Journal of the Japanese Society of Snow and Ice

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In recent years, the occurrence mechanism of a superior mirage, caused by light refraction between a cold air layer and a warm air layer, has been studied in various parts of Japan. Our research was focused on winter superior mirages in Shari, facing the Sea of Okhotsk, in eastern Hokkaido. We examined the theory that cold air formed on land through radiative cooling flows into the sea and generates a mirage. We aimed to establish method to investigate the temperature structure over the land at the time of occurrence of a superior mirage. We measured the temperature difference by installing a weather meter at the same spot of height. We also attempted to obtain an image using fixed point cameras, which we first operated at low temperatures at night, and vertical temperature distributions, at low temperatures, using a drone. Results showed that, in Shari, during the occurrence of a mirage, cold air from radiation cooling forms a ground inversion layer upto a height of 60m or higher. In addition, we found that they occurs all day long regardless of time zone. We propose that our observation methods will be of significant help to future studies.

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We observed in-situ the penetration of ice by a brass wire with a diameter of 0.25mm. Both vapor bubbles and water droplets were observed in ice after wire cutting at pressures between 0.1MPa and 0.6MPa. Analyzed wire velocities were roughly constant at pressures higher than 0.4MPa. However, this was not the case at pressures lower than 0.3MPa. Furthermore, we analyzed the relationship between wire velocities and the ratio of vapor contact to the length of wire. Under 0.2 MPa, the wire velocities increased with decreasing ratio of vapor contact to the length of wire. Therefore, we concluded that wire velocities were inhibited by the formation of vapor bubbles.

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