Lars R. Hole

Climate Change Impact on Atmospheric Nitrogen Deposition in Northwestern Europe: A Model Study

Abstract A high-resolution chemical transport model, driven by meteorology representing current and future climate, was used to investigate the effects of possible future changes in climate on nitrogen deposition in northwestern Europe. The model system was able to resolve the climatology of precipitation and chemical properties observed in northern Europe during the 1980s, albeit with some underestimation of the temporal and spatial variability of meteorological parameters and chemical components. The results point toward a substantial increase (30% or more) in nitrogen deposition over western Norway as a consequence of increasing precipitation but more moderate changes for other areas. Deposition of oxidized nitrogen will increase more than the deposition of reduced nitrogen. Over Sweden, oxidized nitrogen will increase only marginally and reduced nitrogen will decrease, although annual precipitation is expected to increase here as well. This is probably because more reduced nitrogen will be removed further west in Scandinavia because of the strong increase in precipitation along the Norwegian coast. The total deposition of oxidized nitrogen over Norway is expected to increase from 96 Gg N y−1 during the current climate to 107 Gg N y−1 by 2100 due only to changes in climate. The corresponding values for Sweden are more modest, from 137 Gg N y−1 to 139 Gg N y−1.

Northern Plants and Ozone

Abstract Forests in northern Fennoscandia are mainly composed of the O3-sensitive species—Scots pine and downy, mountain, and silver birches. Seminatural vegetation also contributes to biodiversity, carbon cycling, and ecosystem services as a part of forests, mires, meadows, and road verges. Fumigation experiments show that current O3 concentrations of 30–50 ppb reduce plant biomass production and reproduction. Visible foliar injury is attributable to peak O3 concentrations and relates to fast phenological development and high growth rate. Trees can acclimate to O3-induced water stress by producing more xeromorphic leaves or needles. The direct effects of O3 on grassland vegetation also translate to changes in the structure and size of the soil microbial community, and ecosystem N cycling. It is necessary to reduce the emission of O3 precursors and maintain high biodiversity to protect northern ecosystems. Regular, systematic, countrywide monitoring and validation as well as quantification of the effects of O3 on plants in the Nordic countries are also necessary.

Effect of Climate Change on Flux of N and C: Air-Land-Freshwater-Marine Links: Synthesis

Abstract Projected climate change might increase the deposition of nitrogen by about 10% to seminatural ecosystems in southern Norway. At Storgama, increased precipitation in the growing season increased the fluxes of total organic carbon (TOC) and total organic nitrogen (TON) in proportion to the water flux. In winter, soil temperatures near 0°C, common under a snowpack, induced higher runoff of inorganic nitrogen (N) and lower runoff of TOC. By contrast, soil temperatures below freezing, caused by little snow accumulation (expected in a warmer world), reduced runoff of inorganic N, TON, and TOC. Long-term monitoring data showed that reduced snowpack can cause either decreased or increased N leaching, depending on interactions with N deposition, soil temperature regime, and winter discharge. Seasonal variation in TOC was mainly climatically controlled, whereas deposition of sulfate and nitrate (NO3) explained the long-term TOC increase. Upscaling to the river basin scale showed that the annual flux of NO3 will remain unchanged in response to climate change projections.

An Experimental and Theoretical Study of Propagation of Acoustic Pulses in a Strongly Refracting Atmosphere

Abstract This paper presents measurements from a long range sound propagation experiment, and compares these data to theoretical calculations in the time domain. Propagation of airborne pulses from explosive sources, 1 and 8kg C4 charges, is studied in three well-defined meteorological situations. These are strong upwind and downwind conditions, and a case of almost homogeneous stratification. For these situations, theoretical predictions are made with a viscoelastic Fast Field Program (FFP) code, OASES. Experimental and theoretical waveforms are compared out to a range of 1400 m. Measured and predicted peak overpressures changes by a factor of more than three while going from upwind to downwind. Predictions of peak overpressures are accurate to within an average of 1.3 dB in all cases in the refracting atmosphere, but are not satisfactory in the almost homogeneous atmosphere. This is probably because ground effects are more important in this last case. As expected, wave-forms and ground response are not currently well described by the model.

Simulation of a morning air temperature inversion break-up in complex terrain and the influence on sound propagation on a local scale

Abstract A mesoscale atmospheric model is used to model the break up of a morning air-temperature inversion during a clear weather situation with low wind speeds at ground. Modified slope-radiation parameterization in the model results in more realistic predicted air temperature profiles when compared to profiles measured with a tethered balloon. A wave number integration code is used to demonstrate how the modelled atmospheric profiles can be used to predict the reduction of sound level along ground during inversion break-up.

Air pollution in the Nordic countries from biomass burning in Eastern Europe : A Policy brief

Polluted air with impacts on human health and ecosystems is transported with the winds over very long distances. Large-scale biomass burning is an important source for polluted air over the norther ...

Modeling of acoustic pulse propagation over topographic ground

A hybrid coupled wave‐number integration model and a time domain finite difference (TDFD) model have been used to predict propagation of low‐frequency (below 500 Hz) acoustic pulses above ground with a hill present. The former model is also applied to study propagation along an upward slope. Ground conditions are described by poroelastic and viscoelastic theory. Air–ground interactions as well as the effect of important parameters such as permeability and thickness of poroelastic layers are discussed. Results are also compared with data from full‐scale experiments.

Air–ground interaction effects in the propagation of low‐frequency impulse noise

Four large‐scale sound propagation experiments performed in Norway from 1994 to 1996 under both summer and winter conditions clearly demonstrate that air–ground interaction has a significant effect on the propagation of low‐frequency impulse noise. During the experiments, specific measurements were made for detailed investigation of this interaction. The paper will present the instrumentation used, and some typical measured data. Various numerical simulations of the experiments are made, covering both poro‐elastic and visco‐elastic description of the ground. Based on the measured data, theoretical considerations, and the numerical simulations, the paper will discuss mechanisms for acoustic energy loss from the air into the ground. Special emphasis will be put on the effect of the interaction of the propagating air pressure with the slow p‐waves and with the dispersive Rayleigh waves in the ground. The relative importance of these two interaction mechanisms on the energy loss and thus on the sound attenuat...