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921.
1996年8月8日闽西地区特大暴雨过程分析 总被引:3,自引:2,他引:1
本文研究了9601号热带风暴减弱为低压环流后引起突发性大暴雨的成因。结果表明:9610号热带风暴减弱后的低压环流移支福建省南部地区,造成闽西地区湿斜压锋区和不稳定能量明显增强,在低压西侧辐合线所提供的福合上升运动激发下,中尺度对流云团迅速发展,导致远离低压中心的闽西突发大暴雨。闽西特殊的地形对特大暴雨的产生起了组织和增幅作用。另外,还通过逐时数字红外云团图的分析,揭示中尺度对流云团发展演变特征与突发性大暴雨的关系,供日常短时预报参考。 相似文献
922.
用天气学方法对1997年10月19日全州县境内出现的一场历史上罕见的冰雹过程的中小尺度进行分析,揭示这次过程的一些机制,为掌握冰雹发生前中小尺度系统的活动和演变规律积累经验,对提高今后的预报服务能力将有所帮助. 相似文献
923.
924.
1997年度(1996年12月至1997年11月),广西各地年平均气温16.6~23.3℃,属正常;年降水量1259.5~2825.3mm,正常到偏多2~5成;年日照时数852.8~2139.3h,大部地区比常年偏少200~500h。1997年度,广西主要气候事件及其影响以洪涝和寒露风最为突出,其次是大风和冬旱;日照不足,降水偏多,洪涝及寒露风灾害严重,全年气候条件对工农业生产的影响弊多利少,属偏差年景。 相似文献
925.
本文以海河流域15个测站1951—1976年6—8月的降水量确定夏季旱涝年份。用500毫巴欧亚月平均图分析旱涝年的平均环流特征,发现:具有明显的差别。采用西风指数结合西太平洋副热带高压(以下简称副高)西伸脊点,概括得到夏季旱涝型,并揭示亚洲中、高纬西风分布具有一定的稳定性。夏季旱涝的环流特征在春季就有所反映。给出了一些可供长期预报参考的指标。 通过最近三年实况的检验,证明对于海河流域夏季旱涝的西风指数型是可用的,其前期指标是有预报参考价值的。 相似文献
926.
927.
928.
Rainfall prediction is of vital importance in water resources management. Accurate long-term rainfall prediction remains an open and challenging problem. Machine learning techniques, as an increasingly popular approach, provide an attractive alternative to traditional methods. The main objective of this study was to improve the prediction accuracy of machine learning-based methods for monthly rainfall, and to improve the understanding of the role of large-scale climatic variables and local meteorological variables in rainfall prediction. One regression model autoregressive integrated moving average model (ARIMA) and five state-of-the-art machine learning algorithms, including artificial neural networks, support vector machine, random forest (RF), gradient boosting regression, and dual-stage attention-based recurrent neural network, were implemented for monthly rainfall prediction over 25 stations in the East China region. The results showed that the ML models outperformed ARIMA model, and RF relatively outperformed other models. Local meteorological variables, humidity, and sunshine duration, were the most important predictors in improving prediction accuracy. 4-month lagged Western North Pacific Monsoon had higher importance than other large-scale climatic variables. The overall output of rainfall prediction was scalable and could be readily generalized to other regions. 相似文献
929.
A quantitative analysis of the spatial pattern of rural settlements in the upper reaches of the Minjiang River was made with
the major data sources being the relevant ETM image and the national geographical database of China (including contour line,
river and road) at the scale of 1:250 000, and using image interpretation and field investigation to obtain spatial information
on rural settlements. The results of the spatial analysis technique of GIS and correlation analysis showed that most settlements
(78.2 %) were located in the mountain area at 1500 ∼ 2700 m altitude, and almost half in the arid valley area. More than 80.0
% of settlements had their slopes above 15°. Most settlements had good access to water resources, roads and communications,
and tended to cluster close to the road network rather than the river. About half of the rural settlements in the study area
were relatively concentrated, while the others were decentralized. Those with higher altitude usually had land with steep
slope, inconvenient water and road accesses, and were located far apart from each other. In view of such a situation, further
research should be done to make reasonable countermeasures on these settlements for better living conditions and ecosystem
stability. 相似文献
930.
River restoration projects have installed j‐hook deflectors along the outer bank of meander bends to reduce hydraulic erosion, and in this study we use a computational fluid dynamics (CFD) model to document how these deflectors initiate changes in meander hydrodynamics. We validated the CFD with streamwise and cross‐channel bankfull velocities from a 193° meander bend flume (inlet at 0°) with a fixed point bar and pool equilibrium bed but no j‐hooks, and then used the CFD to simulate changes to flow initiated by bank‐attached boulder j‐hooks (1st attached at 70°, then a 2nd at 160°). At bankfull and half bankfull flow the j‐hooks flattened transverse water surface slopes, formed backwater pools upstream of the boulders, and steepened longitudinal water slopes across the boulders and in the conveyance region off the mid‐channel boulder tip. Streamwise velocity and mass transport jets upstream of the j‐hooks were stilled, mid‐channel jets were initiated in the conveyance region, eddies with a cross‐channel axis formed below boulders, and eddies with a vertical axis were shed into wake zones downstream of the point bar and outer bank boulders. At half bankfull depth conveyance region flow cut toward the outer bank downstream of the j‐hook boulders and the secondary circulation cells were reshaped. At bankfull depth the j‐hook at 160° was needed to redirect bank‐impinging flow sent by the upstream j‐hook. The hooked boulder tip of both j‐hooks funneled surface flow into mid‐channel plunging jets, which reversed the secondary circulation cells and initiated 1 to 3 counter rotating cells through the entire meander. The main outer bank collision zone centered at 50° without the j‐hook was moved by the j‐hook to within and just beyond the 70° j‐hook boulder region, which displaced other mass transport zones downstream. J‐hooks re‐organized water surface slopes, streamwise and cross‐channel velocities, and mass transport patterns, to move shear stress from the outer bank and into the conveyance and mid‐channel zones at bankfull flow. At half bankfull flows a patch of high shear re‐attached to the outer bank below the downstream j‐hook. J‐hook geometry and placement within natural meanders can be analyzed with CFD models to help restoration teams reach design goals and understand hydraulic impacts. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献