Day and Night Cloudiness Using Satellite Data from Different Sources

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Day-time and night-time cloudiness and their difference were assessed based on various satellite data (AIRS-LMD, CERES, MODIS, CALIPSO-GOCCP, PATMOS-x) and surface observations. It was found that day-time cloudiness prevails over land and over the entire Northern Hemisphere while night-time cloudiness prevails over the ocean and over the Southern Hemisphere, moreover difference between cloudiness over land and over the ocean (and consequently over both hemispheres) is higher at the nighttime. Regionally, difference between day-time and night-time cloudiness over land is up to 20–40%, mostly over mountain regions and midlatitudes. Over the ocean, night-time cloudiness prevails in low latitudes in summer (mostly over the eastern parts of the oceans) where it is up to 15–20% more than day-time cloudiness. A disagreement between different data is noted over the vast equatorial and highmountain regions in Eurasia, Africa, South America, Australia, North Pacifi c and North Atlantic. Particularly, some data display that day-time cloudiness prevails in that regions, other data shows the opposite. It was shown, that time of observations can affect the estimate of total cloudiness. Though, only day-time measurements lead to an overestimation of cloudiness over land (up to 20% of the total daily cloudiness) and underestimation over the ocean. On the contrary, only night-time observations (or observations at the morning) lead to an overestimation of cloudiness over the ocean (up to 5–7%) and underestimation over land (up to 8–10%). Regional differences are even more suffi cient.