资源环境科技发展态势分析平台

Abstract. In situ cloud probe data from the NASA ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) field campaign were used to estimate effective radius (R_e), cloud optical thickness (τ), and cloud droplet concentration (N_c) for marine stratocumulus over the southeast Atlantic Ocean. The in situ R_e, τ, and N_c were compared with co-located Moderate Resolution Imaging Spectroradiometer (MODIS) retrievals of R_e and τ, and MODIS derived N_c. For 145 cloud profiles, a MODIS retrieval was co-located with in situ data with a time gap of less than 1 hour. On average, the MODIS R_e and τ (11.3 μm and 11.7) were 1.6 μm and 2.3 higher than the in situ R_e and τ with Pearson’s correlation coefficient (R) of 0.77 and 0.73, respectively. The average MODIS N_c (151.5 cm^-3) was within 1 cm^-3 of the average in situ N_c with R of 0.90.

The 145 cloud profiles were classified into 67 contact profiles where aerosol concentration (N_a) greater than 500 cm^-3 was sampled within 100 m above cloud tops and 78 separated profiles where N_a less than 500 cm^-3 was sampled up to 100 m above cloud tops. Contact profiles had higher in situ N_c (by 88 cm^-3), higher τ (by 2.5) and lower in situ R_e (by 2.2 μm) compared to separated profiles. These differences were associated with aerosol-cloud interactions (ACI) and MODIS estimates of the differences were within 5 cm^-3, 0.5, and 0.2 μm of the in situ estimates when profiles with MODIS R_e > 15 μm or MODIS τ > 25 were removed. The agreement between MODIS and in situ estimates of changes in R_e, τ, and N_c associated with ACI was driven by low biases in MODIS retrievals of cloud properties across different aerosol regimes. Thus, when combined with estimates of aerosol location and concentration, MODIS retrievals of marine stratocumulus cloud properties over the southeast Atlantic can be used to study ACI over larger domains and longer timescales than possible using in situ data.