The properties of sensitive area predictions based on the ensemble transform Kalman filter (ETKF)

G. N. Petersen, S. J. Majumdar, A. J. Thorpe

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)697-710
Number of pages14
JournalQuarterly Journal of the Royal Meteorological Society
Issue number624 PART A
StatePublished - Apr 2007


  • Adaptive observations
  • Forecast uncertainty

ASJC Scopus subject areas

  • Atmospheric Science


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