| The heat flux, including sensible heat flux and latent heat flux, exchanges in the Atmospheric Boundary Layer (ABL) and works as one of the most important mechanisms to climate change, and it is also crucial for air-sea interaction. With the evaporation and sensible heat flux, the atmosphere and ocean exchanges heat energy. At the same time, the momentum flux affects up-layer temperature, density, and oceanic salinity structure. The exchange of air-sea fluxes has been a hot topic in ocean and atmosphere research. Learning and understanding the turbulent structure of ABL is the premise, which also is very important for air-sea interaction. In this paper, using eddy covariance analysis, with the observed data from a settled location at the mouth of Zhu-Jiang River, the turbulent characteristics of ABL and heat flux in spring in 2006 have been investigated. The main conclusions are as below:(1) The atmospheric stratification is approximately neutral in spring. The friction velocity is linear with wind speed increasing.(2) The non-dimensional wind standard deviation accords with the power of 1/3, based on the Monin-Obukhov similarity theory (MOST). The turbulent intensity reaches its minimum value when the wind speed is between 4m/s and 6m/s, and when the wind speed is less than 2m/s the turbulent intensity is likely to reach the maximum value. The strong wind with its speed larger than 6m/s is likely to increase the turbulent intensity in horizontal direction.(3) The sea surface dynamic roughness has a quadratic curve relationship with 10m height wind speed. Under neutral condition the average drag coefficient is 1.180×10-3 and it displays linear change with wind speed when it is larger than 4m/s.(4) The heat flux increases from March to May, and it is much larger in May than in the two previous months. It is shown that several"pulse"processes induced by incursions of cold surges with cold and dry air masses influence the heat flux greatly. Because of the difference between air temperature and underlying surface temperature, the sensible heat flux in the stationary processes is negative in March and April, but it is positive in May. Monthly average data in different processes displays that the latent heat flux is alaway larger than the sensible heat flux, and it means the latent heat flux is dominant in this season.(5) During the observational period there are about 16.5% of total days in which cold surges occur, while the heat flux in cold surge days accounts for approximately 25.6% of the total heat flux variation, suggesting that the incursions of cold surges have significant impacts on the ABL heat flux.(6) The monthly average data of sea surface net radiation (RN) and net heat flux (QN) increase with months, and the increasing amplitude of RN from March to April are larger than that from April to May. But at the some time, QN in May is a little less than that in April, because evaporation and sensible heat flux become more active in May, making the ocean releases much more heat energy to atmosphere, which indicates that the heat flux stored up by ocean in April is the most.(7) During the monthly or seasonal diurnal cycle, the latent heat flux, with a maximum at 15:00 in the afternoon, is always positive. However, the sensible heat flux is positive in the daytime but negative in many hours at night, reaching its peak at about 9:00 in the daytime. RN and QN vary with the same time. Both of them are positive in the daytime, and RN is more than QN, but in the nighttime, both of them are negative, and the absolute value of QN is a little larger than RN. The difference between RN and QN in May is much greater than that in March and April, because the exchange capacity of heat fluxes has been reinforced in May, and it makes the ocean release much more heat energy. |
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