Fant 9896 publikasjoner. Viser side 129 av 396:
2010
2013
2013
2013
2013
2019
2019
The Tibetan Plateau (TP) region, often referred to as the Third Pole, is the world's highest plateau and exerts a considerable influence on regional and global climate. The state of the snowpack over the TP is a major research focus due to its great impact on the headwaters of a dozen major Asian rivers. While many studies have attempted to validate atmospheric reanalyses over the TP area in terms of temperature or precipitation, there have been – remarkably – no studies aimed at systematically comparing the snow depth or snow cover in global reanalyses with satellite and in situ data. Yet, snow in reanalyses provides critical surface information for forecast systems from the medium to sub-seasonal timescales.
Here, snow depth and snow cover from four recent global reanalysis products, namely the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 and ERA-Interim reanalyses, the Japanese 55-year Reanalysis (JRA-55) and the NASA Modern-Era Retrospective analysis for Research and Applications (MERRA-2), are inter-compared over the TP region. The reanalyses are evaluated against a set of 33 in situ station observations, as well as against the Interactive Multisensor Snow and Ice Mapping System (IMS) snow cover and a satellite microwave snow depth dataset. The high temporal correlation coefficient (0.78) between the IMS snow cover and the in situ observations provides confidence in the station data despite the relative paucity of in situ measurement sites and the harsh operating conditions.
While several reanalyses show a systematic overestimation of the snow depth or snow cover, the reanalyses that assimilate local in situ observations or IMS snow cover are better capable of representing the shallow, transient snowpack over the TP region. The latter point is clearly demonstrated by examining the family of reanalyses from the ECMWF, of which only the older ERA-Interim assimilated IMS snow cover at high altitudes, while ERA5 did not consider IMS snow cover for high altitudes. We further tested the sensitivity of the ERA5-Land model in offline experiments, assessing the impact of blown snow sublimation, snow cover to snow depth conversion and, more importantly, excessive snowfall. These results suggest that excessive snowfall might be the primary factor for the large overestimation of snow depth and cover in ERA5 reanalysis. Pending a solution for this common model precipitation bias over the Himalayas and the TP, future snow reanalyses that optimally combine the use of satellite snow cover and in situ snow depth observations in the assimilation and analysis cycles have the potential to improve medium-range to sub-seasonal forecasts for water resources applications.
European Geosciences Union (EGU)
2019
2019
2017
2012
2007
2015
2024
2008
Evaluation of the Swedish national air monitoring programme "Programområde Luft". NILU report
Rapporten presenterer en evaluering av det svenske Programområde luft, gjennomført høsten 2015.
2016
2013
Urban air pollution is a challenge in several European cities. For most Norwegian cities, the major challenge is the reduction of the NO2 annual mean concentration in order to comply with the limit value in the European Directive 2008/50/EC, but also too many high NO2 hourly values occur during strong inversions in cold winter periods. In Oslo, the main contributor to NO2 concentration levels is diesel exhaust and hence the proposed measures in this study are targeting road traffic. An extensive array of individual and grouped measures were constructed and we studied the change in traffic and NO2 concentrations by performing consecutive modelling studies which included traffic, emissions, and dispersion models. These measures were intended for permanent and temporary action. They included increases of the tolls that give access to the inner parts of the city, the establishment of low emission zones (LEZs), allowing for temporary free public transport, odd-even driving, defining priority lanes for low emission vehicles, and imposing higher parking fees. We concluded that the most efficient measures were the creation of LEZs and the increase of parking fees. We also explain how the findings from this work have helped to implement Norwegian air quality control policies.
Elsevier
2020
2023
Evaluation of urban scale time-dependent dispersion model with subgrid elements, in Oslo, Norway. NILU OR
2000
2018
2018
2018