seasonal: Uni-modal seasonality
In dkneis/diatools: Utilities for Diagenetic Modeling

Description Usage Arguments Value Note Author(s) Examples

Approximation of seasonal variation by a (possibly asymmetric) sine function

1	seasonal(daynum, day1, day2, y1, y2)

`daynum`	Day of the year (value in range 1:366). Can be a vector.
`day1`	First day with fixed value, scalar.
`day2`	Second day with fixed value, scalar. Must be > `day1`.
`y1`	Value at `day1`, scalar.
`y2`	Value at `day2`, scalar.

Numeric vector of the same length as daynum.

A year is assumed to consist of 365 days. The result for day 366 is the same as for day 365. See the example for how this function can be used with values of class POSIXct.

David Kneis david.kneis@tu-dresden.de

# Lake temperature: min. of 3 degree C at day 20, max. 23 degree C at day 210
times= seq(from=ISOdatetime(2000,1,1,0,0,0),
  to=ISOdatetime(2002,1,1,0,0,0), by=3600)
dayofyear= as.integer(format(times, "%j"))
plot(times, seasonal(dayofyear, 20, 210, 3, 23), type="l", ylab="Temperature")