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  • Author or Editor: Steven R. Hanna x
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Steven R. Hanna

Abstract

The vertical eddy diffusivity coefficient K is hypothesized to depend upon the parameters that determine the energy spectrum of the vertical velocity fluctuations. Vertical velocity spectra from the lowest 320 m of the atmosphere are used to verify a relation among the rate of dissipation of eddy energy per unit mass, the standard deviation of the vertical velocity fluctuations, and the wavenumber of the peak of the energy spectrum of the vertical velocity fluctuations. Observations at Round Hill, Mass., and Cedar Hill, Tex., are employed to verify that the vertical eddy viscosity KM is proportional to the product of any two of the above parameters. However, the Richardson number must be included with these parameters in order to estimate the vertical eddy conductivity KH. In addition, it is shown that the wavenumber maximum of the vertical velocity spectrum and the nondimensional ratio σ w/u* may be approximated at heights less than 320 m by empirical formulae.

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Adel F. Hanna, Duane E. Stevens, and Elmar R. Reiter

Abstract

A two-level, global, spectral model is used to study the response of the atmosphere to sea surface temperature anomalies. Two sea surface temperature anomaly patterns are investigated. The first, called the El Niño pattern (Experiment 1), represents a warm anomaly in the equatorial Pacific, whereas the second pattern (Experiment 2) represents coupled midlatitude (cold)/ equatorial (warm) sea surface temperature anomalies in the pacific Ocean.

The results demonstrate that both of these sea surface temperature anomaly patterns produce statistically significant midtropospheric geopotential responses in middle latitudes. However, the geopotential response forced by the coupled sea surface temperature anomaly is qualitatively more similar to the geopotential height pattern which is observed in association with the negative phase of the Southern Oscillation (Horel and Wallace). Analysis of the differences (anomaly minus control) of the meridional transports of momentum. sensible heat and latent heat indicates that the coupled pattern tends to largely enhance the northward transports of momentum and sensible heat, especially for the transient and stationary eddy components. The maximum difference in the total (transient, stationary eddies and mean meridional circulation) transport of momentum is nearly double that revealed by the El Niño experiment.

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