80 research outputs found

    The effect of energetic electron precipitation on middle mesospheric night-time ozone during and after a moderate geomagnetic storm

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    Using a ground-based microwave radiometer at Troll Station, Antarctica (72°S, 2.5°E, L = 4.76), we have observed a decrease of 20–70% in the mesospheric ozone, coincident with increased nitric oxide, between 60 km and 75 km altitude associated with energetic electron precipitation (E > 30 keV) during a moderate geomagnetic storm (minimum Dst of −79 nT) in late July 2009. NOAA satellite data were used to identify the precipitating particles and to characterize their energy, spatial distribution and temporal variation over Antarctica during this isolated storm. Both the ozone decrease and nitric oxide increase initiate with the onset of the storm, and persist for several days after the precipitation ends, descending in the downward flow of the polar vortex. These combined data present a unique case study of the temporal and spatial morphology of chemical changes induced by electron precipitation during moderate geomagnetic storms, indicating that these commonplace events can cause significant effects on the middle mesospheric ozone distribution

    Sur la taille, l'envergure, le périmètre thoracique et la hauteur du buste chez les populations de l'intérieur et des côtes de la Norvège

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    Daae A., Daae H. Sur la taille, l'envergure, le périmètre thoracique et la hauteur du buste chez les populations de l'intérieur et des côtes de la Norvège. In: Bulletins et Mémoires de la Société d'anthropologie de Paris, V° Série. Tome 7, 1906. pp. 158-164

    Utvandringstidspunkt og marin åtferd hjå smolt frå Lærdalselva

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    Kartlegging av utvandringstidspunkt og marin åtferd hjå smolt av villaks, klekkeriprodusert laks og vill aure frå Lærdalselva vart undersøkt ved hjelp av akustisk telemetri. Av dei 40 fiskane som vart merka frå kvar gruppe vart 34 villaks, 31 klekkerifisk og 21 aure registrert i sjø. Sjølv om studien er basert på få individ av kvar gruppe, fanga ein opp ulike utvandringstoppar hjå smolten. I 2009 var vassføring den utløysande faktoren for utvandringa. Klekkeriprodusert laksesmolt hadde eit likt utvandringsforløp som vill laksesmolt. Klekkeriprodusert fisk vandrar ikkje berre på same dato som villfisk, han syner også same mønster i høve til vandringstid på døgeret. Både klekkerismolt og laksesmolt har relativt kort opphaldstid i utløpsområdet, og begge grupper av fisk søkjer seg raskt utover mot kysten. Auresmolten har ikkje den same retningsbestemte forflyttinga mot utløpet av fjorden som laksesmolten og ein stor del av auresmoltane vart registrert på lyttebøyene både i Årdals- og Lusterfjorden. Det er ikkje registrert auresmolt lenger ute enn til Balestrand-Vangsnes, men dette kan også skuldast mykje mindre tettleik av lyttebøyer i midtre og ytre del enn kva som er tilfellet i indre del av fjorden. Studiet indikerer at laksesmolten bruker omlag 14 dagar på å komme seg ut av Sognefjorden, noko som tilseier at hovudmengda av laksesmolt passerte ytre del av fjordsystemet i perioden medio mai til medio juni i 2009

    Spatiotemporal Dispersal and Deposition of Fish Farm Wastes: A Model Study from Central Norway

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    A spatially explicit coupled hydrodynamic-mass transport model system was used to simulate dispersal of particulate organic matter from Atlantic salmon (Salmo salar) farming in central Norway. Model setups of 32 m horizontal resolution were run for periods of up to 650 days for 3 sites of different oceanographic characteristics: one fjord location, one medium-exposed location influenced by fjord water, and one coastal location. Records on feed used for each cage at each location were converted to feces released based on a published mass balance model. The results from the simulations were compared with scores from corresponding mandatory benthic surveys (MOM-B) of the sediment layer beneath the farms. The correspondence between simulated and measured thickness of the sediment layer was good, and improved with the inclusion of resuspension processes. At all sites the distribution of organic matter in the bottom layer was non-homogeneous, with significant temporal variation and transport and settling of matter up to at least 0.5 km away from one of the farms. Our results indicate that the monitoring practice used in Norway until now, with a few sediment grab samples taken mainly within the fish farm, may not adequately determine the areal impacts of all salmon farming operations. The patchy distribution of organic matter and the correspondence between simulation and survey results is attributed to the use of full 3D current fields of a high spatiotemporal resolution and a good model for resuspension processes that some previous model studies have failed to properly account for.publishedVersio

    Observations of energetic turbulence on the Weddell Sea continental slope

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    Turbulence profile measurements made on the upper continental slope and shelf of the southeastern Weddell Sea reveal striking contrasts in dissipation and mixing rates between the two sites. The mean profiles of dissipation rates from the upper slope are 1–2 orders of magnitude greater than the profiles collected over the shelf in the entire water column. The difference increases toward the bottom where the dissipation rate of turbulent kinetic energy and the vertical eddy diffusivity on the slope exceed 10−7 W kg−1 and 10−2 m2 s−1, respectively. Elevated levels of turbulence on the slope are concentrated within a 100 m thick bottom layer, which is absent on the shelf. The upper slope is characterized by near-critical slopes and is in close proximity to the critical latitude for semidiurnal internal tides. Our observations suggest that the upper continental slope of the southern Weddell Sea is a generation site of semidiurnal internal tide, which is trapped along the slope along the critical latitude, and dissipates its energy in a inline image m thick layer near the bottom and within inline image km across the slope
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