A Preliminary Analysis Of Sources And Transport Pathways That Contribute To Trace Profiles Measured In The South Asian High

The South Asian High (SAH) is a dominant atmospheric feature in the upper troposphere-lower stratosphere (UTLS) during boreal summer besides the Arctic polar vortex. Satellite observations have shown that the anticyclone has a significant impact on the distribution of chemical tracers at UTLS region. However, the critical details of the mechanism of SAH which impact on the tracers are still unknown. Kunming campaign, which has great help on this problem, is the first in-situ measurements of water vapor and ozone within the anticyclone, and all of eleven balloon soundings showed different layered structures within the tracer profiles in UTLS. In this paper, backward trajectory of sampled air was calculated using a kinematic trajectory model to understand the sources and transport pathways, and to study the causes of the layered structures of ozone and water vapor within their profiles. The modelling results of the case at August 10th show that there are two important transport pathways contributed to the content of ozone and water vapor at UTLS-deep convection by Typhoon and vertical convection over Tibetan Plateu-both of them have significant impact on the distribution of chemical composition within SAH. Typhoon Morakot transports clean air containing much water vapor on sea surface to 160hPa-100hPa in the anticyclone, led to a higher relative humidity and lower ozone maxing ratio level at this altitude; while the vertical convection above the Tibetan Plateau transports the air on the land surface to the 200hPa-160hPa, compared to the air on the sea surface, the land surface air contains less water vapor and more ozone, thus it appears low relative humidity and high ozone mixing ratio at 200hPa-160hPa. On the other hand, the modelling results suggest that, although the SAH anti-cyclonic circulation is strong enough to prevent the air exchange between inside and outside of the SAH, the effect of the block is not completely. The southward invasion of mid-latitude stratosphere can influence the distribution of tracers inside SAH.We use TRAJ3D model to simulate backward trajectories of sampled air mass of these two cases, and analyze the air composition and their changes according to the source and transport pathways of the air mass, and give reasonable explanations of typical characteristic from the sounding results in Kunming. The TRAJ3D model with FNL wind fields as input data has a high application value in analyzing the influence of the distribution of tracers which made by convection and horizontal transport inside SAH. And it proved to be a successful tool for understanding the three-dimensional structure of SAH.