Showing papers by "Eugenia Kalnay published in 1986"

Large-Amplitude, Short-Scale Stationary Rossby Waves in the Southern Hemisphere: Observations and Mechanistic Experiments to Determine their Origin

Abstract: Further observational evidence of the existence of large-amplitude stationary waves in the Southern Hemisphere during January 1979 is presented. Possible forcing mechanisms for the stationary waves are discussed, and two control experimental forecasts are presented: 15-day integrations with the GLAS Fourth Order GCM, starting from January 5 and Febuary 4, 1979. These forecasts are compared with the GLAS analyses for the same periods, discussing the extent to which the observed January waves are reproduced in the forecast. Several mechanistic experiments are reported in which the Andean orography, tropical heating, regional heating, and initial westerly flow are artificially modified. The effects of these changes on the stationary waves are discussed.

Mechanistic experiments to determine the origin of short-scale Southern Hemisphere stationary Rossby waves

Abstract: Publisher Summary This chapter examines the mechanistic experiments to determine the origin of short-scale Southern Hemisphere stationary Rossby waves. Simple numerical experiments with a hemispheric two-level quasigeostrophic model and with a shallow water barotropic model are presented. They indicate that placing a source of tropical heating in the Amazon region leads to the development within a few days of a train of short subtropical waves not unlike the ones observed during January. The results also show a strong sensitivity of the stationary waves in the South Atlantic to the precise position and extension of a heat source representing the South Pacific Convergence Zone. In the February forecast, the stationary waves over South America are weaker than in January, and in agreement with the analysis, are tilted in the northwest-southeast direction. The forecast has also succeeded in placing the cyclone center in the correct position, 20°S and 40°W. The role of tropical heating in the maintenance of the Southern Hemisphere stationary waves was assessed by reducing the tropical heating.

Global analysis of ocean surface wind and wind stress using a general circulation model and Seasat scatterometer winds

Abstract: Instantaneous and 15-day time-averaged fields of surface wind, wind stress, curl of the wind stress, and wind divergence are presented. These fields are derived from the Goddard Laboratory for Atmospheres four-dimensional analysis/forecast cycle, for the period September 6-30, 1978, using conventional data, satellite temperature soundings, cloud-track winds, and subjectively dealiased Seasat scatterometer winds.

The Effect of a Gravity Wave Drag Parameterization Scheme on GLA Fourth Order GCM Forecasts

Abstract: Ten-day forecast experiments have been performed to determined whether the introduction of a simple orographic gravity wave drag scheme into a fourth-order GCM would reduce the climate drift of the fine resolution model and improve the model's medium range predictive skill. Error reduction due to the gravity waves is found in stratospheric predictions, where the improvement is confined mainly to the zonal mean component. Improvements are noted in the Northern Hemisphere climatology, where low level westerlies are weakened and shifted poleward, and in the Southern Hemisphere, where the roaring forties and fifties are better simulated.