An ensemble strategy for high-resolution regional model forecasts |
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Authors: | V Misra M K Yau |
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Institution: | (1) Center for Ocean-Land-Atmosphere Studies, Institute of Global Environment and Society, Calverton, Maryland, US;(2) Department of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec, CA |
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Abstract: | Summary
An ensemble methodology is proposed for very high-resolution regional model Quantitative Precipitation Forecasts. To facilitate
a systematic study, the model and the boundary conditions are assumed to be perfect. The generation of perturbations is derived
on the basis that the largest errors in precipitation forecasts at very high resolutions arise from miss-specified diabatic
heat sources and sinks which feedback erroneously to the grid scale variables in the initial state. This methodology is tested
in a Proxy Observed System Simulation Experiment (POSSE) involving an intense cyclone over eastern Canada. The perturbations
of wind and temperature in this ensemble strategy are obtained as normalized coefficients of a Combined Empirical Orthogonal
Function analysis of the difference fields between the control and the diabatically initialized model runs. These perturbations
are added to and subtracted from the control initial state to obtain a set of two perturbed initial states. Several such perturbed
initial states are obtained from initializing observed rain rates at different times close to the time of the analysis. The
results from the POSSE reveal that the Quantitative Precipitation Forecast of the ensemble mean outperforms the control model
run.
Received August 8, 2000/Revised November 1, 2000 |
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Keywords: | |
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