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A comparison of the ECMWF forecast model with observations over the annual cycle at SHEBA |
University of Washington, University of Washington, ECMWF
roode@atmos.washington.edu
For single-column modeling over SHEBA, one must specify the time-varying tendencies from horizontal and vertical advection. Due to the difficulty of directly obtaining these tendencies, SHEBA and FIRE-ACE chose to specify them from the operational forecast model of the Euro pean Centre for Medium Range Weather Forecast (ECMWF), into which SHEBA radiosonde and surface synoptic observations were routinely assimilated. The authors compare SHEBA sound ings, cloud and boundary layer observations with the ECMWF analyses throughout the SHEBA year. They find that above the boundary layer, the model was faithful to the SHEBA radiosonde observations and maintained a proper long-term balance between advective and nonadvective ten dencies of heat and moisture. This lends credence to use of the ECMWF-predicted advective ten dencies for other single-column modeling studies.
The model-derived cloud properties and precipitation (which were not assimilated from observations) are compared with cloud radar, microwave radiometer, and surface measurements. The overall height distribution of cloud was well-simulated in all seasons. Surface longwave radiative fluxes were also in reasonable agreement with observations. The observations suggest that the ratio of cloud ice to cloud water tends to be excessive in the model clouds. During summertime, persistent unobserved drizzle was produced from the model boundary-layer cloud, despite its liq uid water content being realistic.
Observed turbulent sensible and latent heat fluxes were small throughout SHEBA. During high- wind periods during the winter, the ECMWF model predicted downward heat fluxes of up to 100 W/m2. A detailed comparison suggests that this error was due to both inadequate resolution of the 31-level model and a deficient parameterization of sea-ice thermodynamics.
