A Comparison Study of Global Dust Climatology derived from CALIOP and MODIS Aerosol retrievals

Abstract:

In this study, we derive and compare two decadal (2007-2016) and global dust climatology datasets derived from the satellite observations. Both datasets contain the horizontal distribution of dust optical depth (DAOD) on a global scale. One is based mainly on CALIOP observations that distinguish dust from other types of aerosols using lidar depolarization signal caused by the irregular non-spherical shape of dust. The other is based on MODIS observations that detect dust aerosols using their relatively large size in comparison with other types of aerosols. The comparison reveals that MODIS DAOD is generally larger than CALIOP DAOD. The CALIOP-based DAOD is in good correlation with MODIS-based DAOD over the Sahara Desert and Atlantic Ocean although on average, CALIOP DAOD is 26%~30% smaller. However, the correlation is poor for Asian dust and dust over Northwest Pacific Ocean (NWP). Despite the discrepancy in the magnitude of DAOD derived from two sensors, both sensors show very similar annual variability in DAOD. For dust aerosol over NWP, both MODIS and CALIOP show a declining trend with a decreasing rate of -1.5% yr^-1 based on MODIS retrieval and -2% yr^-1 based on CALIOP retrieval. This annual decreasing trend was likely attributed to a decreasing trend of -2.6% in spring (MAM) from MODIS retrieval and -2.8% in spring (MAM) from CALIOP retrieval but negligible trends in the other seasons. Furthermore, we found the decreasing trend of dust over NWP is potentially due to the decline of dust aerosol generated from Gobi Desert with an annual decreasing rate of -2.3% based on CALIOP and -3.5% based on MODIS. Moreover, DAOD trend will be analyzed in other dust sources and dust outflow regions.