Reduced Sensitivity of Tropical Cyclone Intensity and Size to Sea Surface Temperature in a Radiative-Convective Equilibrium Environment

Abstract

It has been challenging to project the tropical cyclone (TC) intensity, structure and destructive potential changes in a warming climate. Here, we compare the sensitivities of TC intensity, size and destructive potential to sea surface warming with and without a pre-storm atmospheric adjustment to an idealized state of Radiative-Convective Equilibrium (RCE). Without RCE, we find large responses of TC intensity, size and destructive potential to sea surface temperature (SST) changes, which is in line with some previous studies. However, in an environment under RCE, the TC size is almost insensitive to SST changes, and the sensitivity of intensity is also much reduced to 3% °C⁻¹–4% °C⁻¹. Without the pre-storm RCE adjustment, the mean destructive potential measured by the integrated power dissipation increases by about 25% °C⁻¹ during the mature stage. However, in an environment under RCE, the sensitivity of destructive potential to sea surface warming does not change significantly. Further analyses show that the reduced response of TC intensity and size to sea surface warming under RCE can be explained by the reduced thermodynamic disequilibrium between the air boundary layer and the sea surface due to the RCE adjustment. When conducting regional-scale sea surface warming experiments for TC case studies, without any RCE adjustment the TC response is likely to be unrealistically exaggerated. The TC intensity–temperature sensitivity under RCE is very similar to those found in coupled climate model simulations. This suggests global mean intensity projections under climate change can be understood in terms of a thermodynamic response to temperature with only a minor contribution from any changes in large-scale dynamics.

摘要

预测热带气旋的强度、结构特征和破坏力对气候变化的响应始终充满挑战. 本文利用大气数值模式对比了进行背景场辐射对流平衡调整(Radiative-Convective Equilibrium)前后, 热带气旋对海表温度的响应. 研究发现, 如果背景场没有进行辐射对流平衡调整, 气旋强度、大小和破坏力指标均对海面升温产生较强响应. 这一结果与前人结论相似. 然而, 若背景场在模拟气旋之前被调整到辐射对流平衡状态, 模拟的气旋尺寸几乎对海面升温不敏感, 且气旋强度的敏感度也大幅下降至3-4%/C. 进一步研究发现, 气旋特征对海表升温敏感度下降可归因为在辐射对流平衡环境中减弱了的海气界面热力学不平衡性(thermaldynamic disequilibrium). 因此, 在进行热带气旋的海表温度敏感性实验时, 若不先对背景场进行辐射对流平衡调整, 那么所模拟的气旋敏感性会被放大. 与耦合气候模式对比后发现, 辐射对流平衡调整后得到的热带气旋对海表温度的敏感性与耦合气候模式模拟得到的敏感性基本一致. 该发现说明:在全球气候变化背景下, 热带气旋强度对海表温度变化的响应主要受控于热力学过程而非大尺度动力学过程.