Science Seminars

3/19/2015 – Spatiotemporal variability of cirrus cloud properties inferred from MODIS infrared band measurements

Speaker: Hironobu Iwabuchi (Tohoku Univ.)
Date: Thursday, Mar 19, 2020
Time: 4:00 PM
Location: SPSC W120

Seminar Abstract:

The present understanding of cirrus cloud microphysics and their radiative effects is limited, which is an important key for improving climate models. An optimal estimation-based algorithm using three infrared bands of the Moderate Resolution Imaging Spectroradiometer (MODIS) to retrieve cirrus radiative and microphysical properties has been developed. This IR method is suitable when cloud optical thickness is moderate (within a range of 0.5–6). Retrieval errors of cloud optical thickness and effective particle radius are mainly from uncertainties in a priori cloud top and surface temperatures and a few model parameters. A case study over a tropical ocean demonstrates advantages of the method; particularly, the ability to be applied to more pixels with optically thin cirrus in comparison with the method using solar reflection in visible and near-infrared bands and the ability of the optimal estimation framework to produce useful diagnostics of retrieval uncertainties and reliability. This method has been applied to global-scale remote sensing. Global mean of effective particle radius of single-layer cirrus cloud is about 30 µm with mean optical thickness of 1.6, whereas the optical thickness exhibits large dispersion with nearly flat frequency distribution over a range between 0.1 and 10. Tropical cirrus clouds have smaller particle sizes, compared to midlatitude cirrus. The effective particle size generally increases at warmer temperature with lower depolarization ratio obtained from collocated CALIPSO lidar observations. There is no significant day–night differences in the statistics of microphysical and optical properties when averaged over the globe. Radiative effects of cirrus cloud should be reproduced in models by including the characteristics obtained.