Evaluation of Radiatively Active Frozen Hydrometeors Mass in CMIP6 Global Climate Models Using CloudSat-CALIPSO Observations

This study uses derived 2C-ICE estimates of frozen hydrometeors path (IWP) and vertical profile of ice water content (IWC) from CloudSat-CALIPSO satellite measurements to evaluate stratiform floating ice (CIWP/CIWC), falling ice (snow) (SWP/SWC) and total ice (TIWP/TIWC) simulated by three subsets of CMIP6 models. They include those neglecting the falling ice (snow) radiative effects (NOS) or those considering these effects (SON) but with separate (SON2) or combined (SON1) frozen hydrometeors (cloud ice and falling ice) interacting with radiation. CIWP from NOS subset agrees with 2C-ICE estimates better than SON2 except for overestimating over the trade-wind regions. This is also the case for vertical profiles of regionally-averaged CIWC, with the exception of overestimates in the lower troposphere of high latitudes by NOS. Falling ice (SWP/SWC) is simulated reasonably well in SON2 models against 2C-ICE estimates, but with significant underestimates over mid- and high-latitudes. Vertical shapes of regionally-averaged SWC profiles are well reproduced but magnitudes are underestimated for all regions except for the middle troposphere of the tropical region. The inclusion of snow improves the agreement between the simulated TIWP/TIWC of SON1 and SON2 subsets and 2C-ICE estimates, compared to the NOS subset. However, TIWP/TIWC are underestimated over the storm track and high latitude for all three subsets except for the tropical region of SON2. The aforementioned discrepancies are likely due to model physics, but observational estimates of frozen hydrometeors mass and content are also highly uncertain. Further studies are needed to improve both models and observational estimates of frozen hydrometeors mass.