Taiwan Yushan Snowfall Activity and Its Association with Atmospheric Circulation from 1979 to 2009     

TSAI Li-Min  LIU Koung-Ying  WANG Zifa 《大气科学进展》2011,28(6):1423-1432

Yushan is the most famous location for snow in Taiwan,while snowfall in the subtropical zone is rare.When it is snowing in Yushan,people are experiencing unusually cold and wet weather elsewhere in Taiwan.In this study,Yushan snowfall activity from 1979 to 2009 and the related atmosphere circulation were examined with the Taiwan Central Weather Bureau’s Yushan weather station observations and the National Centers for Environmental Prediction/Department of Energy(NCEP/DOE) reanalysis atmospheric data.To provide a quantitative measure of snowfall events,a snowfall activity index(SAI) was defined in this study.The time series of yearly SAIs shows that Yushan snowfall activity for an active year,such as 1983(SAI =39 153) was ～118 times larger than for an inactive year,such as 1999(SAI=331).Our analyses show that snowfall activity is closely related to the position of the East Asian Trough(EAT) and the strength of the West Pacific High(WPH).In active years,when the EAT shifted eastward and the strength of WPH increased,an anomalous anticyclone occurred in the West Pacific.This anticyclone introduced anomalous southwesterly flows along the southeastern cost of mainland China and over Taiwan,resulting in a wetter-than-normal atmosphere that favored snowfall.Alternatively,in inactive years,a drierthan-normal atmosphere resulted in sluggish snowfall seasons.  相似文献   

Features of the Extremely Severe Drought in the East of Southwest China and Anomalies of Atmospheric Circulation in Summer 2006   总被引：1，自引：0，他引：1       下载免费PDF全文

LI Yonghu  XU Haiming  LIU De 《Acta Meteorologica Sinica》2011,25(2):176-187

The spatial-temporal features of the extremely severe drought and the anomalous atmospheric circulation in summer 2006 are analyzed based on the NCEP/NCAR reanalysis data, the characteristic circulation indices given by the National Climate Center of China, and the daily precipitation data of 20 stations in the east of Southwest China (ESC) from 1959 to 2006. The results show that the rainless period started from early June and ended in early September 2006 with a total of more than 80 days, and the rainfall was especially scarce from around 25 July to 5 September 2006. Precipitation for each month was less than normal, and analysis of the precipitation indices shows that the summer precipitation in 2006 was the least since 1959. The extremely severe drought in the ESC in summer 2006 was closely related to the persistent anomalies of the atmospheric circulation in the same period, i.e., anomalies of mid-high latitude atmospheric circulation, western Pacific subtropical high (WPSH), westerlies, South Asian high, lower-level flow, water vapor transport, vertical motion, and so on. Droughts usually occur when the WPSH lies anomalously northward and westward, or anomalously weak and eastward. The extreme drought in summer 2006 was caused by the former. When the WPSH turned stronger and shifted to the north and west of its normal position, and the South Asian high was also strong and lay eastward, downdrafts prevailed over the ESC and suppressed the water vapor transfer toward this area. At the same time, the disposition of the westerlies and the mid-high latitude circulation disfavored the southward invasion of cold air, which jointly resulted in the extremely severe drought in the ESC in summer 2006. The weak heating over the Tibetan Plateau and vigorous convective activities over the Philippine area were likely responsible for the strong WPSH and its northwestward shift in summer 2006.  相似文献   

Evaluation and Improvement of a SVD-Based Empirical Atmospheric Model     

YU Jia-Yuh  CHANG Cheng-Wei  TU Jien-Yi 《大气科学进展》2011,28(3):636-652

An empirical atmospheric model(EAM) based on the singular value decomposition(SVD) method is evaluated using the composite El Ni(?)o/Southern Oscillation(ENSO) patterns of sea surface temperature (SST) and wind anomalies as the target scenario.Two versions of the SVD-based EAM were presented for comparisons.The first version estimates the wind anomalies in response to SST variations based on modes that were calculated from a pair of global wind and SST fields(i.e.,conventional EAM or CEAM).The second version utilizes the same model design but is based on modes that were calculated in a region-wise manner by separating the tropical domain from the remaining extratropical regions(i.e.,region-wise EAM or REAM). Our study shows that,while CEAM has shown successful model performance over some tropical areas, such as the equatorial eastern Pacific(EEP),the western North Pacific(WNP),and the tropical Indian Ocean(TIO),its performance over the North Pacific(NP) seems poor.When REAM is used to estimate the wind anomalies instead of CEAM,a marked improvement over NP readily emerges.Analyses of coupled modes indicate that such an improvement can be attributed to a much stronger coupled variability captured by the first region-wise SVD mode at higher latitudes compared with that captured by the conventional one. The newly proposed way of constructing the EAM(i.e.,REAM) can be very useful in the coupled studies because it gives the model a wider application beyond the commonly accepted tropical domain.  相似文献   

The GRAPES Variational Bias Correction Scheme and Associated Preliminary Experiments          下载免费PDF全文

WANG Xiang  LI Gang  ZHANG Hu  WANG Hui  GUO Rui 《Acta Meteorologica Sinica》2011,25(1):51-62

The variational assimilation theory is generally based on unbiased observations. In practice, however, almost all observations suffer from biases arising from observational instruments, radiative transfer operator, precondition of data, and so on. Therefore, a bias correction scheme is indispensable. The current scheme for radiance bias correction in the GRAPES 3DVar system is an offline scheme. It is actually a static correction for the radiance bias before the process of cost function minimization. In consideration of its effects on forecast results, this kind of scheme has some shortcomings. Thus, this study provides a variational bias correction (VarBC) scheme for the GRAPES 3DVar system following Dee’s idea. In the VarBC scheme, the observation operator is modified and a new control variable is defined by taking the predictor coefficients as the control parameters. According to the feature of the GRAPES-3DVAR, an incremental formulation is applied and the original bias correction scheme is maintained in the actual process of observations. The VarBC is designed to co-exist with the original scheme, because it is a dynamic revision to the observational operator on the basis of the old method, i.e., it adjusts the model state vector along with the control parameters to an unbiased state in the process of minimization and the assimilation system remains consistent with available information automatically. Preliminary experimental results show that the mean departures of background-minus-observation and analysis-minus-observation are reduced as expected. In a case study of the heavy rainfall that happened in South China on 11–13 June 2008, the 500-hPa geopotential height is better simulated using the analyzed field from the VarBC as the initial condition.  相似文献   

呼和浩特市城区发展对大气环境的影响分析     

李喜仓  白美兰  马玉峰  刘克利  冯晓晶  杨晶 《气象》2011,37(12):1572-1577

基于呼和浩特市近50年逐日定时地面气象资料、2002—2006年的逐日07时和19时各标准层探空资料、2001—2006年逐日主要污染物浓度和主要污染源源强、1961—2006年社会经济数据、2002年城区建设现状及1996—2010年城市总体规划资料,利用区域边界层模式模拟方法,研究了呼和浩特市城区建设发展对大气环境的影响。结果表明：（1）呼和浩特市城区发展后（规划后）气温高于现状（规划前）,城区中心气温与周边地区气温差增大,城市热岛效应增强;（2）呼和浩特城区规划后冬季气流汇集辐合区域增多,辐合能力增强,从而使冬季大气污染加剧;（3）呼和浩特市城区扩展后引起的下垫面热力与动力参数变化,将导致气流场发生显著变化,使得污染物的辐合能力增强。总体而言,呼和浩特市城区规划后虽增加了部分绿地等面积,但建筑物的增高增密、下垫面性质的改变,将使大气环境扩散能力减弱,大气污染加重。  相似文献   

重庆春播期间降水特征及其与北太平洋海温的关系     

周浩  程炳岩  罗孳孳 《气象》2011,37(9):1134-1139

运用NCEP/NCAR全球高度场再分析资料、美国NOAA全球海温资料以及重庆34个站春播期间降水资料,对重庆春播期间降水特征及其与前期秋季海温场的关系进行分析。结果表明：重庆春播期间降水与前期秋季北太平洋暖流附近（20°～40°N、165°E～140°W）的海温有显著负相关关系,而与北太平洋阿拉斯加暖流附近（40°～60°N、165°E～140°W）的海温则有显著正相关关系,即南、北海温呈现相反的相关性。当前期秋季北太平洋副热带地区海温异常偏高,中高纬度地区海温异常偏低时,后期重庆春播期间降水将异常偏多;反之,北太平洋副热带地区海温异常偏低,中高纬度地区海温异常偏高时,重庆春播期间降水将异常偏少。针对秋季北太平洋南、北海温异常的反相分布特征定义了用于诊断和预测重庆春播期间降水的判别指数,该指数代表了北太平洋海温异常南北反相的分布特征。该前期判别指数具有重要的天气气候学意义和一定的指示和预测能力。其代表的北太平洋海温异常与西太平洋区域500 hPa高度场有密切联系,其可使大气环流场产生持续性的异常,大气环流的异常特征能一直持续到春播期间,将影响重庆春播期间降水变化。  相似文献   

海温强迫下的东亚夏季大气环流潜在可预报性特征   总被引：2，自引：2，他引：0  

李忠贤  陈海山  曾刚  倪东鸿 《南京气象学院学报》2011,34(3):281-287

利用大气环流模式NCARCAM3,进行22a（1979—2000年）、每年8个初值的集合试验,并采用方差分析方法,研究了观测海温强迫下东亚夏季大气环流的潜在可预报性。结果表明,夏季东亚地区海平面气压场的潜在可预报性总体偏低,在中国区域呈东南高、西北低的分布特征;850hPa纬向风场、对流层500～200hPa平均温度场和500hPa位势高度场在低纬度地区的潜在可预报性明显高于中高纬度地区。500hPa位势高度场的潜在可预报性较高,东亚大部分地区大于0.5,尤其华南地区大于0.7。夏季东亚500hPa位势高度场的潜在可预报性具有明显的年际变化特征,并与夏季南海海温异常关系密切。与正常年份相比,在夏季南海海温偏暖或者偏冷年,东亚500hPa位势高度场的潜在可预报性较高  相似文献   

利用FY-3A近红外资料反演水汽总量   总被引：4，自引：1，他引：3       下载免费PDF全文

胡秀清  黄意玢  陆其峰  郑婧 《应用气象学报》2011,22(1):46-56

该文介绍了利用搭载在FY-3A卫星上的中分辨率光谱成像仪 (MERSI) 的近红外 (NIR) 通道反演大气水汽总量 (PWV) 的方法。根据预先建立的查找表,大气水汽总量可以通过水汽通道与窗区通道的卫星测值相比反演得到。对MERSI近红外水汽通道灵敏度进行估算,结果表明:处于吸收带两翼的905 nm和980 nm通道对不同水汽量的敏感性表现比较接近,对较大水汽含量最为敏感;当水汽较弱时,强吸收的940 nm通道非常敏感。基于这3个通道对水汽含量敏感性的不同表现,采用3个通道水汽总量的加权平均值作为PWV产品的最终反演值。文中设计了水汽总量业务算法反演流程,并基于FY-3A/MERSI最新观测资料进行晴空大气水汽总量的业务处理生成试验,顺利生成MERSI单轨道水汽总量产品及日拼图中国区域产品和全球产品,同时生成多天合成产品,产品反映出MERSI具有较好的近红外水汽探测能力。将卫星反演结果与探空数据进行初步比对检验,显示卫星反演值有20%~30%系统性偏低,需要进一步改进反演查找表。  相似文献   

基于系留气艇平台的红外辐射传输算法实验验证   总被引：1，自引：0，他引：1       下载免费PDF全文

章文星  吕达仁  霍娟  王勇  孙宝来  李立群 《应用气象学报》2011,22(6):654-662

中国科学院大气物理研究所中层大气和全球环境探测重点实验室 (LAGEO) 建立了以系留气艇为平台的综合探测系统。通过气艇在大气边界层上升、下降过程获得不同高度的气象参数和同时的辐射参数。以气象参数为输入,应用辐射传输模式 (MODTRAN4.0) 获得模式辐射输出,将其与实测辐射值作对比,验证MODTRAN4.0模式的准确性,为有关目标识别与遥感提供基础。2006年8月在中国科学院大气物理研究所香河综合观测站利用系留气艇平台进行了验证实验,并对热红外波段的模式对比结果进行分析。结果表明:所建实验系统具备进行模式验证的能力,在热红外波段,MODTRAN4.0模式输出结果与实测辐射亮度之间的相对误差的均方差在边界层大气条件下小于3%。  相似文献   

一次雷暴前后大气折射率的多普勒天气雷达测量试验及结果   总被引：3，自引：1，他引：2  

黄兴友  孙伟  葛文忠  王凌震  冷亮 《南京气象学院学报》2011,34(4):433-438

由温度、气压和水汽压决定的大气折射率会影响天气雷达电磁波的传播路径和目标回波的相位。因此,通过测量目标回波相位的变化能够算出大气折射率的变化,进而得到水汽信息,为研究局地对流天气和水汽平流提供资料。本文阐述了多普勒天气雷达反演大气折射率的原理和方法,并利用江苏省气象台的S波段多普勒天气雷达反演了一次雷暴过程前后的大气折射率,表明了雷达探测大气折射率的可靠性。这项工作有望为研究水汽变化和天气过程提供高分辨率的遥感资料,也可以为数值模式提供水汽场辅助数据,有良好的应用前景。  相似文献