边界强迫场订正的区域气候模式对2013年夏季中国东部极端高温预测的改进试验

使用NCEP再分析资料对国家气候中心全球海气耦合模式BCC_CM1.0的多年平均场进行订正,然后嵌套区域气候模式RegCM3,建立基于边界强迫场订正的区域气候模式系统。使用该系统进行28年夏季回报及2013年夏季业务预测,并与直接使用BCC_CM1.0模式与RegCM3模式嵌套的模式系统进行对比。结果表明,引入边界强迫场订正技术后,区域气候模式系统对多年平均夏季气温、降水回报能力有了显著提高,且回报的高温界限值分布更接近于观测。除对2013年夏季东北地区气温距平预测效果变差外模式系统对于2013年中国东部中部地区夏季气温距平异常偏高、夏季高温日数异常偏多等观测事实的预测性能有显著提高。区域气候模式系统回报的多年平均夏季西太平洋副热带高压与观测更为接近是其对2013年夏季极端高温事件预测能力提高的关键所在。     

基于CMIP6强迫模拟分析人为气溶胶的气候效应(一)——介绍NUIST模式评估结果

为减少不同气候模式评估气溶胶气候效应的差异,第六次耦合模式比较计划(Coupled Model Intercomparison Project Phase 6,CMIP6)直接给定了人为气溶胶强迫数据。因此,有必要基于此强迫数据重新评估气溶胶气候效应。本研究首先将CMIP6给出的描述人为气溶胶强迫的模块引入南京信息工程大学(Nanjing University of Information Science and Technology,NUIST)的地球系统模式(The NUIST Earth System Model,NESM)。之后,利用NESM模式评估地球辐射收支平衡对此人为气溶胶强迫的响应,并分析模式模拟结果的不确定性。评估给出的人为气溶胶有效辐射强迫为-0. 45(±0. 28) W·m~(-2)。其中,气溶胶直接辐射效应为-0. 34(±0. 01) W·m~(-2),与第二次气溶胶比较计划(The second phase of Aerosol Comparisons between Observations and M odels,Aero ComⅡ)的评估结果基本一致;气溶胶对云辐射强迫的影响(包括半直接效应和间接效应)为-0. 10(±0. 30) W·m~(-2),明显受到模式内部变率的干扰,具有较大的不确定性。     

夏季青藏高原地区降水和低涡的数值预报试验

本文首先分析了１９７９年６—７月的ＦＧＧＥIIIｂ级资料风场和相对湿度场在青藏高原地区的偏差，指出在高原西部应予以订正。然后利用一有限区域模式，通过综合订正初始风场和相对湿度场，改进模式部分物理过程，并提高其水平分辨率，共设计了６组预报试验，对该年的两例高原低涡切变线降水过程进行了２４小时预报。结果表明，利用改进了的初始场和部分物理过程，可明显改善高原地区的降水预报，并在一定程度上改善了流场的预报，即上述改进方案是可行的；但在高原地区嵌套预报方案尚待修改，还应继续努力提高模式对高原低涡流场的预报能力。     

长三角盛夏—初秋强降水的延伸期过程预报探析

针对长三角汛期强降水过程,根据不同降水类型的特性,提出分时段建立低频模型并给出建模流程。综合分析长三角汛期强降水期的低频特性,将低频气旋及反气旋区分划分7个关键区。重点研究盛夏—初秋时段的强降水特征,在总结强降水期低频特征的基础上,借助EOF分解建立延伸期大—暴雨的预报模型:1区或2区有低频气旋维持并发展;6区、7区或5区存在低频反气旋。并且在7个关键区中1、2区的低频气旋及5、6、7区的低频反气旋为主要低频系统,起决定作用,而3区的低频系统为次要低频系统,起辅助作用。利用该模型提前30 d预报出2012年汛期最强降水过程,并分析本次过程的低频系统演变,给出动态演变模型。     

与数值模式预报结合的冬季延伸期强降温过程预测方法及业务化应用

首先对NCEP-CFSv2模式预报的2017年1-3月和10-12月1～30天700 hPa 8个关键区低频波效果做了定量评估,然后,在此基础上将模式1～30天低频波预报结果和低频波预测模型相结合,在2018年1-4月和2018年11月至2019年1月对上海地区做了15次延伸期强降温过程业务预测,结果显示：（1）模式预报的关键区低频波位相和演变趋势与实况高度吻合,预报的延伸期（11～30天）关键区低频波与实况相关系数达0.839;预报的延伸期（3～6候）关键区低频波趋势平均准确率达83.3%,准确率为100%的比例高达45.8%。（2）15次延伸期强降温过程业务预测的平均准确率、 Cs评分和Zs评分分别为61.2%, 0.149和0.158,并准确给出2018年年初和年末两次最强降温过程发生时段,预报时效分别为18天和16天,显示出一定的预测技巧;评分结果显著高于未应用CFSVv2模式结果的2015年和2016-2017年1月同期业务预测。     

一个适合青藏高原地区的修改了的郭型积云参数化方案

本文利用复杂地形条件下的有限区域模式和1979年6－7月的FGGEⅢb级资料，首先检验的原修改了的郭型积云参数化方案（下称原方案）在青藏高原地区的预报效果。然后根据其存在的问题，结合该地区积云活动的特点，应用修改了的Kirshnamurti多元回归方法，考虑中尺度水汽辐合，由该地区的散度、层结稳定度拟合了增湿系数b和中尺度水汽辐合参数η（下称新方案）。最后用新方案作了9例24小时预报和诊断分析。结果表明：原方案在高原地区的降水预报明显偏大；而新方案改进了高原和我国东部地区的降水及形势场的预报。同时，高原地区的增湿系数b和对流加热、增湿垂直廓线也更为合理。     

Monthly Extended Predicting Experiments with Nonlinear Regional Prediction.PartⅡ:Improvement of Wave Component Prediction

Based on Chen et al. (2006), the scheme of the combination of the pentad-mean zonal height departure nonlinear prediction with the T42L9 model prediction was designed, in which the pentad zonal heights at all the 12-initial-value-input isobar levels from 50 hPa to 1000 hPa except 200, 300, 500, and 700 hPa were derived from nonlinear forecasts of the four levels by means of a good correlation between neighboring levels. Then the above pentad zonal heights at 12 isobar-levels were transformed to the spectrum coefficients of the temperature at each integration step of T42L9 model. At last, the nudging was made. On account of a variety of error accumulation, the pentad zonal components of the monthly height at isobar levels output by T42L9 model were replaced by the corresponding nonlinear results once more when integration was over. Multiple case experiments showed that such combination of two kinds of prediction made an improvement in the wave component as a result of wave-flow nonlinear interaction while reducing the systematical forecast errors. Namely the monthly-mean height anomaly correlation coefficients over the high- and mid-latitudes of the Northern Hemisphere, over the Southern Hemisphere and over the globe increased respectively from 0.249 to 0.347, from 0.286 to 0.387, and from 0.343 to 0.414 (relative changes of 31.5%, 41.0%, and 18.3%). The monthly-mean root-mean-square error (RMSE) of T42L9 model over the three areas was considerably decreased, the relative change over the globe reached 44.2%. The monthly-mean anomaly correlation coefficients of wave 4-9 over the areas were up to 0.392, 0.200, and 0.295, with the relative change of 53.8%, 94.1%, and 61.2%, and correspondingly their RMSEs were decreased respectively with the rate of 8.5%, 6.3%, and 8.1%. At the same time the monthly-mean pattern of parts of cases were presented better.     

Monthly Extended Predicting Experiments with Nonlinear Regional Prediction.PartⅠ:Prediction of Zonal Mean Flow

Systematic errors have recently been founded to be distinct in the zonal mean component forecasts, which account for a large portion of the total monthly-mean forecast errors. To overcome the difficulty of numerical model, the monthly pentad-riean nonlinear dynamic regional prediction models of the zonal mean geopotential height at 200, 300, 500, and 700 hPa based on a large number of historical data (NCEP/NCAR reanalysis data) were constituted by employing the local approximation of the phase space reconstruction theory and nonlinear spatio-temporal series prediction method. The 12-month forecast experiments of 1996 indicated that the results of the nonlinear model are better than those of the persistent, climatic prediction, and T42L9 model either over the high- and mid-latitude areas of the Northern and Southern Hemispheres or the tropical area. The root-mean-square of the monthly-mean height of T42L9 model was considerably decreased with a change of 30.4%, 26.6%, 82.6%, and 39.4%, respectively, over the high- and mid-latitudes of the Northern Hemisphere, over the high- and mid-latitudes of the Southern Hemisphere, over the tropics and over the globe, and also the corresponding anomaly correlation coefficients over the four areas were respectively increased by 0.306-0.312, 0.304-0.429, 0.739-0.746, and 0.360-0.400 (averagely a relative change of 11.0% over the globe) by nonlinear correction after integration, implying that the forecasts given by nonlinear model include more useful information than those of T42L9 model.     

上海梅汛期强降水的低频特征及延伸期预报

利用2007-2013年NCEP/NCAR的700 hPa经、纬向风场及水汽场逐日再分析资料和上海市11站逐日降水资料。进行周期分析,提取低频信息,并利用向量场的经验正交函数方法进行分型。结果表明：上海地区梅汛期降水存在30-50 d的显著周期。强降水发生期,低频系统存在4个主要聚集区。贝加尔湖以西至河套地区存在并维持低频反气旋、鄂霍次克海附近多为低频气旋,这两地是中高纬冷空气的主要活动区域;孟加拉湾附近的低频反气旋及热带洋面的低频气旋是水汽的两大源地。这些区域的显著低频系统的生消是延伸预报的主要依据。上海入梅首场强降水发生前,多为偏北气流控制。南北低频气流辐合区向北移动至30°N附近,上海地区梅汛期强降水发生。低频风场及水汽场的北传与梅雨带的移动有较好的对应,当低纬低频水汽稳定北传至30°N附近时,江南北部入梅,随后偏南水汽或继续北进或滞留,对应梅雨带的持续北抬或间歇性停滞。低频经向风及水汽输送的特征是梅汛期延伸期强降水的前兆信号。跟踪监测低频偏南气流的北传进程有助于预报入梅强降水过程。