Apply Mann-Kendall trend test.
The function determines the trend from data of a single CM SAF NetCDF input file basing on a Mann-Kendall test.
cmsaf.mk.test( var, infile, outfile, nc34 = 4, overwrite = FALSE, verbose = FALSE )
var |
Name of NetCDF variable (character). |
infile |
Filename of input NetCDF file. This may include the directory (character). |
outfile |
Filename of output NetCDF file. This may include the directory (character). |
nc34 |
NetCDF version of output file. If |
overwrite |
logical; should existing output file be overwritten? |
verbose |
logical; if TRUE, progress messages are shown |
A NetCDF file including three data layers is written. One layer contains a measure for the significance of the calculated mann-kendall statistic (S). A very high positive value of S is an indicator of an increasing trend and a very low negative value indicates a decreasing trend. Another layer (Z) contains the calculated normalized test statsitic Z. A positive value of Z is an indicator of an increasing trend and a negative value indicates a decreasing trend.
Other temporal operators:
cmsaf.detrend(),
cmsaf.regres(),
timmax(),
timmean(),
timmin(),
timpctl(),
timsd(),
timsum(),
trend_advanced(),
trend()
## Create an example NetCDF file with a similar structure as used by CM
## SAF. The file is created with the ncdf4 package. Alternatively
## example data can be freely downloaded here: <https://wui.cmsaf.eu/>
library(ncdf4)
## create some (non-realistic) example data
lon <- seq(10, 15, 0.5)
lat <- seq(50, 55, 0.5)
time <- seq(as.Date("2000-01-01"), as.Date("2010-12-31"), "month")
origin <- as.Date("1983-01-01 00:00:00")
time <- as.numeric(difftime(time, origin, units = "hour"))
data <- array(250:350, dim = c(11, 11, 132))
## create example NetCDF
x <- ncdim_def(name = "lon", units = "degrees_east", vals = lon)
y <- ncdim_def(name = "lat", units = "degrees_north", vals = lat)
t <- ncdim_def(name = "time", units = "hours since 1983-01-01 00:00:00",
vals = time, unlim = TRUE)
var1 <- ncvar_def("SIS", "W m-2", list(x, y, t), -1, prec = "short")
vars <- list(var1)
ncnew <- nc_create(file.path(tempdir(),"CMSAF_example_file.nc"), vars)
ncvar_put(ncnew, var1, data)
ncatt_put(ncnew, "lon", "standard_name", "longitude", prec = "text")
ncatt_put(ncnew, "lat", "standard_name", "latitude", prec = "text")
nc_close(ncnew)
## Determine the trend of the example CM SAF NetCDF file and write the
## output to a new file.
cmsaf.mk.test(var = "SIS", infile = file.path(tempdir(),
"CMSAF_example_file.nc"), outfile = file.path(tempdir(),
"CMSAF_example_file_mktrend.nc"))
unlink(c(file.path(tempdir(),"CMSAF_example_file.nc"),
file.path(tempdir(),"CMSAF_example_file_mktrend.nc")))Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.