We derived two observation-based global monthly mean dust aerosol optical depth (DAOD) climatological datasets from 2007 to 2019 with a 2^∘ (latitude) × 5^∘ (longitude) spatial resolution, one based on Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) and the other on Moderate Resolution Imaging Spectroradiometer (MODIS) observations. In addition, the CALIOP climatological dataset also includes dust vertical extinction profiles. Dust is distinguished from non-dust aerosols based on particle shape information (e.g., lidar depolarization ratio) for CALIOP and on dust size and absorption information (e.g., fine-mode fraction, Ångström exponent, and single-scattering albedo) for MODIS, respectively. The two datasets compare reasonably well with the results reported in previous studies and the collocated Aerosol Robotic Network (AERONET) coarse-mode AOD. Based on these two datasets, we carried out a comprehensive comparative study of the spatial and temporal climatology of dust. On a multi-year average basis, the global (60^∘ S–60^∘ N) annual mean DAOD is 0.032 and 0.067 according to CALIOP and MODIS retrievals, respectively. In most dust-active regions, CALIOP DAOD generally correlates well (correlation coefficient R>0.6) with the MODIS DAOD, although the CALIOP value is significantly smaller. The CALIOP DAOD is 18 %, 34 %, 54 %, and 31 % smaller than MODIS DAOD over the Sahara, the tropical Atlantic Ocean, the Caribbean Sea, and the Arabian Sea, respectively. Applying a regional specific lidar ratio (LR) of 58 sr instead of the 44 sr used in the CALIOP operational retrieval reduces the difference from 18 % to 8 % over the Sahara and from 34 % to 12 % over the tropical Atlantic Ocean. However, over eastern Asia and the northwestern Pacific Ocean (NWP), the two datasets show weak correlation. Despite these discrepancies, CALIOP and MODIS show similar seasonal and interannual variations in regional DAOD. For dust aerosol over the NWP, both CALIOP and MODIS show a declining trend of DAOD at a rate of about 2 % yr⁻¹. This decreasing trend is consistent with the observed declining trend of DAOD in the southern Gobi Desert at a rate of 3 % yr⁻¹ and 5 % yr⁻¹ according to CALIOP and MODIS, respectively. The decreasing trend of DAOD in the southern Gobi Desert is in turn found to be significantly correlated with increasing vegetation and decreasing surface wind speed in the area.

中文翻译：

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从年代际尺度上 CALIOP 和 MODIS 气溶胶反演得出的全球尘埃光学深度气候学：区域和年际变率

我们导出了 2007 年至 2019 年两个基于观测的全球月平均尘埃气溶胶光学深度 (DAOD) 气候数据集，其中 2 ^∘ （纬度）  ×  5 ^∘（经度）空间分辨率，一种基于正交偏振云气溶胶激光雷达 (CALIOP)，另一种基于中分辨率成像光谱仪 (MODIS) 观测。此外，CALIOP 气候数据集还包括尘埃垂直消光剖面。根据 CALIOP 的颗粒形状信息（例如，激光雷达去极化率）和 MODIS 的灰尘大小和吸收信息（例如，精细模式分数、Ångström 指数和单散射反照率），分别将灰尘与非灰尘气溶胶区分开来. 这两个数据集与先前研究报告的结果和并置的气溶胶机器人网络 (AERONET) 粗模式 AOD 的结果相当。基于这两个数据集，我们对灰尘的时空气候学进行了全面的比较研究。^∘  S–60 ^∘  N) 根据 CALIOP 和 MODIS 反演，年平均 DAOD 分别为 0.032 和 0.067。在大多数尘活动区，CALIOP DAOD 通常具有良好的相关性（相关系数R >0.6) 与 MODIS DAOD，尽管 CALIOP 值要小得多。CALIOP DAOD 在撒哈拉、热带大西洋、加勒比海和阿拉伯海分别比 MODIS DAOD 小 18%、34%、54% 和 31%。应用 58 sr 的区域特定激光雷达比率 (LR) 而不是 CALIOP 业务检索中使用的 44 sr，可以将撒哈拉沙漠上的差异从 18% 减少到 8%，将热带大西洋上的差异从 34% 减少到 12%。然而，在东亚和西北太平洋 (NWP)，这两个数据集显示出弱相关性。尽管存在这些差异，但 CALIOP 和 MODIS 在区域 DAOD 中表现出类似的季节和年际变化。对于 NWP 上的沙尘气溶胶，CALIOP 和 MODIS 都显示出 DAOD 的下降趋势，其下降速度约为 2 % yr ^-1. 这种下降趋势与根据 CALIOP 和 MODIS 分别以3 % yr ^-1和 5 % yr ^-1的速率在南部戈壁沙漠观察到的 DAOD 下降趋势一致。反过来发现，戈壁沙漠南部DAOD的下降趋势与该地区植被增加和地表风速降低显着相关。