R/add_longwave.R

In ropenmeteo: Wrappers for 'Open-Meteo' API

#' Add longwave to ensemble forecast dataframe using Idso and Jackson (1969).  Requires cloud cover and temperature variables in input data frame.
#'
#' @param df data frame output from one of the functions that gets a data frame from the API (e.g., `get_ensemble_forecast`).  The data frame must has `cloud_cover` and `temperature_2m` as variables
#'
#' @returns data frame with the same columns as the input `df` but with `longwave_radiation` added as a variable
#' @export
#' @examples
#'
#' file <- system.file("extdata", "test-data.csv", package="ropenmeteo")
#' df <- readr::read_csv(file, show_col_types = FALSE)
#' df  |>
#' add_longwave()
#'
add_longwave <- function(df) {

  unit_table <- df |>
    dplyr::distinct(variable, unit) |>
    dplyr::bind_rows(dplyr::tibble(variable = "longwave_radiation", unit = "(W/m2)"))

  df |>
    dplyr::select(-unit) |>
    tidyr::pivot_wider(names_from = variable, values_from = prediction) |>
    dplyr::mutate(cloud_cover = ifelse(cloud_cover < 0, 0, cloud_cover)) |>
    dplyr::mutate(
      eps_star = (1.0 + 0.275 * cloud_cover / 100) * (1.0 - 0.261 * exp(-0.000777 * temperature_2m ^ 2.0)),
      longwave_radiation = round((1 - 0.03) * eps_star * 5.67E-8 * (273.15 +
                                                            temperature_2m) ^ 4.0, 2)
    ) |>
    dplyr::select(-eps_star) |>
    tidyr::pivot_longer(-dplyr::any_of(c(
      "datetime", "ensemble", "model_id", "reference_datetime", "site_id", "parameter", "family")),
    names_to = "variable",
    values_to = "prediction") |>
    dplyr::left_join(unit_table, by = "variable") |>
    dplyr::select(dplyr::any_of(c("datetime", "reference_datetime", "site_id", "model_id", "parameter", "family", "ensemble", "variable", "prediction","unit")))

}