干旱区一次春季沙尘过程的大气气溶胶垂直分布结构及其特征

采用微脉冲激光雷达(Micro-Pulse Lidar,MPL)对干旱荒漠代表站张掖站上空一次春季沙尘暴过程的边界层和自由大气的气溶胶分布和大气环境进行了观测。结果表明,气溶胶的垂直廓线可分为高、中、低3层,高层气溶胶出现在5～9km,主要是通过上风方向的高海拔区域或低层气溶胶通过对流等过程突破边界层顶进入自由大气输送而来,其分布高度在一天中随着时间的推移逐渐降低;中层气溶胶位于2.5～4.5km,其消光特性随高度的增加没有明显的变化,具有垂直混合现象;低层气溶胶在2.5km以下,其消光特性随着高度增加反而降低;中、低层气溶胶主要来源于外部源区或当地沙尘源区和沙壤土起沙。气溶胶垂直分布表现出3种形式:在大气稳定条件下,气溶胶随高度增加呈单峰型减小趋势;不稳定条件下随高度增加指数型降低;混合层中随高度增加而保持稳定。由于受边界层日变化的影响,气溶胶分布的上界出现单峰型日变化特征,具体表现为下午较高,早晨较低。     

黄土高原陆面水分的凝结现象及收支特征试验研究

中国黄土高原是全球独特的地理区域,其陆面水分过程比较特殊。利用黄土高原陆面过程试验研究(LOPEX)的陇中黄土高原定西陆面过程综合观测站的资料,分析了陆面水分凝结现象及其出现频率与局地微气象条件的关系,研究了露水(霜)量及其出现频率的季节分布特征以及受降水和天气阴、晴的影响规律。同时,对比分析了降水、露水、雾水和土壤吸附水对陆面水分的贡献率,讨论了涡动相关法、蒸渗计和蒸发皿观测的陆面蒸发量的差别及其与陆面水分来源的年平衡关系,给出了半干旱区陆面水分平衡的日循环特征。发现露水对风速、大气湿度、近地层温度梯度的依赖很强,一般在风速为1.5 m/s、相对湿度大于80%和逆温强度为0.25℃的情况下露水(霜)量最大;刚降水后的晴天露水量比较大;实际蒸散量与蒸发力的差距十分明显,陆面水分平衡特征表现为一个"呼吸"过程。     

Comparison of different land-surface perturbation methods in short-range ensemble forecasts

为了比较不同陆面扰动方法对短时集合预报的影响,本研究设计了陆面模式扰动实验(LSMPE),初始土壤湿度扰动实验(ISMPE),陆面-大气耦合系数扰动实验(LCCPE)以及大气扰动对照实验(GEFSPE).结果表明,在三组陆面扰动实验中,LSMPE能代表最大的不确定性且误差最小;ISMPE的离散度要比LCCPE稍大,但是...     

一次强对流天气过程中尺度对流系统特征分析

利用NCEP／NCAR再分析资料、FY2C云图及广州新一代多普勒天气雷达产品,对2007年6月9～10日发生在广东省的一次强对流天气过程中的中尺度对流系统（MCS）进行了分析,主要结论有：1）对流层中高层辐散低层辐合,以及“上千下湿”相配置的垂直环流结构特征,和不稳定的大气层结为此次暴雨的形成提供了所需的动力条件和水汽条件;2）MCS云系生成、发展于南支槽和西南低涡东南侧的暖湿气流所形成的云系中;3）在雷达回波图上,MβCS回波的发展具有明显的右移风暴移动特点和“列车效应”,且发展成熟阶段的回波呈显著的“弓形”和“人字形”水平回波演变结构。     

亚洲季风区不同形态中尺度对流系统的特征分析

利用16 a的TRMM卫星观测资料,分析了亚洲季风区准圆状、线状和拉长状中尺度对流系统(MCSs)的空间分布、对流属性及其区域变化特征。结果表明:拉长状MCSs的数量最多,准圆状的其次而线状的最少。自西向东,准圆状(线状)MCSs数量占各区域MCSs总数的比例逐渐减小(增加),线状MCSs在副热带和洋面地区的产生几率相比更大。MCSs的发生频次呈现以暖季(5—9月)为峰值的单峰分布,准圆状和拉长状MCSs的暖季峰值比线状MCSs的大。MCSs主要发生在下午—傍晚时段,但线状MCSs在午夜—凌晨出现的概率比其它两种大。3种类型MCSs的整体强度基本表现为副热带地区弱于近热带地区,但不同类型MCSs的强度差异在各区域不尽相同,如中国中东部地区和西北太平洋地区的准圆状MCSs强度最强,但东海及其以东洋面的线状MCSs强度最强。     

基于VAD技术的迭代法在实测多普勒速度缺测区域的填补研究

多普勒天气雷达径向速度场缺测区域的存在是影响速度二次产品算法精确度的重要因素,在实际风场为线性分布的假设条件下,文中详细介绍了一种基于VAD技术的迭代填补技术.在合理考虑迭代约束条件的情况下,应用实测多普勒速度数据,根据缺测区域类型随机制造非连续累积10°-180°缺口的缺测区域和连续累积10°-180°缺口的缺测区域...     

An overview of dry-wet climate variability among monsoon-westerly regions and the monsoon northernmost marginal active zone in China

Climate in mainland China can be divided into the monsoon region in the southeast and the westerly region in the northwest as well as the intercross zone, i.e., the monsoon northernmost marginal active zone that is oriented from Southwest China to the upper Yellow River, North China, and Northeast China. In the three regions, dry-wet climate changes are directly linked to the interaction of the southerly monsoon flow on the east side of the Tibetan Plateau and the westerly flow on the north side of the Plateau from the inter-annual to inter-decadal timescales. Some basic features of climate variability in the three regions for the last half century and the historical hundreds of years are reviewed in this paper. In the last half century, an increasing trend of summer precipitation associated with the enhancing westerly flow is found in the westerly region from Xinjiang to northern parts of North China and Northeast China. On the other hand, an increasing trend of summer precipitation along the Yangtze River and a decreasing trend of summer precipitation along the monsoon northernmost marginal active zone are associated with the weakening monsoon flow in East Asia. Historical documents are widely distributed in the monsoon region for hundreds of years and natural climate proxies are constructed in the non-monsoon region, while two types of climate proxies can be commonly found over the monsoon northernmost marginal active zone. In the monsoon region, dry-wet variation centers are altered among North China, the lower Yangtze River, and South China from one century to another. Dry or wet anomalies are firstly observed along the monsoon northernmost marginal active zone and shifted southward or southeastward to the Yangtze River valley and South China in about a 70-year timescale. Severe drought events are experienced along the monsoon northernmost marginal active zone during the last 5 centuries. Inter-decadal dry-wet variations are depicted by natural proxies for the last 4--5 centuries in several areas over the non-monsoon region. Some questions, such as the impact of global warming on dry-wet regime changes in China, complex interactions between the monsoon and westerly flows in Northeast China, and the integrated multi-proxy analysis throughout all of China, are proposed.     

五道梁地区总辐射的年际变化

利用实测的太阳总辐射通量密度及地气温差资料，建立了月平均地气温差与月平均太阳总辐射通量密度的回归方程，并用该回归方程计算了五道梁地区1980-1993年共14年的月平均总辐射通量密度，分析了该地区总辐射通量密度的年际变化，发现该地区总辐射通量密度具有较明显的6～7年的振荡周期。20世纪后10年年平均总辐射通量密度有增大的趋势。     

周、秦、汉、唐时期关中地区自然灾害与粮食安全问题研究

周、秦、汉、唐时期,关中农业较为发达,为多个王朝建都之地。京师之地的粮食问题十分重要,汉代以后屡屡出现粮食紧张局面,其原因除移民、战乱等因素外,自然灾害的影响不容忽视。研究发现,周、秦、汉、唐时期,关中的粮食在秦以前基本自给,两汉、魏晋以后依赖关东趋于明显,隋唐时期关中粮食所需则自产自给和漕运并重。这一演变过程,与关中自然灾害的发生状况有着紧密联系。随着西汉以后生态环境的破坏和人类垦殖活动的日益加剧,关中地区水旱灾害发生频繁,对粮食安全产生了严重影响。期间的中央政府不断采取扩大农业垦殖、提高农业生产技术和漕运等手段,以解决京师用粮。     

Climatic response of thick leaf spruce (Picea crassifolia) tree-ring width at different elevations over Qilian Mountains, northwestern China

Tree-ring cores of thick leaf spruce (Picea crassifolia) taken from four sites at different elevations, in the middle of the Qilian Mountains, in the arid and semi-arid region of northwestern China, were used to develop four tree-ring width chronologies using standard dendrochronological methods. Results indicate that with increasing altitude the chronologies’ year-to-year variations decreased. Hence, the sensitivity of the tree-ring chronologies to climate decreases with altitude. Further analysis showed that the significant limiting factor on tree growth is spring precipitation. Measurements of stomata density and leaf dry weight suggest the species’ ecological adaptation strategy changes with elevation. At high elevation the metabolic rate of thick leaf spruce decreases, thus showing the effect of the climate.