Angstrom Turbidity Coefficient Research Articles

The turbidity parameters in Athens

In this paper Angstrom's turbidity coefficient β0, wave-length exponent α0 and the decadic turbidity coefficientB after Schuepp have been computed in Athens from pyrheliometric measurements of direct solar radiation for the whole spectrum and of specified spectral regions using Schott filters for the period 1963–1972. Turbidity coefficient β0 shows an annual variation with low values in winter and high values in spring. The wavelength exponent α0 shows a similar but opposite in sense variation. The decadic trubidity coefficientB is low in winter and attains the highest values in late spring and summer. In order to show the diurnal variation of the turbidity parameters this are given for each of the observation hours 0820, 1120, 1420 and 1720. The annual and diurnal variations of the turbidity parameters are discussed in reference to their relation with seasonal changes of synoptic weather situations, to the prevailing winds and the different air masses.

Wavelength exponent for haze scattering in the tropics as determined by photoelectric photometers

Sun photometers using narrow-band interference filters, photoelectric sensors and solid-state operational amplifiers were constructed and intensive measurements of the haze extinction co-efficients at 0.40 and 0.60 ?m wavelengths made at Poona (Lat. 18° N) over a one-year period. The most significant result obtained is that the wavelength exponent for the haze scattering as calculated from 520 pairs of simultaneous observations shows a median value of 0.5 and a mode of about 0.8. These are substantially lower than corresponding values found in the case of middle latitude stations. In general, the exponent is correlated positively with the turbidity itself in the case of wet haze, and under conditions of very clear and dry air it assumes near zero values. A marked diurnal variation in the value of the exponent occurs during the regimes of tropical continental air. The consequences of the prevailing lower values of ? in relation to determination of the Angstrom turbidity coefficient ? in the tropics are briefly discussed. DOI: 10.1111/j.2153-3490.1972.tb01533.x

A Study of Ångström's turbidity parameters from solar radiation measurements in India

Values of Angstrom's turbidity coefficient ? and the wavelength exponent ? have been computed for a number of stations in India from pyrheliometric measurements of direct solar radiation, for the whole spectrum and for specified spectral regions using filters OG 1 , RG 2 and RG 8 . Large seasonal variations are noticed in ?, with high values in summer and low values in winter at all stations. Rainout and washout are effective in the removal of aerosols from the atmosphere and a marked fall is noticed in ? after thunderstorms and after the onset of the monsoon at all stations. Values of ? at stations in the southern half of the subcontinent remain more or less constant throughout the year with a mean value of about 1.0, indicating that smaller haze particles predominate and the size distribution remains the same despite the large increase of turbidity in summer. In the northern half of the sub-continent, ? shows seasonal variations with low values, sometimes becoming zero or negative in summer and the normally accepted values in winter. Over north and central India therefore, while smaller particles are more numerous in winter, large particles predominate in summer. DOI: 10.1111/j.2153-3490.1969.tb00489.x