卫星OLR资料在低纬风场分析中的应用

目前,几乎所有的数值预报试验和业务模式对热带地区的预报效果都不如中高纬地区那样令人满意。其原因是多样的,也是很复杂的。如对物理过程的参数化不可能很完善,象辐射、凝结潜热等这些非绝热过程的处理都还存在许多问题,而这些物理过程的作用在热带地区更为重要。这样也会导致一些物理量的初始化不准确。另外,热带地区的常规观测资料远少于中高纬地区。上述因素所带来的困难     

台风Lekima(1909)登陆前后动热力结构变化对浙江极端降水的影响

利用NCEPFNL 1°×1°的全球再分析资料、FY-2F卫星相当黑体亮温TBB资料、中国自动站与CMORPH降水产品融合的逐时降水资料和多普勒天气雷达资料,重点分析了台风Lekima(2019)发展演变过程中的动热力结构变化和水汽分布特征与浙江极端强降水之间的关系.台风Lekima(2019)近海急剧加强为具有特殊双...     

用青藏高原1～3月OLR作我国夏季降水预报的探讨

对青藏高原１～３月ＯＬＲ与我国夏季降水进行时空综合的ＥＯＦ分析,所得高原ＯＬＲ的时空特征与其单获ＥＯＦ分析的时空特征十分相似,由此,对时空综合ＥＯＦ分析法拟合降水场的收敛速度进行了分析,探讨了用亮原１～３月ＯＬＲ预报我国夏季降水场的可行性,并对预报误差的原因进行了分析。     

暴雨系统中的非平衡运动与有限区域模式的初值化

将非平衡风分成两部分:(1)非平街风的旋度部分(?)′_R和(2)非平衡风的散度部分(?)′_D。在产生暴雨的次天气尺度系统中,这两种非平衡风具有同样重要的作用。所以在有限区域细网格模式的初值化中,不能只考虑散度风,即使用通常称为“散度初值化”的方案,而且要考虑非平衡风的旋度部分。根据散度方程分析,(?)′_R是维持、调整散度场的重要因子。试验了三种风场初值化方案,结果表明,在风场初值中同时考虑(?)′_R和(?)′_D,可以明显改善模式的降水预报。     

Comprehensive test of different cumulus parameterization schemes for the simulation of the Indian summer monsoon

Summary The global spectral model of NCMRWF at T80 horizontal resolution and 18 vertical levels has been integrated for the summer season (July) using different cumulus parameterization schemes namely, the Simplified Arakawa-Schubert scheme (SAS), the Relaxed Arakawa-Schubert Scheme (RAS), and the Kuo-type cumulus parameterization scheme (KUO). The results have been compared with mean analysis of the operational NCMRWF model (ANA) and other available observations. Results indicate that, while the global distributions of basic fields such as the wind, temperature and moisture are fairly well simulated by all the three schemes, there are many differences seen in the simulation of the typical features of the Indian summer monsoon. The strength of the Low Level Westerly Jet (LLWJ), the Cross Equatorial Flow (CEF), and the Tropical Easterly Jet (TEJ) are better simulated by RAS and SAS as compared to ANA than the KUO scheme. RAS and SAS produce strong rising motion owing to strong intensity of convection produced by these two schemes. This in turn produces stronger Hadley cell by RAS and SAS than compared to the KUO scheme. Simulation of the 200 mb velocity potential and divergent wind by RAS and SAS produced two prominent centers, one in the Bay of Bengal and another in the Western Pacific, which correspond to the intense latent heating by cumulus convection during the active monsoon phase. The velocity potential and divergent winds were weaker in KUO, than compared to RAS and SAS. The simulation of OLR is improved by RAS as compared to observations. The cold bias produced by KUO at 200 mb is reduced by RAS and is substantially improved by SAS. Study of observed and simulated rainfall indicated that RAS and SAS produced better distribution of precipitation over the Western Ghat Mountains and the Arakan coast, where deep cumulus convection is produced due to orographic forcing of the warm moist air. The KUO scheme underestimated the rainfall over these two regions, but produced slightly better distribution of rainfall over the northwest and central India, where the intensity of convection is relatively weaker. Evaluation of overall dynamics, thermal structure and rainfall indicates that in general, SAS is able to provide relatively better results compared to other two schemes. Received October 3, 2000/Revised December 5, 2000     

风廓线雷达垂直速度与地面降雨关系研究：以济南为例

基于风廓线雷达数据产品的垂直速度资料和地面气象观测站2014年分钟降雨记录,采用多项式非线性拟合方法,探讨了各季节特征高度层垂直速度与地面降雨之间的相关关系;并根据场次降雨过程的分钟数据分析了垂直速度阈值对降雨开始、结束时间以及降雨强度的指示性。结果表明,垂直速度能够反映雨滴的下落速度特征,综合各个高度层来看,700 m高度层垂直速度与小时雨量回归方程拟合优度较为稳定,其他高度层在不同季节拟合优度差别略大;垂直速度的大小虽不能完全定量地预报降雨强度,但对于整个过程的雨强波动变化有着明显的指示性作用,700 m高度层垂直速度对于降雨的预报指示效果最为稳定。垂直速度对降水的指示性可用于灾害性天气,如暴雨、冰雹、降雪等的预警及临近预报,其阈值的确定受降水相态、降水类型、气温、湿度、湍流等影响,且并非唯一指标。     

A high resolution global reanalysis highlighting the winter monsoon. Part I, reanalysis fields

Summary This study entails a reanalysis of the TOGA-COARE, CEPEX period covering the months December 1992 through March 1993. Four times daily data sets were reanalyzed for the period. The unique aspect of this reanalysis is that (i) it incorporates physical initialization i.e. assimilation of rainfall from raingauge and satellite (OLR and microwave radiometric data), (ii) this reanalysis is carried out at a very high resolution, T170, global spectral model (space resolution of roughly 70 km at equator) and (iii) ECMWF reanalysis is used as a first guess field for this study.This analysis is global and is carried out at 15 vertical levels using the FSU global spectral model. In this study we have analyzed a large number of meterological variables such as wind, temperature, humidity, surface pressure, vertical velocity, cloud, rainfall, surface fluxes and diabatic heating. In this part of the paper we present the monthly mean and samples of daily fields of the reanalysis. Some of the major results of the reanalysis include the relationships among the flow fields and the ITCZ convection; the shallow northeast monsoon current and its rapid turning towards westerlies with height; an overabundance of middle clouds over the region of the ITCZ; and the distribution of heat sources and sinks. A motivation for this reanalysis is the forthcoming Indian Ocean Experiment (INDOEX), which is an international field experiment to be conducted during the winter monsoon time frame in 1999.With 25 Figures     

风廓线雷达在一次短时暴雨过程中的应用

利用2014年8月24日天津地区一次短时暴雨天气的3部风廓线雷达资料和降水实况资料,对比分析降水发生、维持和消亡期间风廓线雷达资料的变化特征,以探讨风廓线雷达对降水天气的监测能力。结果表明:1)风廓线雷达不仅能够反映大气层结上冷下暖的结构,并且能够探测到切变线的存在,对风的垂直结构有较强的探测能力。2)当降水出现时,垂直速度和大气折射率结构常数明显增大。4 m·s~(-1)的垂直速度出现和消失时刻,对应降水的开始和结束时刻;降水期间,4000 m高度以下的垂直速度越大降水越强。西青、静海站的折射率结构常数与降水强度之间有很好的对应关系,但不同地区的大气折射率结构常数值对降水强度的指示标准并不一致。3)在降水最强阶段,风廓线雷达数据获取率明显下降,因此低的数据获取率对强降水有一定的指示意义。     

KINEMATIC ANALYSIS OF TYPHOON POLLY(No.9216)*

We partition the observed wind field into rotational and divergent wind fields to analyze the stream field of Typhoon Polly(No.9216),which landed on 31 August 1992 and caused severe weather and large damage in the eastern China.The results indicate that the preservation of typhoon intensity after landing and the heavy rainfall took place onthe northern periphery of typho on are due to the strong divergent winds on the regions of low level jet(LLJ) and high level jet(HLJ) around the typhoon.The direction of divergent winds in the LLJ is perpendicular to the observed wind.But,the direction of divergent winds around the HLJ axis is parallel to the observed winds.The stream function and the rotational wind corresponding to the horizontal vorticity display the vertical circulation associated with the heavy rain,which is stronger than the vertical circulation around the typhoon center.The three-dimensional trajectories exhibit the warm and moist air parcels of LLJ traveling northward into the heavy rainfall region and ascending,then turning eastward in the HLJ.     

多普勒天气雷达资料同化对江淮暴雨模拟的影响

利用GSI同化系统 (Gridpoint Statistical Interpolation System) 对我国多普勒天气雷达资料进行直接循环同化分析,并采用WRF-ARW 3.5.1中尺度模式对2013年我国夏季江淮流域典型暴雨过程进行模拟试验。结果表明:经过质量控制的雷达径向风、反射率因子资料经GSI同化系统同化后,可形成合理的分析增量。仅同化径向风,模拟的风场与实况更接近,模拟的降雨落区与观测雨带位置更加接近。仅同化反射率因子,对水平风场的直接调整比较小,通过水凝物含量调整,对水平和垂直风场进行调整,对降水的落区影响较小,主要影响模拟的降水强度。同时同化两种资料,能更好地反映风场特征,并改善强降水的落区和强度的模拟。模拟改善最明显是在积分12~36 h时段内,该时段有效雷达资料量较多,表明同化雷达资料对暴雨模拟确实具有正效果。     

SWCWARMS模式对四川盆地强降水预报的检验分析

利用SWCWARMS模式产品、常规观测等资料,对2017年7月27~28日和2018年7月26~27日四川盆地两次强降水过程中的环境场、降水量和物理量场等进行了12h、24h预报时效的天气学检验分析。得出SWCWARMS模式产品在强降水预报中的3大优势:(1) SWCWARMS模式对两次强降水过程的降水强度、范围等预报效果较好,尤其是降水强度更为突出,参考价值高。(2) SWCWARMS模式对中高纬大尺度环流背景和强降水主要影响系统预报效果较好,对高原低值系统也有较好的描述。(3) SWCWARMS模式对物理量场中水汽条件(比湿场)和不稳定能量CAPE值预报效果较好。同时,还需要注意的有2方面:500hPa风速和高原上空天气系统存在系统性偏弱现象;对低层风速预报偏弱,加之风向预报偏差,直接影响了强降水分布及大暴雨中心位置的正确预报。      

Intercomparison of the performance of MM5/WRF with and without satellite data assimilation in short-range forecast applications over the Indian region

The present study is conducted to verify the short-range forecasts from mesoscale model version5 (MM5)/weather research and forecasting (WRF) model over the Indian region and to examine the impact of assimilation of quick scatterometer (QSCAT) near surface winds, spectral sensor microwave imager (SSM/I) wind speed and total precipitable water (TPW) on the forecasts by these models using their three-dimensional variational (3D-Var) data assimilation scheme for a 1-month period during July 2006. The control (without satellite data assimilation) as well as 3D-Var sensitivity experiments (with assimilating satellite data) using MM5/WRF were made for 48 h starting daily at 0000 UTC July 2006. The control run is analyzed for the intercomparison of MM5/WRF short-range forecasts and is also used as a baseline for assessing the MM5/WRF 3D-Var satellite data sensitivity experiments. As compared to the observation, the MM5 (WRF) control simulations strengthened (weakened) the cross equatorial flow over southern Arabian sea near peninsular India. The forecasts from MM5 and WRF showed a warm and moist bias at lower and upper levels with a cold bias at the middle level, which shows that the convective schemes of these models may be too active during the simulation. The forecast errors in predicted wind, temperature and humidity at different levels are lesser in WRF as compared to MM5, except the temperature prediction at lower level. The rainfall pattern and prediction skill from day 1 and day 2 forecasts by WRF is superior to MM5. The spatial distribution of forecast impact for wind, temperature, and humidity from 1-month assimilation experiments during July 2006 demonstrated that on average, for 24 and 48-h forecasts, the satellite data improved the MM5/WRF initial condition, so that model errors in predicted meteorological fields got reduced. Among the experiments, MM5/WRF wind speed prediction is most benefited from QSCAT surface wind and SSM/I TPW assimilation while temperature and humidity prediction is mostly improved due to latter. The largest improvement in MM5/WRF rainfall prediction is due to the assimilation of SSM/I TPW. The assimilation of SSM/I wind speed alone in MM5/WRF degraded the humidity and rainfall prediction. In summary the assimilation of satellite data showed similar impact on MM5/WRF prediction; largest improvement due to SSM/I TPW and degradation due to SSM/I wind speed.     

Multivariate Objective Analysis of Wind and Height Fields in the Tropics

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黄河流域夏季分区面雨量预报研究

介绍黄河流域分区夏季面雨量预报的研究成果，精心挑选51个具有较好代表性的测站对黄河流域夏季降水的时空演变特征进行分析，使用K均值动态聚类对黄河流域的夏季降水进行了客观分区，并计算出各流域夏季面雨量。通过对黄河流域夏季雨量与500hPa环流，海温、OLR、中纬阻高，高原积雪，欧亚积雪等重要影响因子的关系分析，结合黄河流域夏季面雨量年降和年代际演变特征的分析，研究出黄河流域分区夏季面雨量预测的基本方法和模型，并通过客观化的数学方法建立黄河流域夏季面雨量预测系统，预测系统十年回报的结果显示出具有较的预测技巧。     

GRAPES_Meso V3.0模式预报效果检验

应用国家气象中心模式检验方法对GRAPES_Meso V3.0模式2008年2月-2009年3月的试验预报产品,如降水、中低层高度、温度和风场预报进行统计检验。检验结果表明:V3.0模式降水预报性能得到明显改善,年及四季平均的各级降水TS评分显著提高,除了秋、冬季的48h中雨和暴雨预报外,TS评分明显高于V2.5模式,但V3.0模式的预报偏差偏大,中雨以上偏大更明显。从预报的季节平均降水率分布来看,对秋、冬季我国东部24h降水预报偏小改进明显,对春、夏季强降水中心位置及强度预报也好于V2.5模式,但是48h降水预报明显偏大,逐日降水率演变图也印证了这一点。此外,V3.0模式对500hPa高度和风场及48h预报的850hPa风场和温度场改进显著,对于850hPa高度和温度的24h预报,除夏季外,其他季节预报效果优于业务模式。     

Seasonal transition of summer rainy season over indochina and adjacent monsoon region

The mean onset and withdrawal of summer rainy season over the Indochina Peninsula were investigated using 5-day averaged rainfall data (1975-87). The mean seasonal transition process during onset and retreat phases in Indochina, India and the South China Sea is also examined using 5-day mean OLR (1975-87) and 850 hPa wind (1980-88) date. It was found that the onset of summer rainy season begins earlier in the inland region of Indochina (Thailand) in late April to early May than in the coastal region along the Bay of Bengal. This early onset of rainy sea-son is due to pre-monsoon rain under the mid-latitude westerly wind regime. The full summer monsoon circulation begins to establish in mid-May, causing active convective activity both over the west coast of Indochina and the cen-tral South China Sea. In case of withdrawal, the earliest retreat of summer rainy season is found in the central northern part of Indochina in late September. The wind field, on the other hand, already changes to easterlies in the northern South China Sea in early September. This easterly wind system covers the eastern part of Indochina where post-monsoon rain is still active. In late October, the wind field turns to winter time situation, but post monsoon rain still continues in the southern part of the Indochina Peninsula until late November     

Seasonal Transition of Summer Rainy Season over Indochina and Adjacent Monsoon Region

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Balance characteristics of multivariate background error covariances and their impact on analyses and forecasts in tropical and Arctic regions

For variational data assimilation, the background error covariance matrix plays a crucial role because it is strongly linked with the local meteorological features, and is especially dominated by error correlations between different analysis variables. Multivariate background error (MBE) statistics have been generated for two regions, namely the Tropics (covering Indonesia and its neighborhood) and the Arctic (covering high latitudes). Detailed investigation has been carried out for these MBE statistics to understand the physical processes leading to the balance (defined by the forecasts error correlations) characteristics between mass and wind fields for the low and high latitudes represented by these two regions. It is found that in tropical regions, the unbalanced (full balanced) part of the velocity potential (divergent part of wind) contributes more to the balanced part of the temperature, relative humidity, and surface pressure fields as compared with the stream function (rotational part of wind). However, the exact opposite happens in the Arctic. For both regions, the unbalanced part of the temperature field is the main contributor to the balanced part of the relative humidity field. Results of single observation tests and six-hourly data assimilation cycling experiments are consistent with the respective balance part contributions of different fields in the two regions. This study provides an understanding of the contrasting dynamical balance relationship that exists between the mass and wind fields in high- and low-latitude regions. The study also examines the impact of MBE on Weather Research and Forecasting model forecasts for the two regions.     

The influence of El Niño on the Indian summer monsoon rainfall anomaly: a diagnostic study of the 1982/83 and 1997/98 events

The Indian summer monsoon of 1982 and 1997 depicts disparities, however, maximum sea surface temperature anomaly over Niño 3 region is observed in the following winter of both the years. The inter-annual variation of sea surface temperature anomaly shows maximum peak during 1982/83 and 1997/98 El Niño events. The inter-annual variation of multivariate ENSO index also supports the above observation. The analyses of the entire tropical Pacific basin including the equatorial region reveal an anomalous behavior of the mean sea level pressure (MSLP) and the convective activities. The observations further reveal that the negative anomaly in monsoon rainfall over India prevails throughout the monsoon season except for the month of August in 1982, while in the year 1997 the monsoon rainfall anomaly shows random variations. The comparison between the summer monsoon rainfall of 1982 and 1997 depicts that the magnitude of the positive anomaly is same in the month of August. The condition over tropical Pacific during 1982/83 and 1997/98 has been investigated through the variation of outgoing long wave radiation (OLR), MSLP and pressure vertical velocity. The time–longitude plots of OLR and MSLP reveal the changes in pressure distribution and convective pattern over the tropical equatorial Pacific. The zonal and meridional cross section of pressure vertical velocity over the tropical Pacific and tropical Indian Ocean facilitates to understand the strength of the vertical motion during the monsoons of 1982 and 1997.