Willmott's index, cloud cover, transmissibility, heliophany
Objective: To estimate the monthly average global solar irradiance (Rg), using observed cloudiness data (% of cloudy days), as well as its spatial distribution for the state of Tabasco, Mexico.
Design/Methodology/Approximation: The proposed model by Tejeda-Martínez et al. (1999) was adjusted to estimate the Rg of 35 meteorological stations in the state of Tabasco. The adjustment was performed with daily observed Rg data from
eight automated weather stations and cloudiness data from eight ordinary weather stations.
Results: The proposed model reports a good fit, given that its prediction was optimal according to Willmotts comparison parameter (c = 0.89), and excellent based on the Nash-Sutcliffe efficiency index (E = 0.99) and had a high corrected determination coefficient of Rc2 = 0.87.
Study limitations/implications: It is necessary that in the state of Tabasco the number of automated stations increase, as well as technical maintenance to the existing stations.
Findings/conclusions: The estimated Rg is statistically reliable. The highest Rg values occurred during the dry season, with a maximum of 22.99 MJ m -2 d -1 , distributed mainly in the northern part of the state. The lowest Rg values occurred
during the northeast season (12.52 MJ m -2 d -1 ), distributed in more than 80 % of the total state area.