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Key role of the Madden-Julian Oscillation on humid heat waves. Rôle clé de l'Oscillation de Madden-Julian sur les canicules humides
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Manuscript submitted to Nature Communications the 25/07/2024. Humid heat stress and heatwaves pose significant risks for humans and other mammals from health, ecological, and socio-economic perspectives, and are set to intensify with climate change. How large-scale climate modes drive the week-to-month variability of humid heat remains poorly understood at the global scale, hindering accurate forecasts necessary for risk-management measures, notably in the heavily populated and ecologically fragile regions of the tropics and subtropics. With forecast lead times up to several weeks, the Madden-Julian Oscillation (MJO), a global-scale intraseasonal tropical atmospheric wave circumnavigating the earth in around 30-60 days, provides considerable predictability for weather conditions, and meteorological and oceanic extremes. Here we show that the MJO, and the associated boreal summer intraseasonal oscillation (BSISO), have a significant influence on humid heat and humid heatwaves over much of the tropics and subtropics across all seasons, both over terrestrial and marine regions. Humid heatwave likelihood can double or halve, depending on the MJO phase, in large areas of the earth. The MJO/BSISO influence on wet-bulb temperature is generally primarily via specific humidity rather than dry-bulb temperature anomalies. These results, combined with MJO predictability, suggest the potential of forecasting humid heat episodes several weeks in advance.
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