Papers by Sven-erik Gryning
22nd Conference on Climate Variability and Change, Jan 18, 2010
SUMMARY The paper presents evaluation of model simulations against data on the vertical profiles ... more SUMMARY The paper presents evaluation of model simulations against data on the vertical profiles of mean meteorological parameters and surface turbulent momentum and heat fluxes for Sofia, Bulgaria. The simulation of the vertical profiles is currently a weak point in mesoscale modeling, and needs investigations in view of numerous practical applications.
Agricultural and Forest Meteorology, 1999
The NOPEX two concentrated ®eld efforts (CFEs) (June 1994 and April±July 1995) provide high quali... more The NOPEX two concentrated ®eld efforts (CFEs) (June 1994 and April±July 1995) provide high quality data sets for the Boreal environment. The analysis of these data with traditional meteorological and hydrological approaches allow estimations of¯uxes of latent and sensible heat, but these¯ux estimates are not directly comparable due to differences in temporal and spatial scales. The challenge here has been to overcome these dif®culties so that the different estimates can be critically compared and evaluated in a systematical way. Five different approaches for the estimation of the regional¯ux of sensible and/or latent heat over the NOPEX area have been evaluated: (1) Direct aggregation Ð mixed layer evolution method, (2) Weighted averages of (a) aircraft measurements in the boundary layer and of (b) mast measurements, (3) Numerical models (a) ECOMAG Ð a distributed hydrological model and (b) MIUU Ð a mesoscale meteorological model.
Journal of Atmospheric & Ocean Science, 2005
Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project cal... more Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project called PEP in BALTEX (Pilot study of Evaporation and Precipitation in the Baltic Sea), combining extensive field measurements and modelling efforts. Eddy-correlation-measurements of turbulent heat flux were made on a semi-continuous basis for a 12 month period at four well-exposed coastal sites in the Baltic Proper (the main basin of the Baltic Sea). Precipitation was measured at land-based sites with standard gauges and on four merchant ships travelling between Germany and Finland with the aid of specially designed ship rain gauges (SRGs). The evaporation and precipitation regime of the Baltic Sea was modelled for a 12 month period by applying a wide range of numerical models: the operational atmospheric High Resolution Limited Area Model (HIRLAM, Swedish and Finnish versions), the German atmospheric REgionalscale MOdel, REMO, the operational German Europe Model (only precipitation), the oceanographic model PROBE-Baltic, and two models that use interpolation of ground-based data, the Swedish MESAN model of SMHI and a German model of IFM-GEOMAR Kiel. Modelled precipitation was compared with SRG measurements on board the ships. A reasonable correlation was obtained, but the regional-scale models and MESAN gave some 20% higher precipitation over the sea than is measured. Bulk parameterisation schemes for evaporation were evaluated against measurements. A constant value of C HN and C EN with wind speed, underestimated large fluxes of both sensible and latent heat flux. The limited area models do not resolve the influence of the height of the marine boundary layer in coastal zones and the entrainment (on the surface fluxes), which may explain the observed low correlations between modelled and measured latent heat fluxes. Estimates of evaporation, E, and precipitation, P, for the entire Baltic Proper were made with several models for a 12 month period. While the annual variation was well represented by all predictions, there are still important differences in the annual means. Evaporation ranges from 509 to 625 mm year À1 and precipitation between 624 and 805 mm year À1 for this particular 12 month period. Taking the results of model verification from *Corresponding author. the present study into account, the best estimate of P-E is about 100 AE 50 mm for this particular 12 month period. But the annual mean of P-E varies considerably from year to year. This is reflected in simulations with the PROBE-Baltic model for an 18 year period, which gave 95 mm year À1 for the 12 month period studied here and 32 mm year À1 as an average for 18 years.
Boundary-layer Meteorology, 2001
Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub... more Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub-arctic boreal forest with snow covered ground were analysed. The measurements represent late winter conditions characterised by low solar elevation angles. During the experiment (12–24 March 1997) day and night were about equally long. At low solar elevation angles the forest shades most of the snow
Theoretical and Applied Climatology, 2001
Summary A mesoscale numerical model, incorporating a land-surface scheme based on Deardorffs’ a... more Summary A mesoscale numerical model, incorporating a land-surface scheme based on Deardorffs’ approach, is used to study the diurnal variation of the boundary layer structure and surface fluxes during four consecutive days with air temperatures well below zero, snow covered ground and changing synoptic forcing. Model results are evaluated against in-situ measurements performed during the WINTEX field campaign held in Sodankyl�,
Boundary-Layer Meteorology, 1996
A model for the time and space variation of the internal boundary-layer height over a land area w... more A model for the time and space variation of the internal boundary-layer height over a land area with an irregular coastline is presented. It is based on the analytical model of the boundary-layer height proposed by Gryning and Batchvarova (1990) and Batchvarova and Gryning (199 1). The model accounts for the temperature jump and the mean vertical air motion at the top of the internal boundarylayer. Four cases from experiments in Nanticoke and Vancouver are used for model validation. The agreement between the calculated and measured internal boundary layer height at the observational sites is fairly good. The input information for the model consist of wind speed and direction, friction velocity and kinematic heat flux in time and space for the area, and the potential temperature gradient and the mean vertical air motion above the internal boundary layer. For the experiments used in the validation the effect of subsidence is relatively important in the afternoon under low wind speed high pressure conditions, lowering the height of the internal boundary layer by up to lo%, and it is negligible in the morning hours. The effect of the mixing height over the sea is found to be negligible.
Boundary-layer Meteorology, 2000
Results from an experimental investigation of themixing height over inner Danish waters carriedou... more Results from an experimental investigation of themixing height over inner Danish waters carriedout from September 1990 to October 1992, are discussed.
Wind Energy, 2009
The advantages and limitations of the ZephIR®, a continuous-wave, focused light detection and ran... more The advantages and limitations of the ZephIR®, a continuous-wave, focused light detection and ranging (LiDAR) wind profiler, to observe offshore winds and turbulence characteristics were tested during a 6 month campaign at the transformer/platform of Horns Rev, the world's largest wind farm. The LiDAR system is a ground-based sensing technique which avoids the use of high and costly meteorological masts. Three different inflow conditions were selected to perform LiDAR wind profiling. Comparisons of LiDAR mean wind speeds against cup anemometers from different masts showed high correlations for the open sea sectors and good agreement with their longitudinal turbulence characteristics. Cup anemometer mean wind speed profiles were extended with LiDAR profiles up to 161 m on each inflow sector. The extension resulted in a good profile match for the three surrounding masts. These extended profiles, averaged over all observed stabilities and surface roughness lengths, were compared to the logarithmic profile. The observed deviations were relatively small. Offshore wind farm wakes were also observed from LiDAR measurements where the wind speed deficits were detected at all LiDAR heights. Profile-derived friction velocities and roughness lengths were compared to Charnock's sea roughness model. These average values were found to be close to the model, although the scatter of the individual estimations of sea roughness length was large.
Quarterly Journal of the Royal Meteorological Society, 1996
A two-dimensional (x. :) Lagrangian stochastic dispersion model is presented that is correct ( i ... more A two-dimensional (x. :) Lagrangian stochastic dispersion model is presented that is correct ( i s . fulfils the well-mixed condition) for neutral to convective conditions. The probability density function (pd9 of the particle velocities is constructed as a weighted sum of a neutral pdf (u and w jointly Gaussian) and a convective pdf ( w skewed, u and ul uncorrelated). The transition function 9 varies continuously with stability and therefore ensures that the model results are not confined to a finite number of stability classes.
Journal of Atmospheric & Ocean Science, 2005
Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project cal... more Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project called PEP in BALTEX (Pilot study of Evaporation and Precipitation in the Baltic Sea), combining extensive field measurements and modelling efforts. Eddy-correlation-measurements of turbulent heat flux were made on a semi-continuous basis for a 12 month period at four well-exposed coastal sites in the Baltic Proper (the main basin of the Baltic Sea). Precipitation was measured at land-based sites with standard gauges and on four merchant ships travelling between Germany and Finland with the aid of specially designed ship rain gauges (SRGs). The evaporation and precipitation regime of the Baltic Sea was modelled for a 12 month period by applying a wide range of numerical models: the operational atmospheric High Resolution Limited Area Model (HIRLAM, Swedish and Finnish versions), the German atmospheric REgionalscale MOdel, REMO, the operational German Europe Model (only precipitation), the oceanographic model PROBE-Baltic, and two models that use interpolation of ground-based data, the Swedish MESAN model of SMHI and a German model of IFM-GEOMAR Kiel. Modelled precipitation was compared with SRG measurements on board the ships. A reasonable correlation was obtained, but the regional-scale models and MESAN gave some 20% higher precipitation over the sea than is measured. Bulk parameterisation schemes for evaporation were evaluated against measurements. A constant value of C HN and C EN with wind speed, underestimated large fluxes of both sensible and latent heat flux. The limited area models do not resolve the influence of the height of the marine boundary layer in coastal zones and the entrainment (on the surface fluxes), which may explain the observed low correlations between modelled and measured latent heat fluxes. Estimates of evaporation, E, and precipitation, P, for the entire Baltic Proper were made with several models for a 12 month period. While the annual variation was well represented by all predictions, there are still important differences in the annual means. Evaporation ranges from 509 to 625 mm year À1 and precipitation between 624 and 805 mm year À1 for this particular 12 month period. Taking the results of model verification from *Corresponding author. the present study into account, the best estimate of P-E is about 100 AE 50 mm for this particular 12 month period. But the annual mean of P-E varies considerably from year to year. This is reflected in simulations with the PROBE-Baltic model for an 18 year period, which gave 95 mm year À1 for the 12 month period studied here and 32 mm year À1 as an average for 18 years.
Boundary-Layer Meteorology, 2001
Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub... more Measurements carried out in Northern Finland on radiation and turbulent fluxes over a sparse, sub-arctic boreal forest with snow covered ground were analysed. The measurements represent late winter conditions characterised by low solar elevation angles. During the experiment (12-24 March 1997) day and night were about equally long. At low solar elevation angles the forest shades most of the snow surface. Therefore an important part of the radiation never reaches the snow surface but is absorbed by the forest. The sensible heat flux above the forest was fairly large, reaching more than 100 W m −2 . The measurements of sensible heat flux within and above the forest revealed that the sensible heat flux from the snow surface is negligible and the sensible heat flux above the forest stems from warming of the trees. A simple model for the surface energy balance of a sparse forest is presented. The model treats the diffuse and direct shortwave (solar) radiation separately. It introduces a factor that accounts for the shading of the ground at low solar elevation angles, and a parameter that deals with the partial transparency of the forest. Input to the model are the direct and diffuse incoming shortwave radiation. Measurements of the global radiation (direct plus diffuse incoming shortwave radiation) above the forest revealed a considerable attenuation of the global radiation at low solar elevation. A relation for the atmospheric turbidity as function of the solar elevation angle is suggested. The global radiation was simulated for a three month period. For conditions with a cloud cover of less than 7 oktas good agreement between model predictions and measurements were found. For cloud cover 7 and 8 oktas a considerable spread can be observed. To apply the proposed energy balance model, the global radiation must be separated into its diffuse and direct components. We propose a simple empirical relationship between diffuse shortwave and global radiation as function of cloud cover.
Boundary-Layer Meteorology, 2007
suggested, based on measurements from the two sites.
Boundary-Layer Meteorology, 2008
In this article, we present measurements from 2006 of the marine wind speed profile at a site loc... more In this article, we present measurements from 2006 of the marine wind speed profile at a site located 18 km from the west coast of Denmark in the North Sea. Measurements from mast-mounted cup anemometers up to a height of 45 m are extended to 161 m using LiDAR observations. Atmospheric turbulent flux measurements performed in 2004 with a sonic anemometer are compared to a bulk Richardson number formulation of the atmospheric stability. This is used to classify the LiDAR/cup wind speed profiles into atmospheric stability classes. The observations are compared to a simplified model for the wind speed profile that accounts for the effect of the boundary-layer height. For unstable and neutral atmospheric conditions the boundary-layer height could be neglected, whereas for stable conditions it is comparable to the measuring heights and therefore essential to include.
22nd Conference on Climate Variability and Change, Jan 18, 2010
SUMMARY The paper presents evaluation of model simulations against data on the vertical profiles ... more SUMMARY The paper presents evaluation of model simulations against data on the vertical profiles of mean meteorological parameters and surface turbulent momentum and heat fluxes for Sofia, Bulgaria. The simulation of the vertical profiles is currently a weak point in mesoscale modeling, and needs investigations in view of numerous practical applications.
Proc. of …, 2007
During the summer of 2006, two remote sensing instruments, a LiDAR (Light Detection and Ranging) ... more During the summer of 2006, two remote sensing instruments, a LiDAR (Light Detection and Ranging) and a SoDAR (Sound Detection and Ranging) were installed for a wind assessment campaign on the transformer/platform of Horns Rev, the world's largest offshore wind farm, located at the West coast of Denmark. This article presents the first set of results of the evaluation of both sensing instruments under this offshore environment by comparison with data from different masts surrounding the wind farm. LiDAR and SoDAR observations of mean wind speed agree for the first levels but the SoDAR data is few for higher levels due to background sound problems.
Agricultural and Forest Meteorology, 1999
... Author Contact Information , E-mail The Corresponding Author , a , Ekaterina Batchvarova b , ... more ... Author Contact Information , E-mail The Corresponding Author , a , Ekaterina Batchvarova b , Sven-Erik Gryning b , Anders Lindroth c , Dimitris Melas d , Yuri Motovilov a , Michael Frech e , Martti Heikinheimo f , Patrick Samuelsson g , Achim Grelle c and Tony Persson h. ...
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Papers by Sven-erik Gryning