Sven-Erik Gryning

Energy, Water and Carbon Exchange in a Boreal Forest Landscape - NOPEX Experiences

The role of the land surface in controlling climate is still underestimated and access to information from the boreal-forest zone is instrumental to improve this situation. This motivated the organ ...

The turning of the wind in the atmospheric boundary layer

Here we use accurate observations of the wind speed vector to analyze the behavior with height of the wind direction. The observations are a combination of tall meteorological mast and long-range wind lidar measurements covering the entire atmospheric boundary layer. The observations were performed at the Hovsore site in Denmark, which is a flat farmland area with a nearly homogeneous easterly upstream sector. Therefore, within that sector, the turning of the wind is caused by a combination of atmospheric stability, Coriolis, roughness, horizontal pressure gradient and baroclinity effects. Atmospheric stability was measured using sonic anemometers placed at different heights on the mast. Horizontal pressure gradients and baroclinity are derived from outputs of a numerical weather prediction model and are used to estimate the geostrophic wind. It is found, for these specific and relatively short periods of analysis, that under both barotropic and baroclinic conditions, the model predicts the gradient and geostrophic wind well, explaining for a particular case an unusual backing of the wind. The observed conditions at the surface, on the other hand, explain the differences in wind veering. The simulated winds underpredict the turning of the wind and the boundary-layer winds in general.

Measuring Meteorology in Urban Areas – Some Progress and Many Problems

Examples of the use of remote sensing with relevance for the urban boundary layer are presented as an inspiration for future observational studies in urban areas. The examples, involve the measurement of: the vertical wind profile and horizontal variability of the mean wind speed over a forest; and the depth of the marine boundary layer. Research radio-soundings are an indispensable tool in observational campaigns.

Evaluation of Vertical Profiles in Mesoscale Meteorological Models Based on Observations for the COST728 Study of Winter 2003 PM Episodes in Europe

An important new emphasis in meteorological models evaluation is the thorough discussion of vertical profiles of meteorological parameters. This discussion contributes to the understanding of why different mesometeorological models calculate quite different wind and temperature profiles and atmospheric boundary layer heights (even when using the same method) while all show good agreement between simulated and measured surface data. The wind, temperature and turbulence profiles influence significantly the transport and diffusion of pollutants in the air. The calculations of a number of crucial parameters in air quality models, such as deposition and biogenic emissions, also depend on meteorological parameters. The availability of 3D measured wind fields provided by wind profile radars and lidars give a new challenge for such studies. The 3D model to measurements comparisons should consider new performance statistics. This study presents few examples from the COST 728 intercomparison exercise for the winter of 2003 in Europe.

Modelling of the Urban Wind Profile

Analysis of meteorological measurements from tall masts in rural and urban areas show that the height of the boundary layer influences the wind profile even in the lowest hundreds of meters. A parameterization of the wind profile for the entire boundary layer is formulated with emphasis on the lowest 200–300 m and presented here. Results are shown from applying the parameterization of the wind profile on independent measurements from an urban experimental campaign that was carried out in Sofia, Bulgaria in 2003.

Observation and Modelling of Boundary Layer Depth in a Region with Complex Terrain and Coastline

The purpose of this paper is to test the ability of two quite different models to simulate the combined spatial and temporal variability of Thermal Internal Boundary Layer (TIBL) depth and Mixed Layer Depth (MLD) in the complex terrain and coastline of the Lower Fraser Valley (LFV) of British Columbia, Canada during the course of one day. The models (the simple applied model of Gryning and Batchvarova (1996), and the Colorado State University Regional Atmospheric Modelling System (CSU-RAMS) described by Pielke et al. (1992)). will be tested by comparison with data gathered during a field study (called Pacific ‘93) of photochemical pollution in the LFV. The data utilized here are drawn from tethered balloon flights, free flying balloon ascents, and downlooking lidar operated from an aircraft flown at roughly 3500m ASL.

Applied Model of the Height of the Daytime Mixed Layer Including the Capping Entrainment Zone

Dilution of air pollutants by vertical mixing is mainly confined within the atmospheric boundary layer, which consists of the fully mixed layer and the capping entrainment zone. A fairly accurate estimate of the height to which pollutants are mixed is of main importance in air pollution monitoring and assessment studies.

Advances in Urban Dispersion Modelling

The ability to predict the measured crosswind spread of the plume as well as the centerline (maximum) concentrations in the urban environment based on tracer experiments was found generally to be within a factor of 2.

ADVANCES IN URBAN METEOROLOGY MODELLING

In this study we focus on the lowest part of the urban boundary layer, which is connected to a horizontal scale of 2–3 km and a vertical scale covering the surface boundary layer. The structure of the urban surface boundary layer is discussed with an emphasis on the turbulence parameters controlling dispersion processes in it.

Model of Internal Boundary Layer Formation over Inhomogeneous Terrain

The transformation of an air mass passing from the cooler sea surface over the highly heated land in summer is connected with internal boundary layer formation which is of great importance for the dispersion of pollutants in coastal areas. Thus the delightful breezes can be connected with air pollution episodes instead of freshening of the air. A distinct example of such a phenomenon occurs in the area of Athens, where the complex orography and typical weather conditions lead to the formation of shallow internal boundary layers and accumulation of pollutants over the city (Pilinis et al., 1993; Ziomas et al., 1994; Lalas, 1983).