Characteristics of diurnal pattern of global photosynthetically-active radiation at Ilorin, Nigeria

  • S O Udo
  • T O Aro
  • L E Akpabio


A two year data (September 1992 August 1994) on photosynhetically-active radiation (PAR) measured at Ilorin (Lat.: 832´N. Long.:434´E) using LI-190SA quantum sensor are analysed both on daily and monthly mean diurnal bases. This was done with the aim of characterizing the diurnal pattern of this radiation at this location. The typical climatic days chosen were clear, cloudy, partly cloudy and Harmattan days, as defined by clearness index. The result shows that the pattern, whether on daily or monthly basis, varies greatly depending on the atmospheric conditions. The amplitude of variation of the monthly mean diurnal flux could be divided into two distinct groups: the larger ones are associated with months when the atmosphere has less cloud and the Harmattan dust spell is either just setting in or clearing off (February, March, April, October and November) while the smaller amplitudes are associated with cloudy and turbid months (May-September, December and January). The month with highest flux at maximum was March while the lowest was in August. The diurnal pattern shows that crops at Ilorin have a high potential for PAR utilization anytime of the year except, probably, in the months of July and August, provided other necessary conditions for plant growth are favourable.

Keywords: Diurnal pattern, photosynthetically-active radiation, Ilorin

Nigerian Journal of Physics Vol. 18 (2) 2006: pp. 223-226

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eISSN: 1595-0611