This study investigates changes in urban heat island (UHI) intensity with background temperature and humidity and their associations with physical processes. For this, we conducted idealized ensemble simulations with different initial potential temperature and water vapor mixing ratio profiles using the Weather Research and Forecasting (WRF) model. The daytime and nighttime UHI intensities increase with increasing background temperature at rates of 0.03 °C °C−1 and 0.20 °C °C−1, respectively. The daytime and nighttime UHI intensities decrease with increasing background humidity at rates of −0.01 °C (g kg−1)−1 and −0.28 °C (g kg−1)−1, respectively. The increase in background temperature increases the radiative cooling of rural air, enhancing the evening rural 2-m temperature decline. This also decreases the radiative heating of urban air and increases urban advective cooling, but decreases urban turbulent mixing. Consequently, the evening urban 2-m temperature decline is less enhanced, increasing the nighttime UHI intensity. The increase in background humidity decreases the radiative cooling of rural air, weakening the evening rural 2-m temperature decline. This also increases the radiative heating of urban air and decreases urban advective cooling, but increases urban turbulent mixing. Consequently, the evening urban 2-m temperature decline is less weakened, decreasing the nighttime UHI intensity.

中文翻译：

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城市热岛强度随背景温度和湿度的变化及其与近地表热力学过程的关联


本研究调查了城市热岛 （UHI） 强度随背景温度和湿度的变化及其与物理过程的关系。为此，我们使用天气研究和预报 （WRF） 模型进行了具有不同初始潜在温度和水蒸气混合比剖面的理想化集成模拟。白天和夜间 UHI 强度随着背景温度的增加而增加，速率分别为 0.03 °C °C-1 和 0.20 °C °C-1。白天和夜间 UHI 强度随着背景湿度的增加而降低，速率分别为 -0.01 °C （g kg-1）-1 和 -0.28 °C （g kg-1）-1。背景温度的升高增加了农村空气的辐射冷却，加剧了农村夜间 2 m 温度的下降。这也减少了城市空气的辐射加热，增加了城市平流冷却，但减少了城市湍流混合。因此，傍晚城市 2 m 温度下降的增强程度较低，增加了夜间 UHI 强度。背景湿度的增加减少了农村空气的辐射冷却，减弱了夜间农村 2 m 温度的下降。这也增加了城市空气的辐射加热，降低了城市平流冷却，但增加了城市湍流混合。因此，夜间城市 2 m 温度下降的减弱程度较低，从而降低了夜间 UHI 强度。