青藏高原人工水汽通道对西北地区夏季降水及环流的影响Ⅰ.对降水过程个例的模拟试验

为探讨用人工方法在青藏高原地区打开水汽通道后,对西北地区夏季降水及环流的影响,我们使用我国有限区域模式对1998年汛期降水的个例做了模拟试验.结果表明,在青藏高原上打开通道对我国汛期降水有所影响,但要使西北地区降水增加,改变该地区的干旱缺水状况,效果是很不明显的.     

淹没植物条件下明渠KH涡的垂向几何尺度和频率

含淹没植物明渠中存在的Kelvin-Helmholtz（KH）涡,对水流能量交换和物质输移具有直接的影响。基于淹没刚性植物条件下的水槽实验,利用粒子图像测速技术（PIV）得到瞬时流速场和涡量场,定量刻画KH涡的垂向几何尺度（上下边界和垂向作用范围）,结合三维声学多普勒流速仪（ADV）测量的流速时间序列和小波变换方法,分析KH涡的频率,研究植物淹没度对KH涡上下边界位置、作用范围和频率的影响。研究发现:本实验确定的KH涡上、下边界与根据能量分布计算得到的混合层上、下边界基本一致;在本实验条件下,KH涡上边界为0.7~0.8倍水深,下边界在植物密度一定时围绕一常数波动,KH涡的频率在0.14~0.20 Hz之间;随着淹没度的增大,KH涡的上边界升高,下边界变化不明显,作用范围和频率增大。     

山区生态果园建设对农业小气候的影响

在四川省凉山彝族自治州西昌市海拔1 500 m的半山荒坡地种植系列果树,建设生态果园,观察其气温、空气相对湿度和地温变化。数据分析表明,生态果园建设对微区气候条件有很好的调节作用。气温日较差变小,年平均减小0.7℃,空气相对湿度明显增加,年平均提高12%,平均地表温度的日较差减小,年平均减小3.6℃,极端地表高温和极端地表低温有所下降。     

关于《科学发现者》教材和美国学校地理教育的一些思考

近来接连看到了3篇文章介绍美国《科学发现者》教材及其对中国学校地理教育的启示,收获很大,也有不同意见。这里结合我们在编辑和教学工作中对于美国学校地理教育的了解,谈点看法,以求指正。     

THE SPATIOTEMPORAL CHARACTERISTICS OF LIGHT RAIN DAYS AND LOW CLOUD COVER UNDER HEAVY POLLUTION OVER SOUTH CHINA

By using the data set of light rain days and low cloud cover at 51 stations in South China (SC), and the method of linear regression and correlative analysis, we analyze the spatiotemporal characteristics of the light rain days and low cloud cover including annual variation and long-term seasonal change. The results are as follows: (1) The trends of light rain days and low cloud cover over SC are opposite (light rain days tended to decrease and low cloud cover tended to increase in the past 46 years). The value distributed in east is higher than that in west, and coastal area higher than inland area. (2) The regression coefficients of light rain days and low cloud cover during 1960–2005 are 4.88 d/10 years and 1.14%/10 years respectively, which had all passed the 0.001 significance level. (3) Variations of light rain days are relatively small in spring and summer, but their contributions are larger for annual value than that of autumn and winter. (4) There are two regions with large values of aerosol optical depth (AOD), which distribute in central and southern Guangxi and Pearl River Delta (PRD) of Guangdong, and the value of AOD in PRD is up to 0.7. The aerosol index distributed in coastal area is higher than in the inland area, which is similar to the light rain days and low cloud cover over SC. Aerosol indexes in SC kept increasing with fluctuation during the past 27 years. The GDP of the three provinces in SC increased obviously during the past 28 years, especially in Guangdong, which exhibited that there is simultaneous correlation between light rain days with the variables of low cloud cover and release of aerosols over SC during 1960 to 2005.     

Impacts of a Large-scale Adaptive Blending Scheme for CMA-MESO on Regional Forecasts-A Case Study of Typhoon Haima

Large-scale atmospheric information plays an important role in the regional model for the forecasts of weather such as tropical cyclone (TC). However, it is difficult to be fully represented in regional models due to domain size and a lack of observation data, particularly at sea used in regional data assimilation. Blending analysis has been developed and implemented in regional models to reintroduce large-scale information from global model to regional analysis. Research of the impact of this large-scale blending scheme for the Global / Regional Assimilation and PrEdiction System (CMA-MESO) regional model on TC forecasting is limited and this study attempts to further progress by examining the adaptivity of the blending scheme using the two-dimensional Discrete Cosine Transform (2D-DCT) filter on the model forecast of Typhoon Haima over Shenzhen, China in 2016 and considering various cut-off wavelengths. Results showed that the error of the 24-hour typhoon track forecast can be reduced to less than 25 km by applying the scale-dependent blending scheme, indicating that the blending analysis is effectively able to minimise the large-scale bias for the initial fields. The improvement of the wind forecast is more evident for u-wind component according to the reduced root mean square errors (RMSEs) by comparing the experiments with and without blending analysis. Furthermore, the higher equitable threat score (ETS) provided implications that the precipitation prediction skills were increased in the 24h forecast by improving the representation of the large-scale feature in the CMA-MESO analysis. Furthermore, significant differences of the track error forecast were found by applying the blending analysis with different cut-off wavelengths from 400 km to 1200 km and the track error can be reduced less than by 10 km with 400 km cut-off wavelength in the first 6h forecast. It highlighted that the blending scheme with dynamic cut-off wavelengths adapted to the development of different TC systems is necessary in order to optimally introduce and ingest the large-scale information from global model to the regional model for improving the TC forecast. In this paper, the methods and data applied in this study will be firstly introduced, before discussion of the results regarding the performance of the blending analysis and its impacts on the wind and precipitation forecast correspondingly, followed by the discussion of the effects of different blending scheme on TC forecasts and the conclusion section.     

青藏高原人工水汽通道对西北地区夏季降水及环流的影响——Ⅱ.对月降水量的模拟试验

采用数值天气预报模式对月降水量进行模拟．探讨“空中调水”的可能性问题，即观察在青藏高原上打开一些通道对我国西部地区夏季降水将产生何种影响。这里，我们讨论１９９８年６月和７月两月累计雨量的模拟。结果表明，如果在高原中部开一个通道，夏季的暖湿气流可以沿通道向北输送，使得通道内的水汽含量有所增加，在通道中部中心地段，６、７两月份月降水量约增加５０～２００ ｍｍ，亦即在局部地区有明显增雨效果，但除此局部地区之外几无影响，且在入口和出口地区降水反而减少，水汽也不能输送到西北地区。在高原西部打开通道几乎无影响。对模拟环流的分析表明，开凿通道后，仍难于改变高原周围的环流形势，尤其是塔里木盆地上空的下沉气流没有大改变，因而．即使有部分水汽能够到达高原以北．仍很难增加该区域大范围的降水。     

CMIP5气候模式对中国东部夏季降水年代际变化的模拟性能评估

使用分类集合的方法评估了第五次耦合模式比较计划(CMIP5)多个耦合模式对中国东部夏季降水年代际变化的模拟性能.结果表明,在评估的38个模式中,仅有6个模式(第1类模式)可以成功再现1970年代末中国东部夏季降水年代际变化的主要特征,即长江流域降水偏多、而华北和华南偏少.这些模式模拟的成功归因于它们能较好再现1970年代末东亚夏季风的年代际减弱及相关的环流场的变化,包括东亚沿海的偏北风异常以及西太平洋副热带高压的偏向西南、强度增强等.而对降水年代际变化模拟很差的第2类模式,则模拟出不出东亚夏季风的这种减弱特征.进一步的分析表明,两类CMIP5模式对太平洋年代际振荡(PDO)空间分布特征都有较好的再现能力,但对PDO年代际转变特征的模拟能力则差异较大.第1类模式能很好地模拟出1970年代末热带海洋的增暖和相关的PDO位相由负到正的转换,而第2类模式所模拟的PDO位相转变与观测完全相反,且也不能模拟出热带中东太平洋海洋的年代际增暖及江淮流域夏季的变冷,因此导致该类模式对1970年代末东亚夏季风的减弱和中国东部夏季雨型的年代际转变没有模拟能力.由此也表明,对耦合模式来说,中国夏季降水年代际变化的模拟能力在很大程度上取决于模式对海洋年代际变化信号的模拟.