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Roland B. Stull

timestep and ~rid Sl~aCit~g). Thus, it is possible to employ transih'ent turbulencetheory for both the diffusive and boundary layer 0arameterizatious in a large-scale numerical forecast modelthat, by operational necessity, has coarse grid spacing and large timeateps.1. Introduction and review The difficulty of modeling atmospheric turbulencehas stimulatod the formation of a number of schoolsof thought regarding parameterization schemes. Ktheory and mixing-length schools are ,local, first

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Yue Ying and Fuqing Zhang

model itself are not accounted for. Therefore, the NoDA experiment is not intended to account for all realistic sources of forecast errors that can impact practical predictability. Since we only focused on the impact of assimilating data in a limited-area domain for a selected period, one should be cautious in generalizing our findings. Although the 9-km horizontal grid spacing used is comparable to the current operational global models, it will be interesting to further test the sensitivity of EnKF

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Wallace A. Hogsett and Stacy R. Stewart

1. Introduction Tropical cyclone (TC) intensity change often results in large forecast errors when it occurs rapidly ( Rappaport et al. 2009 ). Rapid intensification (RI) presents a tremendous hazard if coastal populations are underprepared, and it is among the most significant challenges facing operational TC forecasting centers. Increasing RI forecast skill is one of the primary goals of the ongoing Hurricane Forecast Improvement Program (HFIP). Despite an ongoing technological revolution

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Vanda Grubišić and Mitchell W. Moncrieff

temporal scales as well. For instance, in midlatitudes, the curl of the surface wind stress drives ocean currents, while the momentum flux divergence within the atmosphere can influence the life cycle and tracks of midlatitude cyclonic storms. Although convective momentum transport parameterization affects the accuracy of weather forecast models and is a factor in climate models ( Gregory et al. 1997 ; Gregory 1997 ), no fundamental explanation is available. Cognizant of these issues, we search for a

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Edmund K. M. Chang

the Northern Hemisphere winte~ season are examinedusing one-point regression maps and longitude-height sections derived from the European Centre for MediumRange Weather Forecasts (ECMWF) operational analyses for seven winter seasons. With the use of unfilteredtime series of normalized 300-rob meridional wind perturbations at a grid point in the Pacific storm track asthe reference time series, regression statistics for perturbations in the horizontal wind, geopotenfial height,temperature, and

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T. N. Palmer, R. Gelaro, J. Barkmeijer, and R. Buizza

(AECM or GFDCM) covariance metric. a. Evidence from analysis fields For atmospheric predictability, the covariances of the initial or analysis error are not well known and are not readily obtained from operational data assimilation schemes. However MBPP made an estimate of an analysis error field associated with one rather poor ECMWF forecast by taking the difference between the ECMWF analysis and a corresponding Deutsche Wetterdienst (DWD) analysis from which a hindcast (using the same ECMWF model

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Eric DeWeaver and Sumant Nigam

1. Introduction Dynamical diagnosis of the atmospheric circulation places enormous demands on observational datasets, for such diagnosis requires knowledge of both circulation patterns and the forcing functions that generate and maintain them. The time-mean circulation patterns are relatively easy to observe, given their large horizontal scales and simple vertical structures, and datasets currently available from operational forecast centers show fairly good agreement in their amplitude and

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Jainn Jong Shi, Simon Chang, and Sethu Raman

) during its life cycle at 12-h intervals for six days. They found that the azimuthal eddy angular momentum flux at large radii was important to the intensification of Elena. They also suggested that operational forecasts of tropical cyclones could benefit from the calculations of eddy momentum flux because they measured the integrated effect in the storm environment, regardless of the complexity of the interactions. DeMaria et al. (1993) calculated the eddy flux convergence (EFC) of relative angular

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Clark J. Weaver, Paul Ginoux, N. Christina Hsu, Ming-Dah Chou, and Joanna Joiner

GCM forecasts. The National Environmental Satellite, Data, and Information Service (NESDIS) provides temperature retrievals from the Television Infrared Observational Satellite (TIROS) Operational Vertical Sounder (TOVS) radiances. These NESDIS TOVS temperatures dominate the observed analyses over ocean. Positive (negative) increments indicate that the GCM is too cold (warm). The increments are the sum of all model and intial condition errors in the GCM. A correlation between our calculated

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Guy Plaut and Robert Vautard

-favoring weather regimes may be forecast in the long range.Conditional probability of occurrence of blocking, 30 days ahead, is enhanced, relative to climatological probability, by a factor of 2 if the phase of the 30-35-day oscillation is known. This also emphasizes the necessityof operational models to represent correctly the extratropical LFOs in order to produce skillful long-range andeven medium-range forecasts of weather regimes.1.IntroductionThe atmospheric extratropical low-frequency variability has

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