Roundy (2026) Zonal Propagation of the Indian Basin MJO Across Varying Background Wind and Seasonal Background Wind States

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Identification

• Journal: Climate
• Year: 2026
• Date: 2026-03-20
• Authors: Paul E. Roundy
• DOI: 10.3390/cli14030074

Research Groups

Not specified in the provided text.

Short Summary

This paper investigates the seasonal variability of the Madden-Julian Oscillation's (MJO) eastward propagation and its relationship with equatorial upper tropospheric background wind patterns, finding that propagation speed is strongly modulated by the strength of these background winds and that upper tropospheric signals are often stronger than lower tropospheric ones.

Objective

• To assess the association between the Indian Basin MJO circulation and convection with variations in equatorial upper tropospheric background wind patterns, including seasonal variability, and to understand the contributions of moist and dry dynamical processes to MJO seasonality.

Study Configuration

• Spatial Scale: Equatorial region, Indian Basin, Western Indian Ocean, Western Hemisphere to East Africa (planetary-scale context).
• Temporal Scale: Seasonal variability (northern spring, northern winter, northern summer) of intraseasonal Madden-Julian Oscillation.

Methodology and Data

• Models used: Not specified.
• Data sources: Observation/Reanalysis data (implied from composites and phase speed spectra analysis of MJO circulation, convection, and background winds).

Main Results

• The fastest MJO eastward propagation over the Indian Ocean (>10 m/s) tends to occur during northern spring, coinciding with the weakest background upper tropospheric easterlies.
• Northern winter MJO signals typically advance eastward between 4 m/s and 10 m/s.
• Strong easterly background wind conditions during northern summer usually prevent eastward MJO propagation along the equator from the Western Indian Ocean.
• Upper tropospheric MJO circulation signals are disproportionately stronger than lower tropospheric ones over the Western Hemisphere to East Africa.
• Upper tropospheric easterly wind anomalies grow first over the Western Indian Ocean, linked to increasing specific humidity in lower tropospheric easterly wind to the east, suggesting that lower tropospheric wind changes depend more directly on moist processes than upper tropospheric winds.

Contributions

• Provides a detailed assessment of the seasonal dependence of MJO phase speed on equatorial upper tropospheric background wind patterns.
• Highlights the critical role of background wind strength in modulating MJO propagation, particularly the inhibitory effect of strong easterlies in northern summer.
• Reveals differential amplitude variations between upper and lower tropospheric MJO signals and suggests distinct dependencies on moist processes for each layer.

Funding

Not specified in the provided text.

Citation

@article{Roundy2026Zonal,
  author = {Roundy, Paul E.},
  title = {Zonal Propagation of the Indian Basin MJO Across Varying Background Wind and Seasonal Background Wind States},
  journal = {Climate},
  year = {2026},
  doi = {10.3390/cli14030074},
  url = {https://doi.org/10.3390/cli14030074}
}