Publications

Zheng, JY; Zhang, ZB; Yu, HB; Garnier, A; Song, QQ; Wang, CX; Di Biagio, C; Kok, JF; Derimian, Y; Ryder, C (2023). Thermal infrared dust optical depth and coarse-mode effective diameter over oceans retrieved from collocated MODIS and CALIOP observations. ATMOSPHERIC CHEMISTRY AND PHYSICS, 23(14), 8271-8304.

Abstract
In this study, we developed a novel algorithm based on the collocated Moderate Resolution Imaging Spectroradiometer (MODIS) thermal infrared (TIR) observations and dust vertical profiles from the CloudAerosol Lidar with Orthogonal Polarization (CALIOP) to simultaneously retrieve dust aerosol optical depth at 10 mu m (DAOD(10 mu m)) and the coarse-mode dust effective diameter (D-eff) over global oceans. The accuracy of the D-eff retrieval is assessed by comparing the dust lognormal volume particle size distribution (PSD) corresponding to retrieved Deff with the in situ-measured dust PSDs from the AERosol Properties - Dust (AER-D), Saharan Mineral Dust Experiment (SAMUM-2), and Saharan Aerosol Long-Range Transport and Aerosol-CloudInteraction Experiment (SALTRACE) field campaigns through case studies. The new DAOD(10 mu m) retrievals were evaluated first through comparisons with the collocated DAOD(10.6 mu m) retrieved from the combined Imaging Infrared Radiometer (IIR) and CALIOP observations from our previous study (Zheng et al., 2022). The pixel-topixel comparison of the two DAOD retrievals indicates a good agreement (R similar to 0.7) and a significant reduction in (similar to 50 %) retrieval uncertainties largely thanks to the better constraint on dust size. In a climatological comparison, the seasonal and regional (2 degrees x 5 degrees) mean DAOD(10 mu m) retrievals based on our combined MODIS and CALIOP method are in good agreement with the two independent Infrared Atmospheric Sounding Interferometer (IASI) products over three dust transport regions (i.e., North Atlantic (NA; R = 0.9), Indian Ocean (IO; R = 0.8) and North Pacific (NP; R = 0 .7)). Using the new retrievals from 2013 to 2017, we performed a climatological analysis of coarse-mode dust D-eff over global oceans. We found that dust D-eff over IO and NP is up to 20% smaller than that over NA. Over NA in summer, we found a similar to 50% reduction in the number of retrievals with D-eff > 5 mu m from 15 to 35 degrees W and a stable trend of D-eff average at 4.4 mu m from 35 degrees Wthroughout the Caribbean Sea (90 degrees W). Over NP in spring, only similar to 5% of retrieved pixels with D-eff > 5 mu m are found from 150 to 180ffi E, while the mean Deff remains stable at 4.0 mu m throughout eastern NP. To the best of our knowledge, this study is the first to retrieve both DAOD and coarse-mode dust particle size over global oceans for multiple years. This retrieval dataset provides insightful information for evaluating dust longwave radiative effects and coarse-mode dust particle size in models.

DOI:
10.5194/acp-23-8271-2023

ISSN:
1680-7324