Parametric representation of the primary hurricane vortex. Part II: A new family of sectionally continuous profiles
Parametric representation of the primary hurricane vortex. Part II: A new family of sectionally continuous profiles
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DOI：
10.1175/mwr3106.1
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发表时间：
2006-04-01
影响因子：
3.2
通讯作者：
Rahn, ME
中科院分区：
文献类型：
--
作者：
Willoughby, HE;Darling, RWR;Rahn, ME
对于诸如风暴承保或风暴潮预报等应用，飓风风廓线通常用连续函数来近似，这些函数在涡旋中心为零，在眼壁增加到最大值，然后在远离中心的地方渐近地减小到零。将最常用的函数与飞机观测结果进行比较，可以发现系统误差。虽然山顶附近的风很强，但随着距离山顶的距离，风的减弱速度也很快。这些剖面的压力-风关系通常高估了最大风速。一种有希望的替代方案是一组截面连续的剖面，其中风在眼内以半径的幂增加，在眼外经过平滑的多项式过渡后呈指数衰减。基于493个观测剖面的样本，幂律的平均指数为0.79，平均衰减长度为243 km。该数据库实际上包含606架次的飞机，但其中113架次没有通过质量控制筛选。比萨菲尔-辛普森2级强的飓风通常需要两个指数来匹配观测到的风的快速减少，其半径在眼外，而在更远的地方则减少得更慢。实验表明，25 km的固定值可以满足更快的衰减长度。较慢衰变长度的平均值为295 km。较快的指数对外部廓线的平均贡献为0.10，但对于最强烈的飓风，它有时超过0.5。快速衰减长度的幂律指数和比例随最大风速而增大，随纬度而减小，而慢速衰减长度随强度而减小，随纬度而增大，这与低纬度地区飓风强度越大，风廓线峰值越陡的定性观测结果一致。
For applications such as windstorm underwriting or storm-surge forecasting, hurricane wind profiles are often approximated by continuous functions that are zero at the vortex center, increase to a maximum in the eyewall, and then decrease asymptotically to zero far from the center. Comparisons between the most commonly used functions and aircraft observations reveal systematic errors. Although winds near the peak are too strong, they decrease too rapidly with distance away from the peak. Pressure-wind relations for these profiles typically overestimate maximum winds.A promising alternative is a family of sectionally continuous profiles in which the wind increases as a power of radius inside the eye and decays exponentially outside the eye after a smooth polynomial transition across the eyewall. Based upon a sample of 493 observed profiles, the mean exponent for the power law is 0.79 and the mean decay length is 243 km. The database actually contains 606 aircraft sorties, but 113 of these failed quality-control screening. Hurricanes stronger than Saffir-Simpson category 2 often require two exponentials to match the observed rapid decrease of wind with radius just outside the eye and slower decrease farther away. Experimentation showed that a fixed value of 25 km was satisfactory for the faster decay length. The mean value of the slower decay length was 295 km. The mean contribution of the faster exponential to the outer profile was 0.10, but for the most intense hurricanes it sometimes exceeded 0.5. The power-law exponent and proportion of the faster decay length increased with maximum wind speed and decreased with latitude, whereas the slower decay length decreased with intensity and increased with latitude, consistent with the qualitative observation that more intense hurricanes in lower latitudes usually have more sharply peaked wind profiles.