Fleet Numerical Weather Central Research Articles

Numerical Simulations of a Case of Explosive Marine Cyclogenesis

Abstract The extratropical cyclone which damaged the liner Queen Elizabeth II in September 1978 is a well-documented example of explosive marine cyclogenesis in which the 24 h surface central pressure fall was 60 mb commencing 1200 GMT 9 September. Operational models of both the National Meteorological Center (NMC) and Fleet Numerical Weather Central (FNWC) predicted virtually none of the observed surface intensification. This study reports on results of simulations performed with a primitive equation model. Emphasis will be placed on discovering why such poor forecasts were made of this storm. The extensive data set compiled by Gyakum (1983a, b) is used both to initialize and verify the model in a series of 24 h simulations, in order to assess the impact of initializing the model with these supplementary data. Physical processes identified observationally by Gyakum as being important in the storm's evolution are also examined numerically for their relative importance. In a series of seven simulations in ...

A brief summary of verification results for the spectral ocean wave model (SOWM) by means of wave height measurements obtained by Geos 3

A brief summary of some of the verification results for the spectral ocean wave model (SOWM) using Geos 3 wave height measurements is given. A NASA contractor's report by Pierson and Salfi (1978) contains the analyses of 44 Geos 3 orbit segments for 1975 and 1976, from which significant wave heights were obtained as overlapping 20‐s averages every 2 or 3 s from the altimeter data. The SOWM is the presently operational wave forecasting model at the Fleet Numerical Weather Central (FNWC). The verifications were carried out for the specification (or hindcast) mode; that is, past meteorological data and wind fields derived therefrom were used to calculate the waves as opposed to forecasts of the wind fields. The major results were that the SOWM specifications were biased too low and that the larger differences between what was measured by Geos 3 and what the model gave could be attributed to poor specifications of the winds over the northern hemisphere oceans. These particular features of the SOWM had been recognized at FNWC by means of verifications by other means, and the bias has been removed, although there are still problems connected with the lack of adequate wind data over the oceans.

The Fleet Numerical Weather Central Tropical Cyclone Model: Comparison of Cyclic and One-Way Interactive Boundary Conditions

Abstract One of the major problems in the development of limited-area models is the specification of reasonable boundary conditions. In this paper, the results of the use of one-way interactive boundary conditions in the Fleet Numerical Weather Central (FLENUMWEACEN) coarse-mesh tropical cyclone model are discussed. Given analyzed fields in 12 h intervals, boundary values are linearly interpolated in time for each time step. Smoothing is done near the boundaries to minimize the excitation of gravity waves. This procedure is carried out through 72 h. The results are compared to forecasts made by the current FLENUMWEACEN coarse mesh model which uses insulated, free-slip walls on the north-south boundaries and cyclic conditions in the east-west direction.

Performance of an Air-Sea Interaction Buoy

Abstract Surface meteorological data from a large instrumented buoy moored in the North Pacific were analyzed and estimates of air-sea interaction fluxes of momentum, sensible heat, latent heat and radiation were made. Good agreement was obtained for one month of buoy operation from redundant sensors for wind speed, air temperature, sea temperature and barometric pressure. Flux estimates were made using the bulk aerodynamic formulas. The buoy data, sampled once per hour, were low-pass filtered to compare with the 6 and 12 h surface analyses of the U.S. Navy Fleet Numerical Weather Central (FNWC) for the area surrounding the buoy. Good agreement was obtained between the buoy data and the independent FNWC analysis.

U. S. Navy Fleet Numerical Weather Central Operational Five-Level Global Fourth-Order Primitive-Equation Model

Abstract The U. S. Navy Fleet Numerical Weather Central (FNWC) operational, global, primitive-equation model (GPEM) is described. It is an extension of the Northern Hemisphere model (NHPEM) described by Kesel and Winninghoff. The GPEM uses a staggered, spherical, sigma-coordinate system with real input data which is interpolated to the sigma surfaces. The streamfunction obtained from the solution of the full balance equation is used to determine the initial velocity field. Fourth-order spatial differencing and centered time differencing are used for all the cases described in this paper. In addition to Euler-backward differencing, a combination of Arakawa's Fourier frequency-amplitude modification scheme and three-point method is used to maintain computational stability at each latitude ring. The calculations of the heating and moisture, source-sink terms and friction in the present version of the GPEM are quite similar to the NHPEM. The only substantial change in these computations involves the parameter...

Numerical weather prediction

Various numerical models are in use for prediction of the large‐scale motions of the atmosphere for operational or research purposes, and all seem to have comparable skill for several days, as shown by Druyan [1974] in a comparison of the Goddard Institute for Space Studies (GISS) [Somerville et al., 1974] model forecasts with those at the National Meteorological Center (NMC) [Shuman and Hovermale, 1968], the Fleet Numerical Weather Central (FNWC) [Kesel and Winninghoff, 1972], and the Geophysical Fluid Dynamics Laboratory (GFDL) [Miyakoda et al., 1972]. There have also been many models developed for treating limited areas with higher resolution, as described in a paper by Chen and Miyakoda [1974], in which many references to such models may be found.The principal topics of this review, however, will be the recent research on the question of the theoretical predictability of the large‐scale motions of the atmosphere, on the design of a global observing and data assimilation system, and on the development of statistical‐dynamical forecasting models. These all relate to the first objective of the Global Atmospheric Research Program (Garp), namely, increasing the accuracy of forecasting over periods of 1 day to several weeks.

The Fleet Numerical Weather Central Operational Primitive-Equation Model

Abstract The U.S. Navy Fleet Numerical Weather Central (FNWC), Monterey, Calif., five-layer, primitive-equation, atmospheric prediction model has been under development since late 1968 and became operational in September 1970. Seventy-two-hour prognoses are generated twice daily, requiring 2 hr per run. The conservation forms of the difference equations are based on the Arakawa technique and are integrated, using a 381-km space step (at 60°N) and a 10-min time step, on sigma surfaces. Realistic mountains are used. Pressure-force terms are replaced by a single geopotential gradient on pressure surfaces synthesized locally to reduce inconsistent truncation error. Lateral diffusion is performed on forecast difference fields to prevent systematic distortions of sigma-surface state parameter distributions. Stress is applied at the lowest level. Restoration boundaries and centered time differencing are used. The integrations are restarted each 6 hr with a Euler-backward step to reduce solution separation. The m...