Observational Study On Air-sea Flux In The North Yellow Sea During Spring And Autumn

Marine Atmospheric Boundary Layer (MABL) of momentum, heat and mass exchange is most important the main way of air-sea interaction , which directly affect the upper ocean and the structure of the lower atmosphere, thereby affecting ocean circulation and atmospheric circulation, causing climate change. Therefore, the turbulent flux of MABL research is very important for understanding air-sea interaction mechanism and improvement of a coupled regional ocean-atmosphere model .This article probes into the processing methods of turbulent data observed on ship and analyses the meteorological characteristics and air-sea flux in the North Yellow Sea during spring and autumn in 2007 by using the data of'908 Special Project'. The main conclusions are as below:(1)Normalized spectra of velocity obey the -2/3 power law of Kolmogorov similarity theory in the inertial subrange. In unstable conditions u spectra and v spectra have similar wavelength of spectral peak. In stable conditions wavelength of spectral peak of v spectra is bigger than u spectra. The vertical wavelength of spectral peak of w spectra is one order of magnitude smaller than the horizontal direction. The wavelength of spectral peak of u,v,w spectra are 80m~400m, 20m~200m, 12m~120m respectively. With stability increasing, turbulence energy decreases and the scale of vortex which has the largest contribution to the turbulent energy becomes smaller. Under stable condition, u spectra and v spectra present the upwarping phenomenon in low frequency, the slope is -2, and the upwarping phenomenon becomes more obvious with the stability enhancing.(2)The turbulence intensity is greater in unstable conditions than in stable conditions. The turbulence intensity has obvious difference in three directions. The longitudinal turbulence intensity is bigger than the lateral turbulence intensity, and vertical turbulence intensity is the smallest. Longitudinal and lateral turbulence intensity are mostly less than 0.5. Vertical turbulence intensity is normally less than 0.45. Turbulence develops strongly and the turbulence intensity can reach at 0.5 around when the wind speed is less than 2m/s; when the wind speed U>4m/s, the turbulence intensity decreases slowly as the wind speed increases; the minimum appears in the wind of 6m/s or so. When the wind speed U>6m/s, the turbulence intensity increases appreciably.(3)The upward solar radiation curve assumes double peak type in a fine weather. This is because after sunrise the angle of incident solar radiation becomes smaller. The incident intensity of short wave radiation increases but reflectivity of sea surface become smaller, which lead to a peak before noon. At noon the reflectivity of sea surface reaches the minimum and upward solar radiation follows by a valley. In the afternoon the angle of incident solar radiation becomes greater and the reflectivity of sea surface gradually increases leading to another peak after noon. Under zero-grade oceanic condition and small wind speed condition, the trend of the double peak type will become more obvious.(4)During the spring cruise the sensible heat flux (SHF) are all negative. The latent heat flux (LHF) are positive at most stations. The values of SHF and LHF are similar with an average of 14W/m2, which shows that the atmosphere transfer heat energy to the ocean through the form of SHF and the ocean transfers heat energy to the atmosphere through the form of LHF. During the autumn cruise LHF and SHF are all positive. The LHF are significantly greater than the SHF with the average of 115W/m2, 22W/m2 respectively, which shows that the ocean transfers heat into the atmosphere by the form of SHF and LHF, and LHF account for the dominant position. The observation data at continuous station during spring and autumn points out the diurnal variation of SHF and LHF is not obvious.(5)The daily average of heat budget at continuous station during spring is 207.8W/m2,shows that the ocean is being heated. The day and night mean heat budget are 396.9W/m2, -47.6W/m2 respectively. The daily average of heat budget at continuous station during autumn is -72.5W/m2,shows that the ocean is losing heat. The day and night mean heat budget are 62.7W/m2, -186.8W/m2 respectively.