Assessing physical processes in the ECMWF model forecasts through the ARM SGP site measurements
| Neggers, Roel | European Centre for Medium-range Weather Forecasts (ECMWF) |
| Cheinet, Sylvain | ECMWF (UK) |
| Beljaars, Anton | ECMWF |
| Koehler, M | European Centre for Medium-range Weather Forecasts, Reading, |
| Morcrette, Jean-Jacques | European Centre for Medium-Range Weather Forecasts |
| Viterbo, Pedro | ECMWF |
In this study, we compare short-term weather forecasts of the ECMWF model (Integrated Forecast System, IFS) to measurements at the Southern Great Plains (SGP) site of the Atmospheric Radiation Measurement (ARM) program in July 2003. By using a number of ARM instruments and complementary satellite and radar network data, a number of systematic deficiencies are characterized in the IFS, focusing on mixing processes.
The IFS correctly predicts the mean flow and the main rain events at the ARM SGP Central Facility. However, it misrepresents the propagation of rainy deep convective systems from the Rockies. It underestimates the intensity of the nocturnal Low-Level Jet (LLJ) and the diurnal temperature range. The night-time deficiencies are improved by decreasing the intensity of mixing in the stable boundary layer. The afternoon cold bias results from an underestimation of local entrainment at the top of the fair-weather boundary layer, consistent with the noted underestimation of the frequency of fair-weather cumuli.
The model suffers from a systematic dry bias at low levels, which potentially explains the low clouds underestimation. Further sensitivity tests show that less intense moist convective processes upwind the LLJ tend to moisten the boundary layer moisture at the SGP. Hence the local lack of moist convective activity could involve an overestimation upstream. Implications of our results in terms of parameterization calibration are discussed.
This poster will be displayed at the ARM Science Team Meeting.