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1.
利用MODIS数据进行云检测   总被引:14,自引:2,他引:12       下载免费PDF全文
介绍了近年来国际、国内利用气象卫星资料进行云检测识别的研究现状,并提出了一种利用中分辨率成像光谱仪(MODIS)红外、可见光谱段数据进行云、晴空分离的实用方法。给出了一些应用个例,个例分析表明算法适用于含有植被、海洋等背景的中低纬度地区。  相似文献
2.
Global monsoon in a geological perspective   总被引:4,自引:1,他引:3       下载免费PDF全文
Monsoon is now considered as a global system rather than regional phenomena only. For over 300 years, monsoon has been viewed as a gigantic land-sea breeze, but now satellite and conventional observations support an alternative hypothesis which considers monsoon as a manifestation of sea-sonal migration of the intertropical convergence zone (ITCZ) and, hence, a climate system of the global scale. As a low-latitude climate system, monsoon exists over all continents but Antarctica, and through all the geological history at least since the Phenorozoic. The time is ripe for systematical studies of monsoon variations in space and time. As evidenced by the geological records, the global monsoon is controlled by the Wilson cycle on the tectonic time scale (106―108 a). A “Mega-continent” produces “Mega-monsoon”, and its breakdown leads to weakening of the monsoon intensity. On the time scales of 104―105 a, the global monsoon displays the precessional cycles of ~20 ka and eccentricity cycles of 100- and 400-ka, i.e. the orbital cycles. On the time scales of 103 a and below, the global monsoon intensity is modulated by solar cy-cles and other factors. The cyclicity of global monsoon represents one of the fundamental factors re-sponsible for variations in the Earth surface system as well as for the environmental changes of the human society. The 400-ka long eccentricity cycles of the global monsoon is likened to “heartbeat” of the Earth system, and the precession cycle of the global monsoon was responsible for the collapse of several Asian and African ancient cultures at ~4000 years ago, whereas the Solar cycles led to the de-mise of the Maya civilization about a thousand years ago. Therefore, paleoclimatology should be fo-cused not only on the high-latitude processes centered at ice cap variations, but also on the low-latitude processes such as monsoons, as the latter are much more common in the geological his-tory compared to the glaciations.  相似文献
3.
An assimilation data set based on the GFDL MOM3 model and the NODC XBT data set is used to examine the circulation in the western tropical Pacific and its seasonal variations. The assimilated and observed velocities and transports of the mean circulation agree well. Transports of the North Equatorial Current (NEC), Mindanao Current (MC), North Equatorial Countercurrent (NECC) west of 140°E and Kuroshio origin estimated with the assimilation data display the seasonal cycles, roughly strong in boreal spring and weak in autumn, with a little phase difference.The NECC transport also has a semi-annual fluctuation resuiting from the phase lag between seasonal cycles of two tropical gyres' recirculations. Strong in summer during the southeast monsoon period, the seasonal cycle of the Indonesian throughfiow (ITF) is somewhat different from those of its upstreams, the MC and New Guinea Coastal Current (NGCC), implying the monsoon's impact on it.  相似文献
4.
磁暴对夜间中低电离层影响的数值模拟   总被引:1,自引:1,他引:0  
从电子连续方程、电子运动方程以及离子运动方程出发,选用IRI-90电子浓度为磁暴初始时的浓度,并采用HEDIN-90剪切时变中性风模式,对中低纬电离层F层在磁暴期间的变化形态进行了数值模拟研究.模拟结果表明:磁暴会引起电离层产生不同程度的扰动,在磁暴时存在的东西方向电场的作用下,电离层F层峰产生垂直漂移.不同情况的模拟表明:不同强度的暴时电场会对电离层F层产生不同的影响,并且纬度越低F层受暴时电场的影响越大,这与磁暴期间观测到的电波实验现象一致.  相似文献
5.
结合MODIS数据的通道特性,分析了云在不同波谱范围的光谱特性,提出了一种基于多光谱综合阈值法的简便新方法.该云检测算法从可见光反射率、热红外亮温出发,逐步建立云检测模板,实现分离云和晴空,通过对不同下垫面类型数据进行云检测检验,结果表明,该算法对中低纬度地区云检测处理有显著效果,尤其能够检测出可见光波段难以识别的薄卷云.该法可使遥感数据特别是MODIS数据在云检测领域的应用提高一个层次,进而提出的云区数据修补方法,使数据反演应用的精度提高更为显著.  相似文献
6.
从增湿系数的角度设计了多种试验方案对Kuo型方案进行改进,数值试验结果表明,增湿系数采用指数型定义法方案较为适合云南低纬高原上的中尺度数值模式。  相似文献
7.
Interglacial or postglacial climates are all of charac-teristic of warmer conditions. However, if condition asso-ciated with the warm feature is wetter or drier than today,it would produce different impacts on natural environ-ments and human society. Quaternary studies found thatclimate with warm-dry or warm-wet conditions had oc-curred in China during the last 40—30 ka BP[1]. For ex-ample, it was warmer than the present during themid-Holocene (3—8 ka BP) and the late phases of MarineIsot…  相似文献
8.
A hierarchical cluster analysis has been made on the geomagnetic and geoelectric data of Nagoya (ϕ=21. 1°), Japan (1978–1981, 1985, 1987) and geomagnetic data of Wuchang (ϕ=19. 1°), China (1985–1995). From the cluster diagram it is seen that the monthly mean occurrence of Pc3–4 observed at these two sites can be best grouped into 3 clusters. Supported by the National Natural Science Foundation of China Zhao Zhengyu: born in 1952, Doctor, Associate professor  相似文献
9.
 利用1992年9月~2005年8月的HALOE资料,对我国低纬高原地区上空平流层中NOx,O3等大气痕量气体的混合比垂直变化进行了研究,并对本区域不同高度上NOx混合比与全球同纬度进行了比较,同时对NOx随时间的演变特征,NOx的变化周期及NOx与O3的相关关系进行了分析.结果表明:①NOx,O3混合比先随高度增加,到极值时又逐渐减小;在极值高度上,各个季节NOx,O3的混合比值都是夏季最高,冬季最低;②在5 hPa以上,春季NO混合比与同纬度地区的纬圈平均相比其值更高,各个季节NO2混合比的总体趋势都要比同纬度地区低;③在100,10 hPa和1 hPa上,NOx混合比随时间变化的总体趋势是各不相同的;④NOx具有准2 a周期变化;⑤在10 hPa附近,NOx与O3存在较明显的反相关关系.  相似文献
10.
在中低纬度多年冻土区多次实验分析如何改善音频大地电磁测深(AMT)高频段出现的"跳点"现象。根据测量结果认为天然电磁场信号、季节气候、采集时间、极距长短对高频段视电阻率数据下跳影响明显。提高野外测量数据质量,AMT高频段视电阻率测点具有真实圆滑连续性,对研究青藏高原冻土分布有重要指导意义。  相似文献
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