Changes of South-Central Pacific Large-scale Environment Associated with Hydrometeors-Radiation-Circulation Interactions in a Coupled GCM

A common deficiency in coupled atmosphere-ocean models is the lack of stratocumulus 27 clouds near the west coasts of continents and shallow cumulus clouds over the trade wind regions. 28 In this study, we examine the changes of large-scale trade wind environment associated with 29 hydrometeors-radiation-circulation interactions, focusing over the south-central Pacific, by 30 carrying out experiments with falling ice (snow) radiative effects (FIREs) on or off using the 31 CESM1-CAM5 coupled model. We found that experiment with FIREs off (NOS) tends to have 32 too-warm (0.3—0.9 K) sea surface temperature (SST) over the east half of the Pacific, weaker 33 surface wind stress over the northeast side but stronger stress over the southwest side of the study 34 domain, lower-tropospheric wind fields with a cyclonic-like wind pattern that is similar to surface 35 wind stress, and weaker subsidence over the northeast side against observations/reanalysis data 36 and experiment with FIREs on (SON). The cyclonic-like wind pattern for changes between NOS 37 and SON causes stronger moisture convergence, accompanied with horizontal warm advection, 38 horizontal moist advection, and stronger effective ascending motion over the northeast side of the 39 study domain, building large-scale environmental conditions to facilitate middle- and high-clouds 40 instead of shallow cumulus clouds in nature. This large-scale environment in conjunction with the 41 warmer SSTs may be also responsible for the lacking of the stratocumulus clouds near the coast 42 of America. Remaining biases in SON such as the double intertropical convergence zone and 43 parameterization deficiencies may also prevent a more realistic simulation of trade wind clouds 44 and their associated large-scale environments.