Sensitivity of simulated wintertime Arctic atmosphere to vertical resolution in the ARPEGE/IFS model |
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| Authors: | Øyvind Byrkjedal Igor Esau Nils Gunnar Kvamstø |
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| Institution: | (1) Bjerknes Centre for Climate Research, University of Bergen, Allegaten 55, 5007 Bergen, Norway;(2) Geophysical Institute, University of Bergen, Allegaten 70, 5007 Bergen, Norway;(3) Nansen Environmental and Remote Sensing Center, Thormoehlensgate 47, 5006 Bergen, Norway;(4) Kjeller Vindteknikk, PO-Box 122, 2027 Kjeller, Norway |
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| Abstract: | The current state-of-the-art general circulation models, including several of those used by the IPCC, show considerable biases
in the simulated present day high-latitude climate compared to observations and reanalysis data. These biases are most pronounced
during the winter season. We here employ ideal vertical profiles of temperature and wind from turbulence-resolving simulations
to perform a priori studies of the first-order eddy-viscosity closure scheme employed in the ARPEGE/IFS model. This reveals
that the coarse vertical resolution (31 layers) of the model cannot be expected to realistically resolve the Arctic stable
boundary layer. The curvature of the Arctic inversion and thus also the vertical turbulent-exchange processes cannot be reproduced
by the coarse vertical mesh employed. To investigate how turbulent vertical exchange processes in the Arctic boundary layer
are represented by the model parameterization, a simulation with high vertical resolution (90 layers in total) in the lower
troposphere is performed. Results from the model simulations are validated against data from the ERA-40 reanalysis. The dependence
of the surface air temperature on surface winds, surface energy fluxes, free atmosphere stability and boundary layer height
is investigated. The coarse-resolution run reveals considerable biases in these parameters, and in their physical relations
to surface air temperature. In the simulation with fine vertical resolution, these biases are clearly reduced. The physical
relation between governing parameters for the vertical turbulent-exchange processes improves in comparison with ERA-40 data. |
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| Keywords: | GCM Large eddy simulation Parameterization Arctic Stable boundary layer ARPEGE |
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