Global Real-Data Forecasts With the Ncar Two-Layer General Circulation Model

Abstract

A number of global real-data numerical forecasts have been calculated using the two-layer NCAR (National Center for Atmospheric Research) general circulation model. The purpose of these experiments was threefold: 1) t o evaluate the model's ability t o predict the real atmosphere, 2) to develop a global forecasting model which will make use of the data obtained by the proposed GARP (Global Atmospheric Research Program), and 3) to help determine some of the internal, empirical constants of the model. In order to evaluate the accuracy of the predictions, several "skill scores" were calculated from the forecasted and observed variables. A by-product of this research was the testing of five different types of data-initialization schemes. Over 50, 4-day forecasts have been run, in which the initialization schemes and internal constants were varied. The results from these experiments indicate that the present two-layer model is capable of forecasting the real atmosphere with reasonable skill out to 2 days a t the surface and 4 days in the middle troposphere. The best initialization scheme for this particular model, thus far, appears to be the complete balance equation. However, several of the simplified initialization techniques are very close in terms of forecasting skill.

Mean and Eddy Transports of Angular Momentum, Water Vapor, and Energy in the Global Atmosphere

“…The global real data analyzed by Baumhefner (1970) for the period of 15-19 January 1958 (IGY) consists of pressure data at seven levels (surface pressure, geopotential heights of 700, 500, 300, 200, 100, and 70 mb) at 12 GMT for the five-day period. The horizontal velocity fields were analyzed only at two levels by averaging sounding data vertically from the surface to 6 km and from 6 km to 12 km in height.…”

“…This result, therefore, supports the implication of Baumhefner (1970) and Smagorinsky et al (1970) that the preparation of detailed initial water vapor data for prediction of the large-scale flow is unimportant.…”

“…Therefore, something must be done to claim the horizontal flow and moisture fields as the initial conditions. In this connection, Baumhefner (1970) examined how fast the water vapor field adjusts to the flow field during the forecast. He performed forecast runs starting from two different initial moisture distributions.…”

“…As a basic data set, Baumhefner (1970) has analyzed global data for the period of 15-19 January 1958 OGY).…”

Numerical weather prediction

“…Awareness of the need for smaller horizontal grid intervals has increased [Orville, 19686;Rao atu Umscheid, 1969;Baumhefner, 1970;Manabe et d [19706]. This awareness has been demonstrated most dramatically in the paper by Manabe et al [ 19705], where a reduction of the typical horizontal increment from 500 to 250 km in a general-circulation mode] resulted in the formation of much more realistic fronts and cyclone families, together with an increase in the previously underestimated magnitude of the eddy kine tic energy.…”