Analysis on mechanisms of anomalous variations of tropopause pressure over the Tibetan Plateau during summer in Northern Hemisphere

Using the monthly mean data from NCEP-NCAR reanalysis, through building tropopause pressure index, we investigated the mechanisms of anomalous variations of tropopause pressure over the Tibetan Plateau during summer in Northem Hemisphere. For comparative analysis we selected representative years of 1992 and 1998 to study, and they were respectively the highest and the lowest year oftropopause pressure anomaly over the Tibetan Plateau. The results are summarized as follows： （1） Over the Tibetan Plateau, the variations of tropopause pressure are well correlated respectively with anomalous temperature and geopotential height in both troposphere and stratosphere. Besides, the anomalous tropopause pressure has also close relation with anomalous surface temperature in the Tibetan Plateau. In 1992, the surface temperature was anomalously low, correspondingly, the tropopause pressure over the Tibetan Plateau was anomalously high; but in 1998, the opposite was the case. （2） Over the Tibetan Plateau, the correlation of tropopause pressure and OLR （Outgoing Longwave Radiation） is found to be positive. Furthermore, by further diagnosing the circulation fields between 850 hPa and 200 hPa levels and the whole troposphere vapour field, we found out that the anomalously high tropopause pressure in 1992 corresponded to the anticyclonic divergence of low level wind fields and the cyclonic convergence of high level wind fields, and coupled with divergence of the whole troposphere vapour fields along with the South Asian High weakened at the same time. While in 1998, the case was opposite to that in 1992. These facts indicated that the anomalous convection resulted in the significant difference oftropopause pressure in 1992 and 1998 over the Tibetan Plateau. （3） The vertically integrated heat budget anomalies were responsible for explaining tropopause pressure anomalies in 1992 and 1998 over the Tibetan Plateau.

Interannual variability in soil respiration from terrestrial ecosystems in China and its response to climate change

Soil respiration is an important process in terrestrial carbon cycle.Concerning terrestrial ecosystems in China, quantifying the spatiotemporal pattern of soil respiration at the regional scale is critical in providing a theoretical basis for evaluating carbon budget.In this study, we used an empirically based, semi-mechanistic model including climate and soil properties to estimate annual soil respiration from terrestrial ecosystems in China from 1970 to 2009.We further analyzed the relationship between interannual variability in soil respiration and climatic factors (air temperature and precipitation).Results indicated that the distribution of annual soil respiration showed clear spatial patterns.The highest and lowest annual soil respiration rates appeared in southeastern China and northwestern China, respectively, which was in accordance with the spatial patterns of mean annual air temperature and annual precipitation.Although the mean annual air temperature in northwestern China was higher than that in some regions of northeastern china, a greater topsoil organic carbon storage in northeastern China might result in the higher annual soil respiration in this region.By contrast, lower temperature, less precipitation and smaller topsoil organic carbon pool incurred the lowest annual soil respiration in northwestern China.Annual soil respiration from terrestrial ecosystems in China varied from 4.58 to 5.19 PgCa-1 between 1970 and 2009.During this time period, on average, annual soil respiration was estimated to be 4.83 PgCa-1 .Annual soil respiration in China accounted for 4.93%-6.01% of the global annual soil CO2 emission.The interannual variability in soil respiration depended on the interannual variability in precipitation and mean air temperature.In order to reduce the uncertainty in estimating annual soil respiration at regional scale, more in situ measurements of soil respiration and relevant factors (e.g.climate, soil and vegetation) should be made simultaneously and historical soil property data sets should also be established.

Climate Analysis of Tornadoes in China

Based on analysis of historical tornado observation data provided by the primary network of national weather stations in China for the period from 1960 to 2009, it is found that most tornadoes in China （85%） occurred over plains. Specifically, large numbers of tornado occurrences are found in the Northeast Plain, the North China Plain, the middle-lower Yangtze Plain, and the Pearl River Delta Plain. A flat underlying surface is conducive to tornado occurrence, while the latitudal variation of tornado occurrence in China is not so obvious. Tornadoes mainly occur in summer, and the highest frequency is in July. Note that the beginning and the time span of tornado outbreaks are different in North and South China. Tornadoes occur during May-September in South China （south of 25°N）, June-September in Northeast China （north of 40°N）, July-September in the middle-lower Yangtze Plain, and July-August in North China （between 25° and 40°N）. More than 80% of total tornadoes occurred during the above periods for the specific regions. The 1960s and 1970s have seen about twice the average number of tornadoes （7.5 times per year） compared to the mean for 1960-2009. The most frequent occurrence of tornado was in the early and mid 1960s; there were large fluctuations in the 1970s; and the number of tornadoes in the 1980s approached the 50-yr average. Tornado occurrences gradually decreased in the late 1980s, and an abrupt change with dramatic decrease occurred in 1994. The decrease in the tornado occurrence frequency is consistent with the simultaneous climatic change in the meteorological elements that are favorable for tornado formation. Tornado formation requires large vertical wind shear and sufficient atmospheric moisture content near the ground. Changes in the vertical wind shear at both 0-1 and 0-6 km appear to be one important factor that results in the decrease in tornado formation. The changing tendency of relative humidity also has contributed to the decrease in tornado formation in China.

A new estimate of global soil respiration from 1970 to 2008

土壤呼吸(R s ) 是在陆上的生态系统加重我们碳周期的理解的关键过程之一。在有在最高、最低的估计之间的 70 Pg C a1 的差别的以前的全球 R s 估计的大无常遗体。因此，现在的学习试图估计全球年度 R s 并且用包括了气候的因素(温度和降水) 和表层土(020 厘米) 的一个半机械学的、以经验为主地基于的模型在全球年度 R s 调查 interannual 和空间可变性器官的碳存储。从 147 个测量地点的年度 R s 的大约 657 出版研究在这元分析被包括。气候，表面空气温度，和土壤性质上的从 1970 ～ 2008 的全球数据集合是镇定的。蒙特卡罗方法被用来宣传模拟错误到全球 R s。结果显示吝啬的年度全球 R s 是 94.4 Pg C a1，增加在粗略地从 1970 ～ 2008 的 0.04 Pg C a1 (0.04% a1 ) 。R s 率增加了从更冷，更干燥并且少些玷污充满碳的区域到更温暖、更潮湿、更充满碳的区域。最高的 R s 率出现在热带森林里，当最低的在极、荒芜的区域时。年度 R s 与全球温度异例直接相关，建议在温度的 interannual 可变性为在预言的全球 R s 的 interannual 变化负责。全球 R s 从高纬度的地区增加了到低纬度的地区。进一步的研究被建议探索在土壤呼吸和植被人物之间的关系。