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Sheung Shui Automatic Weather Station |
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Sheung Shui Automatic Weather Station |
Radiation cooling in Sheung Shui
By Liu Kin Sik
| Objectives
To study the radiation cooling effect in Sheung Shui. The importance of wind speed to this effect is also examined. Data Weather data from automatic weather stations in Kowloon Tong (located at CityU) and Sheung Shui (located at my house). Methodology The temperature difference between Kowloon Tong (urban area) and Sheung Shui (rural area) is used as a measure of the radiation cooling effect in Sheung Shui. The temperature differences at two nights with different wind conditions are compared. |
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Date: 03 -04 Nov 2002
The temperatures in both Sheung Shui and Kowloon Tong decreased gradually after 19:00. At the same time, the wind speed in Sheung Shui decreased. The temperature difference increased to 1.5C at around 21:30. However, this difference decreased as the wind in Sheung Shui strengthened. After midnight, the radiation cooling effect became more significant and a maximum temperature difference of 2C was recorded between 04:00 - 05:00.
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Time series of air temperature in Kowloon Tong and Sheung Shui |
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Time series of 1-minute maximum gust in Sheung Shui |
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Date: 04 -05 Nov 2002
Compare with the previous day, the wind speed in Sheung Shui was much lower. Calm condition prevailed throughout the night. The temperature in Sheung Shui dropped rapidly from 18C at 19:00 to 13C at 01:00. In contrast, a little change of temperature was observed in Kowloon Tong during this period. As a result, a maximum temperature difference of 7C was recorded at around 01:00. The radiation cooling effect was much more significant at that night.
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Time series of air temperature in Kowloon Tong and Sheung Shui |
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Time series of 1-minute maximum gust in Sheung Shui |
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Summary
The above example shows that wind speed is an important factor in determining the degree of radiation cooling effect in rural area. Under calm condition and other favourable conditions (e.g. clear sky), the temperature in rural area (e.g. Sheung Shui) can be significantly lower than that in urban area.