IMPACT OF VERTICAL RESOLUTION,MODEL TOP AND DATA ASSIMILATION ON WEATHER FORECASTING——A CASE STUDY

The impacts of stratospheric initial conditions and vertical resolution on the stratosphere by raising the model top, refining the vertical resolution, and the assimilation of operationally available observations, including conventional and satellite observations, on continental U.S. winter short-range weather forecasting, were investigated in this study. The initial and predicted wind and temperature profiles were analyzed against conventional observations. Generally, the initial wind and temperature bias profiles were better adjusted when a higher model top and refined vertical resolution were used. Negative impacts were also observed in both the initial wind and temperature profiles, over the lower troposphere. Different from the results by only raising the model top, the assimilation of operationally available observations led to significant improvements in both the troposphere and stratosphere initial conditions when a higher top was used. Predictions made with the adjusted stratospheric initial conditions and refined vertical resolutions showed generally better forecasting skill. The major improvements caused by raising the model top with refined vertical resolution, as well as those caused by data assimilation, were in both cases located in the tropopause and lower stratosphere. Negative impacts were also observed, in the predicted near surface wind and lower-tropospheric temperature. These negative impacts were related to the uncertainties caused by more stratospheric information, as well as to some physical processes. A case study shows that when we raise the model top, put more vertical layers in stratosphere and apply data assimilation, the precipitation scores can be slightly improved. However, more analysis are needed due to uncertainties brought by data assimilation.     

近百年东亚季风长期变化中主周期振荡的奇异谱分析

运用海平面气压场资料，计算１８７３—１９９０年的东亚冬、夏季风强度指数，并利用奇异谱分析方法（ＳＳＡ）对这百年的东亚季风长期变化的周期活动进行了研究。研究表明：东亚冬、夏季风都存在准２ａ（ＱＢＯ）、３—６ａ（ＬＦＯ）的年际振荡，１６—１８ａ（ＩＤＯ）的年代际振荡和长期变化趋势。各振荡分量都具有年代际的差别，这种特征ＱＢＯ表现得最典型。冬季风的ＱＢＯ在１９２０年代前振幅较小，且大约呈现１２ａ的大振幅和６ａ的小振幅波状的周期变化；夏季风的ＱＢＯ振幅变化与冬季风相反，且大约呈现６ａ的大振幅和３ａ的小振幅波状的周期变化。夏季风中的年代际变化影响较小。     

ROLE IN MOISTURE TRANSPORTATION OF SEASONAL MEAN AND INTRASEASONAL OSCILLATIONS IN ASIAN SUMMER MONSOON AREA——LONG-TERM AVERAGE CHARACTERISTICS

By use of the May—September 1980—1986 ECMWF daily data of u,v,r and T at 850 hPa,a comparative analysisis performed of basic features of moisture transportation at seasonal mean,quasi-40-day,-biweekly,and-weeklyoscillations,indicating that the seasonal mean transfer plays a decisive role in the moisture flux over the Asian monsoonregion,displaying the integer of the monsoon systems there in character;that the transport related to these tropicalintraseasonal oscillations are of equal importance in the monsoon period except the difference in their behaviors,i.e.,thetransfer shows considerable relative independence in the South-and East-Asian systems;and that the transport at allthese intraseasonal oscillations is found to be feeble at equatorial latitudes with little or no influence on each other forboth hemispheres.     

IMPACTS OF ATOVS DATA ASSIMILATION ON PREDICTION OF A RAINSTORM OVER SOUTHEAST CHINA

Using the Advanced Research WRF (ARW WRF) model and the Gridpoint StatisticalInterpolation (GSI) three-dimensional variational analysis (3DVAR) system, the impact of assimilatingATOVS (Advanced TIROS Operational Vertical Sounder) radiance through the prototype CommunityRadiative Transfer Model (pCRTM) is evaluated on the forecasting of a heavy rainstorm occurring over thecentral Guangdong province in the southeast of China on 20-21 June 2005. A pair of comparisonexperiments (NODA and DA) for this case is conducted with multiple configurations, including nestingdomains with 4-km and 12-km grid distances. The results showed that by changing the initial conditionthrough data assimilation, a modified divergence and moisture field with the structure of dipoles has beenadded to the axis of the rainband with a southwest-northeast orientation. When more moisture carried by asouthwesterly low level jet (LLJ) was converged into the northeast portion of the rainband around theobservatory station of Longmen, the amplitude of moisture static energy (MSE) increased substantially atlow levels much more than at middle levels, resulting in the enlarging of differences in MSE between 500hPa and 850 hPa; the atmosphere became more unstable. Consequently, the convective rainfall increased inthe northeast part of the province around the Longmen station, which was consistent with the observeddistribution of rainfall.     

市场潜力、空间溢出与制造业集聚

为深入分析国内外市场潜力对于中国制造业集聚发展的重要影响,首先引入一个新经济地理学模型,从理论上分析国内外市场潜力对于制造业区位选择的影响,进而结合跨省面板数据,采用空间杜宾模型对中国省域国内外市场潜力对制造业集聚的影响效应进行经验论证。参数估计结果很好地证实了省域内的国内外市场潜力对制造业集聚的显著的直接促进作用以及省域间的国内市场潜力和国外市场潜力对制造业集聚的空间溢出效应。此外,实证结果也证实了交通基础设施和市场化程度对制造业集聚的直接促进作用,劳动生产率对制造业集聚的直接促进作用和正向溢出效应,实际工资水平对制造业集聚的直接和间接阻滞（负溢出）作用。基于地理距离空间权重矩阵和0-1邻接空间权重矩阵的估计结果具有一致性。文章最后指明了上述结论的政策含义。     

超强El Ni?o事件的多样性及其对东亚夏季风降水的影响

利用1979—2017年美国国家海洋和大气管理局(NOAA)重建海温逐月资料(ERSST V5)、气候预报中心(CPC)的Ni?o3.4指数、NCEP/NCAR再分析风场资料以及CMAP降水资料,将1979—2017年Ni?o3.4指数超过2 ℃的El Ni?o事件,定义为超强El Ni?o事件。根据超强El Ni?o事件的定义,从近40年(1979—2017年)选取出三个超强El Ni?o事件(1982—1983年、1997—1998年和2015—2016年)。首先运用海温距平资料,分析超强El Ni?o事件的多样性特征,然后根据这三个超强El Ni?o事件发生年与次年的夏季降水距平,讨论东亚夏季风降水对超强El Ni?o事件多样性的响应差异。研究表明,即使是同为超强的El Ni?o事件,由于其不同的分布特征,东亚夏季风降水的响应场表现出明显的不同。在此基础上,从环流异常、850 hPa风场异常以及副高的变化等方面讨论了这两者之间的联系。      

亚洲夏季风系统准40天振荡与中国南方降水的联系

本文选取了1983年4月1日到9月30日的ECMWF的2.5°×2.5°网格点资料,采用了1000、850、500、200hPa等层的范围为30°-160°E,35°S-40°N的u、v、z三个要素,引用了T.Murakami等人的方法,将各要素场消除季节变化趋势后,对所选定的各等压面上季风系统特征区的要素场进行了谱分析,从而得到了1983年亚洲夏季风系统的风场和气压场普遍存在着的准40天、准两周和准一周的振荡.在低层850hPa上,经向风40天周期振荡在东亚季风区,位相有从南向北传播的特征,赤道对于南北半球的40天振荡的传播具有陷波现象.纬向风40天振荡的位相传播,西太平洋到南海是向西传播的,其传播速度为7-10个经度/天;印度到南海是向东传播,其传播速度为5-8个经度/天.而中国南方各特征区降水和其南侧经向风的40天振荡却有很好的位相关系,一般滞后4-8天.     

北半球对流层中高层环流对冬季欧亚雪盖作用响应的回归统计分析

利用欧亚雪盖的时间序列与北半球对流层中高层高度场之间的回归系数分离出与欧亚雪盖相关的异常环流的响应场。研究表明，这种回归响应场不仅能表示雪盖和环流之间的相关关系，而且能反映相关中心的振幅大小。环流响应场的振幅在中层较大，中上层具有显著的相当正压结构。冬春夏季的环流对冬季积雪的响应场上都存在明显的定常行星波列，冬季为ＮＥＵＰ型和ＮＰＮＡ型，春季略有变化，夏季存在ＬＥＵ型和ＥＡＮＡ型波列。响应场的行星波列具有分支现象，并以波阵面的形成进行能量传播，能量传播在副热带地区出现拦截。