Future trends in isentropic mixing in the lower stratosphere remain largely unexplored, in contrast with other aspects of stratospheric tracer transport. This study examines trends in effective diffusivity (κ_eff), a measure of the potential of the flow to produce isentropic mixing, in recent chemistry‐climate model simulations. The results highlight substantial reduction of κ_eff in the upper flanks of the subtropical jets from fall to spring, which are strengthened in response to greenhouse gas increases. This contrasts with stronger eddy transport, associated with increased wave drag in the region, peaking in summer near the critical lines. The key role of changes in tracer meridional gradients in addition to transport barriers for isentropic mixing trends is evidenced. The projected ozone recovery leads to enhanced κ_eff in polar austral spring and summer, associated with a weaker and shorter‐lived austral polar vortex by the end of the 21st century.

中文翻译：

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平流层下层混合屏障和涡流运输的二十一世纪趋势

与平流层示踪剂运输的其他方面相比，平流层下部等熵混合的未来趋势仍未得到充分探索。在有效扩散本研究探讨发展趋势（κ _EFF），流动的潜在的措施产生等熵混合，近化学-气候模型模拟。结果凸显大幅减少κ _EFF从秋季到春季，在亚热带急流的上腹中，它们随着温室气体的增加而增强。这与更强的涡流传输形成对比，涡流传输与该区域的波浪阻力增加有关，并在夏季在临界线附近达到峰值。证明了示踪子午梯度变化以及等熵混合趋势的传输障碍的关键作用。投影臭氧恢复导致增强κ _EFF极南半球的春季和夏季，由21世纪末较弱和更短的生活，南半球极地涡旋有关。