filename (str) – filepath or url to read for the fixed-width file.
data (Dataframe) – A dataframe with DatetimeIndex and all of the variables in the file.
SOLRAD data resolution is described by the README_SOLRAD.txt: “Before 1-jan. 2015 the data were reported as 3-min averages; on and after 1-Jan. 2015, SOLRAD data are reported as 1-min. averages of 1-sec. samples.” Here, missing data is flagged as NaN, rather than -9999.9.
NOAA SOLRAD Network https://www.esrl.noaa.gov/gmd/grad/solrad/index.html
B. B. Hicks et. al., (1996), The NOAA Integrated Surface Irradiance Study (ISIS). A New Surface Radiation Monitoring Program. Bull. Amer. Meteor. Soc., 77, 2857-2864. DOI: 10.1175/1520-0477(1996)077<2857:TNISIS>2.0.CO;2