Recalde-Coronel G Cristina, Zaitchik Benjamin, Pan William K
Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA.
Facultad de Ingeniería Marítima y Ciencias del Mar, Escuela Superior Politécnica del Litoral, Guayaquil, Ecuador.
Clim Dyn. 2020 Feb;54(3-4):2167-2185. doi: 10.1007/s00382-019-05107-2. Epub 2020 Jan 24.
The Madden-Julian Oscillation (MJO) is the leading driver of intraseasonal rainfall variability in the global tropics. However, the influence of MJO on western tropical South America (WTSA) has not been a focus of research. This is not surprising since the MJO convective core becomes nondescript as it propagates across the eastern Pacific, such that its influence on the Pacific coast of tropical South America is not obvious in global analyses. In this study, we examine MJO impacts on subseasonal rainfall variability in the rainiest season for WTSA (February-April). In order to avoid confusion with El Niño Southern Oscillation (ENSO) signals, only ENSO-neutral years are included in the analysis. We found that the MJO convective core reemerges when it propagates onto land in WTSA, and that it is associated with subseasonal precipitation anomalies of 20-50% relative to climatology. The MJO signal is evident in the Real-Time Multivariate MJO (RMM) index; however, the signal is clearer when a custom subseasonal index for the region based on WTSA outgoing longwave radiation is employed. Dynamically, the MJO influence is consistent with a modulation of the Pacific Ocean Walker Circulation descending branch, which is climatologically located in or near WTSA. Furthermore, MJO drives zonal and vertical motions on moisture and wind fields that influence precipitation in the region. We found that the timing of deep convection on subseasonal timescales captured by the regional index is consistent with a dominant role of the MJO convective core, rather than propagation of equatorial Rossby or Kelvin waves. However, there is evidence that equatorial Rossby waves that emerge over the tropical Atlantic Ocean also influence precipitation in WTSA on MJO timescales.
马登-朱利安振荡（MJO）是全球热带地区季节内降雨变化的主要驱动因素。然而，MJO对热带南美洲西部（WTSA）的影响尚未成为研究重点。这并不奇怪，因为MJO对流核心在穿越东太平洋时变得难以描述，以至于在全球分析中其对热带南美洲太平洋沿岸的影响并不明显。在本研究中，我们考察了MJO对WTSA最雨季（2月至4月）次季节降雨变化的影响。为避免与厄尔尼诺-南方涛动（ENSO）信号混淆，分析中仅纳入ENSO中性年。我们发现，MJO对流核心在传播到WTSA陆地时重新出现，并且它与相对于气候学而言20%-50%的次季节降水异常有关。MJO信号在实时多变量MJO（RMM）指数中很明显；然而，当采用基于WTSA向外长波辐射的该区域自定义次季节指数时，信号更清晰。从动力学角度来看，MJO的影响与太平洋沃克环流下沉支的调制一致，该下沉支在气候学上位于WTSA或其附近。此外，MJO驱动了影响该区域降水的水汽和风场上的纬向和垂直运动。我们发现，区域指数所捕捉到的次季节时间尺度上深对流的时间与MJO对流核心的主导作用一致，而不是赤道罗斯贝波或开尔文波的传播。然而，有证据表明，在热带大西洋上空出现的赤道罗斯贝波也在MJO时间尺度上影响WTSA的降水。
