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1.
为了解西辽河流域归一化植被指数(NDVI)的分布规律、变化趋势及对气候变化的响应,利用2000—2018年西辽河流域11个气象站逐日气象资料和MODIS归一化植被指数数据集,通过线性回归和相关分析,探讨了生长季各月NDVI与气象因子的时滞性,以及气象站周围10 km缓冲区内不同植被类型NDVI与气象因子的相关性。结果表明:西辽河流域年平均气温、最高气温、最低气温和降水量均呈上升趋势。NDVI呈上升趋势,植被有所改善,不同植被类型NDVI均呈增加趋势,耕地增加趋势最快,耕地长势受益于农事活动的完善和增进。NDVI空间分布呈现中间低,四周高特点。生长季各月NDVI与降水量存在明显的滞后性,滞后期为1个月;仅8月NDVI与前1个月平均气温和最高气温存在滞后性。不同植被类型NDVI与平均气温、最高气温的相关性密切。耕地NDVI与气象因子的相关性较好。研究结果可为维护西辽河流域生态系统平衡提供参考。  相似文献   
2.
基于数值预报和随机森林算法的强对流天气分类预报技术   总被引:4,自引:2,他引:2  
李文娟  赵放  郦敏杰  陈列  彭霞云 《气象》2018,44(12):1555-1564
随机森林算法是当前得到较为广泛应用的机器学习方法之一,有着很高的预测精度,训练结果稳定,泛化能力强,解决多分类问题有明显优势。本文将随机森林算法应用于强对流的潜势预测和分类,分短时强降水、雷暴大风、冰雹和无强对流四种类别,基于2005—2016年NCEP 1°×1°再分析资料计算的对流指数和物理量,开展强对流天气的分类训练、0~12 h预报和检验,经2015—2016年独立测试样本检验表明,针对强对流发生站点的点对点检验,整体误判率为21. 9%,85次强对流过程基本无漏报,模型尤其适用于较大范围强对流天气。随机森林算法筛选的因子物理意义较为明确,和主观预报经验基本相符,模型准确率高,可用于日常业务。  相似文献   
3.
阵风锋作为强对流的冷性出流特征,是重要的边界层辐合系统,对其自动监测识别一直是日常气象业务中的难点,该文基于深度卷积神经网络设计了阵风锋的自动识别算法。通过对输入和输出端的重新设计,在Faster RCNN算法和Inception V2网络模型的基础上实现了通过雷达回波数据对阵风锋窄带回波实现端到端自动识别。利用雷达数据绕雷达中心旋转不变性特点,增加了数据样本,降低了需提取特征的复杂度。利用2007—2011年南京雷达数据,对该模型进行了20万步的训练,总损失函数值收敛到0.003。对识别效果的分析表明,在训练样本中识别率100%,漏识率0%,准确率87%。通过对合肥雷达2009年6月5日阵风锋天气过程的32个体扫进行模型泛化能力评估,得到识别率91.7%,漏识率8.3%,正确率73.3%。  相似文献   
4.
基于3 h间隔的浙江快速更新同化模式资料、常规探空资料和临安双偏振雷达资料反演产品对浙江地区2015年12月5日的首场降雪过程的特征进行了分析,得到了较高的云顶高度、较低的云顶温度、较低的零度层高度、较低的低层平均温度、稳定的底层冷平流以及特殊的地形是浙西北地区在较高的地表温度情况下易形成降雪的原因;同时对临安双偏振雷达产品资料进行了分析,首次提出浙江地区此类降雪的双偏振雷达产品特征,并得到了判别阈值.希望借助两方面的研究来减少此类降雪天气的漏报率和可预报性.  相似文献   
5.
Windows 2003 Server提供的远程终端服务功能实现了多用户同时操作,远程终端多用户通过远程终端功能可以同时在远程终端服务上运行程序、保存文件和使用网络资源等,为业务应用提供了便捷.介绍利用Windows Server 2003远程终端(包括远程桌面和终端服务),开发了气象业务中多用户共享MICAPS20、雷达PUP产品及其它气象应用系统的信息服务平台,在实际应用中发挥了很好的应用效果.  相似文献   
6.
With the pros and cons of the traditional optimization and probability pairing methods thoroughly considered, an improved optimal pairing window probability technique is developed using a dynamic relationship between the base reflectivity Z observed by radar and real time precipitation I by rain gauge. Then, the Doppler radar observations of base reflectivity for typhoons Haitang and Matsa in Wenzhou are employed to establish various Z-I relationships, which are subsequently used to estimate hourly precipitation of the two typhoons. Such estimations are calibrated by variational techniques. The results show that there exist significant differences in the Z-I relationships for the typhoons, leading to different typhoon precipitation efficiencies. The typhoon precipitation estimated by applying radar base reflectivity is capable of exhibiting clearly the spiral rain belts and mesoscale cells, and well matches the observed rainfall. Error statistical analyses indicate that the estimated typhoon precipitation is better with variational calibration than the one without. The variational calibration technique is able to maintain the characteristics of the distribution of radar-estimated typhoon precipitation, and to significantly reduce the error of the estimated precipitation in comparison with the observed rainfall.  相似文献   
7.
Typhoon Rananim (0414) has been simulated by using the non-hydrostatic Advanced Regional Prediction System (ARPS) from Center of Analysis and Prediction of Storms (CAPS). The prediction of Rananim has generally been improved with ARPS using the new generation CINRAD Doppler radar data. Numerical experiments with or without using the radar data have shown that model initial fields with the assimilated radar radial velocity data in ARPS can change the wind field at the middle and high levels of the troposphere; fine characteristics of the tropical cyclone (TC) are introduced into the initial wind, the x component of wind speed south of the TC is increased and so is the y component west of it. They lead to improved forecasting of TC tracks for the time after landfall. The field of water vapor mixing ratio, temperature, cloud water mixing ratio and rainwater mixing ratio have also been improved by using radar reflectivity data. The model’s initial response to the introduction of hydrometeors has been increased. It is shown that horizontal model resolution has a significant impact on intensity forecasts, by greatly improving the forecasting of TC rainfall, and heavy rainstorm of the TC specially, as well as its distribution and variation with time.  相似文献   
8.
过去300年大兴安岭北部气候变化特征(英文)   总被引:1,自引:0,他引:1  
The Greater Khingan Mountains(Daxinganling) are China's important ecological protective screen and also the region most sensitive to climate changes. To gain an in-depth understanding and reveal the climate change characteristic in this high-latitude, cold and data-insufficient region is of great importance to maintaining ecological safety and corresponding to global climate changes. In this article, the annual average temperature, precipitation and sunshine duration series were firstly constructed using tree-ring data and the meteorological observation data. Then, using the climate tendency rate method, moving-t-testing method, Yamamoto method and wavelet analysis method, we have investigated the climate changes in the region during the past 307 years. Results indicate that, since 1707, the annual average temperature increased significantly, the precipitation increased slightly and the sunshine duration decreased, with the tendency rates of 0.06℃/10 a, 0.79 mm/10 a and –5.15 h/10 a, respectively(P≤0.01). Since the 21 st century, the period with the greatest increase of the annual average temperature(also with the greatest increase of precipitation) corresponds to the period with greatest decrease of sunshine duration. Three sudden changes of the annual average temperature and sunshine duration occurred in this period while two sudden changes of precipitation occurred. The strong sudden-change years of precipitation and sunshine duration are basically consistent with the sudden-change years of annual average temperature, suggesting that in the mid-1860 s, the climatic sudden change or transition really existed in this region. In the time domain, the climatic series of this region exhibit obvious local variation characteristics. The annual average temperature and sunshine duration exhibit the periodic variations of 25 years while the precipitation exhibits a periodic variation of 20 years. Based on these periodic characteristics, one can infer that in the period from 2013 to 2030, the temperature will be at a high-temperature stage, the precipitation will be at an abundant-precipitation stage and the sunshine duration will be at an less-sunshine stage. In terms of spatial distribution, the leading distribution type of the annual average temperature in this region shows integrity, i.e., it is easily higher or lower in the whole region; and the second distribution type is more(or less) in the southwest parts and less(or more) in the northeast parts. Precipitation and sunshine duration exhibit complex spatial distribution and include fourspatial distribution types. The present study can provide scientific basis for the security investigation of homeland, ecological and water resources as well as economic development programming in China's northern borders.  相似文献   
9.
赵放  王东法  杨军  陈列  徐月飞 《浙江气象》2011,32(3):8-12,27
利用浙江省雷达、自动站等现代探测资料,结合数值预报等,形成连续滚动的高分辨(0.01经纬度格距)0~3 h网格化定量降水预报,通过G IS数字高程模型、遥感数据(地质、土壤、土地利用现状)的数据库分析获取浙江省境内地质灾害易发程度的分布数据,对传统的灾害预警模型以Logistic回归模型为基础进一步改进,再采用逐时滚动递进方式引入"前期有效累积降雨量"算法,应用网格化的处理方式,建立具有高分辨(约1 km×1 km)的强降雨诱发型滑坡、泥石流网格化的客观预报预警模型,期望探索和改进气象灾害的预报技术方法,尝试提高预报的精细化程度。  相似文献   
10.
风廓线下落速度在浙江冬季降水相态识别中的应用   总被引:1,自引:0,他引:1  
孔照林  赵放  彭霞云  吴杨 《气象》2016,42(9):1090-1095
利用浙江7部风廓线雷达探测资料,进行了不同相态降水粒子下落末速的数据分析,统计得到不同降水相态的下落速度阈值,液态降水粒子的下降速度为1.8~6.0 m·s~(-1),固体降水在0.1~1.8 m·s~(-1)。同时对浙江省2011—2014年4年冬季8次雨雪转化过程中的探空资料和地面降水观测资料进行分析,得到最适合浙江省冬季降水相态识别判据是2 m温度、1000 hPa温度、0℃层高度和850和1000 hPa高度差。通过计算各指标的空报率、漏报率和TS评分,得到了最佳阈值,预报雨和雪最佳阈值的TS评分都可达到0.8以上。对雨夹雪的判断,需结合中层暖层指标,可以使判别准确率明显提高。  相似文献   
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