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

马登-朱利安振荡（MJO）是一个由云层和降水组成的大包络，形成于印度洋上空，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，包括大气河流和加州的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“次级”事件似乎是由对流层上部的波浪扰动触发的，这些扰动从北方和南半球的亚热带地区向西传播到印度洋。 上游波浪扰动触发MJO事件已得到很好的记录，但波浪诱导MJO事件的过程还不为人所知，本项目旨在更好地了解它们。 PI的初步工作表明，前兆波并不是冲动地启动MJO的快速移动触发器，而是以季节内时间尺度缓慢传播的罗斯比波。 一种可能性是，次级MJO事件可以由较早的MJO事件促进，该事件在赤道太平洋中部产生Rossby波，该Rossby波向东传播并向高纬度传播，随后折回到热带，在那里它们到达赤道印度洋以诱发随后的MJO。 该项目的重点是非洲，因为前驱波从非洲亚热带进入印度洋。 各种统计方法被用来探测和表征前兆波，这些前兆波是在卫星观测数据和再分析产品中确定的。 然后，水分和动量收支被用来了解波如何有助于形成次级MJO事件。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。 在预测MJO事件的传播方面有一定的技巧，但预测MJO事件的开始将允许更长的提前时间来预测MJO影响。 由于该项目的重点是非洲上空的前兆气象学，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，从而培养这一研究领域未来的劳动力。

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.