臺灣海峽南部大氣邊界層內動量、顯熱與潛熱通量之量測

Measurements of Momentum, Sensible and Latent Heat Flux in Atmospheric Boundary Layers over the Southern Taiwan Strait

林首杰(Shoou-Jye Lin) ； 曾若玄(Ruo-Shan Tseng)

《大氣科學》 25卷1期 (1997/03) Pp. 1-26

摘要

本研究乃利用海研三號在台灣海峽南部海域進行四個航次（1995年6月～1996年3月）海氣資料（風速、氣溫、濕度、海表水溫）的量測，並藉由慣性消散法估算海面動量、顯熱與潛熱（水汽）適量。整體資料的大氣穩定度參數Z/L值範圍-0.417~0.197，平均風速介於3.5~15.8 m/s。在風速、氣溫與濕度頻譜上，屬於能量消散的高頻區（0.5 ~ 10Hz）可明顯發現斜率接近-5/3的慣性領域之存在，並且大致滿足等向性紊流場的條件。研究結果顯示，當大氣穩定度為不穩定狀況時，海面粗糙長度Z0隨風速增大而增加，Zt與Zq（分別為相對應於溫度與濕度之粗糙長度）則隨著風速增大有減小的趨勢，但是資料點的散亂度頗大，而相當於10m高之中性狀態下的曳力係數C(subscript DN)有隨風速增大而成長的關係存在，即10^3 C(subscript DN) =0.62+ 0.052 U10，其中U10為離海面10公尺高的風速，而顯熱通量係數C(subscript TN)與潛熱通量係數C(subscript EN)則為定值，分別為1.27 ± t 0.15(×10^(-3))與1.23 ± 0.16 (×10^(-3)), C(subscript TN)對Z/L的關係大致上呈現兩層的分佈，在不穩定情況下的C(subscript TN)平均值比起穩定狀況下較大。風應力與風速約呈7/3次方的正比關係，而顯熱通量及潛熱通量分別與U10( Ts - θz)、U10(Qs - Qz)呈線性關係，其中Ts為海表水溫，θz為空氣位溫，Qs為海水的飽和濕度，Qz為Z公尺高的空氣絕對濕度，而所求得之各通量值與巨觀法估算結果差異大致皆在20%的範圍內。綜合所有不穩定條件下的溫度與濕度數據，發現熱紊流強度與水汽紊流強度經無因次化之後與Z/L參數之間具有密切的相關性。

關鍵字

慣性消散法 ； 動量通量 ； 顯熱通量 ； 潛熱通量 ； 粗糙長度

並列摘要

Shipboard observations of wind speed, air temperature, humidity and sea-surface temperature were made during four cruises of RN Ocean Researcher III over southern Taiwan Strait between June 1995 and March 1996. Inertial dissipation method was used to estimate turbulent fluxes of momentum, sensible and latent heat(water vapor). Among the total 186 data runs, the range of wind speed is 3.5~15.8 m/s and the stability parameter Z/L is -0.417~0.197. Spectra of wind speed, temperature and humidity fluctuations show the existence of the inertial subrange in the frequency band 0.5 ~ 10Hz, where spectral slopes follow f^(-5/3) and the condition of local isotropy are satisfied . Our results indicate that under unstable condition, the roughness length Z0 increases with increasing wind speed. On the other hand, Zt(for heat) and Zq(for moisture) decrease as the wind speed increases with relatively large data scatters. The neutral drag coefficient at 10 m height, C(subscript DN), is well described by 10^3C(subscript DN)=0.62 + 0.052 U10, where U10 is the wind speed at 10 m height. The Stanton number C(subscript TN) and Dalton number C(subscript EN) are 1.27±0.15(× 10^(-3)) and 1.23±0.16(× 10^(-3)) respectively, and C(subscript TN) under unstable condition is larger than that under stable condition. Wind stress is proportional to the 7/3 power of U10. Sensible and latent heat flux increase linearly with U10(Ts - θz) and U10(Qs -Qz) respectively, where Ts is sea-surface temperature, θz and Qz are potential temperature and absolute humidity, respectively at a height Z, Qs is absolute humidity at sea surface. Comparison of simultaneous bulk and dissipation method estimates of air-sea fluxes is generally within ±20% deviation. Normalized thermal and humidity turbulence levels under unstable conditions were found to be closely related to Z/L.

並列關鍵字

Inertial dissipation method ； Momentum flux ； Sensible heat flux ； Latent heat flux ； Roughness length