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Dendrochronologically dated changes in the limit of pine in northernmost Finland during the past 7.5 millennia 总被引：3，自引：0，他引：3
SAMULI HELAMA MARKUS LINDHOLM MAURI TIMONEN MATTI ERONEN 《Boreas: An International Journal of Quaternary Research》2004,33(3):250-259
Postglacial changes in the occurrence of Scots pine in northernmost Finland and adjacent areas are indicated in data sets of megafossils dated to an accuracy of 1 year using analysis of tree rings. After adjustment for land uplift, results in the altitudinal and latitudinal extent and in the structure of the pine limit are compared in the context of megafossil and pollen evidence from Fennoscandia, the Kola Peninsula and Scotland. Temporal changes in tree density at the forest limit are estimated from chronology sample size. The record from the subregion of Enontekio shows a long-term retreat of pine, corresponding to summer cooling caused by orbital forcing. This long-term trend is superposed by shorter-term fluctuations, which is consistent with other proxy evidence of pine. An abrupt decline in the forest limit occurred during the first millennium BC in two major steps, with no indication of high-altitude pine germination between 800 BC and AD 100. The subregions of Inari and Utsjoki show significant fluctuations at the forest limit in tree density only. 相似文献
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ANDERS LINDROTH FREDRIK LAGERGREN MIKA AURELA BRYNHILDUR BJARNADOTTIR TORBEN CHRISTENSEN EBBA DELLWIK ACHIM GRELLE REAS IBROM TORBJÖRN JOHANSSON HARRY LANKREIJER SAMULI LAUNIAINEN TUOMAS LAURILA MEELIS MÖLDER EERO NIKINMAA KIM PILEGAARD BJARNI D. SIGURDSSON TIMO VESALA 《Tellus. Series B, Chemical and physical meteorology》2008,60(2):129-142
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Vertical variability and effect of stability on turbulence characteristics down to the floor of a pine forest 总被引：3，自引：0，他引：3
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MAXIM G. OGURTSOV OLEG M. RASPOPOV SAMULI HELAMA MARKKU OINONEN MARKUS LINDHOLM HOGNE JUNGNER JOUKO MERILÄINEN 《Geografiska Annaler: Series A, Physical Geography》2008,90(2):141-150
Statistical analysis of a multi-centennial dendrochronological proxy dataset of regional climate, constructed across the latitudinal gradient of 1000 km, was performed. It was shown that centennial ( c. 100 year), tri-decadal (27-32 year), bi-decadal (17-23 year) and decadal (9-13 year) periodicities governed the climate variability in Finland over the last five centuries. Despite the fact that many of the climatic periodicities bore great resemblance to periodicities of solar cycles, little evidence of actual solar influence on Finnish climate was found when the climate proxy records were subjected to linear correlation analysis with sunspot numbers. Highly non-linear response of Northern Fennoscandian climate to solar forcing might be a cause of this result, as well as influence of terrestrial climatic processes (e.g. effect of other forcing factors and internal dynamics of regional climate). Our results show that the presence of internal climate variability at time-scales of solar activity might distort the solar signature in climatic data and complicate its detection. 相似文献
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海冰热力模式的辐射参数化方案在渤海和波罗的海应用的比较 总被引：2，自引：0，他引：2
研究了海冰热力模式中的各种辐射参数化方案,对比了模式计算的太阳短波辐射、大气长波辐射以及海冰热力变化,并利用渤海和波罗的海观测资料进行比较和误差分析.冬季大部分时间太阳短波辐射对海冰热力过程的作用有限.简单计算方案一般满足海冰模式要求.误差主要受云和冰雪表面与大气之间的多重反射影响.长波辐射对表面热平衡和海冰质量变化起重要作用.长波辐射参数化方案的计算结果受环境因素影响.云量参数化有待进一步改进.海冰模式计算结果的精度与长波辐射计算精度有一致性. 相似文献
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SAMULI HELAMA ALAR LÄÄNELAID HANNA TIETÄVÄINEN MARC MACIAS FAURIA ILMO T. KUKKONEN JARI HOLOPAINEN JAN K. NIELSEN ILMARI VALOVIRTA 《Boreas: An International Journal of Quaternary Research》2010,39(4):734-748
Helama, S., Läänelaid, A., Tietäväinen, H., Macias Fauria, M., Kukkonen, I. T., Holopainen, J., Nielsen, J. K. & Valovirta, I. 2010: Late Holocene climatic variability reconstructed from incremental data from pines and pearl mussels – a multi‐proxy comparison of air and subsurface temperatures. Boreas, Vol. 39, pp. 734–748. 10.1111/j.1502‐3885.2010.00165.x. ISSN 0300‐9483. Dendrochronological and sclerochronological records are mean series of arboreal and molluscan increments that are correctly aligned in time by rigorous dating. These records of tree rings and annual shell‐growth increments exhibit climate signals that can be used to reconstruct fluctuations and trends in past climates. Here we present a multi‐proxy reconstruction of temperature histories using a combination of dendrochronological and sclerochronological evidence. Regional curve standardization (RCS) was used to remove the non‐climatic variations from dendrochronological and sclerochronological series prior to palaeoclimatic interpretation. Conventional and signal‐free methods of RCS were compared. It was found that the signal‐free methods produced more reliable chronologies and systematically higher climate–proxy correlations. Consequently, the temperature reconstructions were derived using the chronologies constructed by this method. Proxy‐based histories of summer (July–August) temperatures were reconstructed from AD 1767 onwards. The compound use of proxies resulted in reconstructions that were of higher quality than single‐proxy reconstructions. Further improvement of reconstructions was accomplished by the inclusion of lagging increment values in the transfer functions. The final multi‐proxy model explained 58% of the temperature variance over the instrumental period. The multi‐proxy temperature reconstruction correlated well with the long records of instrumental temperatures from Tornedalen, St. Petersburg, Uppsala and Stockholm. Overall, the reconstruction for the past 250 years agreed reasonably well with borehole temperature reconstructions obtained in northern Finland. In general, this study demonstrates the benefits of the compound use of several proxies in reconstructing climate histories. In particular, the study emphasizes the so far largely unexploited advantages of multi‐proxy data sets obtained by rigorously cross‐dated incremental chronologies to produce more robust palaeoclimatic reconstructions. 相似文献
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1 Introduction The solar and terrestrial radiations are the major energy sources and sinks for the earth climate system. Climatologically, in high latitudes and polar regions, the radiative fluxes are often an order of magnitude larger than the other surf… 相似文献
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Biophysical controls on CO2 fluxes of three Northern forests based on long-term eddy covariance data