The evolution of equatorial Kelvin waves of planetary wavenumber 1 (an analytical solution).

Motivation

The MJO modulates the weather all around the globe and makes weather prediction feasible beyond 2 weeks. However, the intraseasonal period (5 to 9 weeks) of the MJO remains difficult to explain since each MJO theory makes distinct assumptions.

Modeling approaches

My scale analysis approach used the least assumptions to explain the period of the MJO. Only three geometric assumptions are made.

Main findings

My scale analysis results suggest that equatorial Kelvin waves of planetary wavenumber 1 have an intrinsic period of 36 to 64 days, which matches the intraseasonal time scale of the MJO. This time scale arises from the long, narrow, and shallow flow geometry.

Broader Impact and Prospects

My scale analysis uncovers the origin of the period of the MJO. It may be used to improve subseasonal weather prediction.

Project Status

My ongoing side project (2018-)

Publication

Ong, H. (2025). Scale analysis for the Madden–Julian oscillation. Q. J. R. Meteorol. Soc. Accepted.