Vertjcal Profjles of WaveCoherent Momentum Flux and Velocity - - PowerPoint PPT Presentation
Vertjcal Profjles of WaveCoherent Momentum Flux and Velocity Variances in the Marine Atmospheric Boundary Layer Lichuan Wu 1 , Tihomir Hristov 2 , and Anna Rutegersson 1 Lichuan.wu@geo.uu.se 1 Deapartment of Earth Sciences, Uppsala University,
Lichuan Wu1, Tihomir Hristov2, and Anna Rutegersson1 Lichuan.wu@geo.uu.se
1Deapartment of Earth Sciences, Uppsala University, Sweden 2Department of Mechanical Engineering, Johns Hopkins University, Baltjmore
wave-induced momentum fmux turbulence momentum fmux
parameterized as a functjon of the wind speed. parameterized as a functjon of wave parameters. Hogstrom et al., 2015. JAS
The atmosphere turbulence facilitates momentum and energy exchange between the atmosphere and ocean. Many studies suggest that the Monin-Obukhov Similarity Theory needed to be revised in order to considering wave infmuences. The momentum fmux over waves can be expresses as:
The wave-coherent momentum fmux decays exponentjally with height ?
surface wave-induced momentum flux peak wave number coefficient
2
Semedo et al. (2009) and Song et al. (2015)
10
Hanley and Belcher (2008)
1.4 5 for short waves
Makin and Mastenbroek (1996) Högström et al (2015)
The total momentum fmux over waves is roughly constant near the surface.
Sullivan et al., 2014. JAS; Högström et al., 2015. JAS
Measure the momentum fmux at the ocean surface is not possible!
Interpolation?
Do the wave-coherent momentum fmux and variances decay exponentjally with height? If so, Auw, Au and Aw are constant or a functjon of wave parameters?
Hristov et al., 2003. Nature
For neutral convectjve and wave aligned with wind conditjons over waves, the wave correlated fmuctuatjons can be described using Rayleigh equatjon : Based on logarithmic wind profjle, the wave-coherent fmuctuatjons:
a transfer function for the air flow’s response Ψ
The height that wind speed is equal to the wave phase speed
Theoretical model Exponentical decay fit
The wave-coherent momentum fmux decays approximately exponentjally with height.
wave slope
Using wave slope spectrum:
wave age at the spectal peak
Ω = 0.01 Ω = 0.02 Ω = 0.003
Rough Evaporatjon Duct experiment
Projectjng the measured velocity onto the Hiblert space of the wave-coherent signals: Wave coherent signals are calculated from spectral analysis:
(Hristov et al. 1998, 2003) (Veron et al. 2008; Grare et al. 2013)
Exponential fit line 95% confident line
Only the case with |z/L|<0.1 and regression coeffjcient R2>0.7 are shown.
Shear induced stress: Wind profile over waves: The ratio between the wave-induced wind and logarithmic wind:
The wave-coherent momentum fmux and variances decay approximately exponentjally with height. The exponentjal decay coeffjcient decays with the peak wave number. The wave-coherent momentum fmux with the small decay coeffjcient has a larger impact on the logarithmic wind profjle. The surface roughness length impact on the wave impact wind only on the near surface layer.
Comments and Questjons?