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1.
A global forecast model is used to examine various sensitivities of numerical predictions of three extreme winter storms that occurred near the eastern continental margin of North America: the Ohio Valley blizzard of January 1978, the New England blizzard of February 1978, and the Mid-Atlantic cyclone of February 1979. While medium-resolution simulations capture much of the intensification, the forecasts of the precise timing and intensity levels suffer from various degrees of error. The coastal cyclones show a 5-10 hPa dependence on the western North Atlantic sea surface temperature, which is varied within a range (± 2.5℃) compatible with interannual fluctuations. The associated vertical velocities and precipitation rates show proportionately stronger dependences on the ocean temperature perturbations. The Ohio Valley blizzard, which intensified along a track 700-800 km from the coast, shows little sensitivity to ocean temperature. The effect of a shift of - 10?latitude in the position of the snow boundary is negligible in each case. The forecasts depend strongly on the model resolution, and the coarse-resolution forecasts are consistently inferior to the medium-resolution forecasts. Studies of the corresponding sensitivities of extreme cyclonic events over eastern Asia are encouraged in order to identify characteristics that are common to numerical forecasts for the two regions. 相似文献
2.
2011年12月至2012年2月T639、ECMWF及日本模式中期预报性能检验 总被引：2，自引：0，他引：2
对2011年12月至2012年2月T639、ECMWF及日本模式的中期预报产品的预报性能进行天气学检验和对比分析。结果表明：三家模式均对亚洲中高纬环流形势的调整、演变及对流层中低层温度变化具有较好的预报能力。EC模式对西风指数和850 hPa温度的预报最接近零场;日本和T639模式次之。对冬季南支槽的预报,EC模式效果较好,T639和日本模式预报强度偏弱。三家模式对地面冷高压中心强度的预报均存在不同程度的偏弱,日本模式预报误差最小,T639模式和EC模式误差相对较大。 相似文献
3.
Long-range forecasting of forest fire danger based on the SLAV model seasonal ensemble forecasts 总被引：1，自引：0，他引：1
V. M. Khan 《Russian Meteorology and Hydrology》2012,37(8):505-513
Developed is a scheme of the long-range forest fire danger (FD) forecasting based on the computation of the Nesterov??s index and on hydrodynamic forecasts of air temperature and precipitation of the SLAV model. The satellite information on the climatic distribution of the snow cover was taken into account for the forecast issuance. It is proposed to express the FD index not using traditional classes of fire danger but in ??above the norm,?? ??norm,?? and ??below the norm?? gradations. Presented are the results of author??s trials of the method based on the retrospective model data for six years. Discussed are the approaches to the improvement of the method of long-range fire danger forecasting. 相似文献
4.
多时次多尺度波谱相似预报风要素 总被引：3，自引：2，他引：1
利用1975～2004年500hPa高度和850hPa温度格点场的历史资料,分别计算出不同纬度带的超长波和长波合成波,以此作为风要素预报的基本资料。根据谐波分析原理,结合相似系数法和相似距离法建立一套多时次、多尺度波谱相似预报模型,并提出相似离度概念。经过近两年的运行试验,该预报模型运行稳定,检验结果表明,对于由风压定律制约的风要素预报具有较大的参考作用,在大尺度天气形势控制下,与当地地形、地貌结合形成的风要素预报不失为一种简便易行的风向风速预报方法。利用多时次多尺度动态相似法制作风要素预报既考虑了物理量场不同尺度的空间相似,又考虑了连续时间的过程相似,因此这对中期天气过程的预报是有意义的。 相似文献
5.
Public weather services are trending toward providing users with probabilistic weather forecasts, in place of traditional deterministic forecasts. Probabilistic forecasting techniques are continually being improved to optimize available forecasting information. The Bayesian Processor of Forecast (BPF), a new statistical method for probabilistic forecast, can transform a deterministic forecast into a probabilistic forecast according to the historical statistical relationship between observations and forecasts generated by that forecasting system. This technique accounts for the typical forecasting performance of a deterministic forecasting system in quantifying the forecast uncertainty. The meta-Gaussian likelihood model is suitable for a variety of stochastic dependence structures with monotone likelihood ratios. The meta-Gaussian BPF adopting this kind of likelihood model can therefore be applied across many fields, including meteorology and hydrology. The Bayes theorem with two continuous random variables and the normal-linear BPF are briefly introduced. The meta-Gaussian BPF for a continuous predictand using a single predictor is then presented and discussed. The performance of the meta-Gaussian BPF is tested in a preliminary experiment. Control forecasts of daily surface temperature at 0000 UTC at Changsha and Wuhan stations are used as the deterministic forecast data. These control forecasts are taken from ensemble predictions with a 96-h lead time generated by the National Meteorological Center of the China Meteorological Administration, the European Centre for Medium-Range Weather Forecasts, and the US National Centers for Environmental Prediction during January 2008. The results of the experiment show that the meta-Gaussian BPF can transform a deterministic control forecast of surface temperature from any one of the three ensemble predictions into a useful probabilistic forecast of surface temperature. These probabilistic forecasts quantify the uncertainty of the control forecast; accordingly, the performance of the probabilistic forecasts differs based on the source of the underlying deterministic control forecasts. 相似文献
6.
基于EOF分解的中期平均气温距平客观预报方法 总被引：1，自引：0，他引：1
本文通过将500 hPa高度、850 hPa温度、海平面气压的预报与历史要素场进行EOF分解,并假定EOF分解空间函数(即特征向量)是基本稳定的,建立以EOF分解主分量系列的时间系数、预报站点附近基本要素值的时间序列与预报站点平均气温距平的多元线性逐步回归预报方程,结合ECMWF集合预报数值产品,生成全国范围未来10 d平均气温距平客观预报产品投入业务应用,并采用同号率方法检验。结果表明,客观预报产品在检验时段内,同号率平均值为0.77,明显高于ECMWF集合预报模式2 m温度直接计算得出的同类产品同号率0.63;该客观预报产品不仅在分布范围上,同时在距平幅度上预报效果均较好。此外,相关分析也证明同号率方法在检验中期时效气温距平预报中有其合理性。 相似文献
7.
集合预报在数值天气预报体系中具有重要地位，因此如何有效提取集合样本信息以提高集合预报技巧一直是一个重要课题。基于中国全球集合预报业务系统（GRAPES-GEPS）的500 hPa高度场集合资料开展对环流集合预报的分类释用方法研究，并对集合聚类预报结果进行了检验分析。通过在传统Ward聚类法中引入动态聚类的“手肘法”方案，发展了环流集合预报分类释用方法。针对该方法的个例分析表明，对于中国中东部地区环流集合预报的聚类释用方法能够有效地划分出最有可能发生的环流形势类型并提供发生概率。确定性预报综合检验结果显示，集合预报聚类结果中发生概率最高的集合大类相对于集合平均的预报技巧有明显提升，并随着预报时效的延长提升更明显。总体来看，通过集合预报的分类释用方法划分环流形势类型可以为天气预报提供参考依据，具有实际应用价值。 相似文献
8.
In this analysis, the weather research and forecasting model coupled with a single-layer urban canopy model is used to simulate the climatic impacts of urbanization in the Beijing–Tianjin–Hebei metropolitan area, which has experienced significant expansion in its urban areas. Two cases examining current landscapes and the sensitivity test of urban areas replaced by cropland have been carried out to explore the changes in the surface air and atmospheric boundary structure. The impact of urbanization on annual mean surface air temperature has been found to be more than 1 °C in urban areas, and the maximum difference is almost 2 °C. The change in near-surface level temperature is most pronounced in winter, but the area influenced by urbanization is slightly larger in summer. The annual mean water vapor mixing ratio and wind speed are both reduced in the urban area. The effect of urbanization can only heat the temperature inside the urban boundary layer, below 850 hPa. The modeling results also indicate that the underlying surface thermal forces induced by the “urban heat island” effect enhance vertical air movement and engenders a convergence zone over urban areas. The convergence at low level together with the moisture increases in the layer between 850 and 700 hPa triggered the increase of convective precipitation. 相似文献
9.
This study investigates the potential use of a regional climate model in forecasting seasonal tropical cyclone (TC) activity. A modified version of Regional Climate Model Version 3 (RegCM3) is used to examine the ability of the model to simulate TC genesis and landfalling TC tracks for the active TC season in the western North Pacific. In the model, a TC is identified as a vortex satisfying several conditions, including local maximum relative vorticity at 850?hPa with a value?≥450?×?10?6?s?1, and the temperature at 300?hPa being 1°C higher than the average temperature within 15° latitude radius from the TC center. Tracks are traced by following these found vortices. Six-month ensemble (8 members each) simulations are performed for each year from 1982 to 2001 so that the climatology of the model can be compared to the Joint Typhoon Warning Center (JTWC) observed best-track dataset. The 20-year ensemble experiments show that the RegCM3 can be used to simulate vortices with a wind structure and temperature profile similar to those of real TCs. The model also reproduces tracks very similar to those observed with features like genesis in the tropics, recurvature at higher latitudes and landfall/decay. The similarity of the 500-hPa geopotential height patterns between RegCM3 and the European Centre for Medium-Range Weather Forecasts 40 Year Re-analysis (ERA-40) shows that the model can simulate the subtropical high to a large extent. The simulated climatological monthly spatial distributions as well as the interannual variability of TC occurrence are also similar to the JTWC data. These results imply the possibility of producing seasonal forecasts of tropical cyclones using real-time global climate model predictions as boundary conditions for the RegCM3. 相似文献
10.
文章对2010年12月至2011年2月T639、ECMWF(文中简称EC)及日本(文中简称JP)数值模式的中期预报产品进行了对比分析和检验.结果表明:三家模式对大尺度环流形势演变和调整及对850hPa温度变化都有较好的预报能力.比较而言,随预报时效延长EC模式对北方地区850hPa温度的预报性能最好,而对南方地区,JP... 相似文献
11.
基于GRAPES区域中尺度数值预报系统(GRAPES_MESO),针对700 hPa、500 hPa和200 hPa的位势高度场H,温度场T,风场纬向分量U,经向分量V和地面降水场,在给定的模式物理过程下,分别考察了时间步长和空间分辨率对于模式预报效果的影响。研究结果表明,空间分辨率(0.3°×0.3°)相同时,各变量在不同层次的预报几乎都存在最优时间步长使得预报技巧最高,初步说明最优时间步长理论在复杂的偏微分方程组中的适用性。随后,将空间分辨率为0.3°×0.3°时最优时间步长(240 s)的预报结果与当前业务中(空间分辨率为0.15°×0.15°、时间步长为90 s)的预报结果进行比较,发现前者的变量H、T、U、V和地面降水场的预报技巧均高于后者,表明并不是空间分辨率越高预报效果越好。 相似文献
12.
A mesoscale boundary-layer model (BLM) is used for running 12-h low-level wind forecasts for the La Plata River region. Several
experiments are performed with different boundary conditions that include operational forecasts of the Eta/CPTEC model, local
observations, as well as a combination of both. The BLM wind forecasts are compared to the surface wind observations of five
weather stations during the period November 2003–April 2004. Two accuracy measures are used: the hit rate or percentage of
cases with agreement in the wind direction sector, and the root-mean-squared error (RMSE) of the horizontal wind components.
The BLM surface wind forecasts are always more accurate, since its averaged hit rate is three times greater and its averaged
RMSE is one half smaller than the Eta forecasts. Despite the large errors in the surface winds displayed by the Eta forecasts,
its 850 hPa winds and surface temperature forecasts are able to drive the BLM model to obtain surface winds forecasts with
smaller errors than the Eta model. An additional experiment demonstrates that the advantage of using the BLM model for forecasting
low-level winds over the La Plata River region is the result of a more appropriate definition of the land–river surface temperature
contrast. The particular formulation that the BLM model has for the geometry of the river coasts is fundamental for resolving
the smaller scale details of the low-level local circulation. The main conclusion of the study is that operational low-level
wind forecasts for the La Plata River region can be improved by running the BLM model forced by the Eta operational forecasts.
L. Sraibman and G. J. Berri—Members of Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) of Argentina.
An erratum to this article can be found at 相似文献
13.
依据云南省迪庆州3站40年的观测资料,利用统计检验结果,同时结合天气预报的时间和空间尺度理论,论证了迪庆州各旅游景点的气象指数预报。用最靠近景区的气象观测站所提供的天气预报资料和逐时观测资料作为预报景区指数的基础,同时根据景区的经纬度、海拔高度、植被状况进行订正,最终获取旅游景区的特种气象预报指数。旅游景区的特种气象预报软件开发应用天气学、数值方法等理论和业务技术方法,用Fortran语言和vB语言编程,研制了迪庆州各景区的紫外线指数、舒适指数、着装指数、火险等级、旅游气象指数系统。该系统软件已投入业务运行。 相似文献
14.
亚洲东部冬季地面温度变化与平流层弱极涡的关系 总被引：2，自引：1，他引：1
利用NCEP资料计算NAM指数和标准化温度距平,对17次平流层弱极涡事件时亚洲东部温度变化进行了研究。结果表明:平流层环流异常比对流层温度变化超前约15天,地面温度变化的最大距平出现在平流层弱极涡后期,大约以40°N为界,北部比正常年份偏冷而南部偏暖。文中通过位势涡度的分布和变化以及500 hPa东亚大槽的变化讨论了其影响过程和机理,在弱极涡初期和中期,自平流层向下,高位涡冷空气主要局限于60°N以北。从弱极涡的后期开始,在45°N以北地区,高位涡冷空气向南扩张,在对流层中上层,极地附近的高位涡冷空气扩张到45°N附近。同时,500 hPa东亚大槽虽有加强,但低压区向东延伸,而贝加尔湖附近的高压脊显著减弱,致使槽后的偏北气流减弱,槽后冷空气主要影响中国华北、东北及其以北地区,造成这些地区偏冷。而40°N以南地区,从弱极涡的后期开始有南方低位涡偏暖空气向北运动,同时冷空气活动减少,地面显著偏暖。 相似文献
15.
The sea surface temperature (SST) or sea level pressure (SLP) has usually been used to measure the strength of El Niño–Southern Oscillation (ENSO) events. In this study, two new indices, based on the upper-ocean heat content (HC), are proposed to quantify the two “flavours” of El Niño (i.e., the Cold Tongue El Niño (CTE) and Warm Pool El Niño (WPE)). Compared with traditional SST or SLP indices, the new HC-based indices can distinguish CTE and WPE events much better and also represent the two leading modes of the interannual variability of the atmosphere–ocean coupled system in the tropical Indo-Pacific region. The two leading modes are obtained by performing multivariate Empirical Orthogonal Function analysis on two oceanic variables (SST and HC) over the tropical Pacific (30°S–30°N, 120°E–80°W) and six atmospheric variables (outgoing longwave radiation, SLP, streamfunction, and velocity potential at 850?hPa and 200?hPa) over the tropical Indo-Pacific region (30°S–30°N, 60°E–80°W) for the period 1980–2010. Because the two new HC-based indices are capable of better depicting coherent variations between the ocean and atmosphere, they can provide a supplementary tool for ENSO monitoring of and climate research into the two flavours of El Niño. 相似文献
16.
《大气与海洋》2013,51(3):204-223
Abstract The performance of seasonal hindcasts produced with four global atmospheric models in the second phase of the Canadian Historical Forecasting Project is evaluated. Deterministic and probabilistic forecast skill assessments are carried out using common verification measures. Several methods of combining multi‐model output to produce deterministic and probabilistic forecasts of near‐surface air temperature, 500 hPa geopotential height, and 700 hPa temperature for zero‐month and one‐month leads are considered. A variance‐based weighting modestly improves the skill of deterministic and probabilistic hindcasts in some cases. A parametric Gaussian probability estimator is superior to a non‐parametric count‐method estimator for producing multi‐model probability forecasts. Statistical adjustment is beneficial for deterministic and probabilistic hindcasts of near‐surface temperature over the ocean but not always over land. Skill improves with the number of different models used for a given total ensemble size. The four‐model ensemble is shown to be a reasonable multi‐model configuration. 相似文献
17.
利用双流国际机场2013—2018年的逐小时气象观测资料、欧洲中心ERA-interim逐6小时再分析资料、成都市气象局多普勒天气雷达产品资料,运用统计学方法分析双流机场雷暴月变化和日变化特征,并利用相关性分析筛选出双流机场雷暴天气预报因子,在此基础上基于二级逻辑回归法建立潜势预报模型（预报方程和消空方程）,最后进行数据的回代检验。结果表明：对流有效位能、K指数、850 hPa比湿、850与500 hPa假相当位温差、回波顶高、1.5º仰角基本反射率、3.4º仰角基本反射率、垂直累积液态水含量为雷暴天气的主要预报因子,据此建立的潜势预报模型对双流机场雷暴天气的预报具有一定指示性,且综合来看在夏季的预报效果更好。 相似文献
18.
利用NCEP的全球数据同化系统（GDAS）1°×1°分析资料、NOAA的2.5°×2.5°全球格点资料和气象观测资料等,对2010年2月24日沈阳地区大范围冻雨灾害天气过程进行分析。结果表明：冻雨发生前期,沈阳地区的明显增温是导致大范围雨雪冰冻灾害的重要原因;925—750 hPa存在的t≥0℃温厚暖层是冻雨形成的必要条件;西南气流的建立有利于大量暖湿空气向东北地区输送,并决定了低温冰冻灾害发生的区域。中层温厚暖层的建立与破坏时间对冻雨的预报具有一定的指示意义。 相似文献
19.
W. R. Skinner M. D. Flannigan B. J. Stocks D. L. Martell B. M. Wotton J. B. Todd J. A. Mason K. A. Logan E. M. Bosch 《Theoretical and Applied Climatology》2002,71(3-4):157-169
Summary
In Canada, the average annual area of burned forest has increased from around 1 million ha in the 1970’s to over 2.5 million
ha in the 1990’s. A previous study has identified the link between anomalous mid-tropospheric circulation at 500 hPa over
northern North America and wildland fire severity activity in various large regions of Canada over the entire May to August
fire season. In this study, a northern North American study region of the hemispheric gridded 5° latitude by 10° longitude
500 hPa dataset is identified and analysed from 1959 to 1996 for a sequence of six monthly periods through the fire season,
beginning in April and ending in September. Synoptic types, or modes of upper air behavior, are determined objectively by
the eigenvector method employing K-means cluster analysis. Monthly burned areas from the Canadian Large Fire Database (LFDB)
for the same period, 1959 to 1996, are analysed in conjunction with the classified monthly 500 hPa synoptic types. Relationships
between common monthly patterns of anomalous upper flow and spatial patterns of large fire occurrence are examined at the
ecozone level. Average occurrence of a monthly synoptic type associated with very large area burned is approximately 18% of
the years from 1959 to 1996. The largest areas burned during the main fire (May to August) season occur in the western Boreal
and Taiga ecozones – the Taiga Plains, Taiga Shield, Boreal West Shield and Boreal Plains. Monthly burned areas are also analysed
temporally in conjunction with a calculated monthly zonal index (Zim) for two separate areas defined to cover western and eastern Canada. In both western and eastern Canada, high area burned
is associated with synoptic types with mid-tropospheric ridging in the proximity of the affected region and low Zim with weak westerlies and strong meridional flow over western Canada.
Received April 3, 2001 Revised July 13, 2001 相似文献
20.
Summary In this paper, forecasts of thunderstorms for the Cyprus area, are examined, by using various instability indices. In addition, some combinations of the indices are proposed since they proved more successful in thunderstorms forecasting. A statistical method pointed out that the Pickup index (PI) and the suggested combination of the humidity index (HI) with cyclonic curved flow at 500 hPa are more successful than the other ones examined in this study.With 1 Figure 相似文献