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Circulation Modes (circulation + mode)
Selected AbstractsRegime-dependent streamflow sensitivities to Pacific climate modes cross the Georgia,Puget transboundary ecoregionHYDROLOGICAL PROCESSES, Issue 24 2007Sean W. Fleming Abstract The Georgia Basin,Puget Sound Lowland region of British Columbia (Canada) and Washington State (USA) presents a crucial test in environmental management due to its combination of abundant salmonid habitat, rapid population growth and urbanization, and multiple national jurisdictions. It is also hydrologically complex and heterogeneous, containing at least three streamflow regimes: pluvial (rainfall-driven winter freshet), nival (melt-driven summer freshet), and hybrid (both winter and summer freshets), reflecting differing elevation ranges within various watersheds. We performed bootstrapped composite analyses of river discharge, air temperature, and precipitation data to assess El Niño,Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) impacts upon annual hydrometeorological cycles across the study area. Canadian and American data were employed from a total of 21 hydrometric and four meteorological stations. The surface meteorological anomalies showed strong regional coherence. In contrast, the seasonal impacts of coherent modes of Pacific circulation variability were found to be fundamentally different between streamflow regimes. Thus, ENSO and PDO effects can vary from one stream to the next within this region, albeit in a systematic way. Furthermore, watershed glacial cover appeared to complicate such relationships locally; and an additional annual streamflow regime was identified that exhibits climatically driven non-linear phase transitions. The spatial heterogeneity of seasonal flow responses to climatic variability may have substantial implications to catchment-specific management and planning of water resources and hydroelectric power generation, and it may also have ecological consequences due to the matching or phase-locking of lotic and riparian biological activity and life cycles to the seasonal cycle. The results add to a growing body of literature suggesting that assessments of the streamflow impacts of ocean,atmosphere circulation modes must accommodate local hydrological characteristics and dynamics. Copyright © 2007 John Wiley & Sons, Ltd. The copyright in Paul H. Whitfield's contribution belongs to the Crown in right of Canada and such copyright material is reproduced with the permission of Environment Canada. [source] A finite element solution of acoustic propagation in rigid porous mediaINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2005A. Bermúdez Abstract This paper deals with the acoustical behaviour of a rigid porous material. A finite element method to compute both the response to an harmonic excitation and the free vibrations of a three-dimensional finite multilayer system consisting of a free fluid and a rigid porous material is considered. The finite element used is the lowest order face element introduced by Raviart and Thomas, that eliminates the spurious or circulation modes with no physical meaning. For the porous medium a Darcy's like model and the Allard,Champoux model are taken into account. The numerical results show that the finite element method allows us to compute the response curve for the coupled system and the complex eigenfrequencies. Some of them have a small imaginary part but there are also overdamped modes. Copyright © 2004 John Wiley & Sons, Ltd. [source] Time variations of the effects of circulation variability modes on European temperature and precipitation in winterINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 2 2008Romana Beranová Abstract Five modes of variability are identified in winter monthly mean 500 hPa heights over the Euro-Atlantic sector by rotated principal component analysis. Time variations of the effects of the modes on temperature and precipitation at more than 100 European stations are examined for period 1958,1998. Time variations are investigated by running correlations with the 15-year window. At most of the stations, the correlations with circulation patterns vary considerably in time, both for temperature and precipitation. The spatial structure of the variations is assessed by cluster analysis of time variations of correlations. The groupings together with changes in the intensity and position of the circulation modes suggest possible mechanisms of the time variations in the circulation-to-climate effects. Copyright © 2007 Royal Meteorological Society [source] Winter snow depth variability over northern Eurasia in relation to recent atmospheric circulation changesINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 13 2007V. Popova Abstract Mean snow depth time-series for February (1936,2001) over northern Eurasia (incl. Norway, Finland and the former USSR), interpolated into 5 × 5° grid points, are studied using empirical orthogonal function (EOF) analysis. First, five statistically significant rotated PCs are correlated to Northern Hemisphere (NH) teleconnection patterns at the 700 hPa height: North Atlantic Oscillation (NAO), Polar-Eurasia (Pol), Pacific-North American (PNA), West Pacific (WP), and Scandinavia (Scand). The impact of the NH circulation modes on snow depth variations is evaluated using the multiple stepwise backward regression (MSBR). Analyses of the snow depth PCs indicate that within the northern Eurasia territory, there are several regions with snow accumulation, respondent to certain circulation modes. PC1 describes low-frequency snow depth variation to the north from 55 to 60°N between the White Sea and the Lena river basin, and is positively correlated with NAO and negatively,with Scand. MSBR shows that in 1951,1974 the leading role in snow depth variability belongs to Scand. After 1975, Scand has passed over the leading role to NAO. Scand and NAO are also responsible for the surface air temperature changes over the northern Eurasia. Snow depth PC1 and wintertime temperature are closely related to each other. PC2 describes quasi-decadal snow depth variability over eastern Europe and is negatively correlated with NAO. For the Baltic and White Sea coasts, Fennoscandia, and the center of the East European plain, decrease of snow accumulation, related to a positive NAO phase, seems to be caused by mild winters. For the southwestern and central regions of eastern Europe, negative snow depth anomalies could also be caused by decrease of precipitation associated with the eastward shift of cyclone tracks related to the positive NAO phase. Two regions, where snow depth variations are described by PC1 and PC2, respectively, reveal the border between the opposite recent tendencies of snow accumulation. Copyright © 2007 Royal Meteorological Society [source] Influence of seasonal pressure patterns on temporal variability of vegetation activity in Central SiberiaINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 3 2006Sergio M. Vicente-Serrano Abstract This paper analyses the spatial distribution of the inter-annual variability of vegetation activity in central Siberia and its relationship with atmospheric circulation variability. We used NOAA-AVHRR NDVI series from Pathfinder Land Data Set at 1° of spatial resolution, and we calculated the annual vegetation activity in each pixel (aNDVI) from 1982 to 2001. Principal component analysis (PCA) was used to determine the general spatial patterns of inter-annual variability of vegetation activity. We identified three main modes, which explain more than 50% of the total variance, each corresponding to a large region. By means of surface pressure grids, we analysed the main patterns of the seasonal atmospheric circulation in the study area: its variability was summarised by means of a few circulation modes and the patterns differ significantly between winter, spring and summer. However, a pattern with a North,South dipole structure represents the general spatial pattern of atmospheric circulation. We investigated the effect of seasonal atmospheric circulation patterns on the inter-annual variation of vegetation activity. In general, the strongest relationships between the atmospheric circulation variability, climate and the aNDVI variability were found in areas where the climatic characteristics are more limiting for the vegetation development, such as the northern regions. This may be explained by the fact that in these areas the variability of atmospheric circulation modes determines summer temperatures, which have a direct impact on vegetation activity. Copyright © 2006 Royal Meteorological Society. [source] | ||||||||||