A distinctive feature of the Southern Hemisphere extratropical atmospheric circulation is the quasi-stationary zonal wave 3 pattern. This pattern is present in both the mean atmospheric circulation and its variability on daily, seasonal and interannual timescales. While the zonal wave 3 pattern has substantial impacts on meridional heat transport and Antarctic sea ice extent, the reason for its existence remains uncertain, although it has long been assumed to be linked to the presence of three major landmasses in the Southern Hemisphere extratropics. Here we use an atmospheric general circulation model to show that the stationary zonal wave 3 pattern is instead driven by zonally asymmetric deep convection in the tropics, with little influence from extratropical orography or landmasses. Localized regions of deep convection in the tropics form a local Hadley cell, which in turn creates a wave source in the subtropics that excites a poleward- and eastward-propagating wave train, forming quasi-stationary waves in the Southern Hemisphere high latitudes. Our findings suggest that changes in tropical deep convection, either due to natural variability or climate change, fundamentally control the zonal wave 3 pattern, with implications for southern high-latitude climate, ocean circulation and sea ice.

南半球温带大气环流的一个显着特征是准静止的纬向波 3 模式。这种模式存在于平均大气环流及其在每日、季节和年际时间尺度上的变化中。虽然纬向波 3 模式对经向热传输和南极海冰范围有重大影响，但其存在的原因仍然不确定，尽管长期以来一直认为它与南半球温带地区三个主要陆地的存在有关。在这里，我们使用大气环流模型表明，稳定的纬向波 3 模式是由热带地区的纬向不对称深对流驱动的，几乎不受温带地形或陆地的影响。热带深对流局部区域形成局部哈德利单元，进而在亚热带产生波源，激发向极和向东传播的波列，在南半球高纬度形成准静止波。我们的研究结果表明，由于自然变率或气候变化，热带深对流的变化从根本上控制了纬向波 3 模式，对南部高纬度气候、海洋环流和海冰具有影响。