Fant 9896 publikasjoner. Viser side 141 av 396:
2010
2006
2006
2015
2015
2016
On the coupling between polar and tropical regions during springtime: variability of tropical intrusion and Frozen In Anticyclones. Poster P-1108-04
Abstract : Recent observational and modeling transport studies of Arctic stratospheric final warming have shown that tropical/subtropical air masses can be transported to high latitudes and remain confined within a long-lived ¿frozen- in¿ anticyclone (FriaC), embedded in the summer easterlies for several months. We first present a climatology of these sporadic events over the period 1960-2011 using era-40 and era interim reanalyses. this study highlights stratospheric favorable preconditioning for FrIACs occurrence, that is: i) early and abrupt final warming, ii) no stratospheric major warming during the previous winter, and iii) east phase of the Quasi-Biennial Oscillation. We will present in detail the FriaC in spring 2011, which was the largest ever recorded. Our climatology further suggests that the frequency of occurrence of FriaCs has increased over the last decade (among the nine cases detected over the period 1960- 2011, five occurred between 2002 and 2011). A chemistry climate model is then used for the first time to investigate FriaCs characteristics and variability. simulations were performed with the nCar¿s Community earth system Model (CesM, version 1.0.2), a coupled model system including the Whole Atmosphere Community Climate Model (WACCM). FrIACs characteristics (i.e. spatial extent and duration), are overall consistent by comparing with FriaCs detected era-40 meteorological reanalyses. Dynamical analysis reveals that FriaCs are associated with an abrupt and early winter-to-summer stratospheric circulation transition, characterized by an amplification of planetary wave activity. Furthermore, our model results confirm that FrIACs occur preferentially under the easterly phase of the QBO and in absence of MSW during the preceding
2015
Large-eddy simulation (LES) experiments have been performed using the Parallelized LES Model (PALM). A methodology for validating and understanding LES results for plume dispersion and concentration fluctuations in an atmospheric-like flow is presented. A wide range of grid resolutions is shown to be necessary for investigating the convergence of statistical characteristics of velocity and scalar fields. For the scalar, the statistical moments up to the fourth order and the shape of the concentration probability density function (p.d.f.) are examined. The mean concentration is influenced by grid resolution, with the highest resolution simulation showing a lower mean concentration, linked to larger turbulent structures. However, a clear tendency to convergence of the concentration variance is observed at the two higher resolutions. This behaviour is explained by showing that the mechanisms driving the mean and the variance are differently influenced by the grid resolution. The analysis of skewness and kurtosis allows also the obtaining of general results on plume concentration fluctuations. Irrespective of grid resolution, a family of Gamma p.d.f.s well represents the shape of the concentration p.d.f. but only beyond the peak of the concentration fluctuation intensity. In the early plume dispersion phases, the moments of the p.d.f. are in good agreement with those generated by a fluctuating plume model. To the best of our knowledge, our study demonstrates for the first time that, if resolution and averaging time are adequate, atmospheric LES provides a trustworthy representation of the high order moments of the concentration field, up to the fourth order, for a dispersing plume.
Springer
2020
2019
2016
2013
2002
2013
2009
2017
2009
On coarse patterns in the atmospheric concentration of ice nucleating particles
The atmospheric concentration of ice nucleating particles active at around −10 °C (INP−10) is very low. Nevertheless, these particles play a role in the development of cloud systems, so their spatial and temporal patterns merit attention. We collated available datasets on INP−10 to identify such patterns. Among the five low altitude observatories in northern Eurasia, median values throughout May to October were lowest in Scandinavia (4 and 6 m−3), somewhat higher in central Europe (11 m−3), substantially higher in the West Siberian Plain (69 m−3) and highest in the Central Yakutian Lowland (204 m−3), suggesting that the abundance of INP−10 in northern Eurasia may increase with continentality and from West to East. The range of values at the same observatories was narrower throughout November to April (2 to 27 m−3). On average, by an order of magnitude smaller values were reported for the four Arctic observatories. Consequently, increasing poleward transport of air masses from the midlatitudes likely raises the concentration of INP−10 in the Arctic, particularly when air masses had surface contact in eastern parts of northern Eurasia.
Elsevier
2023
2017
På oppdrag fra Alcoa Norway AS dept. Mosjøen har NILU utført målinger i omgivelses-luft rundt smelteverket i Mosjøen. Målingene ble utført med aktiv prøvetaking (fluor, SO2, metaller, PAH, PM10) og passiv prøvetaking (SO2, støvnedfall). Måleprosjektet ble utført i perioden 22. mai – 19. august 2024. Alle målte komponenter var godt under de individuelle grenseverdier, målsettingsverdier og luftkvalitetskriterier i måleperioden. Siden Mosjøen er mest utsatt for utslipp fra aluminiumsverket i sommermånedene, pga. hovedvindretning fra fjorden, over smelteverket mot byen, blir måleresultatene et øvre anslag for bidraget fra smelteverket til konsentrasjonene i Mosjøen over hele året.
NILU
2025
2015