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Abstract The Madden Julian Oscillation (MJO) consists of a tropical convective region that propagates eastward through the Indo‐Pacific warm pool. Decadal climate variability alters sea surface temperature patterns, affecting the MJO's basic state. This investigation examines the impact of projected SST and moisture pattern changes over the 21st Century on MJO precipitation and zonal wind amplitude changes in 80 members of the Community Earth System Model 2 Large Ensemble in the SSP370 radiative forcing scenario, each with its unique representation of decadal variability. Ensemble members with strongest MJO precipitation change in a given 20‐year period have a more El Niño‐like east Pacific warming pattern. MJO amplitude increases for east Pacific warming because of a strengthened meridional moisture gradient that supports MJO eastward propagation. A stronger vertical moisture gradient also exists for ensemble members with preferential east Pacific warming, which supports a stronger MJO under moisture mode theory.
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Tropical Intraseasonal Variability as a Leading Moisture Dynamic Mode of the Warm-Pool Background State
Abstract Tropical intraseasonal variability (ISV) is dominated by the Madden–Julian oscillation (MJO), and its spatiotemporal characteristics vary with the Indo-Pacific warm-pool background on seasonal and longer time scales. Previous works have suggested ISV dynamics in various frameworks, whereas a unifying view remains challenging. Motivated by the recent advance in moisture mode theory, we revisit the ISV as a leading moisture mode modulated by varying background states derived from a reanalysis, using a moist linear baroclinic model (mLBM) improved with a simple convective scheme relating convective precipitation to tropospheric and boundary layer moisture anomalies and simple cloud-radiative feedback representations. Under a boreal winter background state, this mLBM yielded a large-scale but local eastward-propagating mode with a phase speed of 3–5 m s−1over the warm-pool region, resembling the MJO. Background lower-tropospheric winds and thermodynamic fields are important in determining the growth rate and periodicity of the leading mode, whose stability depends on cloud-radiative feedback and background state variations. We further demonstrate why the MJO is locally contained in the Indo-Pacific warm-pool region. The local thermal/moisture condition and Walker circulation greatly enhance its instability, but outside this region, this mode is heavily damped. Thus, the expansion/contraction of this warm-pool condition may enhance/reduce its instability and expand/reduce its domain of activity. Prescribing El Niño background causes eastward displacement of the wintertime ISV activity, reminiscent of the observed MJO modulations by El Niño. Under a summer background state, the eastward-propagating leading mode resembles the boreal summer ISV but is biased, requiring further model improvements.
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- Award ID(s):
- 2219257
- PAR ID:
- 10559481
- Publisher / Repository:
- American Meteorological Society
- Date Published:
- Journal Name:
- Journal of Climate
- Volume:
- 38
- Issue:
- 1
- ISSN:
- 0894-8755
- Format(s):
- Medium: X Size: p. 235-262
- Size(s):
- p. 235-262
- Sponsoring Org:
- National Science Foundation
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