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Gerd Wendler and Yuji Kodama

Abstract

Five years of detailed radiation measurements were taken at Fairbanks, Alaska. These data showed that the El Chichón volcanic cloud had a major impact on the surface radiative regime, the maximum of which was observed in winter 1982/83, about 9 months after the eruption. The direct beam of the solar radiation was reduced by as much as 38% (3-month mean value), the ratio of diffuse over global radiation was increased by 91%, and the global radiation was reduced by about 5%. These values show that the volcanic cloud was a strong forward scatterer, while relatively little energy was absorbed or reflected back to space. Further, the aerosol optical depth and Linke's turbidity factor were calculated, and both displayed substantial increases. Effects of the stratospheric dust cloud were seen all through 1983 and the spring of 1984. In summer 1984, however, the radiative values were back to “normal.” Our values were compared to other observations at lower latitudes and, in general, a good agreement was found.

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Zbigniew Sorbjan, Yuji Kodama, and Gerd Wendler

Abstract

During the austral summer of 1982/83, measurements of wind and temperature profiles were made through the atmospheric boundary layer in Adelie Land, East Antarctica, an area known for strong katabatic winds. It was found that a shallow but strong temperature inversion was developed at night, and destroyed during the day, resulting in the development of a well-mixed layer. Wind hodographs were quite regular and spiral-like at night, but irregular during the day. The mean wind direction was about 40° to the left, looking downslope, but more downslope at night and more cross-slope during the day.

The conclusion was derived that during the polar summer the flow over Antarctica is controlled by the gravitational factor (slope-induced baroclinicity), by the thermal stability (turbulent mixing), and also by the synoptic forcing.

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Yuji Kodama, Gerd Wendler, and Nobuyoshi Ishikawa

Abstract

The data from the boundary-layer experiment carried out in November and December 1985 in Adelie Land, Antarctica, are analyzed. This area is famous for strong surface winds, with highly constant wind direction, which have been explained by the baroclinicity associated with surface radiational cooling over sloping terrain. However, during daytime in summer at D47, the net radiation was found to be positive, and the Richardson number as negative, indicating that the surface boundary layer was unstable. Unexpectedly, the wind directional constancy remained high. It was caused by the highly constant wind direction in the free atmosphere, which could be due to the large horizontal temperature gradient existing between the Antarctic ice sheet and the ice-free ocean along the coast of Adelie Land. A low level wind maximum was found, which was strong at night and weak during daytime. During nighttime, it was due to the slope induced baroclinicity, and during daytime, to the meso-scale baroclinicity caused by the large horizontal temperature gradient.

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Gerd Wendler, Nobuyoshi Ishikawa, and Yuji Kodama

Abstract

A complete but budget investigation was carried out in summer at a site in Adelie Land, some 100 km from the edge of the Antarctic ice sheet. For an average day, the all wave radiation budget based on the fluxes toward the surface being positive was positive for about 11 h, which is a short time considering that the sun was above the horizon between 22 and 24 h a day during the observational period. It is a result of the high albedo, which, on average, was found to be about 83%. Furthermore, with increasing cloudiness, a more positive radiation budget was found, which is in contrast to most studies at lower latitudes. The heat flux in and out of the snow cover was small, and showed a typical sinusoidal diurnal variation. The mean daily values of snow heat flux were negative, as the snow cover was warmed during the observational period. The latent heat flux was negative, on the average, as sublimation took place for most of the time. Deposition was observed only on a few nights. The sensible heat flux was negative around noon, but positive for most of the day, which means that the air above the surface was cooled, an inversion developed, and as the surface is inclined, gravitational flow (katabatic wind) started to occur. While the all-wave radiation balance had its minimum around midnight, the minimum temperature was observed some 3 h law, and the maximum wind speed occurred about 2 additional hours later.

In summary, the mean warming of the snow, the sublimation and the negative all-wave radiation budget for most of the days were compensated by a positive sensible heat flux, which explains the frequent occurrence of the katabatic wind.

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Hiroyuki Hirashima, Yuji Kodama, Norifumi Sato, Tetsuo Ohata, Hironori Yabuki, and Alexander Georgiadi

Abstract

Characteristics of snow cover in a small watershed in Arctic tundra near Tiksi, eastern Siberia, were studied by observation and model simulation. First, helicopter observation, snow survey on three traverse lines, and trigonometric survey of snowdrift were carried out at the end of the winters of 1999 and 2000 to estimate the amount and distribution of snow. The observed locations of snowdrifts in the two years were mostly the same. The area of the snowdrift, including shallow snowdrifts, was larger in the year of high winter precipitation than in the year of low winter precipitation. The snowdrifts were formed on the riverbed and lee sides of cols rather than on steep leeward-facing slopes. Second, snow distribution was simulated using a snow distribution model. The results of simulated snow distribution at the end of winter agreed well with the results of the observations. The results of the simulations showed that approximately 40% of winter precipitation was sublimated. The simulations also indicated that snowdrifts were formed in limited areas such as the valley bottom and riverbed in the first half of winter because of strong wind conditions. In the latter half of winter, when strong wind was rare, shallow snowdrifts were formed in various areas.

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