Yang Young-Min, Lee June-Yi, Wang Bin
Key Laboratory of Meteorological Disaster of Ministry of Education and Earth System Modeling Center, Nanjing University of Information Science and Technology, Nanjing, China.
Department of Atmospheric Sciences and International Pacific Research Center, University of Hawaii, Honolulu, Hawaii, 96822, USA.
Sci Rep. 2019 Oct 29;9(1):15478. doi: 10.1038/s41598-019-51461-w.
The Tibetan Plateau (TP) and Himalayas have been treated as an essential external factor in shaping Asian monsoon and mid-latitude atmospheric circulation. In this study we perform numerical experiments with different uplift altitudes using the Nanjing University of Information Science and Technology Earth System Model to examine potential impacts of uplift of the TP and Himalayas on eastward propagation of the MJO and the associated mechanisms. Analysis of experimental results with dynamics-based MJO diagnostics indicates two potential mechanisms. First, the uplift considerably enhances low-level mean westerlies in the Indian Ocean and convection in the Maritime Continent, which in turn strengthens boundary layer moisture convergence (BLMC) to the east of the MJO convective center. The increased BLMC reinforces upward transport of moisture and heat from BL to free atmosphere and increases lower tropospheric diabatic heating by shallow and congestus clouds ahead of the MJO center, enhancing the Kelvin-Rossby wave feedback. Second, the uplift increases upper tropospheric mean easterlies and stratiform heating at the west of the MJO center, which contributes to eastward propagation of MJO by generating positive moist static energy at the east of MJO center. This study will contribute to a better understanding of the origin of the MJO and improvement in simulation of MJO propagation.
青藏高原（TP）和喜马拉雅山脉被视为塑造亚洲季风和中纬度大气环流的一个重要外部因素。在本研究中，我们使用南京信息工程大学地球系统模型进行了不同隆升高度的数值试验，以检验青藏高原和喜马拉雅山脉隆升对MJO向东传播的潜在影响及其相关机制。基于动力学的MJO诊断对实验结果的分析表明了两种潜在机制。第一，隆升显著增强了印度洋低空平均西风和海洋大陆的对流，进而加强了MJO对流中心以东的边界层水汽辐合（BLMC）。增加的BLMC加强了从边界层到自由大气的水汽和热量向上输送，并增加了MJO中心前方浅薄云和积云性对流云造成的对流层低层非绝热加热，增强了开尔文 - 罗斯贝波反馈。第二，隆升增加了MJO中心西侧对流层上层平均东风和层状云加热，通过在MJO中心东侧产生正湿静能量，促进了MJO向东传播。本研究将有助于更好地理解MJO的起源，并改进MJO传播的模拟。
