1970-2013年南疆渭干河-库车河流域绿洲冰雹时空变化特征和棉花受灾分析

渭干河-库车河绿洲是南疆地区主要棉花生产基地之一, 随着气候变化和棉花种植面积的日益扩大, 雹灾对棉花生产的危害日趋严重. 利用该地区4个气象站44 a逐一地面降雹过程资料和33 a灾情信息, 对冰雹时空变化特征、活动规律、强度、受灾面积和影响因素等进行研究. 结果表明: 降雹空间分布为北部靠山地带多于南部平原地带, 受灾面积的空间分布则相反; 降雹以周期短、强季节性特征为主, 各县中等以上降雹天气占80%以上, 降雹趋于高发和强发的态势. 降雹频次与气温和降水呈较好的相关性, 冰雹多发年气温偏低、降水偏多, 冰雹少发年气温偏高、降水偏少. 位于南部靠近沙漠的沙雅县受灾最为严重, 雹灾与降雹强度、地域、季节和作物面积及类型等有关, 该地区棉花受灾机率大.     

沙尘气溶胶对云和降水影响的模拟研究

采用二维分档云模式,对比背景大气气溶胶分布,讨论了扬沙和沙尘暴天气条件下矿物气溶胶对云微物理结构、光学特性以及降水形成的影响.结果表明:扬沙和沙尘暴天气增加大气中大核和巨核的浓度,促进云中水汽的活化,使降水提前出现,暖云和冷云降水量均大幅增加,但可忽略巨核增加对云光学厚度和反照率的作用;当矿物沙尘粒子同时作为有效的云凝结核和冰核参与云的发展时,冰核浓度增加使水成物有效半径减小,抑制了暖云和冷云降水,云内存留的大量冰晶增强云的光学厚度和反照率.     

湖北保康两次冰雹天气过程的综合分析

利用MICAPS常规资料、TWR01雷达资料及十堰多普勒雷达观测资料,结合地面降雹的实况报告,对2009年6月6日和8月26日发生在保康县的两次冰雹天气过程的天气背景、雷达资料进行了分析。结果表明,高空冷槽、中低层切变线是主要的影响系统。6月6日冰雹由强单体雹云产生,雹云回波具有超级单体回波特点。雷达初始回波高,雹云发展速度快;强中心呈纺锤状,中低层有弱回波区,降雹前垂直液态水含量有明显的变化。8月26日过程发生在副高内部型环流形势下,由合并加强后的雹云产生降雹。     

MULTI-SCALE CHARACTERISTICS STUDY ON THE FREQUENCY OF FOGGY DAYS OCCURRING IN NANJING IN DECEMBER 2007

Based on the number of foggy days in Nanjing in December from 1980 to 2011, we analyzed the surface temperature and atmospheric circulation characteristics of foggy years and less-foggy years. Positive anomalies of the Arctic Oscillation (AO) were found to weaken the East Asian trough, which is not conducive to the southward migration of cold air. Simultaneously, this atmospheric condition favors stability as a result of a high-pressure anomaly from the middle Yangtze River Delta region. A portion of La Ni?a events increases the amount of water vapor in the South China Sea region, so this phenomenon could provide the water vapor condition required for foggy days in Nanjing. Based on the data in December 2007, which contained the greatest number of foggy days for the years studied, the source of fog vapor in Nanjing was primarily from southern China and southwest Taiwan Island based on a synoptic scale study. The water vapor in southern China and in the southwestern flow increased, and after a period of 2-3 days, the humidity in Nanjing increased. Simultaneously, the water vapor from the southwestern of Taiwan Island was directly transported to Nanjing by the southerly wind. Therefore, these two areas are the most important sources of water vapor that results in heavy fog in Nanjing. Using the bivariate Empirical Orthogonal Function (EOF) mode on the surface temperature and precipitable water vapor, the first mode was found to reflect the seasonal variation from early winter to late winter, which reduced the surface temperature on a large scale. The second mode was found to reflect a large-scale, northward, warm and humid airflow that was accompanied by the enhancement of the subtropical high, particularly between December 15-21, which is primarily responsible for the consecutive foggy days in Nanjing.     

Microphysical characteristics of sea fog over the east coast of Leizhou Peninsula, China

Microphysical properties of sea fog and correlations of these properties were analyzed based on the measurements from a comprehensive field campaign carried out from 15 March to 18 April 2010 on Donghai Island (21°35’’N, 110°32’5’’E) in Zhanjiang, Guangdong Province, China. There were four types of circula- tion pattern in favor of sea fog events in this area identified, and the synoptic weather pattern was found to influence the microphysical properties of the sea fogs. Those influenced by a warm sector in front of a cold front or the anterior part of low pressure were found to usually have a much longer duration, lower visibility, greater liquid water content, and bigger fog droplet sizes. A fog droplet number concentration of N≥1 cm-3 and liquid water content of L≥0.001 g m-3 can be used to define sea fogs in this area. The type of fog droplet size distribution of the sea fog events was mostly monotonically-decreasing, with the spectrum width always being >20 μm. The significant temporal variation of N was due in large part to the number concentration variation of fog droplets with radius <3 μm. A strong collection process appeared when droplet spectrum width was >10 μm, which subsequently led to the sudden increase of droplet spectrum width. The dominant physical process during the sea fog events was activation with subsequent condensational growth or reversible evaporation processes, but turbulent mixing also played an important role. The collection process occurred, but was not vital.     

湖北电线积冰统计分析及积冰逆温层结研究

利用2009~2013年冬季华中电网电线覆冰在线观测系统对湖北省500 k V高压输电线路积冰状况进行实时观测获取的资料,结合MICAPS常规气象资料、探空数据及NCEP再分析资料,对湖北形成积冰的天气形势、积冰持续时间以及形成积冰的逆温层结进行研究。结果表明:积冰的高空环流形势主要是小槽发展型、横槽型和低槽东移型3类,分别占43.8%、31.2%、25%;电线积冰主要发生在每年的1月、2月、11月、12月,月平均积冰时数分别为65、42、11、9;积冰可分为降水型积冰和云雾型积冰,降水型积冰过程中,900~700 h Pa高度间存在由北至南风向切变,冷暖空气交汇形成愈加深厚的逆温对降水积冰维持与发展起到重要的作用。     

沙尘天气中气溶胶光学特性的时空分布特征

选取内蒙古境内额济纳旗、乌拉特中旗、东胜、朱日和、锡林浩特5个站的几次沙尘天气过程和晴朗天气下CE-318太阳光度计资料,计算出大气气溶胶光学厚度,结合气象资料分析在沙尘天气发生过程中气溶胶光学厚度的时空分布特征。分析结果显示,在沙尘天气发生过程中,气溶胶光学厚度是一个相当敏感的变量,其随沙尘的发生、发展和消亡表现出明显不同的日变化特征,且光学厚度值随着沙尘天气的发生和发展,在其空间分布变化上与沙尘天气本身的空间分布变化具有很好的一致性,可以很好的反映沙尘输送过程。此外气溶胶光学厚度与大气稳定度也有一致的日变化趋势。因此,对于大气气溶胶光学厚度的监测可以为沙尘天气的预报提供较为准确的客观依据。     

南京一次重霾天气纳米气溶胶观测研究

为加深对南京地区重霾天气过程纳米尺度气溶胶物理特征的了解,对2017年12月21—25日的一次重霾天气过程进行了综合探测,利用宽范围粒径谱仪观测了此次过程中10～1 000 nm颗粒物数浓度,并结合能见度等气象要素,对重霾期间纳米气溶胶谱分布进行了分析。结果表明:此次霾重污染过程出现在低温、高湿、气压上升期间;与非重污染时期相比,重污染期间N_(10-20)与N_(20-100)降低,N_(100-1000)升高;重污染期间气溶胶粒子平均数浓度为17 035个/cm~3,低于非重污染期间粒子数浓度,N_(100-1000)占总数浓度的55.05%;重霾发生期间纳米气溶胶数浓度谱为单峰结构,峰值在100 nm附近,随着污染加重,纳米气溶胶峰值粒径向大粒径偏移,粒子向大粒径段集中;不同温度对不同粒径粒子数浓度的影响不同,20～100 nm粒径段气溶胶与数浓度与温度呈反相关性,100～500 nm粒子数浓度与温度呈正相关性.