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Mean Conditions (mean + condition)
Selected AbstractsHabitat use and foraging success of 0+ pike (Esox lucius L.) in experimental ponds related to prey fish, water transparency and light intensityECOLOGY OF FRESHWATER FISH, Issue 2 2002C. Skov Abstract ,,,This study investigated the habitat use of 0+ pike (9,17 cm) in relation to two different water transparency regimes (clear water/chlorophyll water), two different light regimes (day/night) and the presence/absence of prey using 16 m2 experimental ponds. Pike could freely choose between two structured habitats (a simple structured and a complex structured), an interface habitat (between the structured habitats and open water) and an open water habitat. Foraging success of the pike in relation to water transparency was investigated by comparing mean condition (Fultons K) of the pike as well as the number of surviving prey fish. Habitat use was influenced by the presence/absence of prey and varied between waters with different transparency. The presence of prey intensified the use of structural habitats of 0+ pike in both clear and chlorophyll waters. A preference for complex habitats was found in clear water and was presumably related to foraging. The pike in chlorophyll water, in contrast, appeared more evenly distributed among all habitats, as illustrated by a more intensive use of open water in chlorophyll water compared to the clear water. No detectable impact of water transparency on the foraging success of 0+ pike was found. [source] Mid-latitude wind stress: the energy source for climatic shifts in the North Pacific OceanFISHERIES OCEANOGRAPHY, Issue 3 2000Parrish Analyses of atmospheric observations in the North Pacific demonstrate extensive decadal-scale variations in the mid-latitude winter surface wind stress. In the decade after 1976 winter, eastward wind stress doubled over a broad area in the central North Pacific and the winter zero wind stress curl line was displaced about 6° southward. This resulted in increased southward Ekman transport, increased oceanic upwelling, and increased turbulent mixing as well as a southward expansion of the area of surface divergence. All these factors contributed to a decadal winter cold anomaly along the subtropical side of the North Pacific Current. In summer the cold anomaly extended eastward, almost reaching the coast of Oregon. The increased gradient in wind stress curl and southward displacement of the zero curl line also resulted in an increase in total North Pacific Current transport, primarily on the Equator side of this Current. Thus, surface water entering the California Current was of more subtropical origin in the post-1976 decade. Southward (upwelling favourable) wind stress and sea surface temperature (SST) in the area off San Francisco exhibit at least three different types of decadal departures from mean conditions. In association with the 1976 climatic shift, marine fishery production in the Oyashio, California and Alaska Currents altered dramatically, suggesting that these natural environmental variations significantly alter the long-term yields of major North Pacific fisheries. [source] Climate variability in Malawi, part 2: sensitivity and prediction of lake levelsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 11 2002M. R. Jury Abstract Southern Africa has only a few large lakes, one of which is Lake Malawi. It forms part of the lower Zambezi catchment and the Great Rift Valley. The lake provides food, energy, transport and recreation to the local people. Inflow to the lake increases through summer (December to April) when the equatorial convection zone lies overhead. An analysis of lake levels in the period 1937,95 has been conducted and changes are related to variations in rainfall and atmospheric conditions. Interannual cycles in the time series are consistent with those found for Zambezi River streamflows, suggesting a degree of regional coherence. Years with high inflow are contrasted with mean conditions using the National Centres for Environmental Prediction reanalysis data for the period since 1958. Composite anomalies of wind fields for wet years reveal a zonal overturning circulation. Low (upper) level westerlies (easterlies) link with a sub-tropical trough in the Mozambique Channel to enhance regional convection and lake inflows. The results provide input to predictive models for Lake Malawi to plan better the management of water resources in this part of Africa. Copyright © 2002 Royal Meteorological Society. [source] The impact of mesoscale convective systems on the surface and boundary-layer structure in West Africa: Case-studies from the AMMA campaign 2006THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 648 2010Juliane Schwendike Abstract Within the framework of the AMMA project, atmospheric, surface and soil observations were performed during the pre-onset phase of the monsoon (Special Observing Period SOP 1) and during the summer monsoon (SOP 2) in 2006. Based on several case-studies the paper investigates the impact of mesoscale convective systems (MCSs) on the surface and boundary layer (PBL), the recovery time of the surface and the PBL after MCS passages, and the differences between the two monsoon phases. In the pre-MCS environment the mean conditional and convective instabilities were higher in SOP 1 than in SOP 2 (e.g. CAPE = 1815 J kg,1 and CAPE = 1295 J kg,1, respectively). In both monsoon phases these instabilities, which were strongly reduced by MCSs, recovered within less than 2 days. Precipitation of the MCSs and the resulting soil moisture increase caused a significant decrease in the surface temperature by up to 10 K and an increase in evapotranspiration by up to 2.5 mm d,1. In both phases of the monsoon, these surface anomalies and, hence, the conditions favourable for triggering MCSs by thermally induced circulation systems, diminished largely within 2 to 3 days. Due to the repeated passage of the first MCSs at intervals of a few days during SOP 1, the surface properties exhibited trends towards higher soil moisture, evapotranspiration and humidity, and lower albedo, temperature and Bowen ratio. After two weeks only, the mean conditions present in the summer monsoon were reached. In SOP 2 no significant trends could be detected. Copyright © 2010 Royal Meteorological Society [source] | ||||||||||