R/ncep_utils.R

In dlebauer/climate-utils: clim-utils

##' VPD Calculator
##'
##' Meta-wrapper to calculate climatological mean values of VPD
##' @title VPD Calculator 
##' @param ... values passed to \code{\link{RNCEP::NCEP.gather}}, e.g. lat.southnorth,  lon.westeast, years.minmax, months.minmax
##' @return data table with latitude, longitude, RH, T, and VPD
##' @export
##' @author David LeBauer
##' @examples
##' \dontrun{get.ncep.vpd(lat.minmax = c(-10, 10), lon.minmax = c(-10, 10), years.minmax = c(2011, 2012), months.minmax = c(6, 8))}
get.ncep.vpd <- function(...){
  temp <- gather(var = "air.sig995", ...) 
  rh   <-  gather(var = "rhum.sig995", ...)
  
  rh.dt <- ncep2dt(rh)[,list(latitude, longitude, 
                             RH = mean, 
                             id = 1:length(latitude))]
  temp.dt <- ncep2dt(temp)[,list(latitude, longitude, 
                                 T = mean, 
                                 id = 1:length(latitude))]
  setkey(rh.dt, id)
  setkey(temp.dt, id)
  
  long.data <- rh.dt[temp.dt,
                     ][, list(latitude, longitude, RH, T,
                              VPD = get.vpd(RH, T - 272.15)), 
                       by = id]
  return(long.data)
}


##' Gather Global NCEP data
##'
##' Customized implementation of NCEP.gather from the RNCEP package
##' @title Gather global data 
##' @param ... arguments passed to \code{\link{RNCEP::NCEP.gather}}
##' @return data.table with latitude, longitude, and mean variable value at each lat x lon
##' @author David LeBauer
##' @export
##' @examples
##' 
##' gather(var = "rhum.sig995", lat.southnorth = c(-10, 10), lon.westeast = c(-10, 10), years.minmax = c(2011, 2012), months.minmax = c(6, 8))
gather <- function(...){
  ans <- NCEP.gather(...,
                     level = "surface",
                     reanalysis2 = FALSE,
                     return.units = TRUE,
                     status.bar = FALSE)
  return(ans)
  rm(ans); gc()
}

##' converts NCEP.gather output to data table 
##' @title Gather global data 
##' @param ans output from \code{\link{NCEP.gather}} function
##' @export
##' @return data.table with latitude, longitude, and mean
##' @author David LeBauer
ncep2dt <- function(ans){
  ans.dt <- data.table(NCEP.array2df(ans))
  ans.dt2 <- ans.dt[,#!substr(ans.dt$datetime, 12,13) == "00", 
                    list(date = ymd(substr(datetime, 1, 10)), 
                         latitude, longitude, variable1)]
  ans.dt3 <- ans.dt2[, list(mean = mean(variable1)), by = list(latitude, longitude)] 
  return(ans.dt3)
  rm(list = ls())
  gc()
}