Effect of vertical overturning circulation scale and moist static energy tendency on MJO phase speed

Abstract

The combined effects of vertical overturning circulation (VOC) zonal length scale and moist static energy (MSE) tendency zonal asymmetry on MJO phase speed were investigated based on diagnosis of ERA-Interim data over a 40-year period (1979–2019). In a key region (80°–100°E), 128 MJO events were selected. It was found that the larger the VOC zonal length scale, the faster the MJO eastward propagation. The correlation coefficient between them was 0.52, exceeding the 99% confidence level. A significant positive correlation (0.59) was also identified between the phase speed and MSE tendency zonal asymmetry. A linear regression model based on the aforementioned two parameters was constructed, and the phase speed could be estimated based on the model. The correlation coefficient between the reconstructed phase speed and its observed counterpart was 0.73, exceeding the 99% confidence level with an F-test. A composite analysis of the fast and slow groups indicated that the VOC zonal length scale was modulated by the background state. An El Niño (La Niña)-like SST pattern and associated precipitation anomalies promoted a larger (smaller) VOC zonal length scale and thus a faster (slower) propagation speed. A sensitivity test with a reference point in a different longitudinal zone (120°–140°E) was conducted. Again, there were significant relationships between the MJO phase speed and the two parameters. The correlation between the reconstructed and observed phase speed was 0.67, exceeding the 99% confidence level.摘要本文通过对1979–2019年ERA-I再分析资料进行诊断分析, 研究了MJO垂直环流 (VOC) 纬向尺度和湿静力能 (MSE) 趋势纬向不对称性对MJO传播速度的综合影响. 研究结果表明, MJO传播速度与VOC的纬向尺度和MSE趋势纬向梯度之间存在显著的正相关关系. 基于上述两个参数, 本文建立了线性回归模型, 该模型可以较好的估计MJO的传播速度. 本文对上述结果在不同的地理区域 (120°–140°E) 进行了敏感性测试. MJO传播速度仍然与这两个参数之间有显著的正相关关系.