Abstract:
Aeroelectrostatics and aeroelectrodynamics of basic electrical parameters and
related processes in the atmospheric boundary layer under different atmospheric
stratification conditions were investigated by means of numeral and analytical
techniques.
The well-defined electrode effect was observed under fair-weather when the
atmospheric stratification condition is nearly neutral and the ionisation gradient is
very high. Theoretical space charge profiles calculated with the electrode effect
model given by Tuomi (1982) were compared with experimental profiles measured
in the lowest layer of the atmosphere. Space charge density shows good
approximation at lower levels for all ionisation rates. This approximation is better at
all heights when the ionisation gradient is high. The nature of the ionisation profile
(whether height varying or uniform) does make considerable effect on the space
charge density profile but not the nature of the electric field.
Under very stable atmospheric stratification conditions reverse electrode
effect was observed. Space charge density profiles under height varying ionisation
rate were measured, and temporal variation of average space charge density within
the first 3-m layer from the earth surface was observed with cage method. Polarity of
space charges is found to change from positive to negative in the lowest layer of the
atmosphere, under very stable atmospheric conditions. It was fond that stability of
the atmosphere enhanced the intensity of the negative ion layer. The ionisation
profile in nocturnal temperature inversions with low wind situation decreases linearly
with height.
The high electric fields created by thunderclouds at ground level are
enhanced by the irregularities of the surface. This causes corona discharges to occur
easily. The field strengths prevailed were up to 3 kV m'1 and the maximum space
charge density recorded was 1.2 nC m’*\ A fast increase of the space charge density
was also observed when the electric field higher than 2 kV m’1.
The space charges generated by gasoline engines running on a traffic road
disperse logarithmically with distance in the downwind area. The distribution of the
space charge density was investigated using diffusion grading model. The Gaussian
plume model with slender-plume approximation was used as the solution for the twodimensional
diffusion equation for a continuous crosswind line source in the
presence of wind. From the different horizontal profiles it is noted that the change of
concentrations is greatest near the traffic route and most pronounced for the lowest
wind-speeds. The effect of the traffic route is fairly low in the downwind when the
distance from the road is more than 2 km.
The aero-electrodynamics of a horizontal long-wire antenna collecting the
fair weather air-earth current has also been investigated to find out the effect of the
wind. A new model was developed in the presence of wind. The solution shows that
the resultant effect of wind on the conduction current collected by the antenna is
zero. Further it shows that the conduction current collecting area is inversely
proportional to the speed of air ions. The model developed also suggest that the idea
of a universal effective area of the horizontal long-wire antenna is not valid in the
presence of wind since it is a function of the ambient electric field.