Collocations of selected in situ (ICOADS ship) observations and centred 5-day samples of analysis (ERA Interim) and global (HadGEM2) and local (WRF) numerical model surface marine temperature, humidity, and wind data

In situ surface marine observations of the International Comprehensive Ocean-Atmosphere Data Set (ICOADS Version 3; Freeman et al. 2017) are taken as a reference for numerical model diagnoses of visibility between January 1979 and December 2004. To ensure that observations are of high quality, we consider only a full range of valid variables (wind speed and direction, sea level pressure, air, dew point, and sea surface temperature, present weather, and visibility) and the strictest ICOADS trimming (i.e., values of air and sea surface temperature, zonal and meridional wind component, sea level pressure, and relative humidity are within 2.8 standard deviations of a smoothed monthly climatology). About one percent of these observations are excluded if any duplication of all variables (including latitude and longitude) are found within a few hours of an existing observation. Also, observations are excluded if any type of precipitation was falling at the time visibility was observed. This is done to emphasize hydrometeors of less than about 30 μm (i.e., fog) in determining visibility (Gultepe et al., 2017).