Trends in aerosol radiative effects over Europe inferred from observed cloud cover, solar "dimming" and solar "brightening"
Trends in aerosol radiative effects over Europe inferred from observed cloud cover, solar "dimming" and solar "brightening"
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DOI：
10.1029/2006jd007794
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发表时间：
2007-04-26
影响因子：
4.4
通讯作者：
Wild, Martin
中科院分区：
文献类型：
--
作者：
Norris, Joel R.;Wild, Martin
[ 1]我们使用来自全球能量平衡档案（GEBA）、天气云报告和国际卫星云气候学项目（ISCCP）的月度网格数据，研究了1965 - 2004年欧洲地面向下短波（SW）辐射通量、总云量、SW云效应和相关参数的数十年变化。一个关键问题是区分自然云变率的影响，从长期的人为气溶胶对地面SW通量的影响。相应地，我们引入了云量辐射效应（CCRE）的概念，定义为由云量变化产生的向下SW通量的变化。泛欧时间序列的CCRE异常和GEBA太阳辐射异常之间的相关性为0.88，表明云量变化和相关的云量变化确实主导了月到十年时间尺度上的西南辐射变化。在通过线性回归从GEBA太阳辐射异常中减去CCRE异常来消除这些与天气相关的云效应之后，在剩余的时间序列中保持了明显的减少趋势，然后是明显的增加趋势。根据趋势计算方法，1971 - 1986年期间，泛欧剩余通量每十年下降2.7 - 3.5 W m（-2），具有统计学意义，1987 - 2002年期间，每十年上升2.0 - 2.3 W m（-2），具有统计学意义。事实上，独立的网格框显示大多数在早期的负趋势和大多数在后期的正趋势表明，这些长期变化的SW通量是真实的和广泛的欧洲。云量的变化不能解释地面西南通量的趋势，因为云量在1971 - 1986年期间实际上略有减少，在1987 - 2002年期间略有增加。最有可能的解释是人为气溶胶排放的变化，导致在太阳“变暗”的早期更多的散射和吸收的SW辐射和较少的散射和吸收在太阳“变亮”的后期。''
[ 1] We examine multidecadal changes in surface downward shortwave ( SW) radiation flux, total cloud cover, SW cloud effect, and related parameters over Europe during 1965 2004 using monthly gridded data from the Global Energy Balance Archive (GEBA), synoptic cloud reports, and the International Satellite Cloud Climatology Project (ISCCP). One key issue is distinguishing the effects of natural cloud variability from long-term anthropogenic aerosol influences on surface SW flux. Accordingly, we introduce the concept of cloud cover radiative effect (CCRE), defined as the change in downward SW flux produced by a change in cloud cover. The correlation between pan-European time series of CCRE anomalies and GEBA solar radiation anomalies is 0.88, indicating that cloud cover variability and associated changes in cloud albedo dominate SW radiation variability on monthly to decadal timescales. After these weather-related cloud effects are removed by subtracting CCRE anomalies from GEBA solar radiation anomalies via linear regression, a distinct decreasing trend followed by a distinct increasing trend remain in the residual time series. Depending on the method of trend calculation, pan-European residual flux declined by a statistically significant 2.7 - 3.5 W m(-2) per decade during 1971 - 1986 and rose by a statistically significant 2.0 - 2.3 W m(-2) per decade during 1987 - 2002. The fact that independent grid boxes exhibit mostly negative trends in the earlier period and mostly positive trends in the later period demonstrates that these long-term variations in SW flux are real and widespread over Europe. Changes in cloud cover cannot account for the trends in surface SW flux since cloud cover actually slightly decreased during 1971 - 1986 and slightly increased during 1987 - 2002. The most likely explanation is changes in anthropogenic aerosol emissions that led to more scattering and absorption of SW radiation during the earlier period of solar "dimming'' and less scattering and absorption during the later period of solar "brightening.''