1:45 PM - 3:15 PM
[O11-P74] Simplification of Westerly Wave Model Experiment - Utilization of Thermography -
Keywords:Westerly Wave, Rotating Annulus Experiment, Thermography
1 Background and Purpose of the Study
Westerly wave has a significant impact on middle latitude weather and its characteristics have been actively studied. As the temperature difference between north and south becomes large, Westerly wave meander greatly. When Westerly wave meander further, a cold low pressure system moves southward and a warm high pressure system moves northward, and they are separated from Westerly wave. This is called a blocking phenomenon, in which a low pressure system or a high pressure stagnates for a long period of time, causing abnormal weather (Miyazawa 1991, Maruyama 1995).
A rotating annulus experiment is a model experiment of Westerly wave. In this experiment, hot water is placed in a, water in b, and ice water in c of a triple structure as shown in Figure 1, and the tank is rotated. In this case, the surface of the water in b waves in the same way as the principle of Westerly wave. Therefore, Westerly wave can be analyzed by observing the surface of the water in b (Ogura 1984).
Generally, aluminum powder is used to observe the surface of the water in b. However, aluminum powder is hazardous to the human body and can explode, making it difficult to handle. In this study, we show that a simpler experiment can be performed by using a thermography camera.
2 Experimental Method
In this study, the northern hemisphere as seen from above the North Pole was reproduced in a water tank as shown in Figure 2. First, hot water, water, and ice water were placed in a, b, and c, respectively, as shown in Figure 1. a, b, and c represent the equator, middle atitude, and the North Pole, respectively. The tank was rotated counterclockwise for an hour. c was kept at 5°C, and the temperature difference between a and c was set to (i) 25°C, (ii) 35°C, (iii) 45°C, and (iv) 55°C, respectively. When the temperature difference between a and c changed, hot water or ice was added to maintain the temperatures set as the conditions. To standardize the other conditions, (i), (ii), (iii), and (iv) were all set to a water depth of 40 mm, a rotation speed of 5 rpm, and a channel width of 115 mm.
3 Results
The results are shown in Figure 3. Waves were not recorded for several minutes after the start of rotation because they were not stable. Waves with a wave number of 4 at the time of (ⅲ) and (ⅳ) continued until the end of recording. Therefore, the record is considered to be shorter than the actual wave duration.
4 Discussion
In cases (ⅲ) and (ⅳ), the wave number 4 was stabilized considerably, whereas this was not observed in cases (ⅰ) and (ⅱ). This suggests that increasing the temperature difference makes waves more stable, or that the time from the start of rotation to its stabilization becomes shorter.
When the temperature difference is large, the wave number is found to be stable at 4 for a long time. Since it is known that the wave number varies depending on the temperature difference, rotation speed, water depth, and scale of the device, we do not consider the reason why the wave number 4 is stable in this study.
Before wave number 4 stabilized, wave number 5 was often formed. Therefore, it is not that the wave number 4 was changing from no wave number, but rather that a part of wave number 5 was changing to wave number 4. The stabilization of wave number 4 follows the stabilization of wave number 5.
5 Conclusions and issues
A thermography camera can be used to model experiments of westerly wave. It can be seen that wave number 4 is stable when the temperature difference between the center and the outermost layer of the tank is large. Furthermore, The stabilization of wave number 4 follows the stabilization of wave number 5.
The speed and direction of the waves cannot be observed with this experimental method. This is a disadvantage related to aluminum powder. Aluminum powder and thermography each have their own advantages and disadvantages. Therefore, the choice of which method to use should depend on the purpose of the study.
Westerly wave has a significant impact on middle latitude weather and its characteristics have been actively studied. As the temperature difference between north and south becomes large, Westerly wave meander greatly. When Westerly wave meander further, a cold low pressure system moves southward and a warm high pressure system moves northward, and they are separated from Westerly wave. This is called a blocking phenomenon, in which a low pressure system or a high pressure stagnates for a long period of time, causing abnormal weather (Miyazawa 1991, Maruyama 1995).
A rotating annulus experiment is a model experiment of Westerly wave. In this experiment, hot water is placed in a, water in b, and ice water in c of a triple structure as shown in Figure 1, and the tank is rotated. In this case, the surface of the water in b waves in the same way as the principle of Westerly wave. Therefore, Westerly wave can be analyzed by observing the surface of the water in b (Ogura 1984).
Generally, aluminum powder is used to observe the surface of the water in b. However, aluminum powder is hazardous to the human body and can explode, making it difficult to handle. In this study, we show that a simpler experiment can be performed by using a thermography camera.
2 Experimental Method
In this study, the northern hemisphere as seen from above the North Pole was reproduced in a water tank as shown in Figure 2. First, hot water, water, and ice water were placed in a, b, and c, respectively, as shown in Figure 1. a, b, and c represent the equator, middle atitude, and the North Pole, respectively. The tank was rotated counterclockwise for an hour. c was kept at 5°C, and the temperature difference between a and c was set to (i) 25°C, (ii) 35°C, (iii) 45°C, and (iv) 55°C, respectively. When the temperature difference between a and c changed, hot water or ice was added to maintain the temperatures set as the conditions. To standardize the other conditions, (i), (ii), (iii), and (iv) were all set to a water depth of 40 mm, a rotation speed of 5 rpm, and a channel width of 115 mm.
3 Results
The results are shown in Figure 3. Waves were not recorded for several minutes after the start of rotation because they were not stable. Waves with a wave number of 4 at the time of (ⅲ) and (ⅳ) continued until the end of recording. Therefore, the record is considered to be shorter than the actual wave duration.
4 Discussion
In cases (ⅲ) and (ⅳ), the wave number 4 was stabilized considerably, whereas this was not observed in cases (ⅰ) and (ⅱ). This suggests that increasing the temperature difference makes waves more stable, or that the time from the start of rotation to its stabilization becomes shorter.
When the temperature difference is large, the wave number is found to be stable at 4 for a long time. Since it is known that the wave number varies depending on the temperature difference, rotation speed, water depth, and scale of the device, we do not consider the reason why the wave number 4 is stable in this study.
Before wave number 4 stabilized, wave number 5 was often formed. Therefore, it is not that the wave number 4 was changing from no wave number, but rather that a part of wave number 5 was changing to wave number 4. The stabilization of wave number 4 follows the stabilization of wave number 5.
5 Conclusions and issues
A thermography camera can be used to model experiments of westerly wave. It can be seen that wave number 4 is stable when the temperature difference between the center and the outermost layer of the tank is large. Furthermore, The stabilization of wave number 4 follows the stabilization of wave number 5.
The speed and direction of the waves cannot be observed with this experimental method. This is a disadvantage related to aluminum powder. Aluminum powder and thermography each have their own advantages and disadvantages. Therefore, the choice of which method to use should depend on the purpose of the study.