Seasonal and intra-seasonal fluctuations of polar anticyclone and circumpolar vortex over Antarctica

Fluctuations of the polar anticyclone at sea level and the circumpolar vortex at 500mb are examined by using daily sea level and 500-mb weather maps of 1983. In addition to the seasonal cycle, a remarkable intra-seasonal fluctuation with the period of about 30 days is noticed in the intensity of polar anticyclone and in the circumpolar vortex. It is also noticed that in the seasonal time scale the intensity of polar anticyclone and circumpolar vortex shows a positive correlation while in the intra-seasonal time scale these two are negatively correlated

Dark streams observed on NOAA satellite images over the Katabatic wind zone, Antarctica

In the katabatic wind zone in Antarctica, some characteristic streams are frequently observed in NOAA satellite images especially in the winter season. We call these "dark streams" in this work. These dark streams are observed to move and change location and their width slightly in a series of succesive scenes of NOAA images; however, distributions seem to be restricted to areas of some specific topographies. We measured air temperature and wind speed at one point by means of one of our AWS (Automated Weather Station) system. Air temperature was not particularly low and remained steady, and wind speed was constantly high, 13m/s or more. TBB analyzed from NOAA AVHRR may provide surface temperatures which are thought to be proportional to the air temperature which is equalized to emittance temperature of the blowing and drifting snow particles. On the basis of these data, air temperature inside the stream was 15℃ or higher than that outside. Along the central line of the stream, air temperature was analyzed to vary with height at the dry adiabatic lapse rate. From these observational results it may be considered that these dark stream images are composed of a warmer air stream compared with that of the outside and a strongly forced downward current along the slope

ANNUAL VARIATION OF SNOWFALL AND RADAR ECHO STRUCTURE OF SNOW CLOUDS AT SYOWA STATION, ANTARCTICA

Snow clouds were observed with vertical pointing radar at Syowa Station from February 1988 to December 1989. In order to find the Z-R relationship, the snowfall rate was directly measured by using an electric balance at the ground. The annual amount of snowfall was estimated to be 400mm in 1989 when we used Z=16・R^. The amount of snowfall was 120mm in spring (from October to November), 170mm in fall (from February to April), and 70mm in winter (from June to July). It was less than 20mm in summer (from December to January). Two types of clouds were found to appear above Syowa Station : one had a low cloud top (less than 2km) and the other had a higher cloud top. The former clouds occurred predominantly in winter and the latter in spring and fall. The higher type clouds are related to the warm front of a low pressure system. The activity of lower type clouds are related to the temperature and humidity in the clouds. These conditions might be connected with the area of sea ice

カタバフウタイ ニ ミラレル ダークストリーム

南極のカタバ風の地域におけるNOAAの衛星画像で, 冬季間にしばしば特徴的な流れの模様が観測される。ここでは, それをダークストリームとよぶことにする。このダークストリームの縞模様は一連のNOAA衛星画像の中で, 動きがあり, その位置と幅が変化するのが認められた。しかし動きはするが, その範囲はある特定の地形の地域に限られて見られる特徴がある。幸いに, この領域に設置した無人気象観測点の気温と風速の記録が得られた。気温はあまり低くないが一定の値を保っており, 風は一定して13m/sほどで強いのが特徴であった。NOAAの赤外放射測定で得られる赤外輝度温度(TBB)による地表面温度は地吹雪や飛雪の粒子からの射出によるとすると, 気温に比例するものと考えられる。これによると, ダークストリームの内側の気温は外側にくらべて, 約15℃以上高いことになる。また, ストリームの中心軸に沿った気温と高度から得たプロフィルによると, それは完全な乾燥断熱減率であることがわかった。以上のことから, ダークストリームは周囲に比べて暖かくて強い斜面下降流によって形成されていることが, 結論される。In the katabatic wind zone in Antarctica, some characteristic streams are frequently observed in NOAA satellite images especially in the winter season. We call these "dark streams" in this work. These dark streams are observed to move and change location and their width slightly in a series of succesive scenes of NOAA images; however, distributions seem to be restricted to areas of some specific topographies. We measured air temperature and wind speed at one point by means of one of our AWS (Automated Weather Station) system. Air temperature was not particularly low and remained steady, and wind speed was constantly high, 13m/s or more. TBB analyzed from NOAA AVHRR may provide surface temperatures which are thought to be proportional to the air temperature which is equalized to emittance temperature of the blowing and drifting snow particles. On the basis of these data, air temperature inside the stream was 15℃ or higher than that outside. Along the central line of the stream, air temperature was analyzed to vary with height at the dry adiabatic lapse rate. From these observational results it may be considered that these dark stream images are composed of a warmer air stream compared with that of the outside and a strongly forced downward current along the slope