The roles of aerosol, water vapor and cloud in future global dimming/brightening
The roles of aerosol, water vapor and cloud in future global dimming/brightening
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DOI：
10.1029/2011jd016000
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发表时间：
2011-10-22
影响因子：
4.4
通讯作者：
Shine, Keith P.
中科院分区：
文献类型：
--
作者：
Haywood, Jim M.;Bellouin, Nicolas;Shine, Keith P.
观测证据表明，在全天空和无云条件下，地表太阳辐射存在明显的区域趋势。下降流太阳表面辐照度（SSI）的负趋势被称为“变暗”，而正趋势被称为“变亮”。我们使用气象局哈德利中心HadGEM 2气候模型来模拟从工业化前到现在的无云和总SSI趋势，并将其与观测结果进行比较。由CMIP 5排放驱动的模拟用于模拟到2100年的调光/增亮的未来趋势。模拟的趋势是合理的一致性与观察到的区域趋势变暗和变亮，这是由于人为气溶胶的浓度变化，并可能，由于气溶胶间接效应和/或云反馈机制的云量变化。未来无云SSI的变暗/变亮不仅是由人为气溶胶的变化引起的：气溶胶的影响被水蒸气增加引起的大幅变暗所淹没。在这里使用的气候模式中，随着云量的减少，总的SSI几乎没有趋势，并且补偿了水汽变化的影响。在表面能量平衡方面，SSI的这些趋势明显超过了由增加的水蒸气浓度引起的下降流陆地辐照度的增加所补偿的。然而，该研究表明，虽然水蒸气被广泛认为是一种温室气体，但水蒸气对太阳辐射的大气传输和全球变暗/变亮的未来的影响不应被忽视。
Observational evidence indicates significant regional trends in solar radiation at the surface in both all-sky and cloud-free conditions. Negative trends in the downwelling solar surface irradiance (SSI) have become known as 'dimming' while positive trends have become known as 'brightening'. We use the Met Office Hadley Centre HadGEM2 climate model to model trends in cloud-free and total SSI from the pre-industrial to the present-day and compare these against observations. Simulations driven by CMIP5 emissions are used to model the future trends in dimming/brightening up to the year 2100. The modeled trends are reasonably consistent with observed regional trends in dimming and brightening which are due to changes in concentrations in anthropogenic aerosols and, potentially, changes in cloud cover owing to the aerosol indirect effects and/or cloud feedback mechanisms. The future dimming/brightening in cloud-free SSI is not only caused by changes in anthropogenic aerosols: aerosol impacts are overwhelmed by a large dimming caused by increases in water vapor. There is little trend in the total SSI as cloud cover decreases in the climate model used here, and compensates the effect of the change in water vapor. In terms of the surface energy balance, these trends in SSI are obviously more than compensated by the increase in the downwelling terrestrial irradiance from increased water vapor concentrations. However, the study shows that while water vapor is widely appreciated as a greenhouse gas, water vapor impacts on the atmospheric transmission of solar radiation and the future of global dimming/brightening should not be overlooked.