R/qair2rh.R

In andrew-MET/harpPoint: Point verifition for NWP forecasts

#' Convert specific humidity to relative humidity
#'
#' converting specific humidity into relative humidity NCEP surface flux data
#' does not have RH from Bolton 1980 The computation of Equivalent Potential
#' Temperature
#' \url{http://www.eol.ucar.edu/projects/ceop/dm/documents/refdata_report/eqns.html}
#'
#' This function is lifetd from the data.atmosphere package
#' \url{https://github.com/PecanProject/pecan/blob/master/modules/data.atmosphere/R/metutils.R}
#' @title qair2rh
#' @param qair specific humidity, dimensionless (e.g. kg/kg) ratio of water
#'   mass / total air mass
#' @param temp degrees C
#' @param press pressure in mb
#' @return rh relative humidity, ratio of actual water mixing ratio to
#'   saturation mixing ratio
#' @export
#' @author David LeBauer
qair2rh <- function(qair, temp, press = 1013.25) {
  es <- 6.112 * exp((17.67 * temp) / (temp + 243.5))
  e <- qair * press / (0.378 * qair + 0.622)
  rh <- e / es
  rh[rh > 1] <- 1
  rh[rh < 0] <- 0
  return(rh)
}