A comparison between mesospheric wind measurements made near Christchurch (44°S, 173°E) using the high resolution doppler imager (HRDI) and a medium frequency (MF) radar

We report on the comparison of winds measured by a medium frequency (MF) radar near Christchurch, New Zealand, and by the high resolution doppler imager (HRDI). Previous comparisons have demonstrated that there can be significant differences in the winds obtained by the two techniques, and our results are no different. However, these data show relatively good agreement in the meridional direction, but large differences in the zonal direction, where the radar is regularly measuring the zonal wind as too easterly. To do the comparison, overpasses from the satellite must be obtained when it is close to the radar site. The radar data are averaged in time around the overpass because we know the radars sample phenomena which have spatial and temporal scales which make them invisible to HRDI. There are a limited number of overpass comparisons which limit our confidence in these results, but a detailed analysis of these data show that the proximity of the overpass is often an important factor in the differences obtained. Other factors examined include the influence of the local time of the overpass, and the amount of radar data averaged around the overpass time.     

Climatic features of the Mediterranean Sea detected by the analysis of the longwave radiative bulk formulae

Some important climatic features of the Mediterranean Sea stand out from an analysis of the systematic discrepancies between direct measurements of longwave radiation budget and predictions obtained by the most widely used bulk formulae. In particular, under clear-sky conditions the results show that the surface values of both air temperature and humidity over the Mediterranean Sea are larger than those expected over an open ocean with the same amount of net longwave radiation. Furthermore, the twofold climatic regime of the Mediterranean region strongly affects the downwelling clear-sky radiation. This study suggests that a single bulk formula with constant numerical coefficients is unable to reproduce the fluxes at the surface for all the seasons.     

Letter to the editor A strange cloud in the Arctic summer stratosphere 1998 above Esrange (68°N), Sweden

When the University of Bonn lidar on the Esrange (68°N, 21°E), Sweden, was switched on in the evening of July 18, 1998, a geometrically and optically thin cloud layer was present near 14 km altitude or 400 K potential temperature, where it persisted for two hours. The tropopause altitude was 4 km below the cloud altitude. The cloud particles depolarized the lidar returns, thus must they have been aspherical and hence solid. Atmospheric temperatures near 230 K were approximately 40 K too high to support ice particles at stratospheric water vapour pressures of a few ppmv. The isentropic back trajectory on 400 K showed the air parcels to have stayed clear of active major rocket launch sites. The air parcels at 400 K had travelled from the Aleutians across Canada and the Atlantic Ocean arriving above central Europe and then turned northward to pass over above the lidar station. Parcels at levels at ±25 K from 400 K had come from the pole and joined the 400 K trajectory path above eastern Canada. Apparently the cloud existed in a filament of air with an origin different from those filaments both above and below. Possibly the 400 K level air parcels had carried soot particles from forest wild fires in northern Canada or volcanic ash from the eruption of the Korovin Volcano in the Aleutian Islands.     

高分五号卫星大气参数探测综述

高分五号卫星搭载了大气痕量气体差分吸收光谱仪、主要温室气体探测仪、大气多角度偏振探测仪、大气环境红外甚高分辨率探测仪、可见短波红外高光谱相机和全谱段光谱成像仪共6台载荷,对全球环境监测及中国大气气溶胶、臭氧、二氧化硫、二氧化氮、二氧化碳、甲烷和云等多个环境与气象综合监测方面有着重要的意义。为了更好的了解高分五号卫星任务的大气监测内容,本文对高分五号卫星其中的4个大气探测载荷特征和数据处理算法进展进行了总结,涉及各个载荷参数信息、算法介绍和产品初步结果等相关内容。高分五号卫星是中国专门用于大气环境监测任务的遥感卫星,随着后续卫星的发射升空,将对中国乃至全球大气环境监测提供强有力的数据支撑。     

我国西南地区秋季干湿分类及主要类型 异常年环流特征分析

本文使用我国西南地区97站1960～2009年逐日资料,计算了考虑降水和气温的干湿指数,分析了西南地区秋季及9、10、11月干湿指数的时空变化特征。采用相似方法,构造了综合相似指数,对历年干湿分布进行分类,并给出了秋季各月各类干湿出现的概率。此外还使用再分析资料分月探讨了干湿分布主要类型异常年的大气环流特征。分析结果表明:西南地区秋季存在显著的干旱化趋势,且该地区干湿变化存在全区一致、东西相反和南北相反的特征。根据干湿变化主要模态的空间型,利用综合相似指数可以将历年秋季干湿分为全区一致偏干型、全区一致偏湿型、东湿西干型、东干西湿型、南湿北干型、南干北湿型和非典型型,共7类。全区干湿一致型出现的次数最多（不低于50%）,东西相反型次之（约25%）,南北相反型较少（约15%）,而出现非典型型次数极少（不足10%）。从季节内尺度来看,全区偏干（湿）的持续性较差,但10月份的东部偏湿区域则有较大几率（不低于50%）在下个月扩展到整个区域。全区偏干型异常年,东亚大槽偏弱或偏东,冷空气南侵困难;南海上空低层维持一个异常的气旋环流,西南地区暖湿气流输送偏弱;西太平洋副高偏强、西伸,南亚高压面积偏大,与西太副高重叠,西南地区长期受高压控制。这种异常环流形势的维持,使得该地区天气晴朗少雨,气温偏高,持续干旱。偏湿型异常年则基本呈相反的环流特征。而西南地区东、西部上空异常的垂直运动和东部低层的南、北风异常是造成东湿（干）西干（湿）型异常的重要原因。     

直接观测大气气溶胶成核

大气核化是全球大气气溶胶粒子的主要来源,在气溶胶气候效应中扮演重要角色。大气核化过程的关键步骤发生在2 nm以下的尺寸范围,在如此小的范围直接对其大小隔离观察直到最近才得以进行。本文呈现了1nm流动性直径范围内的大气纳米颗粒和集群的详细观测结果,确定了三个独立的低于2nm直径的尺寸类型,建立了物理、化学、动力一致的大气成核框架,更具体地说,气溶胶通过中性的途径形成。研究结果强调了在大气气溶胶形成过程中有机化合物的重要作用,导致气溶胶增长、辐射强迫及生物排放量、云和气候之间的相关反馈。     

2009年石家庄地区大气气溶胶的飞机探测研究

利用2009年石家庄地区不同季节的3次机载粒子探测系统PMS(Particle Measurement System)的探测资料,结合地面天气形势、风场和探空资料对石家庄地区,晴空背景下大气气溶胶的统计特征、数浓度、平均粒径的垂直分布特征以及谱分布特征进行了分析。结果表明:晴天条件下气溶胶的数浓度随高度递减,粒径随高度变化不大;在数值上,4月16日气溶胶数浓度和粒径最大,其次是10月15日,最小的是6月10日,3次粒径变化幅度都不大;逆温层底层气溶胶明显积累,气溶胶浓度在1.5 km以下大气边界层内明显高于其他层次,逆温层的高度和厚度影响气溶胶的分布;3次不同季节晴天背景下石家庄地区气溶胶谱型基本一致呈单峰分布,小于0.3μm的细粒子对气溶胶的数浓度贡献最大。     

2006年夏季川渝地区伏旱与低频大气热源的关系

利用NCEP/NCAR再分析资料和中国地面观测站的逐日降水资料,研究了2006年夏季中国川渝地区的伏旱与亚洲地区大气低频振荡的联系.结果表明,2006年夏季中国川渝地区降水低频振荡的主要周期约为60 d;在川渝严重干旱期的7月下旬至8月上旬,经向上由于川渝地区上空低频热汇、广西和海南及其以西地区上空低频热源的影响,在1...     

1998年5～6月区域大气角动量收支与东亚天气尺度系统变化

利用NCEP/NCAR再分析资料计算了1998年5～6月区域角动量收支的主要分量,对比分析了范围较大的欧亚区域角动量矩和限制在欧亚大陆范围内的喜马拉雅山角动量矩的差异,发现两者有很好的相关,限制较小范围的计算表明,喜马拉雅山山脉力矩的作用显著。角动量收支项占较大量级的山脉力矩和摩擦力矩,并与梅雨锋区域的700hPa高度...     

探空系统的雷电防护技术探讨

在对测风雷达架设的位置、操作和控制系统、低电压工作特性、以及工作用途分析的基础上,提出了雷达站雷电和静电防护的技术路线,从直击雷、感应雷等方面提出了防护方法。