Global trends of tropopause folds in recent decades

Tropopause folds represent a primary mechanism for stratosphere-troposphere exchange. This study employs a 3D labeling method with ERA5 reanalysis data spanning from 1979 to 2020 to elucidate the spatiotemporal variations of tropopause folds. The results reveal distinct seasonal and regional variations in trends of tropopause folds. Notably, tropopause folds exhibit an increasing trend, with the magnitude varying seasonally. Significant increasing trends of tropopause folds are observed in northern spring, summer, and winter, primarily along subtropical jets. Further analysis reveals that the increase in tropopause folds is related to the strengthening of frontogenesis due to enhanced atmospheric baroclinicity, while the intensification of meridional potential temperature gradients enhances secondary circulations and may further promote an increase in folds activities. 摘要 对流层顶折卷是平流层-对流层物质交换的主要机制.本研究采用三维标记方法, 利用1979-2020年间的ERA5再分析数据, 分析了对流层顶折卷的时空变化特征及机理.研究结果表明, 全球对流层顶折卷的多年变化趋势存在明显的季节性和区域性差异.总体上, 对流层顶折卷呈增加趋势, 其中北半球的春季,夏季和冬季, 对流层顶折卷主要沿副热带急流区呈现明显增加的趋势.进一步分析表明, 对流层顶折卷发生频率的增加与大气斜压性增大导致的锋生增强有关, 而经向位温梯度的增大使得次级环流增强, 也可能促进了对流层顶折卷活动的增多.