1:45 PM - 3:15 PM
[O11-P45] Conditions for the occurrence and observation of floating island and the scientific principles Ⅱ
Keywords: lower mirage, Reproduction experiment, Tide level
[Background and Purpose] While studying "Shiranui", which is considered a type of mirage, we learned that floating islands are also mirages. Therefore, we began research to clarify the conditions for the occurrence and observation of the floating island. From the previous year's research, we know that the conditions to observe floating islands are: ①early morning on a clear day in December to January, when the temperature difference between the air and sea water is large. ②the height of the observation point is low on the beach at high tide. ③the appropriate distance to the observation target, which is about 10 km. Therefore, the following three objectives will be pursued this time. 1. To observe well-floated floating islands and confirm the conditions. 2. To identify the best time of year to observe mirages by clarifying the time of year when visibility is good. 3. To investigate the location of the temperature layer required for light refraction.
[A: Field Observation] We made 14 observations of floating island in Shiranui Sea this winter. Through observations, we observed the phenomenon in which the degree of floating differed greatly, despite the same observation conditions known from previous studies. Therefore, we focused on the condition of the sea at the time of the observation, and found that there was a large tide level difference. So, we revealed the tide level has a significant effect on the observation of the phenomenon, and that the higher the tide level, the more floating islands can be observed. Therefore, we concluded that the best time to observe the phenomenon in Shiranui Sea is “two to three days before full or new moon days”, when the tide level is highest in the early morning.
[B: Effect of visibility] Since there were days when visibility was good and days when visibility was bad during field observations, we conducted research with the objective of finding the best time to observe mirages by clarifying when visibility was good. The photographs were taken at a fixed point at 8:00 a.m. every day at three different distances to the north from Udo High School (Figure 1). In addition, data on atmospheric particulate matter, which is thought to be affected by visibility, was collected to determine its effect on visibility. As a result, it was found that the best time to observe the phenomenon with good visibility is from summer to fall.
[C: Position of the temperature layer required for refraction of light] A study was conducted to determine the position at which light is refracted in an experiment to reproduce a floating island. The experiment was conducted with 8 heaters lined up, with one heater shifted one at a time and another heater shifted at all but one of the heaters. The height of the observation point was 0 mm and 5 mm. As a result, it was found that (1) the temperature difference near the target was important, and (2) the location where light is refracted moved closer to the target when the height of the observation point was increased. We also applied these results to our own simulations and found the same thing.
[Summary] From the field observations, it was found that it is necessary to take into account tidal changes in the Shiranui Sea, where tidal changes are large. From visibility observations, it was found that the best time to observe floating islands is from summer to autumn, when visibility is good. From the simulation and the replication experiment, the location of the temperature layer necessary for the refraction of light was found out.
[A: Field Observation] We made 14 observations of floating island in Shiranui Sea this winter. Through observations, we observed the phenomenon in which the degree of floating differed greatly, despite the same observation conditions known from previous studies. Therefore, we focused on the condition of the sea at the time of the observation, and found that there was a large tide level difference. So, we revealed the tide level has a significant effect on the observation of the phenomenon, and that the higher the tide level, the more floating islands can be observed. Therefore, we concluded that the best time to observe the phenomenon in Shiranui Sea is “two to three days before full or new moon days”, when the tide level is highest in the early morning.
[B: Effect of visibility] Since there were days when visibility was good and days when visibility was bad during field observations, we conducted research with the objective of finding the best time to observe mirages by clarifying when visibility was good. The photographs were taken at a fixed point at 8:00 a.m. every day at three different distances to the north from Udo High School (Figure 1). In addition, data on atmospheric particulate matter, which is thought to be affected by visibility, was collected to determine its effect on visibility. As a result, it was found that the best time to observe the phenomenon with good visibility is from summer to fall.
[C: Position of the temperature layer required for refraction of light] A study was conducted to determine the position at which light is refracted in an experiment to reproduce a floating island. The experiment was conducted with 8 heaters lined up, with one heater shifted one at a time and another heater shifted at all but one of the heaters. The height of the observation point was 0 mm and 5 mm. As a result, it was found that (1) the temperature difference near the target was important, and (2) the location where light is refracted moved closer to the target when the height of the observation point was increased. We also applied these results to our own simulations and found the same thing.
[Summary] From the field observations, it was found that it is necessary to take into account tidal changes in the Shiranui Sea, where tidal changes are large. From visibility observations, it was found that the best time to observe floating islands is from summer to autumn, when visibility is good. From the simulation and the replication experiment, the location of the temperature layer necessary for the refraction of light was found out.