Changes to the Madden‐Julian Oscillation in Coupled and Uncoupled Aquaplanet Simulations With 4xCO₂

Abstract

The impacts of rising carbon dioxide (CO2) concentration and ocean feedbacks on the Madden‐Julian Oscillation (MJO) are investigated with the Community Atmospheric Model Version 5 (CAM5) in an idealized aquaplanet configuration. The climate response associated with quadrupled CO2 concentrations and sea surface temperature (SST) warming are examined in both the uncoupled CAM5 and a version coupled to a slab ocean model. Increasing CO2 concentrations while holding SST fixed produces only small impacts to MJO characteristics, while the SST change resulting from increased CO2 concentrations produces a significant increase in MJO precipitation anomaly amplitude but smaller increase in MJO circulation anomaly amplitude, consistent with previous studies. MJO propagation speed increases in both coupled simulations with quadrupling of CO2 and uncoupled simulations with the same climatological surface temperature warming imposed, although propagation speed is increased more with coupling. While climatological SST changes are identical between coupled and uncoupled runs, other aspects of the basic state such as zonal winds do not change identically. For example, climate warming produces stronger superrotation and weaker mean lower tropospheric easterlies in the coupled run, which contributes to greater increases in MJO eastward propagation speed with warming through its effect on moisture advection. The column process, representing the sum of vertical moist static energy (MSE) advection and radiative heating anomalies, also supports faster eastward propagation with warming in the coupled run. How differing basic states between coupled and uncoupled runs contribute to this behavior is discussed in more detail.

Cross‐Equatorial Surges Boost MJO's Southward Detour Over the Maritime Continent

“…(2020)). While it is evident that MJO amplitude is indeed suppressed over the central and northern parts of the MC during periods of the CES (see our Figures 2a–2f, 3c–3f, and 5), the MJO amplitude over the SMC is actually enhanced compared to its initial amplitude over the Indian Ocean. Therefore, it is clear that the MJO's amplitude is not entirely suppressed during the CES; rather, it undergoes a shift and amplification toward the SMC due to enhanced convection (see the illustration in Figure 5).…”

“…Given the observed relationship between stronger zonal moisture convergence and intraseasonal wind intensification during CES events, one intriguing question arises: Could the amplification of the MJO southward detour be attributed to stronger wind‐evaporation feedback in the presence of the CES? The wind‐evaporation feedback, also known as wind‐induced surface heat exchange, is a crucial process in the propagation and maintenance of the MJO (Bui & Maloney, 2020; Kang et al., 2022; Maloney & Sobel, 2004). Here, we hypothesize that the stronger westerlies in the presence of the CES can result in a stronger surface latent heat flux, leading to more moisture being supplied to the atmosphere over the SMC.…”

Emergence of Madden-Julian oscillation precipitation and wind amplitude changes in a warming climate

“…3a-f). As previous studies mostly focused on the absolute changes of the MJO [9][10][11][12][13][14][15][16][17][18] (for example, MJO precipitation amplitude change from −10% to +20% relative to the current climate, while MJO circulation anomalies increase at a slower rate or weaken), the result here suggests that uncertainties in MJO prediction and its teleconnection impacts may be higher because both absolute changes and emergence time need to be considered.…”

“…In contrast, the change in MJO circulation amplitude is projected to weaken or increase at a slower rate than MJO precipitation amplitude 10 . Increases in MJO precipitation amplitude have been found in aquaplanet models 11 , single climate models 12,13 , multimodel analyses from the Coupled Model Intercomparison Project (CMIP) phase 3/5/6 10,14,15 , and also observations 16 . Projected increases in MJO precipitation and weakening or slower increases of MJO wind anomaly amplitude with warming are consistent with increases in dry tropical static stability, which are proportional to increases in tropical sea surface temperature (SST) 17 .…”

Drivers of Future Extratropical Sea Surface Temperature Variability Changes in the North Pacific

“…There is a substantial body of literature characterizing future changes to specific modes of climate variability such as the El Niño-Southern Oscillation (ENSO) [2][3][4][5][6][7][8] and the Madden-Julian Oscillation [9][10][11][12]. However the broader study of climate variability changes is an emerging field with many outstanding questions [13][14][15].…”