Using FLUXNET observations and 4-km WRF CONUS simulations to diagnose surface coupling strength

Uncertainties in representing land-atmosphere interactions can substantially influence regional climate simulations. Among these uncertainties, the surface exchange coefficient, Ch, is a critical parameter controlling the total energy transported from the land surface to the atmosphere and directly impacts the land-atmospheric coupling strength. Yet it has not been properly evaluated for regional climate models. This study assesses the representation of surface coupling strength in 4-km WRF simulations through comparing Ch derived from WRF simulations, from offline Noah-MP simulations, and from data collected at eight FLUXNET sites of the Canadian Carbon Program (CPC), which were then categorized into four ecoclimate regions. The seasonal variations of Ch for different land-cover types in Canada calculated by using 10-year half-hourly FLUXNET data are used to evaluate surface coupling strength in WRF. Also, Ch calculated from offline Noah-MP simulations is used to contract to these from WRF to understand the impacts of uncertainties in coupled WRF simulations and in offline Noah-MP simulations on Ch. Such analysis is used to evaluate 4-km WRF simulated surface heat fluxes.