Study On Boat Based Observations Of The Air-sea Flux In The Summer Over The Bohai Sea

Previous studies on turbulence in the atmosphere boundary layer showed that the transferring of turbulence properties plays significant roles in the transferring and balance of momentum, heat and water vapor. Since the 20 century, people have realized the importance of ocean, and also known the close relationship between ocean and atmosphere. Atmospheric-oceanic boundary is the bridge of energy and matter exchange between air and sea. The observation of turbulent flux between air and sea is much important in the study of global climatic variation.In this study, we tried to observe the air-sea momentum, heat and CO2 fluxes in the summer over Bohai Sea by eddy correlation system with help of ship movement and gesture monitoring system. The ship movement and gesture monitoring system could record the speed of eddy correlation system relative to earth coordinate, and also the rotating, rocking and rolling angles in high precision. Moreover, we calculated the real 3-D wind speed according to boat movement modified equation proposed by Edson (1998). By this observation and data process, we studied the basic effects of ship shaking on air-sea flux observation.Based on the observation data from summer cruise over the Bohai Sea in 2005, we analyzed turbulence structure and air-sea fluxes in different weather conditions. Moreover, the influences of wind speed and air temperature on turbulence intensity and air-sea flux are also investigated. Conclusions are listed as follows.1. In clear sky condition, when air-sea boundary layer is in unsteady stratification, the normalized spectrum of wind speed complies with -2/3 exponential rule in the inertial subarea, but when the stabilization parameterξis close to 0, i.e. the neutral stratification, the normalized spectrum of wind speed doesn't comply with this classic rule in the inertial subarea. In foggy condition, the spectrum still abides by the rule in this subarea. Additionally, turbulence meets the isotropic condition approximately in clear sky, and it entirely meets the isotropic condition in foggy sky. 2. In clear sky condition, turbulent intensity increases with increases of the stabilization, which indicates the particularity of turbulent intensity. In foggy condition, turbulent intensity decreased with increases of the stabilization, and the wind speed has no clear effect on the turbulent intensity. In a typhoon process, turbulent intensity increases with the increases of the stabilization, and they have significant positive correlation.3. The influences of wind speed on turbulent intensity are different in different sky conditions. If it is in the neutral stratification, turbulent intensities are Iu>Iv>Iw, but in the typhoon, Iv is usually close to Iw, and in some times, Iv>Iu. Iw reaches the maximum in the clear condition, but Iu and Iv get the maximum in the typhoon process. The total turbulent intensity in typhoon is the strongest, and then the clear sky condition and the weakest is in the foggy condition.4. Both in clear and foggy conditions, sensible and latent heat flux have negative correlations to the air temperature. In clear sky, the daily mean of sensible heat flux is 3.0 W/m~2. In foggy condition, it is -5.9 W/m~2, and transferred from atmosphere to ocean. However in the clear condition, transfer direction of sensible heat may alter due to the variation of air temperature. Latent heat flux has significantly positive correlation with wind speed in the clear sky, and the daily mean value is 88.5 W/m2.5. In clear sky, the mean wind speed is 8.2 m/s; mean momentum flux is 0.138 N/m~2s. In foggy sky, wind speed is 6.1 m/s; momentum flux is 0.03 N/m~2s. In typhoon process, wind speed is 12.0 m/s, momentum flux is 0.30 N/m~2s. We could sum up that the wind speed is key factor of the momentum flux.6. In worse sea environment, it is necessary to revise the 3-D wind speed by ship movement and gesture monitoring system when we use eddy correlation to observe the air-sea boundary layer. If it is not revised, the calculation result will deviate a lot from the real condition.