Why does convection weaken over Sumatra Island in an active phase of the MJO?
Why does convection weaken over Sumatra Island in an active phase of the MJO?
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DOI：
10.1175/mwr-d-21-0251.1
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发表时间：
2022-01
影响因子：
3.2
通讯作者：
N. Zhao;P. Wu;S. Yokoi;Miki Hattori
中科院分区：
文献类型：
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作者：
N. Zhao;P. Wu;S. Yokoi;Miki Hattori
这项研究基于现场和卫星观测以及对流，研究了2015年12月海洋大陆（YMC）前期观测活动期间苏门答腊岛上马登-朱利安振荡（MJO）活跃阶段的对流日循环。允许对流的数值模型。观测表明，在12月初的MJO活跃阶段之前，岛上的对流在下午和午夜频繁发生。相比之下，在12月中旬MJO的活跃阶段，岛上的下午对流被推迟和抑制，午夜对流被抑制。数值实验也成功地复制了所观察到的调制的主要特征。一般来说，在MJO活跃阶段，对流层变得干燥的苏门答腊地区。当云层减少了陆地上的太阳辐射时，海风也被延迟和减弱。因此，下午对流的启动被推迟和减弱。进一步的分析表明，海风减弱主要是由于地形的滞止效应，而不是海陆温度对比度的轻微降低。另一方面，层砧云的增多导致对流层中层蒸发冷却异常，并在夜间产生岛屿尺度下沉，最终导致内陆对流的抑制。总的来说，我们的研究揭示了调制的周日对流在苏门答腊岛的活跃阶段的MJO，也显示了潜在的作用，陆-海相互作用对流的启动和维持。
This study investigated the diurnal cycle of convection over Sumatra Island in an active phase of the Madden-Julian Oscillation (MJO) during the Pre-Years of the Maritime Continent (YMC) observation campaign in December 2015 based on in-situ and satellite observations and a convection-permitting numerical model. Observations suggest that before the active phase of the MJO in early December, convection occurred frequently over the island during the afternoon and at midnight. By contrast, during the active phase of the MJO in mid-December, afternoon convection over the island was delayed and suppressed, and midnight convection was suppressed. Numerical experiments also successfully replicated the main features of the observed modulations. In general, during the active phase of the MJO, the troposphere became drier in the Sumatra region. While the clouds reduced the solar radiation over the land, the sea breeze was also found to be delayed and weakened. As a result, the afternoon convection initiation was delayed and weakened. Further analyses suggested that the sea breeze was weakened mainly due to the orographic stagnation effect rather than the slightly reduced land-sea temperature contrast. On the other hand, the increased stratiform-anvil clouds induced the anomalous evaporative cooling in the mid-troposphere and generated island-scale subsidence during the nighttime, which finally led to the suppression of inland convection. Overall, our study reveals the modulation of diurnal convection over Sumatra Island by an active phase of the MJO and also shows the potential role of land-sea interaction in convection initiation and maintenance.