Tropical Rainfall Variability Accompanying Global Normal Mode Oscillations
Tropical Rainfall Variability Accompanying Global Normal Mode Oscillations
复制标题
伴随全球正模振荡的热带降雨变化
DOI：
10.1175/jas-d-20-0288.1
复制
发表时间：
2021
影响因子：
3.1
通讯作者：
T.
中科院分区：
文献类型：
--
作者：
Sakazaki;T.
使用全球降水数据集（GSMaP，TRMM）和最新的再分析数据（ERA5），我们进行了一个全面的分析，伴随着全球尺度，低频正常模式的热带降雨变率：罗斯比，罗斯比重力，开尔文模式。交叉谱分析和滞后回归分析都表明，相干降水变化不仅伴随着波数为1的最严重的Rossby模态（“5天”波），但其他低频模态。正常模式降雨量的变化在亚马逊盆地等地区得到增强，但也包括在公海上具有相当大幅度的环球旅行结构。这些结果在包括ERA5降雨数据在内的三个数据集之间具有显著的一致性。环全球降水信号主要是对正态模动力变化的响应。我们发现，降雨和动力场变率之间的相位关系强烈依赖于模态的类型，甚至对纬向波数。我们认为，这是由两个基本过程的相对重要性的差异：1）水分通量的收敛和2）与绝热冷却相关的降水增强。我们确定的降雨信号是响应准单色，周期性波，有一个简单的垂直结构，代表对流层波降雨耦合的一个特殊情况。12小时的降雨振荡被认为是被迫由大气潮汐的机制的影响也被考虑。
Using global precipitation datasets (GSMaP, TRMM) and the latest reanalysis data (ERA5), we performed a comprehensive analysis of the tropical rainfall variability that accompanies global-scale, low-frequency normal modes: Rossby, Rossby–gravity, and Kelvin modes. Cross-spectral analysis and lag-regression analysis both showed that coherent rainfall variations accompany not only the wavenumber-1 gravest Rossby mode (“5-day” wave) but other low-frequency modes. The normal mode rainfall variations are enhanced in regions such as the Amazon basin, but also include circumglobally traveling structures with substantial amplitude over the open ocean. These results are remarkably consistent among the three datasets including even ERA5 rainfall data. The circumglobal rainfall signals may be considered primarily as a response to the normal mode dynamical variations. We found that the phase relationship between rainfall and dynamical field variability is strongly dependent on the type of mode and even on the zonal wavenumber. We suggest that this is explained by the difference in relative importance of two underlying processes: 1) moisture-flux convergence and 2) rainfall enhancement associated with adiabatic cooling. Our determined rainfall signals are the response to quasi-monochromatic, periodic waves that have a simple vertical structure and represent one special case of tropospheric wave–rainfall coupling. Implications for the mechanism of 12-h rainfall oscillations believed to be forced by the atmospheric tide are also considered.