Enthalpy and Momentum Fluxes during Hurricane Earl Relative to Underlying Ocean Features
Enthalpy and Momentum Fluxes during Hurricane Earl Relative to Underlying Ocean Features
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DOI：
10.1175/mwr-d-13-00277.1
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发表时间：
2015-01-01
影响因子：
3.2
通讯作者：
Uhlhorn, Eric W.
中科院分区：
文献类型：
--
作者：
Jaimes, Benjamin;Shay, Lynn K.;Uhlhorn, Eric W.
利用热带气旋Earl（4级飓风）期间27架飞机飞行的下投探空仪、现场观测和卫星数据，研究了大量的焓和动量海气通量与强度变化和上层海洋热结构的关系。在厄尔快速强化（RI）期间，相对于26℃等温线的海洋热含量（OHC）变率超过90 kJ cm(-2)，海面冷却小于0.5℃。厄尔峰值强度的焓通量估计接近1.1 kWm（-2）。RI期、成熟期和减弱期的日海面热损失分别为-6.5 +/- 0.8、-7.8 +/- 1.1和+2.3 +/- 0.7 kJ cm（-2）。焓（C-K）和动量（C-D）交换系数的CK/CD比值在0.54和0.7之间，产生了相对于热含量变化的通量的可靠估计，即使在RI期间也是如此；比值C-K/ c - d51高估了通量。最重要的结果是，总体焓通量是由海面和近地面空气之间的热力学不平衡控制的，与风速无关。这种不平衡受到下伏暖海洋特征的强烈影响；在这些涡旋特征上，在水汽不平衡的紧密水平梯度上发展出局部最大焓通量。这些区域的局部浮力强迫在国际风暴期间优先发展。水分不平衡的总体大小(δ q - q（s) - q(a)）由海表温度下的饱和比湿度（q(s)）而不是由大气环境的比湿度（q(a)）决定。这些结果支持了一个假设，即强烈的局部海洋浮力可能是热带气旋在温暖海洋特征上增强的重要机制。
Using dropsondes from 27 aircraft flights, in situ observations, and satellite data acquired during Tropical Cyclone Earl (category 4 hurricane), bulk air-sea fluxes of enthalpy and momentum are investigated in relation to intensity change and underlying upper-ocean thermal structure. During Earl's rapid intensification (RI) period, ocean heat content (OHC) variability relative to the 26 degrees C isotherm exceeded 90 kJ cm(-2), and sea surface cooling was less than 0.5 degrees C. Enthalpy fluxes of similar to 1.1 kWm(-2) were estimated for Earl's peak intensity. Daily sea surface heat losses of -6.5 +/- 0.8, -7.8 +/- 1.1, and +2.3 +/- 0.7 kJ cm(-2) were estimated for RI, mature, and weakening stages, respectively. A ratio CK/CD of the exchange coefficients of enthalpy (C-K) and momentum (C-D) between 0.54 and 0.7 produced reliable estimates for the fluxes relative to OHC changes, even during RI; a ratio C-K/C-D 51 overestimated the fluxes.The most important result is that bulk enthalpy fluxes were controlled by the thermodynamic disequilibrium between the sea surface and the near-surface air, independently of wind speed. This disequilibrium was strongly influenced by underlying warm oceanic features; localized maxima in enthalpy fluxes developed over tight horizontal gradients of moisture disequilibrium over these eddy features. These regions of local buoyant forcing preferentially developed during RI. The overall magnitude of the moisture disequilibrium (Delta q - q(s) - q(a)) was determined by the saturation specific humidity at sea surface temperature (q(s)) rather than by the specific humidity of the atmospheric environment (q(a)). These results support the hypothesis that intense local buoyant forcing by the ocean could be an important intensification mechanism in tropical cyclones over warm oceanic features.