01 December 2016

Select Strengths and Biases of Models in Representing the Arctic Winter Boundary Layer: The Larcform 1 single column model intercomparison


Weather and climate models struggle to represent lower tropospheric temperature and moisture profiles and surface fluxes in Arctic winter, partly because they lack or misrepresent physical processes that are specific to high latitudes. Observations have revealed two preferred states of the Arctic winter boundary layer. In the cloudy state, cloud liquid water limits surface radiative cooling, and temperature inversions are weak and elevated. 


In the radiatively clear state, strong surface radiative cooling leads to surface-based temperature inversions. Many models lack the cloudy state, and some substantially underestimate inversion strength in the clear state. Here, the transformation from a moist to a cold, dry air mass is modeled using an idealized single-column experiment (Larcform 1). 


The comparison reproduces the typical biases of large-scale models: some models lack the cloudy state of the boundary layer due to the representation of mixed-phase microphysics or to the interaction between micro- and macrophysics. In some models, high emissivities of ice clouds or the lack of an insulating snow layer prevent the build-up of surface-based inversions in the radiatively clear state. Models disagree on the amount of cloud liquid water in the cloudy state and on heat fluxes under clear skies.

Brian Medeiros
National Center for Atmospheric Research (NCAR)