Publications

Witte, MK; Yuan, TL; Chuang, PY; Platnick, S; Meyer, KG; Wind, G; Jonsson, HH (2018). MODIS Retrievals of Cloud Effective Radius in Marine Stratocumulus Exhibit No Significant Bias. GEOPHYSICAL RESEARCH LETTERS, 45(19), 10656-10664.

Abstract
Satellite retrievals of cloud effective radius re are frequently validated using aircraft in situ measurements. Past intercomparisons have found a significant bias toward larger remotely sensed re. Explanations for this bias have focused on retrieval algorithms and large-scale heterogeneity, with in situ measurement uncertainty regarded as a minor factor. We compare Moderate Resolution Imaging Spectroradiometer re with in situ observations of marine stratocumulus clouds from three aircraft campaigns using a phase Doppler interferometer probe. Retrieved and in situ re typically agree within uncertainty in both nonprecipitating and drizzling conditions with no apparent systematic bias (mean bias of -0.22 mu m, mean relative bias 3%). Agreement depends on the choice of in situ probe as well as microphysical context. We demonstrate that probes must adequately characterize the width of the drop size distribution to avoid systematic underestimation of r(e). Plain Language Summary Satellite measurements provide the only global-scale picture of cloud properties and are widely used in the research community. Since the first comparisons of satellite and aircraft measurements of characteristic cloud drop size, significant disagreement between the two has been found. Past studies assumed that disagreement is because of faults in how the satellite observations are handled as opposed to issues with the aircraft measurements. In this study we show that which aircraft instrument is chosen for comparison with satellite measurements can affect whether satellite and aircraft measurements agree and that an appropriate choice of aircraft instrument leads to robust agreement between satellite and aircraft measurements. Using a database of over 200,000 aircraft measurements in cloud, we show why some aircraft instruments are unable to accurately measure cloud properties in certain meteorological settings.

DOI:
10.1029/2018GL079325

ISSN:
0094-8276