Four types of the Madden-Julian Oscillation

Madden-Julian Oscillation (MJO) is the main mode of intraseasonal atmospheric variability in the tropical Indo-Pacific Oceans and the major source of subseasonal predictability of precipitation and extreme weather events in many parts of the globe. Although MJO is known as an eastward propagating equatorial atmospheric kelvin wave, not all MJO events are identical in terms of their strength and propagation patterns. In an article published in Science Advances, a team of scientists led by Bin Wang performed a cluster analysis of propagation patterns of observed MJO events during November – April to find four types of MJO: (1) standing, (2) jumping, (3) slow eastward propagation, and (4) fast eastward propagation. The propagating types are characterized by tight coupling between the Kelvin wave response and convection, while the nonpropagating types are characterized by weak coupling. During El Nino conditions, the Indo-Pacific warm pool expands, leading to an increase in the MJO zonal scale and favoring the development and growth of the Kelvin wave response to the east of the major convection, leading to a strong and fast-propagating Kelvin wave response. During La Nina conditions, on the other hand, the Indo-Pacific warm pool shrinks, leading to a decrease in the MJO zonal scale and favoring weaker and nonpropagating MJO types. The results from this study may help improve and validate the current-state-of-the-art weather and climate forecast models.

Figure 2 from Wang et al. (2019): Four types of MJO propagation patterns along the equator. Composited longitude-time diagram of intraseasonal OLR anomalies (contour, W m⁻²) averaged between 10°S and 10°N during boreal winter from November to April for (A) standing, (B) jumping, (C) slow propagation, and (D) fast propagation clusters. The dashed black contour is the −5 W/m² contour. The shading shows significant signals at 95% confidence level. The black solid lines in (C to D) indicate phase propagation, which is obtained by a least-square fit of the minimum OLR. The phase speed is shown on the top right corner of the panels.

Wang, B., Chen, G., & Liu, F. (2019). Diversity of the Madden-Julian Oscillation. Science Advances, 5, eaax0220. https://advances.sciencemag.org/content/5/7/eaax0220