Scatter of hmF2 values as an indicator of trends in thermospheric dynamics     

A.D. Danilov   《Journal of Atmospheric and Solar》2009,71(14-15):1586-1591

Analysis of the variability of the @F2-layer height, @hmF2@, from the 1950s to 1960s to the 1990s is performed on the basis of vertical sounding data for a series of midlatitude ionospheric stations. It is found that the scatter of the @hmF2@ values (standard deviation) increases sharply from the earlier decades to the later ones. This increase is better pronounced in the spring period of the year and does not depend on geomagnetic activity. The increase in the scatter of @hmF2@ indicates, evidently, the presence of systematic changes (trends) in thermospheric dynamics, the existence of these trends having been suggested in the recent publications of the author on the basis of the analysis of the foF2(night)/foF2(day) and R(foF2) parameters.  相似文献   

Using GIS for modelling the impact of current climate trend on the recharge area of the S. Susanna spring (central Apennines,Italy)     

M. Spadoni  M. Brilli  F. Giustini  M. Petitta 《水文研究》2010,24(1):50-64

Though the S. Susanna spring system is one of the biggest water sources in the central Apennines, its hydrogeological dynamics have been scarcely investigated. This study tried to clarify some of the factors controlling the recharge/discharge processes of this spring by modelling the available climate series, water balance equations and new isotopic and quantitative data, using statistical and raster overlay functions embedded in a Geographic Information System (GIS). Oxygen and hydrogen isotopic data were recorded monthly over a 2‐year period at the spring itself and in eight rain gauges in Reatini Mountains. The effective infiltration rate was calculated using the Kennessey coefficients and the Turc equation. Finally, the recharge area was identified with the help of an expert evaluation procedure. Local δ¹⁸O and δD versus altitude regression curves were used to validate the digital recharge model by comparing their expected values with the values actually measured. Recharge process was framed within the perspective of the ongoing local climate trends. The current discharge rate of 4·1 m³·s^?1 is significantly lower than the average value of 5·5 m³·s^?1 measured up to the 1980s, confirming the fall in the recharge/discharge rate. The hydrogeological system shows a delayed response, due to an average groundwater residence time in the aquifer, which is estimated to be about 15/20 years on the basis of the offset between calculated and observed isotope data at the main spring. For this reason the system is presently not equilibrated and is gradually changing towards a final equilibrium discharge estimated in about 3·4 m³·s^?1. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

青藏高原积雪变化趋势及其与气温和降水的关系   总被引：6，自引：5，他引：6  

柯长青  李培基 《冰川冻土》1997,19(4):289-294

根据６０个地面基本气象台站１９５７￣１９９０年逐日雪深，月平均气温，月降水量观测记录，用ＡＲＭＡ（ｐ，ｑ）模型检验了青藏高原积雪变化趋势。结果表明，高原积雪变化呈增加趋势，与南极大陆及格陵兰冰盖表面雪积累率的增加相一致。  相似文献   

天山西部中山带积雪变化趋势与气温和降水的关系——以巩乃斯河谷为例   总被引：7，自引：0，他引：7  

张丽旭  魏文寿 《山地学报》2001,19(5):403-407

根据位于巩乃斯河谷的天山积雪雪崩研究站近30a来的年最大雪深、月平均气温、月降水量观测记录，用平均差值法、最小二乘法、自回归滑动平均法检验了天山西部中山带积雪、冷季降水、冷季平均气温的变化趋势，结果表明，天山西部中山带积雪呈增加趋势，近30a来年平均增加1．43％，与青藏高原、南极大陆及格陵兰冰盖表面积雪积累增加相一致。天山西部中山带冷季气温和降水的变化趋势也是增加的，其中冷季降水平年平均增加0．12％，而冷季气温升高了0．8℃，积雪与冷季气温之间存在着弱的负相关关系，而与冷季降水呈显著的正相关关系。积雪的增加主要是因为气候变暖引起的冷季降水的增加对积雪增加的贡献大于由于冷季气温升高而造成积雪减少的贡献的结果。  相似文献   

“九七”后香港与内地合作趋向及港资进入内地策略   总被引：1，自引：0，他引：1  

杨英  周辉 《热带地理》1997,17(2):122-130

本文讨论香港与内地进行经济合作基础与环境，分析了“九七”后两地经济合作的新趋向及港资进入内地将采取的基本策略，并对如何更好地引导港资进入内地提出若干对策和措施。  相似文献   

Trends in Interdiurnal Temperature Variation for the Central United States, 1945–1985     

Kay R. S. Williams  Kathleen C. Parker 《The Professional geographer》1997,49(3):342-355

Temporal variation in the absolute value of interdiurnal variability (AIDV) of January maximum temperatures is examined for the period 1945–1985 in the central United States (90°–105°W). AIDV indicates the magnitude of day-to-day changes in the maximum temperature. Five-year running-mean AIDV values decreased significantly throughout the period. This trend was apparent for the region overall and for the 10 of the 20 study sites analyzed individually. Temporal variation in AIDV values was significantly related to mid-tropospheric flow patterns over the central United States. Meridional circulation was associated with smaller AIDV values in all sites except those in the northwestern and southeastern corners of the study area, whereas zonal flow was linked to larger interdiurnal temperature change. The analysis of selected individual years indicated that mid-tropospheric circulation patterns were more persistent with meridional flow, and surface cyclones and their associated surface fronts tracked through the study area less frequently than in years with zonal flow. Analysis at a daily temporal resolution revealed an added dimension of trends in temperature variability beyond those apparent with a coarser monthly resolution. These results emphasize the importance of finer temporal resolution in the analysis of both past and projected climate change; regionally summarized monthly temperature values mask important variation in temperature trends apparent at shorter temporal and more local spatial scales.  相似文献   

Trends in planetary wave activity inferred from Hungarian radio wave absorption measurements     

Jan Lastovička  Ferenc Märcz 《Studia Geophysica et Geodaetica》1995,39(4):420-424

Summary The nighttime and sunset LF radio wave absorption measured at Nagycenk, western Hungary over 1967–1991 is used to infer planetary wave activity and its long-term trend in the upper middle atmosphere (85 – 100 km). The very moderate positive and mostly statistically insignificant trends are consistent with the pattern provided by previous analyses of various day- and night-time absorption measurements. The trends could be of anthropogenic origin.  相似文献   

Metal concentration in biota in the North sea: changes and causes     

Pedersen  Britta 《ICES Journal of Marine Science》1996,53(6):1008-1013

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Is juvenile salmon abundance related to subsequent and preceding catches? Perspectives from a long-term monitoring programme   总被引：1，自引：0，他引：1  

Niemela  E.; Erkinaro  J.; Julkunen  M.; Hassinen  E. 《ICES Journal of Marine Science》2005,62(8):1617-1629

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Comparing spatial grain-size trends inferred from textural parameters using percentile statistical parameters and those based on the log-hyperbolic method   总被引：1，自引：0，他引：1  

Jesper Bartholdy  Christian Christiansen 《Sedimentary Geology》2007,202(3):436-452

The Folk&Ward (F&W) and the log-hyperbolic methods are applied to a small - and easy to overlook - number of typical sand sized grain-size distributions from the Danish Wadden Sea. The sand originates from the same source, and the pattern of change in the grain-size distributions is, therefore, exclusively linked to dynamic sorting. In general, the F&W parameters reflect the observed grain-size trends far better than the corresponding log-hyperbolic parameters. The log-hyperbolic “typical log grain size”, ν, is sensitive to changes in skewness and cannot replace mean grain size, Mz, in grain-size trend analysis. The four log-hyperbolic parameters describing dispersion δ, τ^− 1, κ^− 1 and ζ are not able to give an unambiguous picture of spreading trends. The F&W sorting parameter, Sd, can therefore not be replaced by any of the log-hyperbolic parameters in grain-size trend analysis. In skewed grain-size distributions, there seems to be a general defect in the log-hyperbolic approximation of the best represented tail. This makes χ less sensitive to indicate the correct sign of slightly skewed grain-size distributions than Sk. However, when examining trends, the relative change between χ and Sk by and large seems to be the same. The log-hyperbolic peakedness parameter, ξ, is preferable to the F&W peakedness (kurtosis) parameter, Kg, because the latter is hypersensitive to small, insignificant variations in a grain-size distribution. By contrast, the concept of peakedness as defined by ξ, seems to relate more directly to sedimentary environmental conditions. In conclusion, the log-hyperbolic method has both advantages and disadvantages when compared with the F&W method. It is thus suggested that a sensible combination of the two methods could be advantageous to sediment trend analysis.  相似文献