Methods
Dearchived sounding Melbourne & Giles Airport data 2013 (00, 12Z) from the Bureau of Meteorology http://tcz.bom.gov.au:8889/tcz/anon/Sf1?sf1dist_tbl=d&sf1state_tbl=d
Downloaded ECMWF Era Interim T and RH grib data for a restricted domain over Melbourne & Giles Airport sounding sites (airport lat+-5 degrees lat, lon+-5 deg lon). Converted all grib files to netCDF.
For all Melbourne/Giles Airport BoM soundings in 2013 (n=728/n=361):
To estimate T and RH (all levels) at the sounding site, (a) identified 4 Era Interim grid points surrounding the BoM site, (b) 2D linear interpolation was used at all levels
Era Interim TD using RH and TD approximation formula by Lawrence (2005, equation 8, accurate between -40 degC < T < 50 degC, 1% < RH < 100% ). NOTE - TD(T,RH) formula successfully calculated Equation 8 values in Table 1 of Lawrence 2005.
Tbom and TDbom mapped to Era Int pressure levels by identifying Tbom (TDbom) at levels common to both the BoM and Era levels ie no vertical interpolation
calculating Tdiff = Tbom-Tera, TDdiff = TDbom-TDera at all common eralevs
At 00Z and 12Z for Melbourne (00Z Giles only), calculate MEAN(Tdiff), MEAN(TDdiff), STD(Tdiff), STD(TDdiff) at every common Era Interin level where ’n’ > 100. NOTE - standard deviations were calculated using the n-1 method (assumes that arguments are a sample of the population).