一次副高外围雨雾的诊断分析

应用实测资料和ECMWF、T213模式再分析资料,对2008年7月7-9日由于西太平洋副高的北进南撤,在河北中南部产生的雨雾天气过程进行了诊断分析.分析表明:500 hPa我国大陆高度场和温度场均是∏字型结构,对西太平洋副高的进一步西伸和水汽向河北的输送起到了制约作用;河北中南部上暖下冷的气团配置,是造成河北中南部大气稳定的一个原因.对流层弱的气压场和风场,是大气层结稳定的一种表现.500 hPa小冷槽的东移,是产生雷暴和短时强降水的触发机制,以及导致西太平洋副高南撤的一个重要因素.地面均压场的建立及近地面辐射冷却为大雾的形成提供了有利的风速和冷却条件.     

Evaluation of the 2.5-km Cloud-Resolving Storm Simulator in Predicting Local Afternoon Convection during the Summer in Taiwan

The forecast of summertime afternoon convection by numerical weather prediction models is highly challenging because of its weak dynamical forcing, small scale, and low predictability. To assess such an ability for future improvement, we evaluated the performance of the 2.5-km Cloud-Resolving Storm Simulator (CReSS) in predicting afternoon convection in Taiwan under weak synoptic conditions during the summers (May–October) of 2011 and 2012. For a total of 89 target days, daily CReSS forecasts in three ranges, starting at 0000 UTC (0800 LST) on the same day (D0), the day before (D-1), and 2 days before (D-2), were examined. With regard to the occurrence of afternoon convection anywhere in Taiwan, the predictive skill of the model was considerably high, as evidenced by the threat score (TS) and post-agreement (PA) of D0 (D-1) forecasts reaching 0.75 and 0.90 (0.50 and 0.79), respectively. While the score values decrease when Taiwan is divided into four regions (i.e., the forecast must be in the correct region to be considered a hit), the TS and PA for D0 (D-2) forecasts remain respectable at 0.44 and 0.73 (0.29 and 0.59). Among the four regions, the TS (0.48–0.65) and PA (0.77–0.83) for Central Taiwan are the highest with the best predictive skill. Overall, while the prediction of afternoon convection in the correct region is challenging, the 2.5-km CReSS model has considerable skill (TS ~ 0.30) even 2 days in advance, and can provide useful guidance for afternoon convection in Taiwan.     

The latest iteration of IPCC uncertainty guidance—an author perspective

The latest iteration of Intergovernmental Panel on Climate Change (IPCC) uncertainty guidance is simpler and easier to use than the previous version. However, its primary focus remains assessing “what is at risk” under climate change, thus is most suitable for dealing with the scientific uncertainties in Working Group I and part of Working Group II findings. I distinguish between tame and complex risks, arguing that the guidance is most suited to assessing tame risks. Climate change is a complex risk, and as such as can be divided into idealized, calculated and perceived risks. While science has claims to objectivity, risk has a specific value component: when measuring gain and loss, calculated risks compete with risky options to manage those risks. The IPCC is charged with calculating risk (IPCC 2007, p22) but the communication of key findings takes place in an environment of competing perceived risks. Recommendations for managing this complex environment include separating scientific and risk-based findings, treating uncertainties for each separately; strengthening the philosophical basis of uncertainty management; application of a methodical scientific research program; clearly communicating competing findings, especially in the social sciences; and application of multiple frame to policy-relevant findings as reflected in the literature.     

Measurements of stable carbon isotopic composition of ethane and propane over the western North Pacific and eastern Indian Ocean: A useful indicator of atmospheric transport process

Stable carbon isotopic composition of ethane and propane over the western North Pacific and eastern Indian Ocean between 31°N and 26°S was investigated from February through March 2004. The isotopic composition of ethane ranged from −28 to −18‰ and showed a gradual increase from north to south. Conversely, that of propane was between −31 and −24‰; it showed no systematic latitudinal variation. Investigation of the ethane/propane ratio indicates that ethane and propane that originated from northern mid-latitude countries in the eastern part of Eurasia were both transported into the western North Pacific region. However, the results of the isotopic analyses indicate the contribution of oceanic emission to the atmospheric propane during transport, although that contribution can not be discerned for ethane. A ship based stationary observation conducted in the western equatorial North Pacific showed that the isotopic composition of ethane varied from −25 to −19‰ and showed clear systematic diurnal variation: propane ranged between −32 to −26‰ and no such isotopic diurnal signal was observed. The diurnal variation for ethane is explained by entrainment of free tropospheric air, whereas the variation for propane was influenced by oceanic emissions as well as the entrainment. The contribution of oceanic emissions to the atmospheric propane inventory was considered from our isotopic observation. Isotopic composition of dissolved propane is estimated to be less than −38‰, and the contribution up to 79% was calculated when the isotopic composition of dissolved propane is assumed to be −40‰. Our study demonstrates that isotopic analysis can be more useful than ratio-based analysis to improve our present understanding of transport processes, especially for impact of the oceanic emissions on the atmospheric distribution of low level C₂–C₅ non-methane hydrocarbons such as propane in the remote marine atmosphere.