风对Chandler摆动激发贡献的比较

Comparison of Wind Contributions to Chandler Wobble Excitation

应用日本气象厅(JMA)最近发表的以美国大气与环境预测中心(NCEP)修正前、后的reanalysis数据计算出的全球和南、北半球风角动量资料,估计了风对Chandler摆动的平均激发能量,以及风的激发与观测激发之间的相干系数和相干相位．结果表明, 1980-1993(1980-2003)年期间,全球对流层风和(对流层+平流层)风对Chandler摆动的激发能量可分别解释观测激发的68％和72％(58％和51％),对流层风起着主导作用;它们与观测激发的相干系数分别达到0．49和0．32(0．50和0．39),而且具有接近于零的相干相位．这些结果充分说明风在Chandler摆动激发中的重要作用．分析结果也展示了分别应用NCEP修正前,后的reanalysis数据、从实际表面和海平面开始积分的风角动量对Chandler摆动激发的不同影响．

This study estimates the mean energies of the observed Chandler wobble （CW） excitation, various wind excitations, the mean coherent coefficients and phases between them by using methods of the FFT and multitaper coherent analysis and data of the space2003 polar motion series and various wind angular momenta for 1980-1993 and 1980-2003, respectively. The various wind momenta were calculated recently by integral from the real surface or mean sea level （1000 hPa） to the model height （100 hPa or 10 hPa） by using the modified or unmodified reanalysis data of the National Center for Environmental Prediction （NCEP） by Japan Meteorological Agency （JMA）. The results show that the mean excitation energies of the global tropospheric wind （integral from the real surface to 100 hPa） and tropospheric ＋ stratospheric wind （integral from the real surface to 10 hPa） can explain about 68% and 72% （58% and 51%） of the observed CW excitation for 1980-1993 （1980-2003） respectively, with dominant contributions from the tropospheric winds. And the squared coherence between these wind excitations and the observed CW excitation are 0.49 and 0.32 （0.50 and 0.39） respectively, with approximate zero coherent phases. It reveals the important role of the wind contribution in CW excitation. This study also shows the different effects of various wind angular momenta calculated by integral from different layers and model heights, and by using the modified or unmodified reanalysis data of the NCEP on the estimates of the CW excitation. Detailed results of the mean energies, squared coherence and coherent phases of the various wind excitations in Chandler band （0.8-0.9 cpy） are listed in table 1. As an example, the power spectral density （a） of the various wind excitations and observed CW excitation, squared coherence （b） and coherent phases （c） are shown in Fig. 1 for 1980-2003. Also shown in Fig. 2 are the temporal variations of the mean energies, squared coherence and coherent phases in Chandler band which are calculated by using 12-year sliding window with a 3-month step forward.