GPS无线电掩星后向传播方法          下载免费PDF全文

徐贤胜  黄思训  郭鹏  洪振杰 《地球物理学报》2011,54(9):2193-2200

在大气多路径传播条件下,讨论了两种无线电信号的反演方法:几何光学方法和后向传播方法.当大气存在多路径效应时,采用几何光学方法反演大气参数会引入较大误差.后向传播方法将无线电信号从多路径区域反推至单路径区域,减少了大气多路径效应的影响.为了比较不同的反演方法,利用多相位屏模型,数值模拟了大气多路径条件下无线电信号在大气中...  相似文献   

Synoptic weather conditions and aerosol episodes over Indo-Gangetic Plains,India     

D. G. Kaskaoutis  E. E. Houssos  D. Goto  A. Bartzokas  P. T. Nastos  P. R. Sinha  S. K. Kharol  P. G. Kosmopoulos  R. P. Singh  T. Takemura 《Climate Dynamics》2014,43(9-10):2313-2331

The present study focuses on identifying the main atmospheric circulation characteristics associated with aerosol episodes (AEs) over Kanpur, India during the period 2001–2010. In this respect, mean sea level pressure (MSLP) and geopotential height of 700 hPa (Z700) data obtained from the NCEP/NCAR Reanalysis Project were used along with daily Terra-MODIS AOD₅₅₀ data. The analysis identifies 277 AEs [AOD₅₀₀ >  \( \overline{AOD} \) ₅₀₀ + 1STDEV (standard deviation)] over Kanpur corresponding to 13.2 % of the available AERONET dataset, which are seasonally distributed as 12.5, 9.1, 14.7 and 18.6 % for winter (Dec–Feb), pre-monsoon (Mar–May), monsoon (Jun–Sep) and post-monsoon (Oct–Nov), respectively. The post-monsoon and winter AEs are mostly related to anthropogenic emissions, in contrast to pre-monsoon and monsoon episodes when a significant component of dust is found. The multivariate statistical methods Factor and Cluster Analysis are applied on the dataset of the AEs days’ Z700 patterns over south Asia, to group them into discrete clusters. Six clusters are identified and for each of them the composite means for MSLP and Z700 as well as their anomalies from the mean 1981–2010 climatology are studied. Furthermore, the spatial distribution of Terra-MODIS AOD₅₅₀ over Indian sub-continent is examined to identify aerosol hot-spot areas for each cluster, while the SPRINTARS model simulations reveal incapability in reproducing the large anthropogenic AOD, suggesting need of further improvement in model emission inventories. This work is the first performed over India aiming to analyze and group the atmospheric circulation patterns associated with AEs over Indo-Gangetic Plains and to explore the influence of meteorology on the accumulation of aerosols.  相似文献   

Characteristics of the atmospheric circulation associated with cold-season heavy rainfall and flooding over a complex terrain region in Greece     

G. A. Efstathiou  C. J. Lolis  N. M. Zoumakis  P. Kassomenos  D. Melas 《Theoretical and Applied Climatology》2014,115(1-2):259-279

Raingauge data from four meteorological stations in Chalkidiki peninsula (Greece) were used to identify the characteristics of the synoptic circulation patterns associated with cold-season heavy rainfall events and corresponding flooding over the area. Precipitation climatology over the complex topography of Chalkidiki is characterized by limited annual rainfall, but in the occurrence of heavy rainfall episodes daily accumulations are exceptionally high with increased precipitation rates, leading often to severe flooding. Fifty-five cases of high daily accumulations for the period of 1997 to 2010, mostly observed during December and October, were classified into eight clusters by applying S-Mode Factor Analysis and Cluster Analysis to the ERA-Interim grid point reanalysis data. The results revealed that, in most cases, intense rainfall and flooding is produced by synoptic scale disturbances that generate and sustain cyclonic activity over south Italy, the Ionian, and less frequently over the Aegean Sea. In particular, the atmospheric circulation patterns associated with heavy rainfall are characterized by the presence of a southeasterly–easterly low-level humid flow over Chalkidiki in conjunction with the potentially unstable lower troposphere influenced by mid-level cyclonic vorticity advection and enhanced low-level convergence over the complex terrain.  相似文献   

Differences between cropland and rangeland MODIS phenology (start-of-season) in Mali     

《International Journal of Applied Earth Observation and Geoinformation》2014

Start-of-season data are more and more used to qualify the land surface phenology trends in relation with climate variability and, more rarely, with human land management. In this paper, we compared the phenology of rangeland vs cropped land in the Sahel belt of Africa, using the only currently available global phenology product (MODIS MCD12Q2 – Land Cover Dynamics Yearly), and an enhanced crop mask of Mali. The differences in terms of start-of-season (SOS) are spatially (north south gradient), and temporally (10 years, 2001–2009) analyzed in bioclimatic terms. Our results show that globally the MODIS MCD12Q2 SOS dates of croplands and rangelands differ, and that these differences depend on the bioclimatic zone. In Sahelian and Guinean regions, cropland vegetation begins to grow earlier than rangeland vegetation (8-day and 4-day advance, respectively). Between, in the Sudanian and Sudano-Sahelian parts of Mali, rangeland vegetation greens about one week earlier than croplands. These results are discussed in the context of the land surface heterogeneity at MODIS scale, and in the context of the natural vegetation ecology. These results could help interpreting phenological trends in climate change analysis.  相似文献   

Using multi-date high spectral resolution data to assess the physiological status of macroscopically undamaged foliage on a regional scale     

《International Journal of Applied Earth Observation and Geoinformation》2014

Forests play an important role in regulation of the global climate; moreover, they provide human beings with a whole range of ecosystem services. Forest health and ecosystem functioning have been influenced by anthropogenic activities and their consequences, such as air pollution, surface mining, heavy metal contamination, and other biotic and abiotic stress factors, which had an especially serious effect on central Europe. Many aspects of the physiological state of trees are more or less related to the concentrations of two main groups of leaf photosynthetic pigments: chlorophylls and carotenoids. Therefore, their contents can be used as non-specific indicators of the actual tree physiological status, stress and the pre-visible tree damage. Variations in leaf biochemical composition affect foliar optical properties and can be assessed remotely using high spectral resolution data (hyperspectral data). These data were successfully used in earlier studies to detect vegetation stress and damage. However, only a few approaches have dealt with the use of hyperspectral remote sensing to assess vegetation physiological status on a regional scale. Moreover, little or no research has been done on assessing vegetation health while utilizing multi-date hyperspectral images.In this study, the method for assessing forest health conditions using optical indices retrieved from hyperspectral data was applied to the two temporal HyMap date sets acquired in 07/2009 and 08/2010 to detect stress for the Norway spruce forests in Sokolov, NW Bohemia, a region affected by long-term extensive mining. The classification results were validated by ground truth data (total chlorophyll – Cab, carotenoids – Car and carotenoid to chlorophyll ratio – Car/Cab) and were associated with the geochemical conditions of the forest stands. Both biochemical analysis of the sampled foliage and classification of 2009 and 2010 hyperspectral image identified the same sites affected by vegetation stress. In addition to higher Car/Cab, which enabled detection of the stressed trees using hyperspectral image data, these sites showed critically low pH and lower values for the macronutrient parameters in both organic horizons and, in addition, both sites exhibit critically low base cation to aluminum ratios (Bc/Al) for lower organic and top mineral (0–20 cm) soil horizons.The results of this study demonstrate (i) the potential application of hyperspectral remote sensing as a rapid method of identifying tree stress prior to symptom expression, and (ii) the added value of multi-temporal approaches for hyperspectral data and its further potential for monitoring forest ecosystems.  相似文献   

Variation of the spacecraft potential in the magnetosphere     

《Journal of Atmospheric and Solar》2002,64(16):1735-1744

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Measurements of Damping of Temperature Fluctuations in a Tube     

Erik Sahlée  William M. Drennan 《Boundary-Layer Meteorology》2009,132(2):339-348

Using field measurements we evaluate a previously deduced semi-empirical model for the dampening of temperature fluctuations in a circular tube. The measurements show that the model is a reasonably good approximation, and the previous recommendation of using a tube length of the order of 1,000 times the inner diameter of the tube to remove most of the temperature fluctuations seems to hold. Part of the difference between the empirical results and the model is possibly due to deviations from the idealized conditions assumed in the model such as no inclusion of the influence from the ambient atmospheric stability. Limitations of the measurements are also likely to affect the evaluation.  相似文献   

利用ASTER数据反演南京城市地表温度   总被引：3，自引：1，他引：2  

赵小艳  申双和  杨沈斌  赵小平  周强 《南京气象学院学报》2009,32(1):128-133

利用针对ASTER数据的分裂窗算法,反演了南京城市地表温度,并用实际观测资料和同步的MODIS数据对反演结果进行了验证,结果表明：基于ASTER数据的地表温度反演结果与实际观测资料相差0.9℃,与MODIS数据的反演结果具有较好的空间一致性;基于ASTER数据反演的当日南京地表温度在23～56℃范围内,城市地表温度普遍高于35℃,市内公园地表温度略低,多位于30～35℃,长江水体温度低于30℃,地表温度存在明显的空间差异;南京城市夏季白天存在明显＂热岛效应＂,热岛强度的空间差异与南京城市发展、规划有关。  相似文献   

A deep stratospheric intrusion event down to the earth’s surface of the megacity of Athens     

D. Akritidis  P. Zanis  I. Pytharoulis  A. Mavrakis  Th. Karacostas 《Meteorology and Atmospheric Physics》2010,109(1-2):9-18

This case study investigates a stratospheric intrusion event down to the earth’s surface (near sea-level pressure) of the greater area of Athens (23.43°E 37.58°N), which occurred on 9 October 2003 and caused a remarkable increase in surface ozone concentrations not related to photochemical production. This event is among the rare case studies investigating, on the one hand, a deep stratospheric intrusion down to the earth’s surface at near sea-level pressure and, on the other, an event affecting the near surface ozone of a megacity such as Athens. The synoptic situation is described by a deep upper lever trough at 300 and 500 hPa extending over Greece, which is related to a deep tropopause fold as revealed by vertical cross sections of potential vorticity, relative humidity, divergence and vertical velocity. The analysis of potential vorticity at several isentropic levels indicates a hook-shaped streamer of high PV values (greater than 4 pvu at the 315 K isentropic level) over southeast Europe, which coincides with a streamer of dry air as observed from satellite images of water vapor. The aforementioned structure characterizes a textbook case study of stratosphere-to-troposphere transport. The Lagrangian particle dispersion model FLEXPART was used to calculate the trajectories of air particles reaching the receptor site and the fraction of particles with stratospheric origin. It reveals an important direct stratospheric impact within 1 day related to the tropopause fold described in this study with the fraction of stratospheric particles reaching maximum values of 1.9 and 4.5% for threshold values of the dynamical tropopause 2 and 1.5 pvu, respectively. Furthermore, a larger indirect aged stratospheric contribution is also revealed 4 to 5 days prior to the release, related to stratospheric intrusion events at the western Atlantic Ocean, reaching maximum values of 2.5 and 6.9% of particles crossing the 2 and 1.5 pvu potential vorticity surfaces, respectively.  相似文献   

基于Ｌｏｔｋａ Ｖｏｌｔｅｒｒａ方程的基因调控网络的稳定性分析   总被引：1，自引：0，他引：1  

罗琦  袁焱 《南京气象学院学报》2010,33(2):180-184

在2007年7—8月棉花生长旺季,将冠层按高度分多层,通过简单的试验方法确定了棉冠内叶片丛聚指数（clumping index,Ω）,以此区分计算出田间各层逐时阳叶（受光叶）和阴叶（被遮荫叶）叶面积指数的动态值。在8月23日用LI-6400R便携式光合测量系统分多层分别测定阴、阳叶单张叶片净光合作用的日变化,结合阴、阳叶面积权重,探讨利用Ω区分阴阳叶之后对整个冠层日总光合作用的影响。试验结果表明：（1）花铃期棉花冠层内Ω约为0.68;（2）利用Ω计算得到8月23日冠层日间（09：00—18：00）总净光合作用日平均值大约为20.3μmol·m-2·s-1,其中阳叶贡献约占总量的72%,阴叶约占总量的28%;（3）上层叶片贡献约占总量的75%,中层叶片约占总量的22%,下层叶片约占总量的3%。  相似文献