Cloud distributions are analyzed from AVHRR data of the NOAA satellite received at Syowa Station (69°00'S, 39°35'E), Antarctica. Satellite observations of clouds and sea ice are major components of the Japanese program of Antarctic Climate Research. Algorithms to derive cloud amount using the brightness temperature differences between infrared channels 3 (3.7μm) and 4 (11μm), 4 and 5 (12μm) are assessed by comparing to the manual cloud amount and the downward longwave radiation at the ground surface. Cloud amounts obtained from the brightness temperature difference between channels 3 and 4 in summer (month) agree with the manual cloud amounts at the surface (correlation coefficient r≈0.88) and highly correlate to the downward longwave fluxes (r≈0.95). Cloud amounts from channels 4 and 5 show rough agreements with the surface cloud amounts throughout the year. The brightness temperature difference of thick cloud overlaps that of clear area and the temperature dependence of clear pixels accompanies some uncertainties which makes the cloud detection uncertain. Characteristics of cloud distributions around Syowa Station of 500km scale are examined for two months. Cloud amount was higher than 0.5 over sea and sea ice, and was less than or equal to about 0.3 over the inland snow field, in both July and December. The average brightness temperature itself varies only within 12K in summer within the area; however, the variance differs greatly according to the region and was largest at the coast. In winter, the average brightness temperature varied 30K, from 220 to 250K, and the correlation between the brightness temperature and cloud amount became low.


Yamanouchi Takashi National Inst. Of Polar Res. And Dep. Of Polar Sci. The Graduate Univ. For Advanced Studies 10-3 Mid