Intercomparison of methods of coupling between 1 convection and large - scale circulation . 2 : Comparison 2 over non - uniform surface conditions

As part of an international intercomparison project, the two-4 way interaction between convection and large-scale dynamics is studied in 5 a set of single column models (SCMs) and cloud-resolving models (CRMs) 6 using two large-scale parameterization methods: the weak temperature gra-7 dient (WTG) method and the damped gravity wave (DGW) method. For 8 each model, the implementation of the WTG or DGW method involves a sim-9 ulated column which is coupled to a reference state defined with profiles ob-10 tained from the same model in radiative-convective equilibrium. In Part 1 11 of this study, the simulated column has the same sea surface temperature 12 (SST) as the reference state. In this paper, the reference state is held fixed 13 while the SST in the simulated column is varied. For each value of SST, we 14 performed two sets of systematic comparisons: a comparison of the WTG 15 and DGW methods with a consistent implementation in models with differ-16 ent physics and numerics, and a comparison of the behavior of those mod-17 els using the same large-scale parameterization method. 18 The sensitivity of precipitation rate to the SST differs from model to model 19 and also depends on whether the WTG or DGW method is used to param-20 eterize the large scale circulation. In general, SCMs display a wider range 21 of behaviors than CRMs. CRMs show a fairly linear relationship between pre-22 cipitation and circulation strength, but a few SCMs deviate from this lin-23 ear relationship. All CRMs using either the WTG or DGW method show a 24 nonlinear increase of mean precipitation rate with SST. In contrast, SCMs show sensitivities of the mean precipitation rate to the SST which are not 26 always monotonic. Within an individual SCM, a WTG simulation and a cor-27 responding DGW simulation can produce different signs of the circulation. 28 In general, DGW simulations produce large-scale pressure velocity profiles 29 which are smoother and less top-heavy compared to those produced by the 30 WTG simulations. 31 Consistent with observations and other numerical model studies, precip-32 itation rate increases with column-relative humidity. A large proportion of 33 the models show a rapid increase of mean precipitation rate when column-34 relative humidity increases pass a threshold value. CRMs using either the 35 WTG or DGW method show very similar relationships between mean pre-36 cipitation rate and column-relative humidity, while SCMs exhibit a much wider 37 range …