Intraseasonal Extratropical Precursors to the Indian Ocean Madden-Julian Oscillation (MJO) Proximate to Africa

麦登-朱利安涛动（MJO）是在印度洋上空形成的一个由云和降水组成的大包层，并缓慢向东传播到赤道太平洋中部。它影响全球的天气状况，包括加利福尼亚的大气河流和洪水以及墨西哥湾的飓风形成。一些MJO事件似乎是独立形成的，并被指定为“主要”事件。其他“次要”事件似乎是由对流层上层的波浪扰动引发的，这些扰动从北半球和南半球的亚热带地区向西传播到印度洋。上游波浪扰动对MJO事件的触发已经有了很好的记录，但波浪诱发MJO事件的过程尚不清楚，本项目旨在更好地理解它们。PI的初步工作表明，前驱波并不是快速移动的触发因素，不是冲动地启动MJO，而是在季节内时间尺度上缓慢传播的罗斯比波。一种可能性是，一次较早的MJO事件可以促进二次MJO事件，它在赤道太平洋中部产生罗斯比波，这些波向东传播并向高纬度地区传播，然后返回热带，到达赤道印度洋上空，诱发随后的MJO。该项目将重点放在非洲，因为前驱波是从非洲亚热带进入印度洋的。各种统计方法被用于探测和表征从卫星观测数据以及再分析产品中识别的前驱波。然后利用水分和动量收支来了解这些波是如何促成二次MJO事件的形成的。由于与MJO相关的各种天气影响，这项工作具有更广泛的社会影响。对MJO事件传播的预测是有技巧的，但是对MJO事件开始的预测可以使MJO影响的预测提前更长的时间。由于该项目侧重于非洲的前兆气象，该项目也可能有助于了解和预测非洲的天气。此外，该项目还为两名研究生提供支持和培训，从而为该研究领域建立未来的劳动力。

The Madden-Julian Oscillation (MJO) is a large envelope of clouds and precipitation that forms over the Indian Ocean and slowly propagates eastward to the middle of the equatorial Pacific. It affects weather conditions worldwide including atmospheric rivers and flooding in California and hurricane formation in the Gulf of Mexico. Some MJO events appear to form independently and are designated as "primary" events. Other "secondary" events appear to be triggered by wave disturbances in the upper troposphere which propagate into the Indian Ocean from regions to the west, in the subtropical belts of the Northern and Southern Hemispheres. The triggering of MJO events by upstream wave disturbances has been well documented, but the processes through which the waves induce MJO events are not well known, and this project seeks to better understand them. Preliminary work by the PI suggests that the precursor waves are not fast moving triggers that impulsively kick-start the MJO, but slowly propagating Rossby waves with intraseasonal timescales. One possibility is that a secondary MJO events can be promoted by an earlier MJO event, which generates Rossby waves in the central equatorial Pacific which propagate eastward and toward higher latitudes, later recurving back into the tropics where they arrive over the equatorial Indian Ocean to induce the subsequent MJO. The project has a focus on Africa because the precursor waves enter the Indian Ocean from the African subtropics. A variety of statistical methods are used to detect and characterize the precursor waves, which are identified in observational data from satellites as well as reanalysis products. Moisture and momentum budgets are then used to understand how the waves contribute to the formation of secondary MJO events.The work has societal broader impacts due to the variety of weather impacts associated with the MJO. There is some skill in forecasts of the propagation of MJO events, but predictions of the initiation of MJO events would allow greater lead times for prediction of MJO impacts. As the project focuses on precursor meteorology over Africa, the project may also have benefit for understanding and predicting African weather. In addition, the project provides support and training to two graduate students, thereby building the future workforce in this research area.