![]() ![]() Because the reflectance of ice for the sodium D line (1.3090 for ice at –3☌ Reference HobbsHobbs, 1974) is similar to that of the water for the sodium D line (1.3339493 for water at 0☌: Reference Eisenberg and KauzmannEisenberg and Kauzmann, 1969), it was difficult to identify ice grains in water. This value is close to the observed surface height difference in Kitami on 1 November 2009. Based on 79 measurements, the average thickness was 1.1☐.5 mm. We measured the thickness of air bubbles in the white spotted wet snow by measuring the air volume and diameter of white spots in the winter of 2010/11. ![]() We consider that the thickness of the bubbles was close to the surface height difference of 1 mm. There was an air bubble between the two layers. Ice pellets 1 mm in diameter were enclosed in the mixed ice– water layer. A thin water layer (2–5 mm thick) was present on the asphalt pavement, and a mixed ice–water layer (2–3 mm thick) was present on the thin water layer. The vertical structure of the spots was examined and is shown in Figure 3a. Because the heat conductivity of air at 0☌ (0.024 W m –2 K –1) is ~1/20 of the heat conductivity of water at 0☌ (0.561 W m –2 K –1), the ice grains on the white spots did not melt, whereas ice grains located elsewhere did. Some ice grains have clustered at intervals of several centimetres. Figure 2e shows the condition 3 hours after the photograph in Figure 2d was taken. These simple experiments revealed that the white spots were formed by air bubbles below the mixed ice– water layer. When the ice pellets were removed from the surface of the mixed ice–water layer near the spots, air was released from them ( Fig. When the spots were pushed, they moved easily. The centres of the white spots were raised ~1 mm above the snow. (e) After the disappearance of the white spots (11:32) at the same location shown in (a–d). (d) Air released from the white spots (09:36). (b) Horizontal distribution of white spotted wet snow (09:00) and (c) close-up photograph (09:35). (a) White spotted wet snow on a road (taken at 09:01). White spotted wet snow in Kitami (1 November 2009). This paper presents the characteristics of white spotted wet snow observed in Kitami and Oketo on 1 November 2009.įig. One of the authors (S.T.) has lived in Kitami for more than 30 years but had not seen this phenomenon previously. However, there have been no investigations of the formation process, meteorological conditions that lead to its formation, its vertical structure and the horizontal pattern of the white spots. All these reports describe observations of white spotted wet snow. The Daily News in Niigata (local community newspaper published in Niigata district in Japan) published a beautiful picture of white spotted wet snow on 28 February 2004, which was taken by Noriko Kawano on 25 February 2004 at Joetsu, Niigata. Reference Kominami and YokoyamaKominami and Yokoyama (2004) reported observations of ‘white spotted wet snow’ at Jyoetsu, Niigata Prefecture, on 7 March 2004. He presented a photograph of white spotted wet snow, as did Reference HayashiHayashi (1985). Reference NohguchiNohguchi (1984) wrote that ‘After snow deposition of 1 or 2 cm in thickness and rain, snow with air bubbles will appear’ (translated from Japanese). This phenomenon has been noted in Japan previously. Most of the white spotted wet snow was observed on an asphalt paved road, but it was also observed on concrete and tile pavements, which are almost impermeable to water. ![]() We refer to this phenomenon as ‘white spotted wet snow’. Many curious white spots of 1–10 cm diameter were found on wet snow (~10 mm thick) on the morning of 1 November 2009 in Kitami and Oketo in Hokkaido, Japan. ![]()
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