Numerical investigation with a coupled single-column surface-atmosphere model and an application to central Mediterranean

An atmospheric single-column model (SCM) developed in the framework of the Canadian Regional Climate Model, CRCM, driven by NCEP-NCAR reanalyses is applied to study the non-linear interactions between the surface and the planetary boundary layer (Goyette et al., 2020). The approach to solve the model equations and the technique described may be implemented in any RCM system environment as a model option. The working hypothesis underlying this SCM formulation is that a substantial portion of the variability simulated in the column can be reproduced by processes operating in the vertical dimension and a lesser portion comes from processes operating in the horizontal dimension. This SCM offers interesting prospects as the horizontal and vertical resolution of the RCM is ever increasing. Due to its low computational cost, multiple simulations may be carried out in a short period of time. In this paper, a range of possible results obtained by changing the lower boundary from open water surface to land, and by varying model parameters are mainly shown for central Mediterranean but also for other applications. Results show that the model responded in a highly nonlinear but coherent manner in the lowest levels with changes in air temperature, moisture and windspeed profiles. The latter are consistent with those of the surface vertical sensible, latent heat and momentum fluxes. For example in the central Mediterranean, during a simulated year, air temperature is increased during all the seasons. Specific humidity is increased during the autumn and winter seasons but decreased by during the spring and summer seasons thus showing the contrasting influence of the land surface. The potential for further developments, as well as some guidance as to how to handle mixed land/open water coupling in RCMs, is also provided.

GOYETTE, Stéphane, FONSECA, Cédric, TRUSCELLO, Léonard. Assessment of nonlinear effects of a deep subgrid lake with an atmospheric single‐column model. In: International Journal of Climatology, 2020. doi: 10.1002/joc.6890