Enhancement of the consistency of MODIS thin cirrus with cloud phase by adding 1.6 μm reflectance

Optically thin cirrus derived from the Moderate-resolution Imaging Spectroradiometer (MODIS) instrument is examined in connection with its cloud phase (ice crystal or liquid droplet) for quasi-single layer thin cirrus (either single-layer thin cirrus or thin cirrus overlying low-level thin clouds) over water surface conditions. Analysing 142 MODIS data samples during the period 1-16 March 2000, it is found that only about 20% of MODIS thin cirrus having a total-column cloud optical depth less than 2.0 was detected as ice phase. In the present study, MODIS cloud phase datasets are newly reproduced by adding the 1.6 μm reflectance to an existing infrared trispectral algorithm of MODIS which used the 8.7, 11 and 12 μm bands. The percentage of ice phase in the thin cirrus is estimated at about 80% when new cloud phase is incorporated. The increase is found for all regions, in particular in mid-latitudes.