Study On Atmospheric Boundary Layer Over The Arctic Ocean By Using SHEBA Data

The investigation of atmospheric boundary layer structure over the Arctic Ocean is an important issue in the Arctic environment science. Understanding the Arctic boundary layer structure can not only provide the basis for the study of atmospheric pollution in the Arctic but also enrich the boundary layer theory and contribute to improving the accuracy and precision of regional and global climate models. Revealing the characteristic of the Arctic boundary layer height helps better understand the boundary layer structure over Arctic Ocean.Utilizing the aircraft sounding data collected from SHEBA campaign (1998.5-1998.7), we identified the suitable profile method for Arctic boundary layer height estimation through validating against the'true'boundary layer height from aircraft turbulence measurement. Furthermore, in order to inspect the characteristic of the Arctic boundary layer height, this method was applied to estimate the boundary layer height from the one-year GPS sounding obtained during the SHEBA campaign (1997.10-1998.10). We found that the temperature gradient method gives a good estimation of the boundary layer height and the optimal threshold value of temperature gradient for stable boundary layer and convective boundary layer should be taken as 6.5 K/100m and 1.0 K/100m respectively. The median values of the Arctic boundary layer height in May and June are 400m and 430m and they are much greater than those in July and August, which are 180m and 320m respectively. The maximum boundary layer height was 1150m occurring in May.We also characterized the boundary layer inversion and low-level jet over the Arctic Ocean. Results show that 96% soundings (11:15和23:15) have near-surface inversion layers, therein 22% were surface-based and 70% were between 250 m and 850 m. In the winter half year, the frequency of the surface-based inversion, the inversion depth and the temperature change in the inversion layer were stronger than those in summer half year. During the year, the low-level jets occurred with the frequency of 41% and the average height of 520 m. The jets appeared mostly around 150 m, and 70% of them were below 600 m. The mean speed of the jets was 10.6 ms-1 with the predominant wind direction East and northeast, and 75% of them have the speed from 4 ms-1 to 13 ms-1. From the analysis of turning angle distribution between the jet core and the ground wind, it could be inferred that inertial oscillation is the main cause of the low-level jet in the Arctic region.Clear sky is more often in winter than it is in summer in the Arctic. The relative humidity over the sea ice in summer is always up to 100%. The humidity inversion often developed with the temperature inversion, it may be caught by the temperature.