Savarin Ajda, Chen Shuyi S
Department of Atmospheric Sciences University of Washington Seattle WA USA.
J Adv Model Earth Syst. 2022 Jun;14(6):e2021MS002929. doi: 10.1029/2021MS002929. Epub 2022 Jun 24.
This study investigates effects of atmosphere-ocean coupling on MJO precipitation and eastward propagation, and upper ocean conditions during and after MJO passage. To explore pathways for improving MJO prediction, three model experiments are conducted using the Unified Wave Interface-Coupled Model at convection-permitting (4 km) resolution: (a) uncoupled atmosphere-only, (b) coupled atmosphere-ocean, and (c) coupled atmosphere-ocean with improved air-sea flux algorithm simulations. The model simulations are compared with observations from the DYNAMO field campaign in 2011. Both coupled atmosphere-ocean simulations produced eastward propagation of the MJO where the uncoupled, atmosphere-only simulation did not. The uncoupled model overestimates both precipitation and surface winds associated with the MJO, while coupled model simulations substantially reduce model bias. Improved air-sea fluxes lead to systematic improvements in precipitation, winds, sea surface temperature, and the ocean mixed layer when compared to the original coupled simulation. This leads to further improvement of the MJO's eastward propagation speed compared with observations. Despite these improvements, the regional coupled simulations still have difficulty representing the extent of convectively suppressed conditions in the Indian Ocean after MJO passage, which indicates the importance of the large-scale environment from lateral boundary conditions. Coupled model simulations also reveal some issues in the representation of upper ocean stratification in the ocean model, especially errors in salinity, which result in overestimation of the mixed layer depth after MJO passage.
本研究调查了大气 - 海洋耦合对大气季节内振荡（MJO）降水和向东传播的影响，以及MJO通过期间和之后的上层海洋状况。为了探索改进MJO预测的途径，使用对流允许（4公里）分辨率的统一波界面耦合模型进行了三个模型实验：（a）仅大气的非耦合实验，（b）大气 - 海洋耦合实验，以及（c）具有改进海气通量算法模拟的大气 - 海洋耦合实验。将模型模拟结果与2011年动态季风实验（DYNAMO）实地考察的观测结果进行了比较。两个大气 - 海洋耦合模拟都产生了MJO的向东传播，而仅大气的非耦合模拟则没有。非耦合模型高估了与MJO相关的降水和地表风，而耦合模型模拟则大幅减少了模型偏差。与原始耦合模拟相比，改进的海气通量在降水、风、海表面温度和海洋混合层方面带来了系统性的改善。这导致与观测相比，MJO向东传播速度进一步提高。尽管有这些改进，但区域耦合模拟在表示MJO通过后印度洋对流抑制状况的范围方面仍有困难，这表明来自侧向边界条件的大尺度环境的重要性。耦合模型模拟还揭示了海洋模型中上层海洋分层表示方面的一些问题，特别是盐度误差，这导致MJO通过后混合层深度的高估。
