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The Atmospheric Boundary Layer Height (ABLH) over Sea can have an important influence on the spread of pollution, the exchange between oceanic and atmospheric energy, the generation of sea fog, and the development of cumulus convection. In this paper, we analyzed the temporal and spatial variation of ABLH using the daily high-resolution L-band radar sounding data of Dalian Qingdao and Taizhou from 2005 to 2008. The main conclusions are as follows.(1) The boundary height in the evening in Qingdao and Taizhou is a little higher than that in the morning, and they are mostly in a stable and neutral condition. As for Qingdao, the highest ABLH occurs in the spring, which is related to the April-to-July seasonal inversion. As for Taizhou, the stable boundary layer occurs in the fall and winter, and it is influenced by the radiation inversion with an inversional height higher than that of Qingdao. However, the convectional boundary layer over Taizhou most occurs in summer, for it is influenced by the seasonal variation of the time of sunset and sunrise.(2) On the daily variation of ABLH of Qingdao, among the results of 01, 07, 13 and 19 LST, the highest boundary layer occurred at 13 LST, while the 19 LST one was a little higher than that of early morning, and the amplitude was situated between the land and the ocean. Wavelet analyses show that the daily variation of boundary layer is most dominant in September, which is because the prevailing wind in July and August in Qingdao is south wind and the temperature difference during day and night is decreased due to the effect of the ocean. Meanwhile, there is more cloudy and rainy weather in July and August, so the daily variation accounted for by thermal factors is decreased. Through the analyses of typical cases, the ABLH which was caused mainly by convection was found to be higher than that was caused mainly by dynamic shears.(3) The dry adiabatic method (DAM) and potential temperature gradient method (TGM) were both used to calculate the height of mixing layer. Compared with observational noon boundary layer height, the DAM is closer to the real. The seasonal variation of coastal stations, which is different from that of inland stations, has a lowest boundary layer in summer and a highest in fall. The boundary layer height of coastal stations in fall and winter is similar to that of the inland stations, but significantly lower in spring and summer. In spring, the seasonal stable stratification is the main factor of preventing the development of turbulence. In summer, due to the effect of the ocean, the temperature difference between day and night at coastal stations are obviously less than inland, resulting a lower mixing layer height. In that of Taizhou, the boundary layer height is lower due to the descend airflow caused by subtropical high; However, in the fall and winter, the prevailing wind is north wind with dry air mass from mainland; the daily variation caused by thermal factors increases, and the strengthened wind shear is also good for the development of turbulence; they are all contributing factors to higher boundary layer height; In fall and winter, the radiation inversion contributes less to the development of the mixing layer.(4) Wavelet analyses found that the ABLH at coastal stations have a 2-4 day weather scale oscillation, 10-20 day quasi-two-week oscillation, and 30-60 day quasi-40-day oscillation. The dominant time of the former two is the spring and fall. Taizhou is later than the other two stations by 1 month. The quasi-40-day oscillation in Dalian and Qingdao was dominant in summer, while winter for Taizhou. So the intraseasonal oscillation is regionally different.(5) The ABLH of the Yellow-East China Sea has significant seasonal variation -- the lowest in the summer and the highest in the autumn, its space distribution is lower in the northwest and higher in the southeast. The most important influence on the seasonal variation of ocean ABLH is SST-SAT and wind seasonal variations, which is different from the inland ABLH. Deeply exposed to this influence, the sensible and latent heat fluxes also make the same changes, and have an opposite phase compared to those inland. The east-west distribution of ABLH in the Yellow Sea is most obvious in November and December, significant north-south distribution of ABLH is obvious in the summer. The region which has the most distinct seasonal variation is the north yellow sea, which has a boundary layer up to 1000m, in contrast with the East China Sea with 700m boundary layer height.
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