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Choji Magono and Katsuhiro Kikuchi

Abstract

Observations of snow crystals were made in mid-winter at Inuvik, N.W.T., Canada, in order to study the snow crystal of cold temperature type. The following results were obtained:

1) The cloud temperature was, in general, warmer than expected during the observation period, that is, nearly the same as observed in snow clouds in midlatitudes, although the surface temperature was lowered to −30 or −40°C.

2) Regarding the type of snow crystals, Nakaya's Ta-s diagram was well applicable to the snow crystal in Arctic Canada.

3) Almost every day during the observation period, snowfalls were observed; however the fall intensity was as light as 1 or 2 cm day−1. In the case of a moderate snowfall of 5.1 cm day−1, the snowfall was caused by an arctic front at the 850 mb level. The vapor for the snowfall was supplied from the warm surface of the eastern or northern Pacific Ocean.

4) One day, small supercooled raindrops were observed, but no cloud region of temperature warmer than 0°C was detected in the clouds within 1000 km around the observation site. However, rain occurred in between RAOD observation times.

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Choji Magono, Katsuhiro Kikuchi, Tsutomu Nakamura, and Tadashi Kimura

Abstract

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Choji Magono, Katsuhiro Kikuchi, Tsutomu Nakamura, and Tadashi Kimura

Abstract

In July 1961 an artificial fog dissipation experiment was carried out, using a helicopter. The experiment was based on the idea that fog will be dissipated by downward air current caused by fall of water drops sprinkled from the helicopter. The preliminary experiment showed that the effective width of distribution area of water drops was about 20 m under the sprinkling condition used. The vertical distributions of air temperature and humidity in sea fog were observed at the sea side near where the fog dissipation experiment was made. According to the observation, it was seen to be general in the sea fog in the daytime that strong temperature inversion existed near the fog top and that the air layer under the fog base was unstable with respect to the dry adiabatic. The sprinkling of water drops was carried out on the top of the advected sea fog, a smooth and flat area being selected; it was found that a few minutes after the sprinkling treatment, the flat and smooth fog layer changed to fracto-cumulus, then was dissipated if the fog was not dense. The dimensions of area of the modified fog were much larger than the effective width estimated in the preliminary experiment. This suggests that the water sprinkling served as only a trigger action causing vertical convection to occur in the lower unstable part of the fog.

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Yoshio Asuma, Soshi Iwata, Katsuhiro Kikuchi, G. W. Kent Moore, Ryuji Kimura, and Kazuhisa Tsuboki

Abstract

In the fall of 1994, the Beaufort and Arctic Storms Experiment (BASE) was held to collect information on the structure and evolution of mesoscale weather systems over the southern Beaufort Sea and the Mackenzie River delta of the western Canadian Arctic. As part of the experiment, X-band Doppler radar observations were carried out at Tuktoyaktuk, a village on the shore of the Beaufort Sea. In this paper, the precipitation features, structure, and moisture transport associated with two distinctly different weather systems that were observed during BASE are described with a variety of datasets. Climatologies of storm activity in the area suggest these two types of different weather systems, the so-called Pacific origin and storm track disturbances, are the most frequently observed in this region during the fall months.

The characteristic feature of a Pacific origin weather system is a pronounced layering of the air masses. In the upper layer, the air mass is of Pacific origin and is associated with a deep low in the Gulf of Alaska. As a result it is moist and is capable of producing precipitation. In contrast, the lower layer is initially of continental origin and is associated with a secondary lee cyclogenesis event in the Mackenzie River basin. As the secondary disturbance moves to the east, there is a shift in the wind direction that advects air from the Beaufort Sea into the lower layer. This results in a moistening of the lower layer that allows precipitation from the upper layer that had previously evaporated in the lower layer to be enhanced and reach the surface. The detailed structure of this type of storm is strongly affected by the topography of the region and the presence of open water in the southern Beaufort Sea.

The storm track weather system is markedly different and is associated with the passage of a mesoscale low over the southern Beaufort Sea. In this sort of system, there is a well-defined frontal structure of a type previously identified in the midlatitudes. Two different precipitation regimes are identified that are associated with the passage of the warm and cold front. In this sort of system, the sources of moisture are the Bering Sea and the open water in the southern Beaufort Sea.

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