Canadillas, B.

Emeis, S.

Foreman, R. J.

Kinder, F.

Neumann, T.

English

KITopen

First Eddy-Covariance measurements The influence of humidity fluxes on atmospheric Preliminary resultsIntroduction: Knowledge of turbulence fluxes over the sea is relevantand is essential to improving bulk parameterizations used in numericalthe assessment of atmospheric stratification or static stability of the marinetemperature, but also the humidity content of the air close to the marineAlthough the impact of the humidity effect in the stability estimationneglected and rarely monitored in offshore conditions. As a part of theand assessment of the impact of turbulent humidity (Feuchte) fmeasurement system has been installed at FINO1 and has been operatingLI-7500A) was installed close to the existing sonic anemometer (Gilltemperature, wind velocity components and humidity are recorded atThis new measurement set-up at FINO1 gives us the opportunitybetween the sea and atmosphere. This poster presents the measurementimpact of the humidity fluxes on the estimation of atmospheric stabilityExperimental setupBeatriz Cañadillas1*, R.J. Foreman2, F. Kinder1DEWI GmbH - Deutsches Windenergie-Institut, Wilhelmshaven, Germany.  E2Institute of Meteorology and Climate Research, Karlsruhe Institute 2345Bowen ratio [−]Mast shadow Location: FINO1 offshore mast(lat. 54°0.86’N, long. 6°35.26’E) Height: 41.5 m LAT Data resolution: 20 Hz Instruments:Sonic anemometer: GillInstrument SOLENT R3-50.Open path infrared H2O/CO2 gasanalyzer: LI-COR LI-7500A.Fluxes are calculated on a 30-minbasis using the eddy-correlation (E-C)technique [1]. Rain data arediscarded.Additional mean meteorological data(temperature, pressure, relativehumidity,...) are used for the bulkformulation.Importance of Humidity Flux on Static StabilityIn Figure 2 the contribution of latent heat flux to the total buoyancy isevaluated by using the Bowen ratio =(QLH/QLE).Figure 1. Eddy-covariance system atFINO1.It can be seen that outsideof the mast shadow, themean Bowen ratio is about0.1, the expected value inthe MABL.0 30 60 90 120 150 180 210 240 270 300 330 360−2−101Wind Direction [°]Bowen ratio [−]References[1] G. Geernaert, S. Larsen. On the role of humidity in estimating marine surface layer stratification andscatterometer cross section. JGR 98: 927-932. 1993[2] E.L. Andreas. Spray-Mediated Enthalpy flux to the Atmosphere and Salt Flux to the Ocean in highwinds. J. Phys. Ocean. 40:608-619. 2008. where θ and θν are the potential and virtual potential air temperaturerespectively, κ the Von Karman constant (=0.40), g the gravity, u* thefriction velocity and <w’θ’> and <w’q’> the mean covariance oftemperature and humidity.Presented at: 11th German Wind Energy Conference7. - 8. November Figure 3 shows the importance of humidity to stability (zL-1), zL-1 increasing(conditions become more unstable) if zL-1LE is added in unstable conditionsand zL-1 decreasing (conditions become closer to neutral) if zL-1LE is addedin stable conditions.AcknowledgementsAs shown in [1], the static stability (zL-1), using the definition of virtualpotential temperature, can be partitioned between contributions due totemperature (zL-1H) and humidity (zL-1LE ) flux, i.e.,Figure 2. Bowen ratio as afunction of wind direction.The RAVE-TUFFO project is funded by the Federal Ministry for the Environment, Nature Conservationand Nuclear Safety (BMU). FKZ-0325304.1  zLHat FINO1stabilityfor a better general understanding of air-sea exchange processesmodeling to be applied in wind energy. Of particular importance isboundary layer (MABL) which depends on the wind speed andsurface and above.is well-known, the contribution of the latent heat flux is oftenRAVE research initiative within the new project TUFFO (Detectionluxes on turbulence in offshore wind parks), an eddy-covariancesince June 2012. The infrared fast-response hygrometer (LicorR3-50) at 41.5 m LAT (Figure 1). Turbulent measurements ofa sampling rate of 20 Hz.to accurately determine fluxes of momentum, heat and moistureset-up together with preliminary results concerning the relative.1, S. Emeis2, T. Neumann1-mail1* : b.canadillas@dewi.deof Technology, Garmisch-Partenkirchen, Germany0.40.5−2]Momentum flux75100−2]Heat flux−1 −0.75 −0.5 −0.25 0 0.25 0.5 0.75 1−1−0.75−0.5−0.2500.250.50.75zL−1 [−] zLLEFluxes: Eddy covariance versus bulk formulaFigure 3 : Contribution of zL-1LE (latent heat flux contribution) and zL-1H (sensible heatflux contribution) to the total value of zL-1 (Eq. 1) in different stability conditions.In Figure 4, the wind stress, heat and humidity fluxes are compared with abulk formulation [2] which also calculates the amount of latent heattransfer based on the generation of sea spray. The sea spray component ofthe total humidity flux is negligible at low wind speeds but will tend toincrease to roughly 10% of the total humidity flux at 15 ms-1.0 0.1 0.2 0.3 0.4 0.500.10.20.3E−C [Nm−2]Bulk [Nm−2]0 25 50 75 10002550E−C [Nm−2]Bulk [Nm−2]0 100 200 3000100200300E−C [Nm−2]Bulk [Nm−2]Humidity flux0 5 10 15 200.010.1110100100010000Humidity flux [Wm−2]Wind speed [ms−1]  Total Humidity fluxSea spray2012 Bremen, GermanyFigure 4. Comparison between measurements of the wind stress, heat and humidityfluxes with that calculated by a bulk meteorological model. Also included is a modelestimate of the contribution from sea spray to the total humidity flux as a function ofwind speed.ConclusionsThe humidity flux can contribute up to 25% of the magnitude of the staticstability. In general, this means that humidity fluxes make the ABL moreunstable (and hence less wind shear).

First Eddy-covariance measurements at FINO1. The influence of humidity fluxes on atmospheric stability. Preliminary results

https://publikationen.bibliothek.kit.edu/220092344/3816337

First Eddy-covariance measurements at FINO1. The influence of humidity fluxes on atmospheric stability. Preliminary results

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