Observational Analyses of Baroclinic Boundary Layer Characteristics during One Frontal Winter Snowstorm

The evolution and characteristics of the baroclinic boundary layer for one frontal winter snowstorm were analyzed by using the well-documented dataset during Intensive Observation Period (IOP) 17 of STORM-FEST. It is found that when the warm moist air was lifted across the front, a great amount of latent heat release because of snowing increased the frontal temperature contrast to intensify frontogenesis. It is shown in the zig-zag section diagram of potential temperature that when the frontogenesis got stronger, a cold trough was formed and both low-level jet (LLJ) and upper-level jet (ULJ) emerged ahead of the front. In the strongest stage of frontogenesis, the frontal contrast of potential temperature of cold trough reached as high as 20 K. Hereafter the LLJ ahead of the front tended to weaken and the LLJ behind the front tended to strengthen. The frontal circulation system was dominated by the cold air advection behind the front, which transported the cold air behind the front forward to the warm area ahead of the front to weaken the cold trough and finally frontolysis occurred. It is shown by the analyses of turbulent characteristics of frontal baroclinic boundary-layer that the vertical shear (WV) above the boundary layer was very large, and the pumping of the strong wind shear in turbulent energy budget made the characteristic variables within the PBL well mixed. Sufficient moisture carried by southerly flow from the Mexico Gulf, and the strong baroclinity of the frontal boundary layer played key roles in this frontal winter snowstorm, and the large-scale ULJ behind the cold front is also advantageous to the development of the convective boundary layer.

ANALYSIS OF THE ATMOSPHERIC AEROSOL OPTICAL DEPTH OVER CHINA IN 1980s

This paper retrieves the yearly and monthly mean 0.75μm aerosol optical depth(AOD)of 41 A-class solar radiation stations over China from 1979 to 1990,and analyzes the spatial and temporal distribution of AOD over China mainland.The data employed are daily direct solar radiation and sunshine duration,as well as the TOMS version-7 ozone observation data in the same time.The results indicate that the Siehuan Basin is the largest center of yearly mean AOD over China.and the other two larger centers lie in Wuhan City and the South Xinjiang Basin, separately.AOD values are also relatively larger in the middle-and-lower reaches area of Changjiang River.Shandong Peninsula and coastal area of Guangdong Province:while in Yunnan Province,coastal area of Fujian Province.most parts of Northwest and Northeast China,AOD values are relatively smaller.The distribution of AOD varies with different months.In most parts of China.the maximum of AOD occurs in spring season;but the minimum varies in different regions,From 1979 to 1990.in the Qinghai-Xizang Plateau,West Siehuan Basin,North Guizhou Province.most areas of the middle-and-lower reaches of Changjiang River,Shandong Peninsula and west part of South Xinjiang Basin.AOD shows an increasing trend.But in Northeast China, most part of Northwest China,Yunnan-Guizhou Plateau,western Guangxi Region and the coastal areas of East China,AOD shows decreasing tendency.Generally,the seasonal variation characteristics of AOD in China can be classified into four typical models,i.e.,mono-modal types A and B,bimodal and Poly-modal.

Carbon emissions and sinks in agro-ecosystems of China

Besides ruminant animals and their wastes, soil is an important regula ting medium in carbon cycling. The soil can be both a contributor to climate cha nge and a recipient of impacts. In the past, land cultivation has generally resu lted in considerable depletion of soil organic matter and the release of greenho use gases (GHGs) into the atmosphere. The observation in the North-South Transec t of Eastern China showed that climate change and land use strongly impact all s oil processes and GHG exchanges between the soil and the atmosphere. Soil manage ment can restore organic carbon by enhancing soil structure and fertility and by doing so mitigating the negative impacts of atmospheric greenhouses on climate. A wide estimation carried out in China shows that carbon sequestration potentia l is about 77.2 MMt C/a (ranging from 26.1—128.3 MMt C/a) using proposed IPCC a ctivities during the next fifty years.