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Ronald D. McPherson

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Ronald D. McPherson

Abstract

The modification of the sea breeze circulation by irregular coastlines is examined by integrating a three-dimensional nonlinear numerical sea breeze model with a large bay incorporated into the surface boundary conditions. The results show that the presence of a bay produces a landward distortion of the sea breeze convergence zone and that within the zone there develop definite extrema of vertical motion, the positions of which are closely related to the bay. Furthermore, the intensity of convergence and upward motion within the zone are distributed asymmetrically with respect to the bay. This is a result of the Coriolis acceleration and the bay-induced component of the pressure-gradient force acting in concert on one side of the bay and in opposition on the other.

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Ronald D. McPherson

The National Meteorological Center is being restructured to serve a broader mission, which includes operational climate and ocean prediction as well as short-range weather prediction. Its successor organization is called the National Centers for Environmental Prediction and will consist of eight components: six service-oriented centers that will generate environmental prediction products and two central support activities to develop and operate the numerical models on which the predictions are based. This paper describes these components, together with their operation as an integrated organization.

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Ronald D. McPherson

A summary of recent research in meteorological data assimilation is presented, together with an assessment of the current state of the field. The primary emphasis is placed upon those recent papers dealing with real-data experiments. Problems still confronting the designers of data assimilation systems are outlined, and the future of such systems is discussed.

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Tsann-Wang Yu
and
Ronald D. Mcpherson

Abstract

Two days of global scatterometer-derived oceanic surface winds during the period of 0000 GMT 16 July-0000 GMT 18 July 1978 from the SEASAT-A satellite are used in the NMC's global data assimilation and forecast experiments to gain a preliminary appreciation of the impact of this dataset. The NMC's global data assimilation system used in this study is described. The nature of the scatterometer winds and their error characteristics are discussed.

Two parallel 48-hour data assimilation experiments are conducted: one including scatterometer wind data (SASS), the other without (NCSASS). After 48 hours of assimilation, large differences have evolved between SASS and NOSASS analyses due to the scatterometer winds. Comparison of the analyses with the operational analysis generated by the Australian Bureau of Meteorology suggests that the influence of scatterometer winds was beneficial in the Southern Hemisphere.

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Ronald D. McPherson
and
David A. Olson

Abstract

No abstract available

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Joseph P. Gerrity Jr.
and
Ronald D. McPherson

Abstract

A new scheme is presented for the numerical integration of the quasi-static system of hydrodynamical equations. The main advantage of the proposed method is its efficiency for the economical production of short-range, high-resolution meteorological forecasts. The method combines an implicit formulation of the linear non-advective processes and a staggered spatial-temporal arrangement of the dependent variables upon the calculation lattice. Results of experimental integrations using a free-surface barotropic model are presented. These results confirm the theoretical order-of-magnitude reduction in computation time by the new method as compared with the conventional explicit method.

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JOSEPH P. GERRITY JR.
and
RONALD D. McPHERSON

Abstract

A limited area, fine-mesh, primitive equation barotropic model has been integrated using data observed at 500 mb. The lateral boundary conditions used in the model required that no change occur on the boundary during the 24-hr forecast. The predictions compare favorably with those obtained with the barotropic and baroclinic models in operational use at the National Meteorological Center.

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JOSEPH P. GERRITY JR.
,
RONALD D. McPHERSON
, and
PAUL D. POLGER

Abstract

Second- and fourth-order accurate finite-difference approximations of the equations governing a free surface autobarotropic fluid are compared with each other and with a second-order approximation on a one-half mesh. It is concluded that once the mesh size has been reduced sufficiently to adequately resolve the scales of interest then further reduction in mesh size would be inefficient in comparison with the use of more accurate finite-difference approximations.

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Eugenia Kalnay
,
Stephen J. Lord
, and
Ronald D. McPherson

In 1939 Rossby demonstrated the usefulness of the linearized perturbation of the equations of motion for weather prediction and thus made possible the first successful numerical forecasts of the weather by Charney et al. In 1951 Charney wrote a paper on the science of numerical weather prediction (NWP), where he predicted with remarkable vision how NWP would evolve until the present. In the 1960's Lorenz discovered that the chaotic nature of the atmosphere imposes a finite limit of about two weeks to weather predictability. At that time this fundamental discovery was “only of academic interest” and not really relevant to operational weather forecasting, since at that time the accuracy of even a 2-day forecast was rather poor. Since then, however, computer-based forecasts have improved so much that Lorenz's limit of predictability is starting to become attainable in practice, especially with ensemble forecasting, and the predictabilty of longer-lasting phenomena such as El Niño is beginning to be successfully exploited.

The skill of operational weather forecasts has at least doubled over the last two decades. This improvement has taken place relatively steadily, driven by a large number of scientific and computational developments, especially in the area of NWP. It has taken place in all the operational NWP centers, as friendly competition and information sharing make scientific improvements take place faster than they would in a single center. Because the improvements have occurred steadily, rather than suddenly, the overall increase in forecast skill due to NWP has not been clearly recognized by the media and the public despite the impact that improved forecasts have on the national economy and on the lives of every American.

In this paper the authors review several measures of operational forecast skill that quantify improvements in NWP at the National Centers for Environmental Prediction (NCEP, formerly the National Meteorological Center) of the National Weather Service, although they are representative of improvements in all major NWP operational centers. The authors point out that there are three major requirements for improved numerical weather prediction: better atmospheric models, better observational data, and better methods for data assimilation. These improvements are generally very computer intensive and can only be made operational with the availability of more powerful supercomputers. Operational forecasts are compared with “reforecasts” from the NCEP–NCAR 40-Year Reanalysis, showing that, if the present-day NWP systems had been available many decades ago, skillful 5-day forecasts would have been possible in the Northern Hemisphere with the upper-air network of the late 1950s. The authors discuss new approaches in the use of observations (variational assimilation of remote observations) and of numerical weather prediction guidance (ensemble forecasting) that have allowed the recent extension of operational predictions into longer ranges and the possibility of adaptive observing systems. The extension of operational forecast skill into seasonal predictions of the El Niño–Southern Oscillation phenomena using coupled ocean-atmosphere models is also discussed. In the last section the authors attempt to “forecast” the future of NWP.

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