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Abstract The Madden-Julian oscillation (MJO) has profound impacts on weather and climate phenomena, and thus changes in its activity have important implications under human-induced global climate change. Here, the time at which the MJO change signal emerges from natural variability under anthropogenic warming is investigated. Using simulations of the Community Earth System Model version 2 large ensemble forced by the shared socioeconomic pathways SSP370 scenario, an increase in ensemble mean MJO precipitation amplitude and a smaller increase in MJO circulation amplitude occur by the end of the 21 st century, consistent with previous studies. Notably, the MJO precipitation amplitude change signal generally emerges more than a decade earlier than that of MJO wind amplitude. MJO amplitude changes also emerge earlier over the eastern Pacific than other parts of the tropics. Our findings provide valuable information on the potential changes of MJO variability with the aim of improving predictions of the MJO and its associated extreme events. 

Abstract In convective quasi-equilibrium theory, tropical tropospheric temperature perturbations are expected to follow vertical profiles constrained by convection, referred to as A-profiles here, often approximated by perturbations of moist adiabats. Differences between an idealized A-profile based on moist-static energy conservation and temperature perturbations derived from entraining and nonentraining parcel computations are modest under convective conditions—deep convection mostly occurs when the lower troposphere is close to saturation, thus minimizing the impact of entrainment on tropospheric temperature. Simple calculations with pseudoadiabatic perturbations about the observed profile thus provide useful baseline A-profiles. The first EOF mode of tropospheric temperature (TEOF1) from the ERA-Interim and AIRS retrievals below the level of neutral buoyancy (LNB) is compared with these A-profiles. The TEOF1 profiles with high LNB, typically above 400 hPa, yield high vertical spatial correlation (∼0.9) with A-profiles, indicating that tropospheric temperature perturbations tend to be consistent with the quasi-equilibrium assumption where the environment is favorable to deep convection. Lower correlation tends to occur in regions with low climatological LNB, less favorable to deep convection. Excluding temperature profiles with low LNB significantly increases the tropical mean vertical spatial correlation. The temperature perturbations near LNB exhibit negative deviations from the A-profiles—the convective cold-top phenomenon—with greater deviation for higher LNB. In regions with lower correlation, the deviation from A-profile shows an S-like shape beneath 600 hPa, usually accompanied by a drier lower troposphere. These findings are robust across a wide range of time scales from daily to monthly, although the vertical spatial correlation and TEOF1 explained variance tend to decrease on short time scales. 

Abstract Midlatitude stationary waves are relatively persistent large‐scale longitudinal variations in atmospheric circulation. Although recent case studies have suggested a close connection between stationary waves and extreme weather events, little is known about the global‐scale linkage between stationary waves and wildfire activity, as well as the potential changes in this relationship in a warmer climate. Here, by analyzing the Community Earth System Model version 2 large ensemble, we show that a zonal wavenumber 5–6 stationary wave pattern tends to synchronize wildfire occurrences across the Northern Hemisphere midlatitudes. The alternation of upper‐troposphere ridges and troughs creates a hemispheric‐scale spatial pattern of alternating hot/dry and cold/wet conditions, which increases or decreases wildfire occurrence, respectively. More persistent high‐pressure conditions drastically increase wildfire probabilities. Even though the dynamics of these waves change little in response to anthropogenic global warming, the corresponding midlatitude wildfire variability is projected to intensify due to changes in climate background conditions.