E. Knudsen

On the natural β-activity of the air in the atmospheric surface layer

Abstract Measurements of the natural β-activity variations in the atmospheric surface layer for the period 1960–1970 are discussed in connection with meteorological variables. The diurnal variation of the β-activity increases, when approaching the ground surface from above. The phase of the diurnal wave increases with height. This means that the time of maximum becomes later with increasing height. The greatest phase velocities occur during late winter and spring. The variations of the natural β-activity seem to agree with temperature for frequencies below 1 period per hour. The influence of atmospheric stability upon natural β-activity is also studied.

On the influence of eddy-motion on air-earth current density

Abstract From theoretical calculations, based in the eddy-exchange hypothesis, estimates of vertical space-charge gradient at the earths surface are obtained from differences in direct and indirect measuremetts of air-earth current density. Studies of the diurnal, correlation and spectrum curves of the two parameters (“vertical current difference” and “vertical space-charge gradient”) show that the mean values of one parameter may reasonably be deduced from the experimental values of the other, using the diffusion equation, provided the time variations of the diffusion coefficients are known.

Measurements of the natural β-activity and the atmospheric polar conductivity in the atmospheric surface layer

Abstract Like the natural radioactivity, the polar conductivity of the air shows a pronounced diurnal variation: the records show a sharp peak in the early morning and a very flat minimum in the afternoon. The diurnal variation is most pronounced from late spring to early autumn, i.e. it is least during late autumn, in the winter and in early spring when the diurnal variation of the turbulent transfer is small. Consequently, the relationship between natural radioactivity and polar conductivities is slight during this period. From correlation studies we observe a relationship between the natural β-activity and the polar conductivities in situations with stable stratification. This probably depends on the influence of stability in the low layer upon the variations of the natural atmospheric radioactivity. When applying Fourier analysis to the variations of the polar conductivities greater amplitudes appear for the negative polar conductivity than for the positive polar conductivity. This feature is found for all wave lengths and throughout the year. We have no explanation for these differences.

Mobilities of Small Ions in the Atmospheric Surface Layer

SummaryThe present study of ion mobility distributions is based upon data obtained from 197 measurements at the Marsta Observatory. These measurements of ion mobility spectra have been made with the help of the cylindrical condenser. The ion mobilities have been determined from currentvoltage curves in fair weather.As a rule, the break-points (mobility lines) of the voltage-current characteristics appear quite sharply. Thus, different groups of mobilities are obtained. Relationships, between the observed mobilities have been found.

Mobility spectrum of ions in the electrode effect layer

By measuring and filtering small ions in aspiration condensers and recording the remaining space charge density in subsequent Obolensky filters, it has been possible to deduce the composition of space charges. The results show clearly that space charges consist of two components: one dominating positive small-ion part generated by the electrode effect and one large-ion part of reverse polarity. The transport mechanism for the two parts differs basically

Correlation and spectrum properties of the potential gradient and space-charge density in the atmospheric surface layer

SummaryCorrelation analysis of simultaneous ground-based measurements of the potential gradient and space-charge density, using antennae placed on a well-exposed site and separated by a horizontal distance of 27 m, shows that the two parameters possess the same ‘patterns’ and ‘scales’ of variation. ‘Self’ and mutual interaction rates of the two parameters are faster in high winds than in low winds, and under near-neutral than stable stratifications.The main contributions to the power spectra of the parameters appear to come from frequencies ranging from 0 to 0.03 cycles/min. The high frequency portion of this range is from measurements made in near-neutral conditions.