estimate_Rs_for_islandLocations {simET}

Estimating solar radiation for island locations

Description

For island locations, where the land mass has a width perpendicular to the coastline of 20 km or less, the air masses influencing the atmospheric conditions are dominated by the adjacent water body in all directions. The temperature method is not appropriate for this situation. Where radiation data from another location on the island are not available, a first estimate of the monthly solar average can be obtained from the empirical relation.

Usage

estimate_Rs_for_islandLocations(Ra, b = 4)

Arguments

Ra

extraterrestrial radiation [MJ m-2 day-1].

b

empirical constant, equal to 4 MJ m-2 day-1.

Value

A vector for solar radiation

Note

This relationship is only applicable for low altitudes (from 0 to 100 m). The empirical constant represents the fact that in island locations some clouds are usually present, thus making the mean solar radiation 4 MJ m-2 day-1 below the nearly clear sky envelope (0.7 Ra). Local adjustment of the empirical constant may improve the estimation. The method is only appropriate for monthly calculations. The constant relation between Rs and Ra does not yield accurate daily estimates.

References

Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. FAO Irrigation and drainage paper No. 56. Rome: Food and Agriculture Organization of the United Nations, 1998.