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. We use 2C-ICE estimates of stratiform floating cloud ice, falling ice (snow) and total frozen hydrometeors from the CloudSat-CALIPSO to evaluate CMIP6 model subsets. The subsets are those models only consider cloud ice but without (NOS) falling ice radiative effects (FIREs) and models separate treatments of ice-cloud radiative properties with separate (SON2) and combined (SON1) cloud ice and snow contents to compute optical properties of frozen hydrometeors. We found that falling ice (snow) is simulated well in SON2 subset against 2C-ICE estimates, but with significant underestimates over mid- and high-latitudes. Total frozen hydrometeors are better simulated with falling ice added but still well underestimated over mid- and high-latitudes. Inclusion of snow improves the agreements of simulated total frozen hydrometeors mass by SON1 and SON2 subsets with 2C-ICE estimates, relative to NOS subset. It should be pointed out that, the data of falling ice is not available in the CMIP6 data port. Therefore, we have requested it from the individual modeling groups specifically for this study. 2C-ICE estimates of stratiform floating cloud ice, falling ice and total frozen hydrometeors are used to evaluate CMIP6 model subsetsFalling ice is simulated well in one subset against 2C-ICE estimates, but with significant underestimates over mid- and high-latitudesTotal frozen hydrometeors are better simulated with addition of precipitating ice but still well underestimated over mid- and high-latitudes