get_Rnl_daily: Get net outgoing longwave radiation (Rnl)
In gopalpenny/fao56:

Description Usage Arguments Details Examples

Get net outgoing longwave radiation, Rnl (FAO 56, Eq. 39) in MJ/m^2/day

1	get_Rnl_daily(Ra, Tmax_C, Tmin_C, ea, Rs, Rso)

`Ra`	downward shortwave radiation, MJ/m^2/day
`Tmax_C`	maximum absolute temperature during the 24-hour period
`Tmin_C`	minimum absolute temperature during the 24-hour period
`ea`	actual vapor pressure, kPa
`Rs`	measured or calculated. (Equation 35) solar radiation [MJ m-2 day-1],
`Rso`	calculated (Equation 36 or 37) clear-sky radiation [MJ m-2 day-1].

This function calculates net outgoing longwave radiation, in MJ/m^2/day. It uses Eq. 39 from FAO 56 in Chapter 3:

Rnl = sigma * (Tmax_K + Tmin_K)/2 * (0.34 - 0.14 * sqrt(e_a)) * (1.35 * Rs/Rso - 0.35)

Tmax_K is Tmax_C + 273.16 Tmin_K is Tmin_C + 273.16 sigma is the Stefan-Boltzmann constant, 4.903e-9 MJ/K^4/m^2/day, Rs/Rso relative shortwave radiation (limited to <= 1.0).

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