Like the seasonal and interannual variations in length‐of‐day (LOD), variations on intraseasonal timescales (periods shorter than 183 days) are also predominantly caused by changes in the angular momentum of the zonal winds. But the smaller intraseasonal LOD excitations from atmospheric surface pressure, oceanic currents, and the ocean bottom pressure are less clear. Here sliding window average filtering is applied to isolate intraseasonal signals from both geodetically observed LOD excitation (shorten to geodetic excitation for convenience) and atmospheric and oceanic LOD excitations. Based on careful comparison between these two‐excitation series, we find that during 1993–2018, atmospheric winds reduce the RMS of observed intraseasonal LOD series from 276.1 to 55.6 μs with a correlation coefficient of 0.9795. Including the effect of surface pressure changes with that of the winds reduced the RMS from 55.6 to 43.3 μs, and increased the correlation coefficient with the observations from 0.9795 to 0.9884. Additionally, including the effects of changes in oceanic currents and bottom pressure further reduced the RMS from 43.3 to 33.9 μs, and further increased the correlation coefficient from 0.9884 to 0.9931. Thus, although the impact of oceans is relatively minor, closer agreement with the observations in the intraseasonal frequency band is obtained when the effects of oceanic processes are added to that of atmospheric. The RMS values and correlation coefficients of ESMGFZ and MPIOM residual series are better than NCEP and ECCO in every component, indicating that NCEP model set is generally poorer than ESMGFZ in the intraseasonal band.

中文翻译：

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日间大气和海洋激发的季节内变化

像日长（LOD）的季节性和年度际变化一样，季节内时间尺度（周期短于183天）的变化也主要是由纬向风角动量的变化引起的。但是，由大气表面压力，洋流和海底压力引起的较小的季节内LOD激发尚不清楚。在这里，应用滑动窗口平均滤波来从季节观测的LOD激发（为方便起见，简称为大地测量激发）以及大气和海洋LOD激发中分离季节内信号。基于这两个激励序列之间的仔细比较，我们发现在1993–2018年期间，大气风将观测到的季节内LOD序列的RMS从276.1降低到55.6μs，相关系数为0.9795。包括表面压力随风变化的影响在内，RMS值从55.6降低到43.3μs，相关系数从0.9795升高到0.9884。此外，包括洋流和海底压力变化的影响，均方根值从43.3降低到33.9μs，相关系数从0.9884进一步提高到0.9931。因此，尽管海洋的影响相对较小，但是当将海洋过程的影响加到大气的影响上时，就可以与季节内频带内的观测结果更加吻合。ESMGFZ和MPIOM残差序列的RMS值和相关系数在每个组件中均优于NCEP和ECCO，表明NCEP模型集通常在季节内范围内比ESMGFZ差。