loadDecadalForecast: Load a grid from a decadal forecast

In SantanderMetGroup/loadeR: A climate4R package for data access <http://meteo.unican.es/climate4r>

Load a grid from a decadal forecast

Description

Load a user-defined spatio-temporal slice from decadal forecasts

Usage

loadDecadalForecast(
  dataset,
  var,
  dictionary = FALSE,
  members = NULL,
  lonLim = NULL,
  latLim = NULL,
  season = NULL,
  years = NULL,
  time = "none",
  aggr.d = "none",
  aggr.m = "none"
)

Arguments

dataset	A character string indicating the database to be accessed. This is usually a path to a local file or a URL pointing to a netCDF or NcML file in the case of netCDF and/or gridded datasets. For station data in standard ASCII format, this is the path to the directory the dataset lives in.
var	Variable code (character string). This is the name of the variable according to the R standard naming (see the next argument). For variables with vertical levels, the vertical level is specified next to the variable name followed by the “@” symbol (e.g. var = "z@700" for geopotential heigth at 700 mb isobaric surface pressure level). It is also possible to enter the variable name as originally coded in the dataset to skip data homogenization.
dictionary	Default to TRUE, indicating that a dictionary is used and the .dic file is stored in the same path than the dataset. If the .dic file is stored elsewhere, then the argument is the full path to the .dic file (including the extension, e.g.: "/path/to/the/dictionary_file.dic"). This is the case for instance when the dataset is stored in a remote URL, and we have a locally stored dictionary for that particular dataset. If FALSE no variable homogenization takes place, and the raw variable, as originally stored in the dataset, will be returned. See details for dictionary specification.
members	Vector of integers indicating the members to be loaded.
lonLim	Vector of length = 2, with minimum and maximum longitude coordinates, in decimal degrees, of the bounding box selected. For single-point queries, a numeric value with the longitude coordinate. If NULL (default), the whole longitudinal range is selected (Note that this may lead to a large output object size).
latLim	Same as lonLim, but for the selection of the latitudinal range.
season	An integer vector specifying the desired season (in months, January = 1 ..., December = 12). Options include one to several (contiguous) months. Default to NULL, indicating a full year selection (same as season = 1:12).
years	Optional vector of years to select. Default (NULL) to all available years. If the requested variable is static (e.g. orography) it will be ignored.
time	A character vector indicating the temporal filtering/aggregation of the output data. Default to "none", which returns the original time series as stored in the dataset. For sub-daily variables, instantantaneous data at selected verification times can be filtered using one of the character strings "00", "03", "06", "09", "12", "15", "18", "21",and "00" when applicable. If daily aggregated data are required use "DD". If the requested variable is static (e.g. orography) it will be ignored. See the next arguments for time aggregation options.
aggr.d	Character string. Function of aggregation of sub-daily data for daily data calculation. Currently accepted values are "none", "mean", "min", "max" and "sum".
aggr.m	Same as aggr.d, bun indicating the aggregation function to compute monthly from daily data. If aggr.m = "none" (the default), no monthly aggregation is undertaken.

Value

A list with the following elements providing the necessary information for data representation and analysis:

Variable

A list with three elements:

• varName A character string indicating which is the variable returned. Same as value provided for argument var

• isStandard Logical value indicating whether the variable returned is standard or not (i.e., wether the dictionary has been used or not.)

• level A numeric value indicating the vertical level of the variable (NULL for 2D variables)

Data	A N-dimensional array. The number of dimensions (N) depends on the type of request given that dimensions of length one are dropped. Thus, N can take values from 4 (several members for a rectangular domain with different values for longitude, latitude, ensemble and time dimensions) to 1 (atomic vector), for single-point and single-member selections, for which only the time dimension is required. The dimensions are labelled by the “dimnames” attribute. Note that the order of the dimensions is not fixed.
xyCoords	A list with x and y components, as required by many standard mapping functions in R (see xy.coords. In addition, the attribute projection provides geo-referencing information as stored in the original dataset.
Dates	A list with two POSIXct time elements of the same length as the ‘time’ dimension in Data, defining the time boundaries of the time axis coordinates in the interval [start, end), or if the loaded field is static, a character string indicating it.

Variable harmonization

The different nature of the various databases, models and variables, and the idiosyncratic naming and storage conventions often applied by the different modelling centres, makes necessary a previous harmonization across datasets in order to implement a truly user-friendly toolbox for data access. This package achieves this aim by defining a common vocabulary to all climate datasets. The particular variables of each dataset are translated -and transformed if necessary- to the standard variables by means of a dictionary, provided by the argument dictionary. In essence, the ‘dictionary’ is a csv file particular for each individual dataset, containing the necessary information for performing the unit conversions to match the standard variable definitions contained in the vocabulary (see C4R.vocabulary). This feature is described in more detail in the loadeR wiki..

Geolocation parameters

Regarding the selection of the spatial domain, it is possible to select the whole spatial domain of the dataset by defining the arguments lonLim=NULL and latLim=NULL. More often, rectangular domains are defined by the minimum and maximum coordinates in longitude and latitude (for instance lonLim=c(-10,10) and latLim=c(35,45) indicates a rectangular window centered in the Iberian Peninsula), and single grid-cell values (for instance lonLim=-3.21 and latLim=41.087 for retrieving the data in the closest grid point to the point coordinate -3.21E, 41.087N. In the last two cases, the function operates by finding the nearest (euclidean distance) grid-points to the coordinates introduced.

In the case of station data (loadStationData), the logic is the same, taking into account that in the case of rectangular domains, all stations falling inside that window will be loaded. For single-point selections, the closest station will be chosen, and a note on-screen will inform about the distance from the selected point to the chosen station.

In case of irregular grids (e.g. the typical RCM rotated pole projections), the regular coordinates are included in the x and y elements of the xyCoords list, while the corresponding geographical coordinates are insode two matrices inside the lon and lat elements.

Author(s)

J. Bedia, S. Herrera, M. Iturbide, J.M. Gutierrez

See Also

Other loading.grid: loadCircularGridData(), loadGridData()

Examples

## Not run: 
latLim <- c(40,50)
lonLim <-  c(-5,10)
season <- 3:5
period <- 1981:1991
loginUDG(username = "myuser", password = "mypassword") 
tasDECA <- loadDecadalForecast(
   dataset = "http://www.meteo.unican.es/tds5/dodsC/specs/gfdl_specs_decadal.ncml", 
   latLim = latLim, 
   lonLim = lonLim,
   var = "tas", 
   years = period, 
   season = season)

## End(Not run)

SantanderMetGroup/loadeR documentation built on July 4, 2023, 4:29 a.m.