[R-sig-Geo] Calculate anomalies on time-series rasters

[Michael Sumner]

I believe the "remote" package has functions for doing exactly this.

HTH

On Sun, Feb 12, 2017, 17:42 Thiago V. dos Santos via R-sig-Geo <
r-sig-geo at r-project.org> wrote:

> Dear all,
>
> I have a netcdf file with monthly temperatures values covering the period
> of January 1961 to December 2010:
>
> library(raster)
> # Create date sequence
> idx = seq(as.Date("1961/1/1"), as.Date("2010/12/31"), by = "month")
>
> # Create raster stack and assign dates
> r = raster(ncol=5, nrow=5)
> s = stack(lapply(1:length(idx), function(x) setValues(r, runif(ncell(r)))))
> s = setZ(s, idx)
>
> First, let's consider only the period from 1961-1990 and take the global
> monthly means (aka climatologies)
>
> # Split 1961-1990 period and take climatology
> s61.90 = subset(s, which(getZ(s)>=as.Date('1961-01-01') &
> getZ(s)<=as.Date('1990-12-31')))
> s61.90.mon = zApply(s61.90, by=months, mean, name=month.abb[])
>
> s61.90.mon is a raster with 12 layers, one for each monthly mean
> temperature.
>
> Now what I need to do is calculate the monthly 'anomaly' for the remainder
> period (Jan 1991 to Dev 2010), i.e. the difference of a single month of the
> period from the corresponding month in the climatological mean.
>
> # Here I split the remainder of the time series (1991 to 2010)
> s91.2010 = subset(s, which(getZ(s)>=as.Date('1991-01-01') &
> getZ(s)<=as.Date('2010-12-31')))
>
> In other words, I need to subtract 'jan' in the raster s.61.90.mon from
> every 'jan' in the raster s91.2010, and so on for every other month.
>
>
> I was wondering what is the best way to do that using raster (and possibly
> zoo) functions?
>
> Thank you very much in advance, -- Thiago V. dos Santos
>
> PhD candidate
> Land and Atmospheric Science
> University of Minnesota
>
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>
-- 
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia

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