用神经天气模型+罕见事件采样,高效估算飓风生成概率。
Conditional Tropical Cyclogenesis Rates via Rare-Event Sampling in a Neural Weather Emulator

- 结合罕见事件采样与神经天气模型,不改动动力方程估算飓风生成率。
- 在98个初始条件下捕捉到近3个量级的生成率差异,计算效率提升14倍平均。
- 可识别不同环境下的关键限制步骤,适合气候风险评估研究者。
我们将统计力学中的前向通量采样(FFS)方法与神经天气模拟器(SDL-WXFormer,1°网格)结合,估算条件性热带气旋生成率——即热带扰动发展为飓风级中心气压的频率,且无需修改模型动力学。热带气旋生成率在不同气候背景下差异可达数个数量级,但常规集合模拟在实际可行的集合规模下无法解析此变异性。FFS将从扰动到成熟气旋的演化路径分解为初态界面压力的通量,以及跨四个中间界面压力的条件穿越概率乘积。使用1°分辨率的模拟器,因需约10⁴条轨迹/初始条件,且其校准的随机层提供了必要探索范围。对2022年8月21日至10月8日大西洋盆地98个初始条件应用该方法,成功分辨出接近三个数量级的生成率,定性符合观测季节变化。自洽性检验显示,FFS速率与独立直接采样速率的均值比为1.03±0.15。计算加速比从3倍(最活跃环境)到140倍(最抑制环境)不等,几何平均达14倍。三例分析揭示:埃德环境的关键限制在于初始热带组织,菲奥娜前身环境的穿越概率普遍较高,而伊恩环境在最终强化阶段存在复合屏障。
原文摘要 · Abstract (English)
We couple Forward Flux Sampling (FFS), a non-equilibrium rare-event technique from statistical mechanics, to a neural weather emulator (SDL-WXFormer, 1° grid spacing) to estimate conditional tropical cyclogenesis rates, or how often a tropical cyclone achieves a hurricane-level central pressure, without modifying model dynamics. Tropical cyclogenesis rates vary by orders of magnitude across regimes, yet direct ensemble sampling cannot resolve this variability at operationally feasible ensemble sizes. FFS decomposes the rare disturbance to mature cyclone intensification path into a flux through an initial interface pressure and a product of conditional crossing probabilities across four intermediate interface pressures. We use the 1° emulator because FFS requires O(10^4) model trajectories per initial condition, and because the model's calibrated stochastic layers provide the necessary exploratory spread. Applied to 98 Atlantic basin initial conditions spanning 21 August - 8 October 2022, FFS resolves genesis rates spanning nearly three orders of magnitude, capturing a seasonal cycle qualitatively consistent with observations. A self-consistency check comparing FFS rates to independent direct-sampling rates yields a mean ratio of 1.03 +/- 0.15 across all initial conditions. Computational enhancement factors range from 3X (most active environment) to 140X (most suppressed), with a geometric mean of 14X. Three case studies illustrate the physical diagnostics the method provides: the rate-limiting step is initial tropical organization for the Earl environment, uniformly high crossing probabilities for the Fiona precursor environment, and a compound barrier at the final intensification stages for the Ian environment. More efficient emulators would enable application of FFS to finer resolutions.
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