ensemble transform Kalman filter (ETKF)
ABSTRACT: The spatial characteristics of ensemble transform Kalman filter (ETKF) sensitive area predictions (SAPs) are explored using ensemble forecasts from the European Centre for Medium-Range Weather Forecasts for the period of the 2003 North Atlantic THORPEX Regional Campaign. The ensemble size...
| Main Authors: | , , |
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.379.7875 http://enkf.nersc.no/Publications/pet07a.pdf |
| Summary: | ABSTRACT: The spatial characteristics of ensemble transform Kalman filter (ETKF) sensitive area predictions (SAPs) are explored using ensemble forecasts from the European Centre for Medium-Range Weather Forecasts for the period of the 2003 North Atlantic THORPEX Regional Campaign. The ensemble size necessary for a robust sensitive area prediction is found to be surprisingly small: a 10-member ensemble is capable of replicating approximately the same sensitive area structure as a 50-member ensemble. This result is corroborated by the fact that the leading eigenvector of the ensemble perturbations explains over 70 % of the ensemble variance and possesses a nearly identical spatial structure regardless of the ensemble size. The structures of the SAPs were found to vary with the lead-time between the ensemble initialization and the adaptive observing time, indicating the necessity of using as recent an ensemble as possible in ensemble-based sensitive area predictions. The ETKF SAPs exhibit similar structures at different levels in the atmosphere and there is no indication of a vertical tilt. A relationship is found between the SAPs and the zonal wind, horizontal temperature gradient and the Eady index, indicating that the ETKF identifies regions with significant gradients in the mass-momentum field as regions of large initial error or large error growth. Copyright © 2007 Royal Meteorological Society |
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