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Hourly and daily clearness index and diffuse fraction at a tropical station, Ile-Ife, Nigeria
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2009 (English)In: International Journal of Climatology, ISSN 0899-8418, E-ISSN 1097-0088, Vol. 29, no 8, 1035-1047 p.Article, review/survey (Refereed) Published
Abstract [en]

Dataset consisting of hourly global and diffuse solar radiation measured over the period February 1992 and December 2002 have been utilized to investigate the diurnal and seasonal variations of hourly and daily clearness index together with the diffuse fraction at a tropical station Ile-Ife (7.5 degrees N, 4.57 degrees E), Nigeria. Statistical analysis (the frequency and cumulative frequency distribution of the hourly and daily clearness index) and Subsequent characterization of the sky conditions over the station based on these were also done, and their implications for solar energy utilization in the area discussed. Daytime (11 : 00-15 : 00 LST) monthly mean hourly diffuse fraction, (M) over bar (d) (explained in a separate 'List of Symbols' provided, along with other symbols used in this article), have values, which are most of the time less than 0.52, 0.54 and 0.60 respectively for January, February and March in the dry season. However, during the months of July and August (which are typical of the wet season), the values range between 0.61 and 0.85 (being generally greater than 0.65) with the corresponding values of the monthly mean hourly clearness index, (M) over bar (T), ranging between 0.23 and 0.45. Statistical analysis of hourly and daily clearness index showed that the local sky conditions at the station were almost devoid of clear skies and overcast skies (clear skies and overcast skies occurred for only about 3.5% and 4.8% of the time respectively). The sky conditions were rather predominantly cloudy (cloudy skies occurred for about 88% of the time) all the year round.

Place, publisher, year, edition, pages
2009. Vol. 29, no 8, 1035-1047 p.
Keyword [en]
clearness index, diffuse fraction, tropical station sky conditions, Ile-Ife
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-142286DOI: 10.1002/joc.1849ISI: 000267445800001OAI: oai:DiVA.org:uu-142286DiVA: diva2:387825
Available from: 2011-01-14 Created: 2011-01-13 Last updated: 2011-01-14Bibliographically approved

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