Humidity trends imply increased sensitivity to clouds in a warming Arctic
Humidity trends imply increased sensitivity to clouds in a warming Arctic
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湿度趋势意味着北极变暖对云的敏感性增加
作者：
C. Cox;V. Walden;P. Rowe;M. Shupe
红外辐射过程与北极变暖和海冰减少有关。地面的红外云辐射效应（CRE）受云的特性调节;然而，CRE也取决于湿度，因为云发射的波长对温室气体是半透明的，最明显的是水蒸气。在这里，我们展示了温度和湿度如何通过中红外和远红外之间的竞争影响来控制CRE。在恒定的相对湿度下，CRE并不像预期的那样随着温度/绝对湿度的增加而减少，而是被发现对于北极的温度特征是近似恒定的。如果相对湿度变化，这种稳定性就会被破坏。我们的研究结果解释了观测到的北极CRE的10 W m − 2量级的季节性和区域性变化。在北极云的物理特性保持不变的情况下，我们计算出最近秋季和冬季的CRE增加了1 - 5 W m − 2，预计到2050年将达到5 - 1-5 W m − 2，这意味着地表对云的敏感性增加。北极的云辐射效应（CRE）在到达地表的红外辐射量中起着重要作用。在这里，作者表明，温度和湿度之间的相互作用通过两个半透明波长范围内的竞争影响来控制CRE。
Infrared radiative processes are implicated in Arctic warming and sea-ice decline. The infrared cloud radiative effect (CRE) at the surface is modulated by cloud properties; however, CRE also depends on humidity because clouds emit at wavelengths that are semi-transparent to greenhouse gases, most notably water vapour. Here we show how temperature and humidity control CRE through competing influences between the mid- and far-infrared. At constant relative humidity, CRE does not decrease with increasing temperature/absolute humidity as expected, but rather is found to be approximately constant for temperatures characteristic of the Arctic. This stability is disrupted if relative humidity varies. Our findings explain observed seasonal and regional variability in Arctic CRE of order 10 W m−2. With the physical properties of Arctic clouds held constant, we calculate recent increases in CRE of 1–5 W m−2 in autumn and winter, which are projected to reach 5–15 W m−2 by 2050, implying increased sensitivity of the surface to clouds. The cloud radiative effect (CRE) in the Arctic plays an important role in the amount of infrared radiation that reaches the surface. Here, the authors show that interplay between temperature and humidity controls CRE through competing influences in two semi-transparent wavelength ranges.