Possible Role of the Diurnal Cycle in Land Convection in the Barrier Effect on the MJO by the Maritime Continent

Abstract

Possible effects of the diurnal cycle in land convection on propagation of the Madden–Julian Oscillation over the Indo‐Pacific Maritime Continent (MC) were investigated using satellite observations. Four features distinguishable from their respective climatology are uniquely associated with MJO events that cross the MC: strong precipitation over land as their convection centers approach the MC, subsequent increased soil moisture, reduced diurnal amplitude of land convection, and the dominance of precipitation over water by nondiurnal convection as their convection centers move over the MC. These results provide observational evidence for a proposed MAritime Continent Convective diurnal Cycle mechanism in which the diurnal cycle in land convection acts as an intrinsic barrier effect on MJO propagation over the MC.

A Damping Effect of the Maritime Continent for the Madden‐Julian Oscillation

“…Moreover, the processes underlying the MC damping effect for MJO propagation as illustrated in this study are applicable for all MJO events crossing over the MC; further investigations are warranted to understand mechanisms responsible for the observed distinct MJO propagation characteristics over the MC; that is, some MJO events can cross over the MC, while others cannot. It will be interesting to further explore how interactions between the MJO and MC are modulated by the large‐scale environment, for example, through the lower‐tropospheric mean moisture distribution (e.g., DeMott et al, ; Gonzalez & Jiang, ; Kim, Kug, & Sobel, ) and diurnal cycle‐related local land‐sea contrast (e.g., Ling et al, ; Zhang & Ling, ), as previously found to be critical in regulating propagating versus nonpropagating MJO events over the MC. Also note that in addition to the moistening process as discussed in this study, the MC diurnal cycle can also interact with the MJO through upscale transport of momentum and heat, which will be reported elsewhere.…”

“…In addition, the vigorous local diurnal cycle is also considered to play a role in damping the MJO when propagating over the MC by limiting the available moist energy (e.g., Neale & Slingo, ; Zhang & Hendon, ). It was also suggested that whether or not the MJO can pass through the MC is subject to a competition between local land and oceanic convection and that the development of oceanic convection over the MC region is critical to promote MJO propagation over the MC (Ling et al, ; Zhang & Ling, ). In a recent idealized modeling study, Majda and Yang () proposed that upscale heat transport by the diurnal circulation can effectively suppress MJO deep convection when it propagates into the MC.…”

A 20‐Year Climatology of Madden‐Julian Oscillation Convection: Large‐Scale Precipitation Tracking From TRMM‐GPM Rainfall

“…The MC is considered to be a barrier for the MJO because many events are diminished or dissipate there (Hendon & Salby, ; KC16; Kim et al, ; Ling et al, ; Rui & Wang, ; Zhang & Ling, ). Vitart and Molteni () showed that, based on the RMM index, around 30% of MJO events are unable to cross from the IO to the west Pacific.…”

The Influences of Convectively Coupled Kelvin Waves on Multiscale Rainfall Variability over the South China Sea and Maritime Continent in December 2016

“…To analyze the diurnal variation of precipitation, the dates are separated into convectively active and suppressed conditions over the western part of MC (see section 5c for details). Ling et al (2019) pointed out that the harmonic analysis may not accurately represent the precipitation DC over the MC, especially over land areas, because the developing phase can be shorter (faster) than the decaying phase in the daily cycle. As the data here only cover a month, the DC phase and amplitude are determined using a simple method.…”