Papers by Torben Mikkelsen
The mesoscale meteorological models have difficulties to predict the profiles, due to complex phe... more The mesoscale meteorological models have difficulties to predict the profiles, due to complex phenomena taking place in nature that are not accounted for in the ABL parameterizations currently used. Worldwide an effort is going on to emphasize the ...
ABSTRACT With the advancement in wind power meteorology and the growth of the modern wind turbine... more ABSTRACT With the advancement in wind power meteorology and the growth of the modern wind turbines, the need to measure and estimate meteorological parameters other than wind speed and direction has become more and more important. The effect on the wind profile, e.g. of the boundary-layer height h, has not (yet) been fully understood and investigated in the wind energy community, nor in the meteorological one. h has a significant effect on the wind profile at heights above 100 m and even lower when the atmospheric conditions are stable, e.g. during nighttime when low-level jets evolve. These heights are already being exploited by large wind turbines. A possible reason for the lack of use of h in wind power meteorology might be that it is interpreted in different fashions and estimated using different techniques. Common sources for the derivation of h are surface turbulence measurements, turbulence profiles, spectral characteristics of turbulence, sodar measurements, radiosoundings, aerosol lidars and RASS that give different estimates because aerosols, turbulence, temperature and fluxes do not necessarily behave similarly in the atmosphere. Furthermore, aerosol or turbulence flux profiles show different characteristics, such as maxima, minima, and inflexions that produce different estimates of h. A practical problem of the use of h as a parameter for its application in wind power meteorology is that it is not often routinely observed when performing wind resource assessment, in which 10-min averaging periods are used. Robust and accurate meteorological measurements of h are performed with radiosoundings launched every hour in the best of the cases. Nevertheless, this is not optimal since h might evolve in much shorter periods. The main idea of this work is to routinely observe the aerosol profile in the entire atmospheric boundary layer from two commercial long-range aerosol lidars, inter-comparing the main characteristics of the lidars' profiles and their estimations of h in the frame of wind power meteorology.
Flow and turbulence studies relating to the motion of a hot, potentially hazardous plume are desc... more Flow and turbulence studies relating to the motion of a hot, potentially hazardous plume are described. The Space Shuttle launch facility at Vandenberg AFB has two flare stacks which will burn hydrogen gas at high flow rates on launch days. Because of the characteristics of the burning and the low density of hydrogen the gas can be imbedded in the local flow. Buoyancy may not become dominant for a considerable travel distance. The result could be a flame that does not rise significantly until after more than 100 feet downwind, which would be a hazard to nearby areas. The transport of ambient air parcels is determined. Two arrays of bivane anemometers were used. The results of the study allow one to easily calculate heat deposition from the hot plume for various hazard scenarios.
Plasma Physics and Controlled Fusion
Diffusion of charged particles in a turbulent, strongly magnetized plasma is considered. The anal... more Diffusion of charged particles in a turbulent, strongly magnetized plasma is considered. The analysis deals with two-dimensional electrostatic fluctuations in the plane perpendicular to an externally imposed homogeneous magnetic field. In the analysis particles are transported in this plane by the gyrocenter drift motion. A nonlinear description is given for absohte diffusion, which yields a Bohm scaling in the case of frozen turbulence or for large amplitudes of electrostatic fluctuations. Particular attention is given to the description of relatire diffusion of two charged particles. This process is described by a generalization of nonlinear Brownian motion, including a first stage of very slow initial relative diffusion. followed by a stage of rapid separation, until a final stage is reached where the particles become uncorrelated and classical Brownian-like diffusion is reached asymptotically. The stage of exponential growth (Lvhich has been measured in fluid turbulence) corresponds to the "ciunip effeci" in plasmas: it is a consequence of nonvanishing statistical correlations between particle trajectories. For a drift-wave turbulent spectrum we obtained an analytical expression for the Lyapunov exponent for the exponential particle separation. a typical feature of chaotic phenomena. The analysis applies to rather general power-spectra for the turbulent electric field fluctuations. Some special cases can be solved analytically. Particular attention is given to a spectral wavenumber subrange, characterized by a spectral index -3, because of its general occurrence: such a subrange is observed for the enstrophp-cascade subrange in ideally twodimensional fluid turbulence and also in Tokamak plasma drift-wave turbulence. Finally, some practical implications of the results are outlined.
Journal of Renewable and Sustainable Energy, 2011
Radiation Protection Dosimetry
... This enables the model to treat plume bifurcation in complex terrain by use of the puff penta... more ... This enables the model to treat plume bifurcation in complex terrain by use of the puff pentafurcation scheme. ... ACKNOWLEDGEMENTS This work was sponsored partly by Hidroeléctrica Española under project PIE-134.036, partly by the CEC Radiation Protection Research ...
LIDAR systems are getting more and more accurate and reliable. It has been shown many times that ... more LIDAR systems are getting more and more accurate and reliable. It has been shown many times that the mean horizontal wind speed measured by a lidar over flat terrain compares very well with that measured by a cup anemometer. But can a lidar measure turbulence? Here we investigate the case of a continuous wave, conically scanning Zephir lidar. First, the wind speed standard deviation measured by such a lidar gives on average 80% of the standard deviation measured by a cup anemometer. This difference is due to the spatial averaging inherently made by a cw conically scanning lidar. The spatial averaging is done in two steps: 1) the weighted averaging of the wind speed in the probe volume of the laser beam; 2) the averaging of the wind speeds occurring on the circular path described by the conically scanning lidar. Therefore the standard deviation measured by a lidar resolves only the turbulence structures larger than a length scale depending on the circle diameter and the mean wind spe...
Atmospheric Environment (1967), 1982
A simple formula for calculating dispersion from a continuous finite line source, placed at right... more A simple formula for calculating dispersion from a continuous finite line source, placed at right angles to the mean wind direction, is derived on the basis of statistical theory. Comparison is made with the virtual source concept usually used and this is shown to be correct only in the limit where the virtual time lag T v is small compared to the timescale of the turbulence t]_.
Journal of Physics: Conference Series, 2014
As wind turbines during the past decade have increased in size so have the challenges met by the ... more As wind turbines during the past decade have increased in size so have the challenges met by the atmospheric boundary-layer meteorologists and the wind energy society to measure and characterize the huge-volume wind fields surpassing and driving them.
Encyclopedia of Environmetrics, 2006
The Veterinary Journal, 2009
The results of a detailed assessment of the atmospheric conditions when foot-and-mouth disease (F... more The results of a detailed assessment of the atmospheric conditions when foot-and-mouth disease (FMD) virus was released from Burnside Farm, Heddon-on-the-Wall, Northumberland at the start of the 2001 epidemic in the UK are consistent with the hypothesis that the disease was spread to seven of the 12 farms in the immediate vicinity of the source by airborne virus, and airborne infection could not be ruled out for three other premises; the remaining two premises were unlikely to have been infected by airborne virus. The distances involved ranged from less than 1 km up to 9 km. One of the farms which was most probably infected by airborne virus from Burnside Farm was Prestwick Hall Farm, which is believed to have been key to the rapid spread of the disease throughout the country. In contrast, the results of detailed atmospheric modelling, based on a combination of clinical evidence from the field and laboratory experiments have shown that by assuming a relationship between the 24-hour average virus concentrations and subsequent infection, threshold infection levels were seldom reached at the farms close to Burnside Farm. However, significant short-term fluctuations in the concentration of virus can occur, and short-lived high concentrations may have increased the probability of infection and explain this discrepancy.
Quarterly Journal of the Royal Meteorological Society, 2007
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Papers by Torben Mikkelsen