For hourly (or shorter) calculations, G beneath a dense cover of grass does not correlate well with air temperature.
cal_soilHeatFlux_hourly(Rn, periods)
A vector for soil heat flux [MJ m-2 day-1]
net radiation.From cal_netRadiation().
"daylight" or "nighttime".
Allen, R. G., Pereira, L. S., Raes, D., & Smith, M. FAO Irrigation and drainage paper No. 56. Rome: Food and Agriculture Organization of the United Nations, 1998.