A method to detect cloud cover in the Antarctic using only the infrared channels of AVHRR is discussed. From the data of NOAA-7 received at Syowa Station, the difference in the brightness temperature of each channel appeared to be useful for the identification of clouds. The brightness temperature of the channels 3 (3.7*m) and 4 (11*m) shows the positive difference when the thickness of clouds are in some particular range, and then tends to show negative difference for the thick cloud. Thin clouds have the difference in the brightness temperature between channels 4 and 5 (12 * m). These tendencies are explained by the radiative properties of model clouds theoretically calculated. On the graph of these temperature difference against the channel 4 brightness temperature, pixels of the same cloud distribute on the particular arch starting from the clear pixel. From the arch, clouds can be distinguished from the ground surface. The particle size, temperature and thickness of the cloud can also be inferred. At the low temperature over the inland snow surface, many troubles arise. The channel 3 brightness temperature accompanies poor resolution and large noise at the low temperature. The brightness temperature difference between channels 4 and 5 shows strong dependence on temperature and viewing angle at the low temperature due to the nonlinearity error and variation of snow surface emissivity. An empirical correction is applied to the low temperature data for the automatic cloud detection.
There occurred a large stratospheric sudden warming in the southern hemisphere in late winter of 1988 which competes in suddenness and size with major mid‐winter warmings in the northern hemisphere. Associated with the dynamical phenomenon of the sudden warming, total ozone increased over the eastern hemispheric part of Antarctica. The sudden warming as well as other warmings which followed it made the 1988 Antarctic ozone hole shallow in depth and small in area.
Measurements and calculations of longwave radiation fluxes were made in order to clarify their characteristic features under a surface inversion and with katabatic winds. Measurements were made under the Japanese POLEX program (POLEX—South), 1979–1981, at Mizuho Station (70°42′S, 44°20′), where the katabatic wind was blowing continuously and a strong surface inversion existed. Direct measurements of the downward and upward longwave fluxes were extended through day and night using pyrgeometers (Eppley PIR) with a simple shading ring to cut off heating by direct solar radiation. Longwave radiation fluxes were also calculated using a simple wide band model, and the effect of the surface inversion was examined. The daily average of the downward flux varies greatly between 90 and 240 W/m2. The large day to day variation is due to clouds. Overcast skies give an increase of about 80 W/m2 in the downward longwave flux in all seasons. The effective emissivity of the atmosphere for clear sky is very small on account of the small amount of column water vapor. The drifting snow near the surface caused by the strong wind increases the downward longwave flux and suppresses the long‐wave cooling at the surface. The relation between the strength of the surface inversion and longwave fluxes is examined and approximated by a linear relation. When the surface inversion becomes strong, the net longwave flux decreases.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.