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  • Author or Editor: Gary K. Greenhut x
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Gary K. Greenhut

Abstract

After reanalyzing the potential temperature data of Peixoto (1958, 1960), a criterion is derived for locating the mean latitude of the subtropical high over West Africa. Using this criterion, it is found that the subtropical high tends to move to higher latitudes, and therefore the amount of rainfall in the Sahel tends to increase, as the concentration of carbon dioxide and particulate matter in the atmosphere increases. We conclude that increasing amounts of atmospheric pollutants are probably not the cause of the severe drought experienced in the Sahel in the early 1970's. This conclusion contradicts that of Bryson (1973) who used the so called Z criterion to predict an opposite response of the subtropical high to changes in the concentration of atmospheric pollutants.

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Gary K. Greenhut
and
Giangiuseppe Mastrantonio

Abstract

Doppler sodar wind measurements made in light wind conditions in September 1979 near a power plant in Turbigo, Italy, are used to derive terms in the turbulence kinetic energy (TKE) budget. Measurements on five days are grouped into two classes: fair-weather conditions and boundary layer interaction with subsiding air. Profiles of σ3 w /z are used to obtain the surface heat flux and the vertical velocity scaling parameter, as well as the buoyancy production term in the TKE budget. The vertical transport of TKE is derived from the profiles of (w′)3 . The horizontal components are approximated using a parameterization based on the data of Lenschow et al. Dissipation in the TKE budget is obtained from a spectral analysis of the Doppler sodar data in the inertial subrange. The resulting TKE budget profiles for the two classes are compared with budgets obtained previously, using a number of different methods.

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Gary K. Greenhut
and
Siri Jodha Singh Khalsa

Abstract

The properties of updrafts and downdrafts through the entire depth of the marine atmospheric boundary layer are investigated using conditional sampling based on an indicator function derived from the vertical velocity time series. Statistics on event size, number density and area occupied are obtained, along with conditional averages of the meteorological variables and percent contributions to the fluxes by updrafts, downdrafts and the environment. A single profile is obtained for convective mass flux based on conditional averaging of updrafts and downdrafts applicable to the fluxes of latent and sensible heat and momentum.

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Siri Jodha Singh Khalsa
and
Gary K. Greenhut

Abstract

Data from two aircraft flights in the marine atmospheric boundary layer are analyzed in an investigation of entrainment processes at the top of the well-mixed layer. Both days had strong wind shear across the inversion, which is reflected in the horizontal wind statistics. Conditional sampling is used to show that near the top of the mixed layer most updrafts are cool, moist and deficient in along-wind momentum (slow) with respect to their environment. About half of these updrafts are still positively buoyant. Downdrafts that are warm, dry and have an excess of along-wind momentum (fast) occupy the greatest area of any downdraft type. Most of them are positively buoyant. Also found near the top of the mixed layer are large numbers of warm/dry/fast updrafts and cool/moist/slow downdrafts, i.e., drafts that have overturned. Time series from this level reveal large masses of cool/moist/slow and warm/dry/fast air, usually containing both upward-moving and downward-moving elements. These observations are related to features seen in returns from clear convective boundary layers, using various remote sensing systems.

Conditional sampling is also used to determine the net buoyant production or consumption of turbulence kinetic energy by each convective element. The results support the process partitioning method of entrainment closure but deviate from the assumption of linear buoyancy flux profiles for each proem.

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