wiki:udg/ecoms/RPackage/examples/pointSelection

Version 13 (modified by juaco, 7 years ago) (diff)

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Single point selections

The following call to loadECOMS will load a time series of summer 2001 (JJA, season = 6:8, years = 2001) surface (2m) daily mean temperature (var = "tas", as defined in the vocabulary) for the coordinate -3.7E 40.4N, (lonLim = -3.7, latLim = 40.4) corresponding to the city of Madrid (Spain), as forecasted the previous March (leadMonth = 2) by the CFSv2 hindcast (dataset = "CFSv2_seasonal_16"). We will select the first 10 members (members = 1:10). Note that the original variable is stored in the CFSv2 database as 6-hourly. Hence, we indicate to the function to compute the daily mean from the 6-hourly data using the argument time = "DD".

First of all, the library is called and we log-in into the ECOMS-UDG:

library(ecomsUDG.Raccess)
loginECOMS_UDG("user","password")

Now we are ready for accessing the ECOMS-UDG:

point.cfs <- loadECOMS(dataset = "CFSv2_seasonal_16", var = "tas", members = 1:10, lonLim = -3.7, latLim = 40.4, season = 6:8, years = 2001, leadMonth = 2, time = "DD")

Note that a number of informative messages will appear on-screen:

[2014-09-02 15:28:42] Defining homogeneization parameters for variable "tas"
NOTE: daily mean will be calculated from the 6-h model output
[2014-09-02 15:28:42] Defining geo-location parameters
[2014-09-02 15:28:42] Defining initialization time parameters
[2014-09-02 15:28:46] Retrieving data subset ...
[2014-09-02 15:31:25] Done

This is the size of the loaded object:

print(object.size(point.cfs)) # 22456 bytes

The returned object contains all the necessary information for data representation (geo-location, time ...). In the next lines we plot the loaded time series for each member. The element Data contains the data itself. In this case, it is a 2D array with the dimensions member (10 members selected) and time (92 days for June, July and August), as indicated by the dimensions attribute.

str(point.cfs$Data)

which returns information on the Data array structure:

 num [1:10, 1:92] 16.3 17.1 12.9 10.4 15.3 ...
 - attr(*, "dimensions")= chr [1:2] "member" "time"

Note that, by convention, the dimensions of the Data array will be always ordered in the canonical form member > time > lat > lon. Several vertical levels are never loaded at the same time, so the dimension level will never appear. This will be indicated in the Variables element of the returned output if existing. In this case it is NULL, because the variable loaded is a surface variable:

str(point.cfs$Variable)

returns the structure of the Variable element of the output:

List of 3
 $ varName   : chr "tas"
 $ isStandard: logi TRUE
 $ level     : NULL

In the following example we plot the time series with the multi-member mean and its dispersion (interquartilic range 25-75):

quartiles <- apply(point.cfs$Data, MARGIN = 2, FUN = quantile, probs = c(.25,.75))
ens.mean <- colMeans(point.cfs$Data)
dates <- as.POSIXlt(point.cfs$Dates$start, tz="GMT")
plot(dates, ens.mean, ylim = range(point.cfs$Data), ty = 'n', ylab = "tas - Daily Mean", xlab = "time")
polygon(x = c(dates, rev(dates)), y = c(quartiles[1, ], rev(quartiles[2, ])), border = "transparent", col = rgb(0,0,1,.4))
lines(dates, ens.mean)

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