Predicting June Mean Rainfall in the Middle/Lower Yangtze River Basin

We demonstrate that there is significant skill in the GloSea5 operational seasonal forecasting system for predicting June mean rainfall in the middle/lower Yangtze River basin up to four months in advance. Much of the rainfall in this region during June is contributed by the mei-yu rain band. We find that similar skill exists for predicting the East Asian summer monsoon index(EASMI) on monthly time scales, and that the latter could be used as a proxy to predict the regional rainfall. However, th...     

Impacts of Multigrid NLS-4DVar-based Doppler Radar Observation Assimilation on Numerical Simulations of Landfalling Typhoon Haikui (2012)

We applied the multigrid nonlinear least-squares four-dimensional variational assimilation(MG-NLS4DVar) method in data assimilation and prediction experiments for Typhoon Haikui(2012) using the Weather Research and Forecasting(WRF) model. Observation data included radial velocity(V_r) and reflectivity(Z) data from a single Doppler radar, quality controlled prior to assimilation. Typhoon prediction results were evaluated and compared between the NLS-4DVar and MG-NLS4DVar methods. Compar...     

THE PRELIMINARY STUDY ON POSSIBLE SCENARIOS OF FLOOD AND DROUGHT IN CHINA IN THE CASE OF GLOBAL WARMING

ＴＨＥ ＰＲＥＬＩＭＩＮＡＲＹ ＳＴＵＤＹ ＯＮ ＰＯＳＳＩＢＬＥ ＳＣＥＮＡＲＩＯＳ ＯＦ ＦＬＯＯＤ ＡＮＤ ＤＲＯＵＧＨＴ ＩＮ ＣＨＩＮＡ ＩＮ ＴＨＥ ＣＡＳＥ ＯＦ ＧＬＯＢＡＬ ＷＡＲＭＩＮＧ ＣｈｅｎＪｉａｑｉ（陈家其）（Ｎａｎｊｉｎ...     

STUDY ON THE FORECAST METHOD FOR THE IMPACT OF CROSSWAY ON TIDAL CURRENT FIELD IN SEA AREA

This paper's method simulates the tidal current field near piles to derive and predict the scale oftheir impacts on the tidal current field, and presents the empirically obtained damp coefficient needed inpedicting the current field. The substituted plans used in the prediction are studied using Qingdao.Crossway as an example.     

一次突发性暴雨的机理分析及短期预报思考

2015年9月4日白天,天津出现突发性暴雨过程,利用多种观测资料对此次过程进行分析,结果表明:偏南气流与高压底部东北风相遇,在蓟州山区以南形成辐合,触发雷暴发展;雷暴形成后,回波形成"后向传播"机制,配合中低空的南风脉动,在天津北部形成南北向的"列车效应",导致北部强降水的发生;上游的高空槽降水在近地面形成冷池,其向东辐散气流与偏东风相遇,在降水区下游触发新的雷暴,使得雨带快速东移,且当辐散气流与偏东风相遇后,出现小尺度辐合性气旋式环流,导致下游强降水增幅;当高空槽降水云团主体移过城区后,在γ中尺度辐合流场作用下,触发小尺度对流云团的生成和发展,影响天津城区再次出现强降水。在短期预报过程中,预报员在大尺度模式环境场分析的基础上,对于中尺度模式仅参考了其降水预报,而忽略了对中尺度环境场的分析,分析表明,虽然中尺度模式对此次过程的降水时段预报存在偏差,但其中尺度环境场预报,可以为此次暴雨过程在短期时效内(24h)的预报订正提供参考。     

上海地区春季最高气温预报失败案例分析

本文分析了2015年3月17—18日上海地区连续两天发生最高气温预报失误的天气背景,并使用当日实况观测和业务预报使用的数值模式资料,剖析预报失败的原因,分析表明:对天空状况的误判是导致17日预报失败的主要原因,且东南风预报偏强更进一步增大了预报误差;冷空气影响时间的判断失误是导致18日预报失败的主要原因。从模式预报的实时检验、预报的跳跃性和不确定性角度分析了预报中存在的问题:预报员应重视本地和上游实况,从传统对单一确定性模式预报的依赖向多模式多起报时次及能提供概率预报和不确定性信息的业务集合预报的分析思路转型。此外,还需加强对集合预报的系统性检验、评估及数值预报释用产品的开发,增加包含不确定性信息的公众天气预报发布形式。     

基于DERF2.0的乌鲁木齐春季降温过程的延伸期预报检验

基于DERF2.0数据,应用均一化标准差、均方根误差等方法,以2013年乌鲁木齐春季逐日温度及24h变温检验为背景,初步评估了该模式对延伸期春季强降温过程的预报能力。结果表明：(1)逐日气温预报整体偏差随预报时效推进而增大,延伸期预报偏差明显大于中期。(2)旬平均温度的中期预报偏差普遍在-2～-8℃,延伸期的预报偏差最小在0℃左右,最大为-15.5℃。(3)日平均气温以及最高、最低气温的逐日偏差均以冷偏差为主,偏差范围为5～-15℃,延伸期预报偏差范围为-5～-15℃。模式对升温阶段的预报冷偏差随升温加剧而增大,对降温阶段的预报偏差随降温加剧而减小。24h变温偏差主要在5℃范围内变化,延伸期的24h变温偏差比中期预报偏大可达|8|℃以上。(4)DERF2.0模式对中短期温度预报有一定水平,延伸期预报能力下降,可参考价值较弱。(5)对强降温过程的结束日的温度预报偏差小,而对过程初始日的温度预报冷偏差大,造成对降温过程的预报暖偏差大,强降温过程普遍漏报。     

三种统计预报模型在江苏省道路低温预警中的应用

为了更好地开展道路交通低温灾害的预警,减轻道路结冰给车辆行驶造成的危害,本文利用2012—2016年江苏省高速公路网AWMS系统交通气象观测数据,在对路面低温发生规律进行分析的基础上,结合多元线性回归、朴素贝叶斯以及支持向量机3种统计预报方法,开展了路面低温预警的统计建模与预报试验。结果表明:(1)江苏全省高速公路网路面温度出现0℃以下、-2℃以下、-5℃以下的低温频率均呈"北高南低"分布。(2)全省高速公路网路面温度出现0℃以下的低温时次大多在15:00到次日06:00之间。(3)在对京沪高速M9308站的单站建模与预报试验中发现,路面低温预报因子组合中以13:00气温、13:00—18:00气温变温、13:00路面温度、13:00—18:00路面变温、13:00路基温度、13:00—18:00路基变温、18:00相对湿度和18:00风速U分量为自变量组合的预报方程效果最好,3种方法中以朴素贝叶斯模型的预报准确率最高;(4)就全省高速公路网而言,3种统计预报模型的路面低温预报准确率均超过75%,通过对全路网路面低温预报的试验结果对比发现,多元线性回归方法对江苏省北部路网的预报效果最好,预报准确率大多在85%以上;而支持向量机模型对江苏省南部路网的预报效果最好,大部分站点的低温预报准确率达95%以上。     

Predictable and Unpredictable Components of the Summer East Asia–Pacific Teleconnection Pattern

The East Asia–Pacific(EAP) teleconnection pattern is the dominant mode of circulation variability during boreal summer over the western North Pacific and East Asia, extending from the tropics to high latitudes. However, much of this pattern is absent in multi-model ensemble mean forecasts, characterized by very weak circulation anomalies in the mid and high latitudes. This study focuses on the absence of the EAP pattern in the extratropics, using state-of-the-art coupled seasonal forecast systems. The results indicate that the extratropical circulation is much less predictable, and lies in the large spread among different ensemble members, implying a large contribution from atmospheric internal variability. However,the tropical–mid-latitude teleconnections are also relatively weaker in models than observations, which also contributes to the failure of prediction of the extratropical circulation. Further results indicate that the extratropical EAP pattern varies closely with the anomalous surface temperatures in eastern Russia, which also show low predictability. This unpredictable circulation–surface temperature connection associated with the EAP pattern can also modulate the East Asian rainband.     

Comparisons of Three-Dimensional Variational Data Assimilation and Model Output Statistics in Improving Atmospheric Chemistry Forecasts

Atmospheric chemistry models usually perform badly in forecasting wintertime air pollution because of their uncertainties. Generally, such uncertainties can be decreased effectively by techniques such as data assimilation(DA) and model output statistics(MOS). However, the relative importance and combined effects of the two techniques have not been clarified. Here,a one-month air quality forecast with the Weather Research and Forecasting-Chemistry(WRF-Chem) model was carried out in a virtually operational setup focusing on Hebei Province, China. Meanwhile, three-dimensional variational(3 DVar) DA and MOS based on one-dimensional Kalman filtering were implemented separately and simultaneously to investigate their performance in improving the model forecast. Comparison with observations shows that the chemistry forecast with MOS outperforms that with 3 DVar DA, which could be seen in all the species tested over the whole 72 forecast hours. Combined use of both techniques does not guarantee a better forecast than MOS only, with the improvements and degradations being small and appearing rather randomly. Results indicate that the implementation of MOS is more suitable than 3 DVar DA in improving the operational forecasting ability of WRF-Chem.