considering that the top layers of the ECMWF and NCEP/NCAR wind fields extend to 1 hPa and 10 hPa respectively, the N AEF wind term is computed by integrating from the Earth's surface to 10 hPa, while the E AE F wind terms are integrated from the Earth's surface to 10 hPa and 1 hPa 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 and 4～20 d high-frequency timescales, about 88％ and 45％ of the observed LOD changes could be explained by the atmospheric excitation respectively. On interannual timescales, the explanation by the atmosphere is about 65％. When compared with the N AEF , the EAEF explains 2％～3％more of the LOD changes. The upper level wind field of 1～10 hPa has little effect on the sub-seasonal 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 lately 2015—2016 El 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Key words
change of length of day/atmospheric excitation/SOI分类
天文与地球科学引用本文复制引用
师思,周永宏,许雪晴..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[J].天文学进展,2017,35(4):448-461,14.基金项目
国家自然科学基金(11373057,11773057,11673049,U1531128) （11373057,11773057,11673049,U1531128）
上海市科学技术委员会资助课题(06DZ22101) （06DZ22101）
