Coastal Zone Surface Stress with Stable Stratification

摘要

Summertime eddy correlation measurements from an offshore tower are analyzed to investigate the dependence of the friction velocity u* for stable conditions on the mean wind speed V, air-sea difference of virtual potential temperature delta theta(upsilon), and nonstationary submeso motions. The quantity delta theta(upsilon) sometimes exceeds 3 degrees C, usually because of the advection of warm air from land over cooler water at this site. Thin stable boundary layers result. Unexpectedly, u*(V) does not depend systematically on the stratification delta theta(upsilon) even for weak winds. For weak winds, u*(V) increases systematically with increasing submeso variations of the wind. The u*(V) relationship for a given V is greater in nonstationary conditions. Additionally, this study examines u*(V) as a function of wind direction. The u*(V) relationship appears to be affected by swell direction for weak winds and advection from land for short fetches.