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Warren J. Tennant, Glenn J. Shutts, Alberto Arribas, and Simon A. Thompson

on the Met Office Unified Model (UM; Davies et al. 2005 ) and uses the ensemble transform Kalman filter (ETKF; Bishop et al. 2001 ) to calculate initial condition perturbations for 23 ensemble members. A control run at the same resolution without perturbations completes a 24-member suite that runs twice a day (global at 0000 and 1200 UTC, and regional at 0600 and 1800 UTC). The regional suite is driven by lateral boundary conditions output from the global suite initialized 6 h earlier and using

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E. A. Irvine, S. L. Gray, J. Methven, and I. A. Renfrew

. (2009) showed that the targeted observations had a small positive impact (approximately 5% in total energy) on the forecast up to 30 h, after which the forecast was degraded. The impact was caused by the modification of the position of a tropopause fold, which was associated with the development of a polar low at the surface. In the current study the dependence of the impact size on the dropsonde observation errors used in the data assimilation scheme is assessed by rerunning the impact experiment

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Mio Matsueda, Masayuki Kyouda, Zoltan Toth, H. L. Tanaka, and Tadashi Tsuyuki

and improvements in blocking prediction in medium-range forecasts, for which the initial-value problem is of greater concern than the boundary-value problem. Advances in these areas may lead to improvements not only in medium-range forecasting skill but also in model performance in climate projections. The NWP technique has progressed rapidly with advances in computer science. A 5-day weather forecast today is as reliable as a 2-day weather forecast 20 years ago, which represents a major

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Thomas M. Hamill, Jeffrey S. Whitaker, Michael Fiorino, and Stanley G. Benjamin

individual member, especially at longer leads, thus contributing to the HFIP goal of a reduction in track error. The diversity of track forecasts and maximum surface wind speed forecasts (TC intensity) could be used to quantitatively assess risk and make more appropriate and earlier decisions about coastal evacuations. The current state of the art of TC forecasts from global operational ensemble systems was recently described in Majumdar and Finocchio (2010) . Two technological improvements that may

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Benoît Vié, Olivier Nuissier, and Véronique Ducrocq

. As physical parameterizations at smaller scales show stronger nonlinearities, convective-scale perturbations grow much faster and even impact the large-scale predictability. The sensitivity to ICs ( Ducrocq et al. 2002 ) is also different between parameterized and resolved convection. Moreover, in addition to the uncertainties on ICs and the model errors, cloud-resolving ensembles must also consider the uncertainty due to lateral boundary conditions (LBCs), since they are run over a limited area

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