Mechanisms of marine low cloud sensitivity to idealized climate perturbations: A single-LES exploration extending the CGILS cases

摘要: [1] Climate change sensitivities of subtropical cloud-topped marine boundary layers are analyzed using large-eddy simulation (LES) three CGILS cases well-mixed stratocumulus, cumulus under and shallow cloud regimes, respectively. For each case, a steadily forced control on small horizontally doubly periodic domain is run 10–20 days into quasi-steady state. The LES rerun to steady state with forcings perturbed by changes in temperature, free-tropospheric relative humidity (RH), CO2 concentration, subsidence, inversion stability, wind speed; responses combined superpose approximately linearly. all regimes 2× forcing perturbations estimated from the CMIP3 multimodel mean, predicts positive shortwave feedback, like most global climate models. At both stratocumulus locations, remains overcast but thins warmer, moister, CO2-enhanced climate, due effects an increased lower-tropospheric vertical gradient enhanced greenhouse effect that reduces radiative driving turbulence. Reduced subsidence weakening tropical overturning circulations partly counteracts these two factors raising allowing layer deepen. These compensating mechanisms may explain large scatter low feedbacks predicted CMIP3-predicted speed, RH have lesser impacts thickness. In regime, precipitation regulates simulated boundary-layer depth structure. Cloud-droplet (aerosol) concentration limits affects feedbacks.