A case study of low level country breeze and inversion heights in the Johannesburg area

Previous studies within a shallow valley east of the city centre of Johannesburg (South Africa) revealed the presence of some anomalies in the mesoscale, winter, nocturnal climate regime. Among them: the valley was relatively warmer during inversion nights; more than one thermal belt was discerned and valley winds dominated the early hours of the mornings. A tethered balloon and a mobile acoustic sounder were used to monitor temperature, wind and humidity profiles in the valley and vicinity, whilst ground mobile units measured temperature. Observations revealed a three layer wind system in which an elevated country breeze is sandwiched between the katabatic flow near the ground and the gradient wind aloft. The double thermal belts observed on the valley's slopes are probably due to the oscillation of the country breeze (the lower) and the meso‐scale valley inversion top (the upper one). The inversion top over the ridge lines is probably caused by the regional nocturnal inversion or an elevated inversion eroded by the urban heat island plume.