Aerodynamic drag coefficient over equatorial coastal industrialized and urban areas

Drag coefficient (CD) in the urban roughness sublayer over industrialized and urban equatorial areas under low wind conditions are reported in this paper. An observation tower was set up in (1) the field of the Institusi Teknologi Tunku Abdul Rahman in the middle of the Prai Industrial Park (5°22′N, 100°23′E), employing a Gill UVW propeller anemometer and a temperature sensor placed at a height of 10 m above the ground level and (2) on the top of a faculty building in Universiti Sains Malaysia (USM) (5°21′N, 100°18′E), employing a sonic anemometer at 18 m above the ground level. Meteorological data were collected for three months in the years 2006 and 2010. Monin–Obukhov similarity theory using local scales was first tested at the sites studied and was found to be applicable. The relationships between CD and mean wind speed, V, local friction velocity, u⁎l, and atmospheric stability, ζl, are also discussed (subscript “l” denotes local). Generally, CD is strongly dependent and increased with u*l for both sites. CD was also confirmed to be influenced by atmospheric stability where it is at its maximum when u*l (and V) is large, which generally occurs in neutral atmospheric conditions. This relationship was seen at both sites, suggesting its generality. Lastly, the measured CDN value obtained was also used to calculate CGN, geostrophic drag coefficient (=1.9×10−3), which is similar to the reported values in the literature.

► Similarity theory using local scales was found to be applicable at the two sites.
► The measured CDN value is 0.038, a large value based on the literature.
► CD values of different surface conditions are the same.
► CGN calculated (=1.9×10−3) is similar to commonly reported value in the literature.