共查询到20条相似文献，搜索用时 31 毫秒
1.
利用全球电离层TEC地图（GIMs）数据,在已经建立TEC气候学模式的基础上,计算了1998年以来固定UT时间的全球TEC起伏指数σDGEC．采用偏相关分析方法对σDGEC与太阳活动（F107指数）及其起伏（dF107）、地磁活动（Ap指数）、季节变化因子（太阳偏置角）等因素,以及上述因素的非线性组合等的相关性进行分析,发现σDGEC与F107、Ap指数具有最强的相关性,与F107指数和半年变化因子的交叉项F107×S、F107指数的二次方具有较好的相关性,同时,与F107指数与年变化因子的交叉项F107×A及F107扰动指数偏离值（dF107）的二次方也具有一定的相关性．据此,以这些因子作为驱动量,建立了σDGEC的多元回归模型．鉴于σDGEC反映全球范围内电离层TEC起伏的平均特性,并与太阳活动F107指数、地磁活动Ap指数具有良好的相关性,为此我们建议,将全球TEC相对起伏指数σDGEC作为描述全球电离层扰动状态及电离层天气特征的一个新参量． 相似文献
2.
一、前言 中纬度地区电离层Es的成因与影响因素是一复杂的问题。远东地区Es既多又强,其它电离层现象也有一些特色,本文在文献[9]的基础上,从分析原始频高图入手,对远东地区夜间f0Es剧增与地磁K指数的关系作了统计研究,发现两者之间关系甚为密切,即地磁K指数的突然变化伴随着夜间Es层临界频率f0Es的剧烈增加。 相似文献
3.
There is a statistical linkage between tropical outgoing longwave radiation (OLR) and all-India summer monsoon rainfall (AISMR). A positive and significant correlation is observed over the surrounding areas of northeast Australia and the Arafura Sea during the months of January and February (J&F) which drops down as the lead month decreases. The OLR index as an area average over the surrounding areas of northeast Australia and the Arafura Sea is found to have 0.4 correlation with AISMR. The index is also found to be strongly correlated with the Indian monsoon index. In view of the teleconnection pattern, the OLR index is used for the development of statistical models using the concept of linear regression (LR) and canonical correlation analysis (CCA). Potential of CCA over LR is observed for the prediction of seasonal rainfall over the northwest, west central and over the whole country as well. The seasonal rainfall predictability basically comes from the months of June and September. 相似文献
4.
Geomagnetism and Aeronomy - The index of integral solar activity F10.7 is one of the main input parameters of existing ionospheric models, including the model used at early-warning radar stations... 相似文献
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Geomagnetism and Aeronomy - This work is a continuation of the author’s earlier analysis of the relationship between the most often used solar-activity index, F10.7, and solar-activity... 相似文献
6.
A Polish-made vertical ionosonde (VI) has been operated at the Kandilli Observatory in Istanbul, for almost one year (May 1993 - April 1994) as part of the COST 238, PRIME Project, The critical frequencies were obtained for every half-hour interval. The data obtained during this campaign, on the descending branch of solar cycle 22, and the data measured earlier in Istanbul for cycle 20 were analysed and the characteristic behaviour of the F2 region ionosphere over Istanbul has been determined. This is a unique data set for this area. Several markers of the solar cycle activities in terms of the daily relative sunspot numbers, F10.7 cm solar radio flux and solar flare index, and the magnetic daily index of Ap were then used to seek the possible influence of the solar and ionospheric activities on the critical frequencies observed in Istanbul. It was found that the solar flare index, as a solar activity index, was more reliable in determining quiet ionospheric days. It is shown that the minimum and maximum time values of the solar activity are more convenient for ionospheric prediction and modelling. 相似文献
7.
Gaussian conditional realizations are routinely used for risk assessment and planning in a variety of Earth sciences applications. Assuming a Gaussian random field, conditional realizations can be obtained by first creating unconditional realizations that are then post-conditioned by kriging. Many efficient algorithms are available for the first step, so the bottleneck resides in the second step. Instead of doing the conditional simulations with the desired covariance (F approach) or with a tapered covariance (T approach), we propose to use the taper covariance only in the conditioning step (half-taper or HT approach). This enables to speed up the computations and to reduce memory requirements for the conditioning step but also to keep the right short scale variations in the realizations. A criterion based on mean square error of the simulation is derived to help anticipate the similarity of HT to F. Moreover, an index is used to predict the sparsity of the kriging matrix for the conditioning step. Some guides for the choice of the taper function are discussed. The distributions of a series of 1D, 2D and 3D scalar response functions are compared for F, T and HT approaches. The distributions obtained indicate a much better similarity to F with HT than with T. 相似文献
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Geomagnetism and Aeronomy - The dependence of the local annual asymmetry index AI on solar activity has been analyzed based on daily data on the noon values of the F2-layer maximum electron... 相似文献
10.
Geomagnetism and Aeronomy - Abstract—By comparing the moving 12-month averaged values of the F107 solar radiation flux at a wavelength of 10.7 cm and ionospheric solar activity index T, we... 相似文献
11.
用近５０个中纬（磁纬在±２０°-５０°之间）电离层垂测站的ｆ０Ｆ２资料,分析与磁暴相伴的电离层暴事例表明：地磁Ｄｓｔ指数与中纬电离层ｆ０Ｆ２暴时变化Ｄｓ（ｆ０Ｆ２ ）有大致相似的发展趋势。但用时序叠加法求得的强度不同、发展过程和持续时间不同的多次电离层暴ｆ０Ｆ２变化的平均值,其物理意义是很不明确的。暴时ｆ０Ｆ２变化的地方时分布Ｄｓ（ｆ０Ｆ２）中,一般说以全日周期扰动幅度（Ａ１）为最强,但电离层负暴峰值后常出现半日周期扰动（Ａ２）的增强,且有时Ａ２＞Ａ１．Ａ１的涨落趋势与Ｄｓｔ（ｆ０Ｆ２）相似,但特强磁暴时,Ａ１值有可能反而变小．以Ａ１ｓｉｎ（ω ｔ＋ １）表示的全日周期扰动中,初位相１值随暴时的发展而变小表明,扰动分布形态是基本上随地球一起转动的。 相似文献
12.
The FORMOSAT-3/COSMIC (F3/C) satellite probes the S4 scintillation index profile of GPS signals by using the radio occultation (RO) technique. In this study, for practical use on the Earth’s surface, a method is developed to convert and integrate the probed RO S4 index, so obtaining the scintillation on the ground. To estimate the worst case, the maximum value on each profile probed by F3/C, which is termed S4max, is isolated. The isolated data are further used to construct the global three-dimensional distributions of S4max for various local times, seasons, solar activities, and locations. The converted S4max for the first time estimates the global distribution of ionospheric scintillations in the GPS L1 band C/A code signal on the ground. The results show that the worst-case scintillations appear within the low-latitude region of ±30°N, peaking around ±20°N magnetic latitude; they begin at 1900 MLT, reach their maximum at 2100 MLT, and vanish by about 0200–0300 MLT. The most pronounced low-latitude scintillation occurs over the South American and African sectors. 相似文献
13.
Estimation of the infiltration/natural recharge to groundwater from rainfall is an important issue in hydrology, particularly in arid regions. This paper proposes the application of The Natural Resources Conservation Service (NRCS) mass balance model to develop infiltration (F)–rainfall (P) relationship from flash flood events. Moreover, the NRCS method is compared with the rational and the Ф-index methods to investigate the discrepancies between these methods. The methods have been applied to five gauged basins and their 19 sub-basins (representative basins with detailed measurements) in the southwestern part of Saudi Arabia with 161 storms recorded in 4 years. The F–P relationships developed in this study based on NRCS method are: F = 39% P with R2 = 0.932 for the initial abstraction factor, λ = 0.2. However, F = 77% P with R2 = 0.986 for λ = 0.01. The model at λ = 0.01 is the best to fit the data, therefore, it is recommended to use the formula at λ = 0.01. The results show that the NRCS model is appropriate for the estimation of the F–P relationships in arid regions when compared with the rational and the Ф index methods. The latter overestimates the infiltration because they do not take λ into account. There is no significant difference between F–P relationships at different time scales. This helps the prediction of infiltration rates for aquifer recharge at ungauged basins from monthly and annual rainfall data with a single formula. 相似文献
14.
Drought hotspot identification requires continuous drought monitoring and spatial risk assessment. The present study analysed drought events in the agriculture‐dominated mid‐Mahanadi River Basin in Odisha, India, using crop water stress as a drought indicator. This drought index incorporated different factors that affect crop water deficit such as the cropping pattern, soil characteristics, and surface soil moisture. The drought monitoring framework utilized a relevance vector machine model‐based classification that provided the uncertainty associated with drought categorization. Using the proposed framework, drought hotspots are identified in the study region and compared with indices based on precipitation and soil moisture. Further, a bivariate copula is employed to model the agricultural drought characteristics and develop the drought severity–duration–frequency (S–D–F) relationships. The drought hotspot maps and S–D–F curves are developed for different locations in the region. These provided useful information on the site‐specific drought patterns and the characteristics of the devastating droughts of 2002 and 2012, characterized by an average drought duration of 7 months at several locations. The site‐specific risk of short‐ and long‐term agricultural droughts are then investigated using the conditional copula. The results suggest that the conditional return periods and the S–D–F curves are valuable tools to assess the spatial variability of drought risk in the region. 相似文献
15.
M. Janga Reddy Vijay P. Singh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(3):475-489
This study investigated the utility of two meta-heuristic algorithms to estimate parameters of copula models and for derivation of drought severity–duration–frequency (S–D–F) curves. Drought is a natural event, which has huge impact on both the society and the natural environment. Drought events are mainly characterized by their severity, duration and intensity. The study adopts standardized precipitation index for drought characterization, and copula method for multivariate risk analysis of droughts. For accurate estimation of copula model parameters, two meta-heuristic methods namely genetic algorithm and particle swarm optimization are applied. The proposed methodology is applied to a case study in Trans Pecos, an arid region in Texas, USA. First, drought severity and duration are separately modeled by various probability distribution functions and then the best fitted models are selected for copula modeling. For modeling the joint dependence of drought variables, different classes of copulas, namely, extreme value copulas, Plackett and Student’s t copulas are employed and their performance is evaluated using standard performance measures. It is found that for the study region, the Gumbel–Hougaard copula is the best fitted copula model as compared to the others and is used for the development of drought S–D–F curves. Results of the study suggest that the meta-heuristic methods have greater utility in copula-based multivariate risk assessment of droughts. 相似文献
16.
GPS（Global Positioning System）周跳是一种GPS信号异常现象.研究发现一定仰角以上的GPS周跳与电离层闪烁有关,是强电离层闪烁造成的GPS载波信号短时失锁现象,因此其可作为表征电离层闪烁效应的参量.本文通过分析由中国低纬度地区GPS台站原始观测数据提取的GPS周跳发生率与地方时、季节、太阳活动以及磁活动之间的关系,开展电离层闪烁效应与这几种参量之间关系的模式化研究.研究结果表明：（1）周跳发生率存在着地方时分布,发生时段主要在日落19：00LT后到午夜02：00LT之前,发生次数在22：00LT左右达到极大,然后缓慢减少,这一变化特点可以用自变量为地方时的Chapman函数形式来描述;（2）周跳发生率存在年变化特点,主要发生在年积日45~135天（春分季节）和225~315天（秋分季节）,可以通过高斯函数来描述每个分季闪烁效应的变化特点;（3）可以利用太阳辐射指数F10.7作为描述周跳随太阳活动周变化的参量,根据周跳随太阳活动周的变化特点,我们使用一个以F10.7为自变量的三次函数来描述这种变化;（4）电离层闪烁与磁活动的关系比较复杂,由于大多数情况下表现为磁活动对电离层闪烁的抑制作用,在本研究中使用一个以地磁活动指数Ap为自变量的的平方根函数来拟合这种变化. 相似文献
17.
本文给出了电离层中存在电离运动时的高频无线电波的多普勒频移的表达式,讨论了用高频多普勒阵研究电离层声重波扰动有关的若干电波传播问题。 相似文献
18.
This study presents copula‐based multivariate probabilistic approach to model severity–duration–frequency (S‐D‐F) relationship of drought events in western Rajasthan, India. Drought occurrences are analysed using standardized precipitation index computed on monthly mean areal precipitation, aggregated at a time scale of 6 months. After testing with a series of probability density functions, the drought variable severity is found to be better represented with log‐normal distribution, whereas duration is well fitted with exponential distribution. Four different classes of bivariate copulas – Archimedean, extreme value, Plackett, and elliptical families are evaluated for modelling joint distribution of drought characteristics. It is observed that the extreme value copula – Gumbel–Hougaard copula – performed better as compared with other classes of copulas, based on results of various statistical tests and upper tail dependence coefficient. The joint distribution obtained from best performing copula is then employed to determine conditional return period and to derive drought severity‐duration‐frequency (S‐D‐F) curves for the study region. The results of the study suggests that the copula method can be used effectively to derive the drought S‐D‐F curves, which can be helpful in planning and adopting suitable drought mitigation strategies in drought‐prone areas. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
19.
本文对比分析了太阳活动高、低年期间高纬日侧顶部电离层离子上行随地磁活动水平的变化特征.按地磁活动水平，将DMSP卫星在太阳活动高年（2000-2002年，F13和F15）及太阳活动低年（2007-2009年，F13；2007-2010年，F15）期间的SSIES离子漂移速度观测数据分为三组：地磁平静期（Kp<3），中等地磁扰动期（3 ≤ Kp < 5）和强地磁活动期（Kp ≥ 5），分别统计分析了高纬日侧顶部电离层离子上行特征的时空分布.对比分析发现：（1）太阳活动低年期间，高纬日侧电离层离子上行发生率以及上行速度峰值均是太阳活动高年的2倍多，而离子上行通量峰值只有高年的1/6-1/4；（2）在相同太阳活动条件下，地磁活动水平对日侧电离层离子上行发生率峰值的影响并不明显，但对离子上行发生率的空间分布有着显著的控制作用：电离层离子上行高发区随地磁活动向低纬度扩展，并在强地磁活动期间呈现饱和的趋势；（3）日侧顶部电离层等离子体似乎存在两个效率相当的上行区域，一个位于极尖/极隙区纬度附近，离子可沿开放磁力线上行进入磁尾；另一个位于晨侧亚极光区附近，离子沿闭合磁力线上行，有可能进入日侧等离子体层边界层. 相似文献