Theory and numerical modelling suggest that tropical cyclones (TCs) will strengthen with rising ocean temperatures. Even though models have reached broad agreement on projected TC intensification , observed trends in TC intensity remain inconclusive and under active debate in all ocean basins except the North Atlantic, where aircraft reconnaissance data greatly reduce uncertainties. The conventional satellite-based estimates are not accurate enough to ascertain the trend in TC intensity , suffering from contamination by heavy rain, clouds, breaking waves and spray. Here we show that weak TCs (that is, tropical storms to category-1 TCs based on the Saffir–Simpson scale) have intensified in all ocean basins during the period 1991–2020, based on huge amounts of highly accurate ocean current data derived from surface drifters. These drifters have submerged ‘holy sock’ drogues at 15?m depth to reduce biases induced by processes at the air–sea interface and thereby accurately measure near-surface currents, even under the most destructive TCs. The ocean current speeds show a robust upward trend of ~4.0?cm?s^?1 per decade globally, corresponding to a positive trend of 1.8?m?s^?1 per decade in the TC intensity. Our analysis further indicates that globally TCs have strengthened across the entirety of the intensity distribution. These results serve as a historical baseline that is crucial for assessing model physics, simulations and projections given the failure of state-of-the-art climate models in fully replicating these trends.

海流显示全球弱台风显著增强

中文摘要：理论和数值模型显示，热带气旋(TCs)的强度将随着海温的上升而加强。尽管各种模型对TC强度增强的预测结果已达成一致，但在不同海域，TC强度观测得到的趋势还没有定论，并仍处于争议之中；除了北大西洋，因为该海域的飞机气象探测大大减小了预测的不确定性。传统的基于卫星的探测估计，受强降雨、云、破碎波和飞沫的影响无法确定TC强度的趋势。在这里，我们基于1991~2020年内Drifter获得的大量高精度海流数据，指出所有洋盆中弱台风（基于Saffir-Simpson分类的热带风暴至等级为-1的TCs）都得到了增强。Drifter在海面以下15米深度配备有水帆，可减小海气界面过程产生的误差，即使在最极端强度的台风过程中，也可准确地测量近表层的流场情况。世界大洋流速呈现出每10年~4.0 cm s^-1的增大趋势，与TC强度每十年 1.8 m s^-1的增强趋势相对应。我们的研究进一步表明全球范围内的TCs在整个强度分布上都将有所加强。由于最前沿的气候模型还未完全重现这些趋势，这些结果对于评估模型物理过程，模型模拟和预测都将至关重要。