daylength function

Daylength

Compute daylength (photoperiod) for a latitude and date.

daylength(lat, doy)

Arguments

• lat: latitude, in degrees. I.e. between -90.0 and 90.0
• doy: integer, day of the year (1..365) for common (non-leap) years; or an object of class Date; or a character that can be coerced into a date, using 'yyyy-mm-dd' format, e.g. '1982-11-23'

Returns

Daylength in hours

References

Forsythe, William C., Edward J. Rykiel Jr., Randal S. Stahl, Hsin-i Wu and Robert M. Schoolfield, 1995. A model comparison for daylength as a function of latitude and day of the year. Ecological Modeling 80:87-95.

Author(s)

Robert J. Hijmans

Examples

daylength(-25, '2010-10-10')
daylength(45, 1:365)

# average monthly daylength
dl <- daylength(45, 1:365)
tapply(dl, rep(1:12, c(31,28,31,30,31,30,31,31,30,31,30,31)), mean)