Total surface shortwave flux distributions 1901-2017 in support of carbon cycle modelling: No stratospheric aerosols

This dataset offers 6-hourly distributions of the total downward shortwave flux over the period 1901-2017. Radiative transfer calculations are based on monthly-averaged distributions of tropospheric aerosol optical depth, and 6-hourly distributions of cloud fraction. Methods follow those described in the Methods section of Mercado et al. (doi:10.1038/nature07949, 2009), but with updated input datasets. This version of the dataset excludes the radiative effects of stratospheric aerosols.<br><br>The time series of speciated tropospheric aerosol optical depth is taken from the historical and RCP8.5 simulations by the HadGEM2-ES climate model (Bellouin et al., doi:10.1029/2011JD016074, 2011). To correct for biases in HadGEM2-ES, tropospheric aerosol optical depths are scaled over the whole period to match the global and monthly averages obtained over the period 2003-2017 by the CAMS Reanalysis of atmospheric composition (Inness et al., doi:10.5194/acp-19-3515-2019, 2019), which assimilates satellite retrievals of aerosol optical depth.<br><br>The time series of cloud fraction is obtained by scaling the 6-hourly distributions simulated in the Japanese Reanalysis (JRA; Kobayashi et al., doi:10.2151/jmsj.2015-001, 2015) to match the monthly-averaged cloud cover in the CRU TS v4.03 dataset (Harris et al. doi:10.1038/s41597-020-0453-3, 2020).<br><br>Surface radiative fluxes account for aerosol-radiation interactions from both tropospheric and stratospheric aerosols, and for aerosol-cloud interactions from tropospheric aerosols, except mineral dust. Tropospheric aerosols are also assumed to exert interactions with cloud. The radiative effects of those aerosol-cloud interactions are assumed to scale with the radiative effects of aerosol-radiation interactions of tropospheric aerosols, using regional scaling factors derived from HadGEM2-ES.<br><br>Atmospheric constituent other than aerosols and clouds are set to a constant standard mid-latitude summer atmosphere.

本数据集提供了1901年至2017年期间逐6小时的总向下短波通量分布。辐射传输（radiative transfer）计算基于对流层气溶胶光学厚度（tropospheric aerosol optical depth）的月平均分布，以及云量（cloud fraction）的逐6小时分布。本研究的方法参照Mercado等人2009年发表于《自然》（doi:10.1038/nature07949, 2009）的方法章节，但使用了更新后的输入数据集。本版本数据集未包含平流层气溶胶（stratospheric aerosols）的辐射效应。

分类型对流层气溶胶光学厚度的时间序列来自HadGEM2-ES气候模型（HadGEM2-ES climate model，Bellouin等人，doi:10.1029/2011JD016074, 2011）的历史情景与RCP8.5情景模拟结果。为校正HadGEM2-ES的模拟偏差，研究人员对整个研究时段的对流层气溶胶光学厚度进行缩放，使其与2003年至2017年期间通过大气成分CAMS再分析（CAMS Reanalysis of atmospheric composition，Inness等人，doi:10.5194/acp-19-3515-2019, 2019）得到的全球及月平均结果一致；该再分析数据同化了气溶胶光学厚度的卫星反演结果。

云量的时间序列则通过对日本再分析资料（Japanese Reanalysis, JRA，Kobayashi等人，doi:10.2151/jmsj.2015-001, 2015）的逐6小时模拟分布进行缩放得到，以匹配CRU TS v4.03数据集（CRU TS v4.03 dataset，Harris等人，doi:10.1038/s41597-020-0453-3, 2020）中的月平均云量。

地表辐射通量考虑了对流层与平流层气溶胶的气溶胶-辐射相互作用，以及对流层气溶胶（矿物粉尘除外）的气溶胶-云相互作用。研究同时假设对流层气溶胶可与云发生相互作用，且这类气溶胶-云相互作用的辐射效应按区域缩放因子与对流层气溶胶的气溶胶-辐射相互作用的辐射效应成正比，该缩放因子由HadGEM2-ES模型推导得到。

除气溶胶与云之外的大气成分，均设置为恒定的标准中纬度夏季大气状态。