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21.
A Composite Approach of Radar Echo Extrapolation Based on TREC Vectors in Combination with Model-Predicted Winds 总被引：3，自引：0，他引：3
LIANG Qiaoqian FENG Yerong DENG Wenjian HU Sheng HUANG Yanyan ZENG Qin CHEN Zitong 《大气科学进展》2010,27(5):1119-1130
Extending the lead time of precipitation nowcasts is vital to improvements
in heavy rainfall warning, flood mitigation, and water resource management.
Because the TREC vector (tracking radar echo by correlation) represents only
the instantaneous trend of precipitation echo motion, the approach using
derived echo motion vectors to extrapolate radar reflectivity as a rainfall
forecast is not satisfactory if the lead time is beyond 30 minutes. For
longer lead times, the effect of ambient winds on echo movement should be
considered. In this paper, an extrapolation algorithm that extends forecast
lead times up to 3 hours was developed to blend TREC vectors with
model-predicted winds. The TREC vectors were derived from radar reflectivity
patterns in 3 km height CAPPI (constant altitude plan position indicator)
mosaics through a cross-correlation technique. The background steering winds
were provided by predictions of the rapid update assimilation model CHAF
(cycle of hourly assimilation and forecast). A similarity index was designed
to determine the vertical level at which model winds were applied in the
extrapolation process, which occurs via a comparison between model winds and
radar vectors. Based on a summer rainfall case study, it is found that the
new algorithm provides a better forecast. 相似文献
22.
危岩应力强度因子的计算研究 总被引：1，自引：0，他引：1
危岩崩塌是山区主要地质灾害之一,其主控结构面的断裂失稳是导致危岩崩塌的根本原因。运用线弹性断裂力学的理论,引入应力集中系数法,建立了自重作用下的危岩应力强度因子的计算公式,可用于主控结构面与裂缝共线的危岩稳定性计算。同时还推导了基于ABAQUS 的J积分、位移外推法计算危岩应力强度因子的过程。通过实例表明,2种数值计算方法与解析结果十分接近,验证了ABAQUS计算危岩应力强度因子的合理性,最后模拟了危岩裂缝角度以及临空面宽度变化对危岩应力强度因子的影响。利用ABAQUS对危岩进行分析,并绘制应力强度因子在各因素影响下的趋势图,可以推测危岩失稳的临界条件。 相似文献
23.
首先介绍方差分析叠加周期外推法,并以郯庐地震带公元1400年以来40次MS5级以上地震为例说明方差分析叠加周期外推法的应用方法,应用该方法分析了不同区域、不同震级的地震序列。结果显示:郯庐断裂地震带、北京-渤海地震带、苏鲁皖交界地区、安徽地区的地震存在显著周期,从统计学的角度可以预测下一次地震的范围。而河北平原地震带、淮河地震带、华东地区的地震经度或纬度则不存在显著周期,无法外推下一次地震的范围。方差分析叠加周期外推法用于地震预测尚属于一种尝试。外推预测值与原始实测值虽然存在一定的误差,但方法的意义在于应用统计理论上把预测地点进行了定量化,缩小了监视范围。从某种意义上,还为研究地震机理,探索地震在时、空、强的演变规律上,提供研究方向。 相似文献
24.
In the mid-eastern China,there are few or no lakes which are in the absence of anthropogenic disturbances,or their sediments remain undisturbed.As a result,the reference lakes distribution and paleolimnological reconstruction approaches usually are inappropriate to estimate lake reference conditions for nutrients.This yields the necessity of using the extrapolation methods to estimate the lake reference conditions for nutrients within those regions.The lake reference conditions for nutrients could be inferred inversely from the law of mass conservation,current lake nutrient concentration,and the loadings from watershed.Considering the scarcity of hydrological and water quality data associated with lakes and watersheds in China,as well as the low requirement of the watershed nutrient loadings models for these data,the soil conservation service(SCS) distributed hydrological model and the universal soil loss equation(USLE) were applied.The SCS model simulates the runoff process of the watershed,thereby calculating dissolved nutrients annually.The USLE estimates the soil erosion and particulate nutrients annually in a watershed.Then,with the loadings from atmospheric deposition and point source,the previous annual average nutrient concentrations could be acquired given the current nutrient concentrations in a lake.Therefore,the nutrient reference conditions minimally impacted by human activities could be estimated.Based on the proposed model,the reference conditions for total nitrogen and total phosphorus of Chaohu Lake,Anhui Province,China are 0.031 mg/L and 0.640 mg/L,respectively.The proposed reference conditions estimation model is of clear physical concept,and less data required.Thus,the proposed approach can be used in other lakes with similar circumstances. 相似文献
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