Reaching Ground Level Research Articles

A theoretical analysis of extensive air showers. III. Muon showers at large zenith angles

For Pt. II see abstr. A15896 of 1968. A theoretical analysis has been made of the muon component of extensive air showers incident at large angles to the vertical. Using the model described previously, calculations have been made of the expected numbers of muons reaching ground level as a function of threshold energy and zenith angle for primary particles of various energies. The data have been combined with alternative primary spectra of cosmic rays, with and without an enhanced contribution from heavy nuclei, to give the expected muon density spectra. It is found that the density spectrum is sensitive to the distribution of transverse momentum among the parents of the muons and to a lesser extent to the mass composition of the primaries. There is thus the possibility of deriving information about the mean transverse momentum, and perhaps setting limits on the mass composition, from a comparison with experiment.

Premier aperçu sur les sols et leur valeur agronomique

Two main categories of soils occur in the Lamto savannas, tropical ferrugineous soils and black clays. The ferrugineous soils are the most widespread, covering all the «high ground» and the valley slopes. They are very poor in Calcium, Potassium, Phosphorus, organic matter and Nitrogen — and their agronomic value is therefore very low. The black clays occur only locally, where amphibolites almost reach ground level ; they are very hydromorphic, rich in Calcium, Magnesium and organic matter, but poor in Potassium and Phosphorus. After the dry season bush fires (table II) a temporary increase in the amount of Potassium, Magnesium and Phosporus of the top soil layer has been observed. This may account for the rapid growth of the new grass.

Introductory remarks

The study of the radiative balance in the atmosphere is very complex and difficult. The factors which determine the equilibrium are known in general terms, but the problem of developing a detailed understanding, particularly if the aim is to assist meteorological prediction, is another matter. Only part of the incoming solar radiation reaches ground level without being affected by the atmosphere; the remainder is either reflected back into space or absorbed or scattered by the atmosphere. The incident radiant energy absorbed in this way is degraded to longer wavelengths and is radiated from the atmosphere as infra-red radiation. Part of this reaches the surface and is absorbed there, while the remainder is re-radiated to outer space. Some heat also reaches the surface from the atmosphere by eddy-current transport. Again, energy leaves the surface in the form of infra-red radiation. Most of this is absorbed by the water vapour in the atmosphere, except in the wavelength region 8 to 13 μ . Radiation in this wave­length ‘window’ passes right through the atmosphere to outer space. Heat is also carried to the atmosphere from the surface by evaporation, condensation and precipitation phenomena.

Thermal Radiation from the Atmosphere*

The influence of ground level temperature and humidity on the intensity and spectral distribution of the thermal radiation reaching ground level from the clear sky has been investigated in the spectral region between 4μ and 15μ. The influence of the thickness of the emitting layer or atmospheric path viewed by the detector has also been studied by making measurements of the sky radiation from various zenith distances. Empirical relationships between the intensity of the atmospheric emission spectrum in various spectral intervals and the ground-level conditions of temperature and humidity are developed and presented in graphical form.