This function requires the daymetr package. This function should replace
the get_daymet_apsim_met
function.
If the filename is not provided it will not write the file to disk,
but it will return an object of class ‘met’. This is useful in case manipulation
is required before writing to disk. The variable ‘srad’ as downloaded from
daymet is average solar radiation, so it is converted to total.
Daily total radiation (MJ/m2/day) can be calculated as
follows: ((srad (W/m2) * dayl (s/day)) / 1,000,000)
Vapor Pressure Deficit (vp) should be in hecto Pascals