Southern Hemisphere Prediction Experiment With a Nine-Level, Primitive-Equation Model

Boundary layer data from the Wangara expedition show that, at a point in the mean winter west wind belt (but near its equatorward limit), eddies on the synoptic scale (periods greater than a day) transferred westerly momentum upward. Except in the lowest 500 m, this upward tranfer predominated over downward fluxes due to micro‐scale (periods less than 2 hours) and meso‐scale (2 ‐ 24 hours) eddies, the latter transfers being very small. The effect of ageostrophic motions, due to accelerations, on this transfer was negligibly small. A characteristic circulation, relative to synoptic systems, in a vertical zonal plane, performing the vertical transfer of westerly momentum, has been deduced. The eddy flux of angular momentum, in the middle latitude boundary layer between 500 and 1,700 m appears to be directed up the angular momentum gradient, both horizontally and vertically, and, at all levels, down the horizontal gradient of angular velocity. An argument is presented to show that the intensity of circulation in the Ferrel cell may be greater than is usually estimated, the maximum absolute value of the stream function (except for the Northern Hemisphere in summer), being normally at least about 30 × 1012 g s−1.

The vertical propagation of angular momentum in the west wind belts

Clarke

1972

Time spectra and cross‐spectra of kinetic energy in the planetary boundary layer

Hess

Clarke

1973

SUMMARYTemporal spectra and cross-spectra of the three turbulent wind components for meso-synoptic scales at 250 m vertical intervals in the planetary boundary layer are presented. The data were derived from hourly simultaneous balloon ascents from a 5-point grid at Hay, New South Wales, Australia (lat. 344S), during the Wangara expedition. The spectra indicate a meso-scale gap for u (eastward component of wind) and u (northward component). The computed w-spectra suggest that no marked gap is present. For periods less than 1 day the u-and v-spectra, with a correction applied for high frequency noise, fall off approximately as n-2.6, where n is the frequency, and this result appears to be invariant with height within and just above the planetary boundary layer. The corrected w-spectra exhibit n dependency in this frequency range. The uv, uw, and uw cospectra also show only small contributions on the meso-scale (periods less than a day) compared to the synoptic scale, indicating that meso-scale motions may not have to be explicitly modelled in atmospheric general circulation models. An inertial peak is found for u and v but the w-spectra show a diurnal peak. The phase angles showed that u and v were in approximate quadrature at the inertial frequency, demonstrating the existence of the inertial cycle. Tests for horizontally two-dimensional isotropy indicated that the turbulence did not obey this simplification.

The effect of a warm mid‐latitude sea surface temperature anomaly on a numerical simulation of the general circulation of the southern hemisphere

SIMPSON

Downey

1975

A mid-latitude Sea Surface Temperature Anomaly (SSTA) is introduced into a 9-level polar stereographic southern hemisphere model. Two 50-day anomaly integrations (STAR1 and SSTAR2) are compared with their respective control integrations. In SSTAR2 the anomaly is introduced 10 days later than in SSTARl. Comparison of the two integrations reveals systematic effects in some regions of the Antarctic trough and the mid-Atlantic and Indian Oceans, but no systematic effect in the immediate area of the SSTA. The latter region shows a weak variation in SSTARZ while SSTARl is characterized by a strong variation and a blocking sequence some 20 days into the integration. The region of enhanced cyclogenesis in SSTARl occurs on the equatorial side of the anomaly and not the region of enhancecl surface baroclinicity. One such large cyclone is a major feature of the blocking sequence. Enhanced latent heat release appears to be an important factor in these developments. * The model is a southern hemisphere version of that developed at GFDL, Princeton, U S A . (Mansbe cf a/. 196S),constructed at the Auslralian Numerical Meteorology Research Centre. 841