Satellite retrievals of (quasi-)spherical particles at cold temperatures

Measurements from NASA's A-train satellites indicate that spherical or quasi-spherical particles may constitute up to 30% of the total cloud particles at temperatures below -30 degrees C, and up to 10% even for temperatures below -40 degrees C, the temperature range typically found in the upper troposphere and the lower stratosphere. Current climate models calculate cloud radiative forcing on the basis on an assumption that essentially no spherical or quasi-spherical particles exist below -40 degrees C (even below -15 degrees C). The findings in this study show that this widely used assumption in climate models may need re-examination. Further research is also needed to confirm and quantify these findings, especially improvements in the satellite retrievals of cloud particle shapes that, in the mean, currently contain about 10% uncertainties. Citation: Choi, Y.-S., C.-H. Ho, J. Kim, and R. S. Lindzen (2010), Satellite retrievals of (quasi-)spherical particles at cold temperatures, Geophys. Res. Lett., 37, L05703, doi:10.1029/2009GL041818.