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PUBLICATION HIGHLIGHT: Influences of the MJO on the space-time organization of tropical convection

Photo: Eduardo Jaeger courtesy unsplash.com
Photo: Eduardo Jaeger courtesy unsplash.com

The Madden and Julian Oscillation (MJO) is a large-scale pattern of tropical rainfall with a period of about 40 days, mainly over the tropical Indo-Pacific Region, which has worldwide impacts. In a new study published in the Journal of Geophysical Research – Atmospheres, researchers from ESRL’s Physical Sciences Division, CIRES, and the University of Hawaii investigate how the MJO interacts with daily-to-weekly rainfall variability and intensity and how the MJO impacts globally integrated rainfall.

The researchers find that while tropical convection is intensified where the MJO is active, it does not significantly impact the behavior of rainfall on shorter time scales. Particular types of large-scale tropical disturbances are not more likely to develop where the MJO is most active, instead the MJO enhances the overall activity of existing disturbances. As a result, the MJO changes the distribution of tropical rainfall, without increasing its total amounts.

Since current operational forecast models still struggle to simulate the MJO, this study offers observational targets for model development. Improvements in the representation of the MJO in forecast models will lead to better forecasts of global weather on daily to climate scales, even outside the tropics, since the MJO has such a large influence on the global atmosphere.

Abstract:

The fact that the Madden-Julian Oscillation (MJO) is characterized by large-scale patterns of enhanced tropical rainfall has been widely recognized for decades. However, the precise nature of any two-way feedback between the MJO and the properties of smaller-scale organization that makes up its convective envelope is not well understood. Satellite estimates of brightness temperature are used here as a proxy for tropical rainfall, and a variety of diagnostics are applied to determine the degree to which tropical convection is affected either locally or globally by the MJO. To address the multiscale nature of tropical convective organization, the approach ranges from space-time spectral analysis to an object-tracking algorithm. In addition to the intensity and distribution of global tropical rainfall, the relationship between the MJO and other tropical processes such as convectively coupled equatorial waves, mesoscale convective systems, and the diurnal cycle of tropical convection is also analyzed. The main findings of this paper are that, aside from the well-known increase in rainfall activity across scales within the MJO convective envelope, the MJO does not favor any particular scale or type of organization, and there is no clear signature of the MJO in terms of the globally integrated distribution of brightness temperature or rainfall.

Authors of Influences of the MJO on the space-time organization of tropical convection are Juliana Dias, Naoko Sakaeda, and George Kiladis of the ESRL Physical Sciences Division, and Kazuyoshi Kikuchi of the University of Hawaii.