The Madden Julian Oscillation: Identification

It is now well-known that the Madden Julian Oscillation (MJO) plays an important role in affecting global circulation patterns. While we have gained a great deal of knowledge pertaining to the MJO and its impact over the past few decades, it is still remarkably difficult to connect the MJO to mid-latitude weather patterns. Since the development of the real-time multivariate MJO (RMM) indices, we are now more prepared to monitor to the MJO on daily timescales in order to make more skillful predictions of extra-tropical behavior in the medium-range and beyond. While the RMM index has made a significant imprint on medium-range prediction applications, there are times where the index is insufficient to fully describe the tropical drivers. In this presentation we will discuss the RMM index, highlighting the strengths and weaknesses. In addition, a series of new MJO-based indices have been created to complement or improve upon the RMM index. One such set is the Velocity Potential MJO (VPM) indices. The VPM indices will be discussed in detail, and we will show evidence that these indices are more effective than the RMM indices in identifying boreal summer MJO events. This increased effectiveness is attributed to the VPM indices focus on the upper-tropospheric circulation of the MJO, not its convective signature. An important conclusion from this analysis is that no particular MJO index is perfect and depending on the index that you choose, you could find a significantly different result. We need to continue to explore new ways to identify the MJO in order to improve forecast skill in the 1-4 week domain.