Enhancement and suppression of urban heat plumes over Johannesburg

Observations of the atmospheric temperature structure over Johannesburg have revealed the existence of both well-developed and suppressed heat plumes. Suppressed plumes appear to be associated with the incidence in a stable atmosphere of positive wind shear and well-developed katabatic flow away from the city. A localised cool region in the atmosphere above the central city is invariably associated with suppressed plume development. A tentative identification of wind shear and katabatic flow as the major influences on such structures is strengthened by the observation that during conditions of negative windshear and reduced katabatic advection, significant heat plumes are developed. It is at present not possible to assess the extent to which the observations and causative processes are site-specific.Visiting from Bar-Ilan University, Israel.