Current status of ENSO prediction skill in coupled ocean–atmosphere models

The overall skill of ENSO prediction in retrospective forecasts made with ten different coupled GCMs is investigated. The coupled GCM datasets of the APCC/CliPAS and DEMETER projects are used for four seasons in the common 22 years from 1980 to 2001. As a baseline, a dynamic-statistical SST forecast and persistence are compared. Our study focuses on the tropical Pacific SST, especially by analyzing the NINO34 index. In coupled models, the accuracy of the simulated variability is related to the accuracy of the simulated mean state. Almost all models have problems in simulating the mean and mean annual cycle of SST, in spite of the positive influence of realistic initial conditions. As a result, the simulation of the interannual SST variability is also far from perfect in most coupled models. With increasing lead time, this discrepancy gets worse. As one measure of forecast skill, the tier-1 multi-model ensemble (MME) forecasts of NINO3.4 SST have an anomaly correlation coefficient of 0.86 at the month 6. This is higher than that of any individual model as well as both forecasts based on persistence and those made with the dynamic-statistical model. The forecast skill of individual models and the MME depends strongly on season, ENSO phase, and ENSO intensity. A stronger El Niño is better predicted. The growth phases of both the warm and cold events are better predicted than the corresponding decaying phases. ENSO-neutral periods are far worse predicted than warm or cold events. The skill of forecasts that start in February or May drops faster than that of forecasts that start in August or November. This behavior, often termed the spring predictability barrier, is in part because predictions starting from February or May contain more events in the decaying phase of ENSO.     

2007年梅汛期异常降水的大尺度环流成因分析

为深入理解江淮梅雨持续性强降水的大气演变过程,探讨中期预报技术途径,利用NCEP/NCAR逐日再分析数据和历史梅雨特征指数等资料,系统地分析了2007年梅汛期异常降水的大尺度环流成因.结果表明:梅汛期,西北太平洋副热带高压稳定和7月中下旬持续偏南,决定了2007年梅汛期降水的时间和地域分布特征.阻塞高压的频繁出现和副热带季风涌的异常强盛为梅雨锋维持和加强提供了有利的动力、热力以及水汽条件;"伊朗型"南亚高压的活动以及东亚上空副热带急流通过高低空耦合动力作用,不仅为持续性暴雨创造了良好的垂直环流结构,也间接抑制了副高北抬.在此研究基础上,归纳出中期预报着眼点,供实际业务预报参考使用.     

宝鸡市干旱气候特征分析

2008年6月28日15时开始,山西省北部和东部部分地区出现强对流回波,当天下午16时起,太原本场及周边开始有大风天气,17时到20时开始出现局地的暴雨,部分地方出现短时冰雹等强对流灾害性天气。21时之后,回波向东南方移出,过程结束。本文主要对此次短时强对流天气过程的多普勒雷达图像资料进行分析,详细分析了太原（本场）周围强对流天气发生、发展、及消失的回波演变特征,并结合当时的雷电资料进行了分析。结果表明：本场未出现降水前,本场周围50km范围内非降水回波的辐合形势对天气过程的发生有很好的指示作用;强对流回波中存在逆风区,与暴雨的落区有很好的对应关系。     

孟加拉湾风暴Mala结构及对云南强降水的影响

利用实时观测资料和NCEP(1°×1°)的6 h再分析资料,对2006年春季发生在孟加拉湾的超强风暴Mala的移动路径、强度变化、环流背景以及风暴温湿场、动力场特征等进行分析。结果表明:Mala在阿拉伯副热带高压和西太平洋副热带高压两高间辐合区生成、加强,并沿西太平洋副热带高压西侧西南或偏南气流移动。风暴发展、成熟到消亡,湿度对风暴的作用比温度明显;动力场结构除具有台风结构的一般特征外,在风暴发展期,中心附近散度场从低层到高层为辐合和辐散交替结构,表明风暴内部高空辐散抽吸作用对于风暴发展起到重要作用。登陆后风暴低压内自身能量和水汽与冷空气共同作用下,在冷暖交汇处出现强烈的上升运动和激发出中尺度辐合线是造成云南强降水主要原因。     

1951—2007年辽宁省农业界限温度变化及其成因探讨

对1951-2007年辽宁省稳定通过0℃、10℃积温和持续日数变化进行了分析.结果表明:(1)近57年来辽宁省稳定通过0℃和10℃积温和持续日数呈递增趋势,其中稳定通过10℃积温和持续日数递增趋势更明显;(2)各标准气候期稳定通过0℃和10℃积温变化趋势不同,第1个和第2个30年标准气候期呈现递增趋势较弱,最近30年标准气候期呈显著递增趋势;各标准气候期稳定通过0℃和10℃持续日数均为递增趋势,而且后期递增较前期更为显著;(3)中部和沿海城市稳定通过0℃、10℃积温和持续日数递增趋势强于北部和西部;(4)城市化引起的热岛效应是观测到的稳定通过0℃、10℃积温和持续日数递增的重要原因,而区域气候变暖则进一步加强了递增趋势.     

基于GIS的贵州省冰雹分布与地形因子关系分析

使用贵州省1961—2004年84个气象台站44年历史冰雹记录及1:1000000全国数字高程模型(DEM)资料, 采用基于GIS的数字地形分析、分区统计和图像分类方法, 研究了冰雹分布与地形高程、坡向、坡度及地形切割深度的关系。研究表明:地形高程是影响贵州省降雹分布的最主要地形影响因子; 微观地形因子如坡向和坡度对降雹日数的变异并没有显著性影响, 但大范围的地势抬升及暖湿空气的迎风坡有利于降雹; 地形切割深度并不是年平均降雹日数差异的显著影响因子; 纬度位置的不同, 使其受暖湿空气影响程度不同, 热力条件也存在差异, 也是影响平均降雹日数差异的因子之一; 根据3个影响因子建模获得的方程及贵州省冰雹风险分区图, 经统计检验和与历史乡镇降雹资料比较, 具有较好的一致性。     

基于内涝模型的西安市区强降水内涝成因分析

利用西安市近10～40年降水资料、市政信息资料,采用统计学方法,分析了强降水内涝的成因.结果表明:短时强降水或过程量偏大的降水天气过程是引发西安市内涝的直接气象因素;排水能力的强弱是发生内涝关键因素;随着城市化的发展,极端雨强的强度及大于10 mm/h降水的总时次数均有上升趋势,强降水发生概率的提高加强了内涝灾害发生频率及强度,城市效应是内涝加强的主要原因.用西安市强降水内涝仿真模型来进行模拟试验表明:西安是一个内涝发生降水雨强临界值偏低的城市,小时雨强3 mm/h、13 mm/h是发生内涝、严重内涝的临界值,天气预报、雨情监测重点及市政防御关键部位是西北区.总体上缩小井距效果好一些.     

Galaxy activity in merging binary galaxy clusters

We present the results of a study of galaxy activity in two merging binary clusters (A168 and A1750) using the Sloan Digital Sky Survey (SDSS) data supplemented with the data in the literature. We have investigated the merger histories of A168 and A1750 by combining the results from a two-body dynamical model and X-ray data. In A168, two subclusters appear to have passed each other and to be coming together from the recent maximum separation. In A1750, two major subclusters appear to have started interaction and to be coming together for the first time. We find an enhanced concentration of the galaxies showing star formation (SF) or active galactic nuclei (AGN) activity in the region between two subclusters in A168, which were possibly triggered by the cluster merger. In A1750, we do not find any galaxies with SF/AGN activity in the region between two subclusters, indicating that two major subclusters are in the early stage of merging.     

An unusual timing and spectral state of a black hole microquasar XTE J1550-564

An unusual timing and spectral state of a black hole microquasar XTE J1550-564 observed with RXTE is analyzed. Millisecond variabilities are found, which are significantly shorter than the minimum possible time scale in the light curves of black hole binaries, as suggested by Sunyaev & Revnivtsev (2000). The X-ray spectral fitting result indicates that there is an unusual soft component in the spectrum, which may be responsible for the millisecond variabilities. The millisecond variabilities as well as the unusual soft spectral component should be produced from some small, but independent active regions in the accretion disk.