On the influence of wind and waves on underwater irradiance fluctuations

[摘要] The influence of various wind and wave conditions on the variability ofdownwelling irradiance E_d (490 nm) in water is subject of this study.The work is based on a two-dimensional Monte Carlo radiative transfer modelwith high spatial resolution. The model assumes conditions that are idealfor wave focusing, thus simulation results reveal the upper limit for lightfluctuations. Local wind primarily determines the steepness ofcapillary-gravity waves which in turn dominate the irradiance variabilitynear the surface. Down to 3 m depth, maximum irradiance peaks that exceedthe mean irradiance E_d by a factor of more than 7 can be observed at low wind speeds up to5 m s⁻¹. The strength of irradiance fluctuations can be even amplifiedunder the influence of higher ultra-gravity waves; thereby peaks can exceed11 E_d. Sea states influence the light field much deeper; gravity waves can causeconsiderable irradiance variability even at 100 m depth. The simulationresults show that under realistic conditions 50% radiative enhancementscompared to the mean can still occur at 30 m depth. At greater depths, theunderwater light variability depends on the wave steepness of thecharacteristic wave of a sea state; steeper waves cause stronger lightfluctuations.

[学科分类] 海洋学与技术