get_Rn_daily: Get net radiation (Rn)

In gopalpenny/fao56:

Description

Get net radiation, Rnl (FAO 56, Eq. 40) in MJ/m^2/day

Usage

get_Rn_daily(
  lat,
  date,
  Tmax_C,
  Tmin_C,
  ea,
  n,
  N,
  albedo = 0.23,
  z,
  as = 0.25,
  bs = 0.5
)

Arguments

lat	latitude in decimal degrees
date	date object or numeric jday
Tmax_C	maximum absolute temperature during the 24-hour period, deg C
Tmin_C,	minimum absolute temperature during the 24-hour period, deg C
ea	actual vapor pressure, kPa
n	actual duration of sunshine, hour
N	maximum possible duration of sunshine or daylight hours, hour
albedo	albedo or canopy reflectance, unitless
z	elevation above sea level, m
as	regression constant, expressing the fraction of extraterrestrial radiation reaching the earth on overcast days (n = 0)
bs	increase in solar radiation on clear days relative to overcast days, ie, as + bs is the fraction of extraterrestrial radiation reaching the earth on clear days (n = N).

Details

This function calculates net radiation, in MJ/m^2/day. It uses Eq. 40 from FAO 56 in Chapter 3:

Rn = Rns - Rnl

In this function, Rns and Rnl are automatically calculated via the functions:

• Ra <- get_Ra_daily(lat, date)

• Rs <- get_Rs_daily(Ra, n, N)

• Rso <- get_Rso_daily(Ra, z)

• Rns <- get_Rns_daily(Rs, albedo)

• Rnl <- get_Rnl_daily(Ra, Tmax_C, Tmin_C, ea, Rs, Rso)

Examples

lat <- -22.9 # Rio de Janeiro
date <- "2019-05-15"
n <- 220 / 31 # 220 hours in a month / 31 days
N <- get_daylight_hours(lat, date)
Ra <- get_Ra_daily(lat, date)
Rso <- get_Rso_daily(Ra, z = 100)
Rs <- get_Rs_daily(Ra, n, N)
Tmax_C <- 25.1
Tmin_C <- 19.1
ea <- 2.1
Rn <- get_Rn_daily(lat, date, Tmax_C, Tmin_C, ea, n, N, z = 100)

gopalpenny/fao56 documentation built on Feb. 14, 2022, 6:01 a.m.