[R] Cycle Regression Analysis in R?

[Carson Farmer]

Hello R community,

Does anyone know of a package that will perform cycle regression 
analysis? I have searched the R-help archives etc. but have come up with 
nothing so far.
If I am unable to find an existing R package to do so, is there anyone 
familiar with fitting sine functions to data.  My problem is this:
I have a long time-series of daily SWE estimates (SWE = snow water 
equivalence, or the amount of water stored in a snowpack) which follows 
a sinusoidal pattern, and I need to estimate the parameters of the sine 
function that best fits this data. While there may be many contributing 
sine functions and/or linear trends, I am only interested in a single 
sine function that most closely fits the data (trends can be removed 
separately if need be).  Perhaps some sort of non-linear least squares 
method would be best?

Any help, or suggestions to get me on the right track are greatly 
appreciated.

Carson