Determination of the Jenkinson and Collison’s weather types for the western Mediterranean basin over the 1948-2009 period. Temporal analysis     

M. Grimalt  M. Tomàs  G. Alomar  J. Martin-Vide  M.C. Moreno-García 《Atmósfera》2013,26(1):75-94

We determined the weather type, according to the Jenkinson and Collison procedure, of the 22 646 days in the 1948-2009 period for the western Mediterranean basin. The analysis is based upon the surface pressure values of the NCEP/NCAR reanalysis, for a grid of nine points with extreme vertices at 45º N, 5º W and 35º N, 15º E, which provides a broad synoptic catalogue for this region. We analyzed the trends of the types and their different groupings during the same period. The most frequent type is U (undetermined), with an annual average of approximately 100 days (99.4, 27.2%), followed by type A (anticyclone), with 75.5 days/ year (20.7%), and C (depression), with 67.8 days/year (18.6%). The high frequency of type U is due to the habitual pressure of baric fields with a low gradient over Mediterranean waters in the warm half of the year. According to their directions, the types from the west are the most frequent and those from the south, the least. The monthly regime of the most frequent types and groupings is quite regular; type C groups, as well as advective and cyclonic curvature groups, present summertime minima and maxima in the cold half of the year, whereas the opposite occurs with types U and A. The main statistically significant annual trends in the 1948-2009 period involve a decrease in type A (–4.19 days/decade, that is, –29.0%) and an increase in type U, the cyclonic types and those presenting an easterly component. On comparing the 31-yr sub-periods 1948-1978 and 1979-2009, the tendencies of A and U were confirmed, and increases can generally be seen in the types presenting an easterly component and a decrease in those with a westerly component. The variation in type A ranged from 2490 days in the first sub-period to 2192 in the second one (p = 0.000), mainly concentrated in summer and autumn. This evident reduction of type A coincides, paradoxically, with an increase in the sea surface pressure variable (+0.31 hPa/decade) throughout the 62 years of analysis. The negative trend found in type A differs from the results of some studies. The different analysis periods, the different scales or areas of study and the variety of methods used to determine the weather types can account for the fact that these results are discordant. Moreover, warming over the last few decades in the waters of the western Mediterranean basin, as well as the clearly cyclogenetic character of the gulfs of Lion and Genoa, might account for the decrease in type A and the increase in the cyclonic curvature types.  相似文献   

http://www.sciencedirect.com/science/article/pii/S1674987112001570   总被引：2，自引：2，他引：0  

R.Damian Nance  J.Brendan Murphy 《地学前缘(英文版)》2013,4(4):439-448

The supercontinent cycle,by which Earth history is seen as having been punctuated by the episodic assembly and breakup of supercontinents,has influenced the rock record more than any other geologic phenomena,and its recognition is arguably the most important advance in Earth Science since plate tectonics.It documents fundamental aspects of the planet’s interior dynamics and has charted the course of Earth’s tectonic,climatic and biogeochemical evolution for billions of years.But while the widespread realization of the importance of supercontinents in Earth history is a relatively recent development,the supercontinent cycle was first proposed thirty years ago and episodicity in tectonic processes was recognized long before plate tectonics provided a potential explanation for its occurrence.With interest in the supercontinent cycle gaining momentum and the literature expanding rapidly,it is instructive to recall the historical context from which the concept developed.Here we examine the supercontinent cycle from this perspective by tracing its development from the early recognition of long-term episodicity in tectonic processes,through the identification of tectonic cycles following the advent of plate tectonics,to the first realization that these phenomena were the manifestation of episodic supercontinent assembly and breakup.  相似文献   

广东省1954—1990年的气候特征及异常   总被引：5，自引：1，他引：5  

刘黎明  陈创买  简裕庚 《热带气象学报》1996,12(4):289-296

用１９５４－１９９０年的月平均温度和降水资料，计算了广东省冬，夏半年和全年３个时距５个不同区域的温度和降水分级指数，讨论了广东省近４０年来的一些基本气候特征和全省气候异常的变化规律。提出：广东各区的气候特别是降水方面有明显差异；全省平均冬装卸温度的分级指数，夏半年降水的分级指数分别有明显的７年和１１年的周期；全年的温度和降水的分级指数分别有７，１３，１１年的周期。  相似文献   

当代水文地质学发展趋势与对策   总被引：15，自引：2，他引：15  

张人权  梁杏  靳孟贵  周爱国  孙蓉琳 《水文地质工程地质》2005,32(1):51-56

当代水文地质学进入了生态环境水文地质学阶段。当代水文地质学的研究目标是:从可持续发展理念出发,构建人与自然协调的、良性循环的地下水系统、水文系统、地质环境系统与生态系统。以系统思想为指导,运用多学科方法,发展向生产领域延伸的地下水工程,是当代水文地质学发展的关键。  相似文献   

摄影测量与遥感的现状及发展趋势   总被引：8，自引：0，他引：8  

李德仁 《武汉大学学报(信息科学版)》2000,25(1):1-6

简要介绍了当前摄影测量与遥感的现状,并就摄影测量与遥感的发展趋势谈一谈个人的观点。  相似文献   

20世纪西北地区降水量变化特征   总被引：143，自引：17，他引：126  

宋连春  张存杰 《冰川冻土》2003,25(2):143-148

利用英国东安哥拉大学气候研究中心(CRU)的Hulme最新的1900-1998年的全球降水量资料,分析了20世纪西北地区降水量的变化特征.结果表明,20世纪西北地区降水量处于下降通道中,后期略有回升;西北地区东部和西部降水量的年代际变化有相反的趋势;20世纪后期西北地区中西部降水量有明显的增多趋势,东部降水量持续偏少,干旱连年发生.  相似文献   

Spatial and temporal distributions of larval sealworm (Pseudoterranova decipiens, Nematoda: Anisakinae), in Hippoglossoides platessoides (Pleuronectidae) in eastern Canada from 1980 to 1990     

McClelland  G.; Misra  R. K.; Martell  D. J. 《ICES Journal of Marine Science》2000,57(1):69-88

  相似文献   

The relationships of population and forest trends   总被引：4，自引：0，他引：4  

A. S. MATHER  C. L. NEEDLE 《The Geographical journal》2000,166(1):2-13

The relationship between national trends in forest area and population is reviewed at the global scale. Evidence of an inverse relationship is confirmed. The relationship, however, may have weakened in recent decades, and it has clearly undergone a reversal in some countries during the nineteenth to twentieth centuries. The theme of a changing relationship through time is thus developed, as is that of an asymmetrical relationship in the sense that the forest area is likely to stabilize before population. On the basis of modelling from the current demographic relationship, the global forest area should stabilize before the middle of the twenty-first century.  相似文献   

Trends in stream and river temperature     

B. W. Webb 《水文研究》1996,10(2):205-226

Information on past and likely future trends in water temperature from different parts of the world is collated. The potential causes of trends in the thermal regimes of streams and rivers are many, but the existing database of water temperature information is inadequate to provide a global perspective on changes during the recent, let alone the more remote, past. Data from Europe suggest that warming of up to ca. 1°C in mean river temperatures has occurred during the 20th century, but that this trend has not been continuous, is distorted by extreme hydrological events, is not correlated with simple hydrometeorological factors and has been influenced by a variety of human activities. Predictive studies indicate that an accelerated rise in stream and river temperatures will occur during the next century as a consequence of global warming. However, forecasts must be tentative because future climatic conditions are uncertain and interactions between climate, hydrological and vegetation changes are complex.  相似文献   

Analysis of trends in annual streamflow to the Arctic Ocean     

Martin Durocher  Ana I. Requena  Donald H. Burn  Jennifer Pellerin 《水文研究》2019,33(7):1143-1151

There is increasing interest in the magnitude of the flow of freshwater to the Arctic Ocean due to its impacts on the biogeophysical and socio‐economic systems in the north and its influence on global climate. This study examines freshwater flow based on a dataset of 72 rivers that either directly or indirectly contribute flow to the Arctic Ocean or reflect the hydrologic regime of areas contributing flow to the Arctic Ocean. Annual streamflow for the 72 rivers is categorized as to the nature and location of the contribution to the Arctic Ocean, and composite series of annual flows are determined for each category for the period 1975 to 2015. A trend analysis is then conducted for the annual discharge series assembled for each category. The results reveal a general increase in freshwater flow to the Arctic Ocean with this increase being more prominent from the Eurasian rivers than from the North American rivers. A comparison with trends obtained from an earlier study ending in 2000 indicates similar trend response from the Eurasian rivers, but dramatic differences from some of the North American rivers. A total annual discharge increase of 8.7 km³/y/y is found, with an annual discharge increase of 5.8 km³/y/y observed for the rivers directly flowing to the Arctic Ocean. The influence of annual or seasonal climate oscillation indices on annual discharge series is also assessed. Several river categories are found to have significant correlations with the Arctic Oscillation, the North Atlantic Oscillation, or the Pacific Decadal Oscillation. However, no significant association with climate indices is found for the river categories leading to the largest freshwater contribution to the Arctic Ocean.  相似文献