Prospects for Erratic and Intensifying Madden-Julian Oscillations

Patrick Haertel

doi:10.3390/cli8020024

Abstract

The Madden–Julian Oscillation (MJO) is a planetary-scale convective disturbance that typically forms in the equatorial Indian Ocean, propagates slowly eastward, and dissipates near the date line. This study examines how the MJO changes in response to a changing radiative forcing in a fully-Lagrangian coupled model (LCM) that is shown to simulate robust and realistic MJOs. After the LCM is spun up for 160 years to reproduce the late 20th century climate, non-water-vapor longwave optical depth is increased over 70 years to model the effects of increasing concentrations of greenhouse gases. The model is then run for another 30 years without additional changes to the radiative forcing. After the radiative forcing is modified, the MJO generally becomes more frequent and intense, but it is also more variable from one year to the next. Not only do composite MJO rainfall perturbations increase, but wind, temperature, and moisture perturbations also become stronger. The aspect of the MJO’s structure that changes the most is the largely dry equatorial Kelvin wave circulation that circumnavigates the globe between moist phases of the MJO. Potential impacts of these changes included alterations to the way in which the MJO modulates tropical cyclones, monsoon disturbances, and El Niño.

Highlights

IntroductionThe Madden Julian Oscillation (MJO) is a large-scale convective disturbance that forms in the equatorial Indian Ocean and propagates slowly eastward before dissipating near the date line [1,2]
The Madden Julian Oscillation (MJO) is a large-scale convective disturbance that forms in the equatorial Indian Ocean and propagates slowly eastward before dissipating near the date line [1,2].Low-level westerly wind perturbations trail the convective envelope, and an upper-level quadrapole gyre structure is centered just east of the convection [3]
There were several limitations to that study in that it did not consider potential feedbacks to sea surface temperatures (SSTs) from changes to the MJO, nor was the radiative forcing adjusted to be consistent with presribed SST changes. This study addresses these shortcomings by coupling the Lagrangian atmospheric model (LAM) to a Lagrangian ocean model (LOM; [38]), and revisiting the question of how the MJO changes in a warming climate

Summary

Introduction

The Madden Julian Oscillation (MJO) is a large-scale convective disturbance that forms in the equatorial Indian Ocean and propagates slowly eastward before dissipating near the date line [1,2]. Low-level westerly wind perturbations trail the convective envelope, and an upper-level quadrapole gyre structure is centered just east of the convection [3]. Smaller-scale eastward and westward propagating convective disturbances are embedded within the large-scale convective envelope of the MJO [4]. A largely dry equatorial Kelvin wave circumnavigates the globe in between MJO convective episodes [5,6]. Despite decades of study and numerous modeling attempts and theoretical interpretrations, the dynamics of the Madden Julian Oscillation (MJO) are not fully understood.

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Discussion

Conclusion