A Comparison of Cloud Microphysical Properties Derived From MODIS and CALIPSO With In Situ Measurements Over the Wintertime Southern Ocean

• Published in: Journal of geophysical research. Atmospheres 2018-10, Vol.123 (19), p.11,120-11,140
• Main Authors: Ahn, Eunmi, Huang, Yi, Siems, Steven T., Manton, Michael J.
• Format: Article
• Language: English
• Subjects: Aerosols; aircraft observations; boundary layer clouds; Cellular convection; cloud droplet number concentration; Cloud microphysics; Clouds; Convection; Droplets; effective radius; Error analysis; Error compensation; Geophysics; Heterogeneity; Imaging techniques; In situ measurement; Lidar; MODIS; Oceans; Optical properties; Polarization; precipitation; Qualitative analysis; satellite observations; Spectroradiometers
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2018JD028535

In situ observations of cloud effective radius (reff), droplet number concentration (Nd), and thermodynamic phase from 11 wintertime flights over the Southern Ocean (43–45°S, 145–148°E) are compared to products from MODerate‐resolution Imaging Spectroradiometer (MODIS) and Cloud‐Aerosol Lidar with Orthogonal Polarization. The in situ observations were in close alignment with A‐train overpasses for a 30‐min window. For open mesoscale cellular convection, which was predominantly observed, clouds were commonly found to be intermittently drizzling, patchy, and mixed phase. Compared to the in situ observations of the cloud thermodynamic phase, the Cloud‐Aerosol Lidar with Orthogonal Polarization and MODIS cloud phase optical property products consistently underestimated the occurrence of mixed‐phase clouds, whereas the MODIS infrared‐based phase product showed a better qualitative agreement despite a frequent classification of uncertainty. The MODIS reff_2.1 overestimated the in situ reff for nondrizzling clouds (by ~13 μm on average) and, to a lesser extent, for lightly drizzling cases. Conversely, MODIS reff_2.1 underestimated the in situ reff for heavily drizzling cases by ~10 μm on average. The overestimation of reff is much greater than that for the stratocumulus over the Southeast Pacific shown in other studies. An examination on subpixel heterogeneity, droplet size variability, a bimodal distribution, and solar zenith angle suggests that all of these factors have measurable impacts on the MODIS reff bias. The MODIS Nd is largely consistent with the in situ observations. However, the Nd of the two high Nd cases (closed mesoscale cellular convection) are highly underestimated. An error analysis suggests that the Nd biases are likely a result of a compensating error effect. Key Points The CALIOP and MODIS cloud phase products underestimated the occurrence of mixed‐phase clouds compared to the in situ observations In comparison to the in situ observations the MODIS effective radius is overestimated for nondrizzling clouds and, to a lesser extent, for lightly drizzling cases Subpixel heterogeneity, cloud droplet size variability, bimodal distribution, and solar zenith angle may have measureable impacts on the MODIS reff retrieval bias