Estimation Of Air-Sea Fluxes From A Buoy Observation

Air–sea fluxes play important roles on air-sea interactions, coupled ocean–atmosphere modeling, dynamic environment prediction of marine and atmosphere.In this paper, a flux system deployed on the buoy has been described which is capable of directly estimating the air-sea fluxes after removing the contamination in the signal due to the buoy motion. A triple loop fitting method has been demonstrated for determining the three angular offsets between measurement axes of the sonic anemometer and motion pack. The data collected during the experiment in the North Yellow Sea is used to discuss the effect of buoy motion on the turbulence spectra, frequency-weighted cospectral density function, Ogive curve and fluxes. Results show that the motion correction not only greatly improved the estimation of the momentum flux but also has large impact on calculated sensible heat flux, latent heat flux and gas exchange (such as water flux and CO2 flux). The correlation coefficients of fluxes calculated by the eddy correlation method and bulk aerodynamic method are greatly improved after motion correction. The water vapor and CO2 fluxes at two levels also become similar after motion correction.Based on a total of 14 days'data obtained from the 1st moored buoy observation located at the Yellow sea, the cutoff time scale (CTS) used in the calculations of the air-sea fluxes by eddy covariance method is determined by the multiresolution decomposition method, the behaviors of the CTS and its effect on the sensible heat flux are analyzed then. Results show that the cutoff time scale estimated by the multiresolution decomposition method can be used to separate the real contribution from turbulent and mesoscale fluxes to the total air-sea fluxes efficiently. The CTS increases with the turbulence intensity or the wind velocity and the CTS of the sensible heat flux is always longer than that of the momentum flux. When the turbulence intensity is less than 0.2 m/s, most of the CTS of momentum and sensible heat fluxes are around 100 s and the difference between the turbulent and total fluxes is large; when the turbulence intensity is larger than 0.3 m/s, most of the CTS are around 800 s and the turbulent flux is similar to the total flux. It is found that the CTS has small effect on the flux average value while large effect on the flux uncertainty when we calculate and analyze the average and uncertainty of sensible heat flux. The difference between the two effects will become smaller as the turbulence intensity increases. The NCEP (NCEP1 and NCEP2) reanalyzed marine meteorological parameters and sea surface heat fluxes are compared with the 2nd moored buoy observation in the north-western Yellow Sea. The analysis shows that: The NCEP reanalyzed marine meteorological parameters are credible over the Yellow Sea. The marine meteorological parameters and turbulent heat fluxes from NCEP2 are more close to that from the buoy while the net radiation flux computed from NCEP1 is more close to that from the buoy. A more appropriate bulk algorithm to recalculate surface heat fluxes is recommended. The NCEP1 recalculated net heat flux is underestimated by 42% while the NCEP2 recalculated net heat flux is overestimated by 5%.