Observational Study Of Atmospheric Boundary Layer Structure Over Heterogeneous Surface In Baiyangdian Area

Heterogeneous underlying surface, which generally means the inhomogeneities over the surfaces, includes mainly thermal and dynamic heterogeneities. Since real underlying surface is always heterogeneous and complex to some extent, the research about it has become the hot topic in the field of current Atmospheric Boundary Layer (ABL) research. The data, which obtained from the radiosondes carried by free balloon in the Baiyangdian Experiment, is used to analyse the structures of ABL over the land and the water surfaces. And some conclusions are drawn as follows:1. During the experiment, the ABL over the two surfaces both show the general characteristics of ABL. That is to say, profiles of wind, temperature and specific humidity all present the typical distribution formation as theirs both in Convective Boundary Layer (CBL) and in Nocturnal Boundary Layer (NBL). In daytime, the ABL over the water surface is deeper than that over the land. For the former, its height is about 2000 m, while for the latter, it is about 1800 m. At the same time, there are both capped inversions at the top of ABL over the two places. In nighttime, because of radiative cooling, inversions together with humidity inversions always appear. Besides, Low-Level Jet (LLJ), whose development is related close with the evolution process of inversion, also emerges sometimes in two places.2. Wind always gets stronger from day to night, while it blows faster over the water than over the land whenever, and the wind velocity difference between the two places is greater when it comes near to the surface or in night. During the experiment, the prevailing wind over the land is southwesterly, and it changes into northerly wind over 1600 m. While, over the water surface, it is northwest by north and changes into southerly wind over 1400 m. In addition, there exists a local circulation, but it is much weak and is mostly in north-south direction.3. Surface water temperature and the air temperature over the water surface are both higher than theirs of the land. The average surface water temperature is about 2.5℃ higher than that of the land surface, and the daily average temperature below 1000 m over the water surface is about 3.14℃higher than over the land. Furthermore, the temperature difference between the two places is greater in night than in day, and it also gets greater with the height within the observed height.4. Specific humidity over the land is larger than over the water, which daily average specific humidity below 1000 m of the former is about 2.35 g?kg-1 larger than the latter. Also the specific humidity difference between the two places is greater in day than in night or when it comes near to the surface, and it is very small when it gets the height about 2000 m. In addition, the diurnal variation of specific humidity over the water is greater than that over the land, and the specific humidity over the water is larger in night than in day, while for the land, on the contrary, it is larger in day than in night.5. Owing to different underlying surface, the inversions over the two places present different characteristics. In a word, over the land surface, surface inversions appear more frequently, and average intensity of inversions below 300 m is greater, and the characteristic of burst of inversions is more obvious. On the other hand, over the water surface, elevated inversions emerge more times, and average thickness of inversions below 300 m is larger. Meanwhile, for the two places, many-layer inversions both appear frequently, and there is both some a negative correlation between inversion intensity and its top height below 300 m, and humidity inversions also often happen together with the inversions.