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Abstract The effects of marine fronts on the local atmospheric surface layer and air‐sea interaction were studied. Several mesoscale fronts were crossed by a research vessel in the Greenland Sea. Air temperature, humidity and stability conditions, and the fluxes of momentum, as well as sensible and latent heat, were investigated. For relatively calm conditions, close air‐sea coupling was observed in the temperature whereas for stronger winds, the air temperature of the surface layer was not markedly modified by the front below. Changes in the moisture content in the frontal area were observed and, in one case, evaporation was observed on the warm water side and condensation on the cold water side of the front. Frontal differences in heating from the sea were assumed to affect the surface‐layer wind field. 相似文献
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Jouko Raitala 《Earth, Moon, and Planets》1988,42(3):277-291
The Alba Patera main graben zone is radial to the Tharsis bulge, indicating the importance of the Tharsis bulge-related peripheral rift tectonics. The concentric grabens around the Alba Patera area are also partly caused by crustal bending due to the central load of the Alba Patera volcano. These two graben sets partly coincide forming composite structures. Both tectonic systems were still active after the last major volcanic lava extrusions took place. After this, the crater chain grabens, radial to the northernmost part of the Tharsis bulge were formed. These collapse craters were evidently caused by the late-tectonic forces due to the northern Tharsis and adjoining lava loads, resulting in flexural tension and activating previous faults. 相似文献
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Jouko T. Raitala 《Earth, Moon, and Planets》1987,38(3):285-297
Topographic information, surface structures and construction of the Martian Tharsis bulge are used to estimate the previous stresses across the low-lying peripheral margins of the crustal blocks in terms of simple compensation models. Hot mantle activity, crustal roots, isostasy, and late-stage extensive lithosphere thickening together with volcanic building have been in combined response to the high-elevated Tharsis bulge. The initial phases of the Tharsis building have been dominated by the mantle plume doming, followed by extrusional dome raising. The volcanism has been most important bulge building factor only after thickening of the crust. During the initial mantle-generated doming and igneous activity the thin-lithosphere block tectonics has been very important. There has been a compressional peripheral zone around the bulge giving rise to dorsa formation while the high bulge crests have been in tensional state. The situation may be favorable for comparative studies with other planets. We may have something to learn from this block tectonics on the one-plate planet Mars even in respect to the Earth's plate tectonic paradigm.On leave from Dept. of Astronomy, University of Oulu, Finland. 相似文献
5.
Ecological optima and tolerances with respect to autumn pH were estimated for 63 diatom taxa in 47 Finnish lakes. The methods used were weighted averaging (WA), least squares (LS) and maximum likelihood (ML), the two latter methods assuming the Gaussian response model.WA produces optimum estimates which are necessarily within the observed lake pH range, whereas there is no such restriction in ML and LS. When the most extreme estimates of ML and LS were excluded, a reasonably close agreement among the results of different estimation methods was observed. When the species with unrealistic optima were excluded, the tolerance estimates were also rather similar, although the ML estimates were systematically greater.The parameter estimates were used to predict the autumn pH of 34 other lakes by weighted averaging. The ML and LS estimates including the extreme optima produced inferior predictions. A good prediction was obtained, however, when prediction with these estimates was additionally scaled with inverse squared tolerances, or when the extreme values were removed (censored). Tolerance downweighting was perhaps more efficient, and when it was used, no additional improvement was gained by censoring. The WA estimates produced good predictions without any manipulations, but these predictions tended to be biased towards the centroid of the observed range of pH values.At best, the average bias in prediction, as measured by mean difference between predicted and observed pH, was 0.082 pH units and the standard deviation of the differences, measuring the average random prediction error, was 0.256 pH units. 相似文献
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Ritta Niinioja Anna-Liisa Holopainen Liisa Lepist Anita Rm Jouko Turkka 《Limnologica》2004,34(1-2):154
Lake Pyhäjärvi, on the border between Finland and Russia in Karelia, is a very valuable clear-water lake of the Lobelia type. It belongs to the European Union's Natura 2000 programme in Finland, and has been included in regional and national monitoring programmes since the 1960s. The main monitoring station is situated near the outlet of the lake. Deterioration of its water quality was suspected already in the 1980s because of decreasing Secchi depths (transparency) and increasing chlorophyll a.The occurrence of algal blooms on the lakeshores is monitored weekly during each summer at one site on Lake Pyhäjärvi (site 1). This is a part of nationwide intensive algae monitoring programme organised by the environmental authorities together with voluntary observers at some 270 lake sites in Finland since 1998. Since 1997, Secchi depth observations have been carried out by volunteers biweekly or monthly at 17 sites on the lake. In the vicinity of one of these transparency observation sites (station 100), intensive monitoring of algae has been carried out. At this lakeshore monitoring site 69 algal observations were made, ten of which recorded algal blooms during the study period 1998–2002. The observed algal blooms were caused by algae of the Anabaena species, mainly by Anabaena lemmermannii. At Lake Pyhäjärvi the number of algal bloom observations received from the public have decreased from the 1990s to the 2000s. The range of Secchi disc transparency was 5.0–8.4 m with a mean value of 6.2 m at station 100 and 4.3–7.7 m (mean 6.1 m) at the main monitoring station 2 during the open water periods in 1998–2002. During this study period, the maximum values at site 100 seem to have increased slightly, which might indicate some improvement in the water quality due to decreased point source loading.We conclude that the intensive algal monitoring results of 5 years at the lakeshore site and the transparency results — both compiled by trained volunteers — reflect an improvement in the state of Lake Pyhäjärvi in Karelia. This conclusion is in accordance with the long-term water quality and short-core studies of sedimentary diatoms in Lake Pyhäjärvi. We suggest that the intensive algal observations and transparency measurements are both suitable methods for the monitoring of lakeshores and lakes, and that both are suitable for voluntary monitoring. We found public participation a good tool for monitoring lakes and lakeshores. 相似文献
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The Characteristics of Polygonal Impact Craters on Venus 总被引：1，自引：0，他引：1
Marko Aittola Teemu Öhman Johannes J. Leitner Jouko Raitala 《Earth, Moon, and Planets》2007,101(1-2):41-53
Polygonal impact craters (PICs) are craters whose shape in plan view is more or less angular instead of being circular or ellipsoidal. This type of craters are present and often common on the Moon, Mercury, Mars and several asteroids and icy moons and after the careful analysis we found on Venus 131 impact craters, which show at least two straight rim segments. This survey proves that there are polygonal impact craters on Venus and they may provide a good tool to analyse the properties of the planet’s surface/crust/lithosphere as well as the impact process itself. This study also collaborates our previous results, that PICs are not an anomaly among craters, but an integral part of all impact craters regardless of their size or environment. We compared the polygonal impact craters to “normal”-shaped craters by using different characteristics (diameter, altitude, geologic setting, morphologic class, floor reflectance, degradation stage, and wall terracing). It turned out that the smaller crater sizes favor the formation of straight rim segments, but otherwise these craters show similar characteristics to other craters. Our study also shows that there are regions where the straight segments of the crater rims most clearly follow the orientations of the dominant tectonic features of the area. Thus, the orientations of crater walls reflect–at least in some places–the local tectonics and zones of weakness also on Venus and could thus tell us about the directions and distributions of fractures or other zones of weakness in the crust. 相似文献
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Jouko Raitala 《Earth, Moon, and Planets》1987,38(2):137-147
It is evident that lunar mare basins have been subsiding and one reason for such subsidence was the existence of their mascons and their volcanic fills as loads that flexed the lithosphere. The additional effects of drying up and cooling of internal hot volumes may also have been important, leading to still more compressional mare environment. The remaining relicic thermal pulse-induced dilatation within large areas surrounding the mare basins may be responsible for the extensional rille tectonics together with the flexural peripheral bulge due to tensional arching and bending due to differences in internal volume changes. The internal attack against the lunar crust has been quite different above and below the mean surface. Below this level the old crust was more easily attacked by volcanic extrusions, causing thick lava covers and, as a consequence, broken by compressional forces; while above this level the old crust has instead been temporarily and in places attacked by tensional forces in dimensions determined by the internal energy sources and their interaction with the lithospheric roof, thus enabling the internal forces together with flexural bending to dome and fault the upper crustal surface to some extent in respect to mare areas. The rille formation can be characterized by peripheral bulging and bending. The share of asthenosphere-related effects in lunar tectonics must be considered to have been very important. If only lava load and mascons have raised compression within mare areas and tension within the surrounding terra how can be explained those rille graben which do not have any extra mass concentrations nor lavas on their sides and why some major mascon basins have so few tensional rille graben structures around them? 相似文献
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In this work we investigated the effects of local weather and snow conditions on the reproduction and survival of semi-domesticated reindeer ( Rangifer t. tarandus ) from 1962 to 1987 in four separate study areas in northern Finland. Reindeer density had no negative effect on calf percentage in slaughter (October-January) in any area. The higher the number of very warm days or mean temperatures in summer, the lower was the calf percentage in all forested areas (Sodankylä, Muonio and Ivalo). In the Muonio area, calf percentage was also reduced by winters with abundant snow accumulation. In the open, mountainous Kevo area, calf percentage was reduced with a high number of warm days (mean T>0°C) during the previous December. However, if the previous May was warm in that area, it had an opposite effect. High reindeer densities seemed to increase mortality only in the Sodankylä area. Abundant snow accumulation during winter reduced the survival index of reindeer both in the Sodankylä and Ivalo areas. In the Muonio area, mortality of reindeer was increased with a high number of warm days in December. In the Kevo area, reindeer density or any climatic parameters could not explain yearly differences in mortality. This study indicated that permanent changes in climatic conditions could have different impacts in woodland as opposed to open, mountainous regions. In general, if global climatic change means weather instability in early winter and more snow, it also brings more difficulties for reindeer. However, if climate change means that snow melts earlier in the spring, some conditions could become more favourable for reindeer. 相似文献
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Derivation of the relationship between the Obukhov stability parameter and the bulk Richardson number for flux-profile studies 总被引：4，自引：0，他引：4
Jouko Launiainen 《Boundary-Layer Meteorology》1995,76(1-2):165-179
Using the relationship between the bulk Richardson numberR
z and the Obukhov stability parameterz/L (L is the Obukhov length), formally obtained from the flux-profile relationships, methods to estimatez/L are discussed. Generally,z/L can not be uniquely solved analytically from flux-profile relationships, and it may be defined using routine observations only by iteration. In this paper, relationships ofz/L in terms ofR
z obtained semianalytically were corrected for variable aerodynamic roughnessz
0 and for aerodynamic-to-temperature roughness ratiosz
0/z
T, using the flux-profile iteration procedure. Assuming the so-called log-linear profiles to be valid for the nearneutral and moderately stable region (z/L<1), a simple relationship is obtained. For the extension to strong stability, a simple series expansion, based on utilisation of specified universal functions, is derived.For the unstable region, a simple form based on utilisation of the Businger-Dyer type universal functions, is derived. The formulae yield good estimates for surfaces having an aerodynamic roughness of 10–5 to 10–1 m, and an aerodynamic-to-temperature roughness ratio ofz
0/z
T=0.5 to 7.3. When applied to the universal functions, the formulae yield transfer coefficients and fluxes which are almost identical with those from the iteration procedure. 相似文献