Title: Key role of the Madden-Julian Oscillation on humid heatwaves Show Chinese title

Title: 湿润热浪中 Madden-Julian 振荡的关键作用

Abstract: Humid heat stress and heatwaves pose significant risks for living organisms, from humans and wildlife to insects, with wide-ranging health, ecological, and socio-economic impacts that are expected to worsen 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 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 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's influence on wet-bulb temperature is primarily via specific humidity rather than dry-bulb temperature anomalies. We find that specific humidity anomalies are influenced by horizontal advection of moisture in the planetary boundary layer, particularly in the subtropics where advection of the climatological moisture gradient by MJO-related anomalous winds is the dominant term. Show Chinese abstract

Abstract: 湿热应激和热浪对生物体构成重大风险，从人类和野生动物到昆虫，其健康、生态和社会经济影响范围广泛，并且随着气候变化预计会进一步恶化。 目前，大规模气候模式如何驱动湿热的周至月尺度变化，在全球范围内仍知之甚少，这阻碍了准确预测，而这些预测对于风险管理措施至关重要，尤其是在人口密集和生态脆弱的热带和副热带地区。 由于预报提前期可达数周， Madden-Julian Oscillation (MJO) 是一种全球尺度的季节内热带大气波，大约在 30-60 天内环绕地球，为天气状况以及气象和海洋极端事件提供了显著的可预测性。 我们发现，MJO 和相关的北半球夏季季节内振荡（BSISO）在所有季节中对大部分热带和副热带地区的湿热浪有显著影响，无论是陆地还是海洋区域。 在地球的广大地区，湿热浪的发生概率可以根据 MJO 的相位翻倍或减半。 MJO/BSISO 对湿球温度的影响主要是通过比湿而不是干球温度异常实现的。 我们发现，比湿异常受到行星边界层中水分的水平平流的影响，特别是在副热带地区，MJO 相关异常风对气候学湿度梯度的平流是主导项。