Atmospheric boundary layer characterizations over Highveld Region South Africa

Abstract

Atmospheric Boundary Layer (ABL) characteristics can be highly complex; the links between spatial and temporal variability of ABL meteorological quantities and existing land use patterns are still poorly understood due to the non-linearity of air-land interaction processes. This study describes the results from Monin Obukhov similarity theory and statistical analysis of meteorological observations collected by a network of ten Automatic Weather Stations (AWSs). The stations were in operation in the Highveld Priority Area (HPA) of the Republic of South Africa during 2008 – 2010. The spatial distribution of stability regimes as presented by both bulk Richardson number (BRN) and Obukhov length (L) indicates that HPA is dominated by strong stability regime. The momentum and heat fluxes show no significant spatial variation between stations. Statistical analysis revealed localization, enhancement and homogenization in the inter-station variability of observed meteorological quantities (temperature, relative humidity and wind speed) over diurnal and seasonal cycles. Enhancement of the meteorological spatial variability was found on a broad range of scales from 20 to 50 km during morning hours and in the dry winter season. These spatial scales are comparable to scales of observed land use heterogeneity, which suggests links between atmospheric variability and land use patterns through excitation of horizontal meso-scale circulations. Convective motions homogenized and synchronized meteorological variability during afternoon hours in the winter seasons, and during large parts of the day during the moist summer season. The analysis also revealed that turbulent convection overwhelms horizontal meso-scale circulations in the study area during extensive parts of the annual cycle