1993—2004年华东部分地区酸雨的时空分布特征及其与气象条件的关系

分析华东地区15个酸雨观测站的1993—2004年数据资料,结果显示华东地区的酸雨灾害在全国范围内较为严重,其中以长江以南的浙江、福建地区尤为突出.1993—2004年华东地区降水的酸度呈现出先减轻后加重的趋势.降水量是影响华东酸雨的电导率和pH值的重要因素.pH值季节变化由高到低为夏、秋、冬、春,酸雨频率随季节的变化不显著.对同期15个观测站的电导率变化的分析显示,12年间华东地区降水的电导率呈现先稳定后变幅增大的趋势,降水酸度和电导率的年际变化存在显著的正相关关系.应当对影响降水酸度和电导率的相关大气成分加强监测与研究.     

An Algorithm for Detecting Ice Cloud at Different Altitudes by Combining Dual CrIS Full Spectrum Resolution CO2 Channels

Using infrared sensors to detect ice clouds in different atmospheric layers is still a challenge. The different scattering and absorption properties of longwave and shortwave infrared channels can be utilized to fulfill this purpose.In this study, the release of Suomi-NPP Cross-track Infrared Sounder(Cr IS) full spectrum resolution is used to select and pair channels from longwave(～ 15 μm) and shortwave(～4.3 μm) CO_2 absorption bands under stricter conditions, so as to better detect ice clouds. Besides, the differences of the weighting function peaks and cloud insensitive level altitudes of the paired channels are both within 50 h Pa so that the variances due to atmospheric conditions can be minimized. The training data of clear sky are determined by Visible Infrared Imaging Radiometer Suite(VIIRS) cloud mask product and used to find the linear relationship between the paired longwave and shortwave CO_2 absorption channels. From the linear relationship, the so-called cloud emission and scattering index(CESI) is derived to detect ice clouds. CESI clearly captures the center and the ice cloud features of the Super Typhoon Hato located above 415 h Pa. Moreover, the CESI distributions agree with cloud top pressure from the VIIRS in both daytime and nighttime in different atmospheric layers.     

里下河地区下垫面变化对降水、气温、风速的影响

近年来,随着苏北地区经济和城市的快速发展,土地覆盖状况发生了显著变化,其中尤以城市化扩展为主。为了分析下垫面变化对天气过程的影响,特别是对降水过程的影响,采用中尺度WRF3.4/Noah/UCM模式,对苏北里下河地区2005年8月6日的一次强降水过程进行了模拟,其中通过改变模式的下垫面特征,设置了三种敏感性分析试验,分别是USGS土地利用类型(CASE1)、修正后的MODIS土地利用类型(CASE2)和城市极端扩张后土地利用类型(CASE3)。研究结果表明,修正后的MODIS土地利用类型数据(CASE2)更能真实地反映里下河地区的下垫面结构,与实测值对比后发现模拟的降水、气温和风速等气象要素更为准确。通过将CASE2、CASE3与CASE1的模拟结果对比发现,城市下垫面增加后会使城市气温明显增加,上空的风速减小;白天地表感热通量增强,潜热通量减小,夜间延长了感热通量由正变负的时间;边界层高度被抬升,在中午前后分别被抬升了近45 m和100 m左右;垂直速度和散度值增大,大气低层的扰动位温增加,云水混合比和雨水混合比均增多。以上这些条件均有助于对流降水天气的发生、发展。