基于雷达和微波辐射计的湖北省冷季“高架雷暴”特征分析

利用常规观测、加密自动气象站、三维闪电定位仪、天气雷达和地基微波辐射计资料等,对湖北冷季（2014年11月）发生的3次高架雷暴过程进行了分析。（1）3次过程发生在地面冷锋后部地面冷气团中,主要以短时强降水和频繁的雷电活动为主,是典型的冷季“高架雷暴”,对流区位于地面冷锋后部500 km左右。（2）地面到925 hPa的冷垫,迫使暖湿气流爬升,在925 hPa逆温层附近触发对流,冷垫之上西南暖湿气流越强,对流越旺盛,雷达径向速度剖面可以明显看到1 km之下的冷垫。（3）冷季高架雷暴雷电活动剧烈,CG（地闪）占总闪比例60%以上,而+CG则占CG的40%左右,闪电频次和降水有很好的时空对应关系,CG出现在较强降水中心附近及周围,IC和CG突增对降水均有一定的时间提前量。CG更靠近强回波中心,且和≥30 dBZ的回波位置对应较好,IC则分布在雷暴单体外侧回波强度≥15 dBZ的区域。0 ℃等温线以上的（最大）回波强度达到43 dBZ以上或者18 dBZ回波顶高超过7.5 km是湖北冷季高架雷暴是否发生雷电的重要预警因子。（4）地基微波辐射计温度、湿度廓线和探空曲线基本吻合,可以看到明显的冷垫、逆温层及西南急流。基于微波辐射计资料计算的不稳定指数变化特征对冷季高架雷暴的短临预报有重要的实际应用价值。当A指数、TT指数、K指数和T_850-500出现快变抖动时,伴随抖动加剧可以判断将会有雷暴天气发生,当波动曲线开始下降并变得平稳,表示雷暴减弱消亡;θ_{se 850}在雷暴出现后跃增并在320 K附近抖动,雷暴结束后下落到290 K的平稳状态;T_d850在雷暴活跃阶段近乎为0 ℃;T_850-500在雷暴发生前是一个缓慢下降的过程,雷暴结束后大气趋于稳定。      

基于卫星遥感和地面观测资料的汾渭平原空气污染分析

选取中国汾渭平原地区作为研究对象,利用MODIS、OMI和CALIPSO多源卫星遥感资料,同时结合环境监测国控站点污染6要素等逐小时地面环境监测数据以及能见度、霾天气现象记录等地面气象要素资料,综合分析了2013—2018年秋冬季汾渭平原空气质量状况、气溶胶的组分,探讨了卫星遥感气溶胶光学厚度（Aerosol Optical Depth,AOD）与地面污染物浓度的关系,并结合中国气象局化学天气预报系统-EMI评估模式（CUACE-EMI）资料对气象条件和污染减排影响进行评估。结果表明：11个代表城市中有6个城市秋冬季有接近或超过一半的时刻处于污染状态,且污染发生时,各代表城市大多数时刻处于中度及其以上污染级别;三门峡、临汾、运城和西安是霾和重度霾高发的城市,其重度霾爆发频率高达11.63%—14.78%;汾渭平原秋冬季首要污染物为PM_2.5和PM₁₀,以污染沙尘、沙漠沙尘和烟尘为主,出现频率分别为36.24%、25.14%和22.96%;MODIS AOD与空气质量指数（Air Quality Index,AQI）、PM_2.5、PM₁₀质量浓度之间的相关系数分别为0.72、0.70和0.64;汾渭平原2018年气象条件的变化使PM_2.5浓度较2013年、2014年、2015年、2016年和2017年同期上升了17.06%、1.58%、4.34%、11.25%和5.75%,减排措施使PM_2.5浓度较2013年、2014年、2015年、2016年和2017年同期分别下降了8.74%、28.01%、4.93%、3.16%和42.62%。     

“Pilot chimney” on the waterloo campus

A brief survey is given of the sources, the methods of injection into the atmosphere, and the mechanisms of deposition into bodies of water for various atmospheric pollutants which contribute significantly to the pollution of large bodies of water. Specific examples of the relative importance of atmospheric sources are included where data are available. Programs of the Canadian Atmospheric Environment Service in this field of research are outlined.     

土壤有机质高光谱估算研究进展

土壤有机质是土壤的重要组成部分,对许多土壤属性有重要影响.利用光谱技术进行土壤有机质的快速测定是实现精细农业的基础.近几十年中,高光谱技术的发展为土壤研究提供了新的手段.受土壤有机质质量分数、组成以及土壤水分、土壤质地的影响,室内光谱的估算结果总体较好;受大气、地表植被等影响,航空或卫星的成像光谱估算精度较低.星载成像技术的进步将在一定程度上提高土壤有机质的估算精度,为快速、大范围土壤有机质质量分数的遥感制图提供技术支持.     

中国大气气溶胶辐射特性参数的观测与研究进展

长期系统的气溶胶辐射特性观测资料是定量研究气溶胶辐射和气候效应的重要基础.本文综合介绍中国大气气溶胶辐射特性观测与研究现状和成果,重点包括以下内容:地面太阳光度计联网观测气溶胶光学厚度、单次散射反照率、尺度谱;从全波段太阳辐射反演气溶胶光学厚度、单次散射反照率;浊度计和黑碳仪测量地面气溶胶散射系数和吸收系数;地基/星载激光雷达观测气溶胶(后向散射系数)垂直分布;极轨/静止卫星遥感反演气溶胶光学特性.     

The Atacama Cosmology Telescope project: A progress report

The Atacama Cosmology Telescope is a project to map the microwave background radiation at arcminute angular resolution and high sensitivity in three frequency bands over substantial sky areas. Cosmological signals driving such an experiment are reviewed, and current progress in hardware construction is summarized. Complementary astronomical observations in other wavebands are also discussed.     

Seasonal inundation patterns in two large savanna floodplains of South America: the Llanos de Moxos (Bolivia) and the Llanos del Orinoco (Venezuela and Colombia)

Inundation patterns in two of the largest savanna floodplains of South America were studied by analysis of the 37‐GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer (Nimbus‐7 satellite). Flooded area was estimated at monthly intervals for January 1979 through to August 1987 using mixing models that account for the major landscape units with distinctive microwave emission characteristics. Results are presented separately for five subregions in each of the two floodplain regions to show the spatial as well as temporal variability in inundation patterns. The total area inundated during the 9 years varied between 2069 and 78 460 km² in the Llanos de Moxos (also spelled as Mojos; median area, 23 383 km²) and 1278 and 105 454 km² in the Llanos del Orinoco (median, 25 374 km²), not including the open‐water area of permanent lakes and river channels. The correlation between flooded area and river stage was used to extend the inundation records over a 30‐year period in the Moxos (1967–97) and a 58‐year period (1927–85) in the Orinoco. Interannual variability in inundation is greater in the Moxos than the Orinoco. Comparison of these data, however, with a previously published analysis of the Pantanal wetland shows that inundation patterns in these two floodplain regions are not as variable across years as they are in the Pantanal. Copyright © 2004 John Wiley & Sons, Ltd.     

An investigation of sand–dust storm events and land surface characteristics in China using NOAA NDVI data

Observations from 560 weather stations in China show that sand–dust storms occur most frequently in April in north China. The region consists of Sub-dry Mid Temperate, Dry Mid Temperate, Sub-dry South Temperate and Dry South Temperate Zones and much of the land surface is desert or semi-desert: it is relatively dry with minimal rainfall and a high annual mean temperature. In most regions of China, the annual mean frequency of sand–dust events decreased sharply between 1980 and 1997 and then increased from 1997 to 2000. Statistical analyses demonstrate that the frequency of sand–dust storms correlates highly with wind speed, which in turn is strongly related to land surface features; on the other hand, a significant correlation between storm events and other atmospheric quantities such as precipitation and temperature was not observed. Accordingly, land surface cover characteristics (vegetation, snowfall and soil texture) may play a significant role in determining the occurrence of sand–dust storms in China. Analysis of Normalized Difference Vegetation Index derived from National Oceanic and Atmospheric Administration and Empirical Orthogonal Function show that since 1995 surface vegetation cover in large areas of Northern China has significantly deteriorated. Moreover, a high correlation is shown to exist among the annual occurrence of sand–dust storms, surface vegetation cover and snowfall. This suggests that the deterioration of surface vegetation cover may strongly influence the occurrence of sand–dust storms in China. Soils with coarse and medium textures are found to be more associated with sand–dust storms than other soils.