Roughness Lengths at Four Stations Within the Micrometeorological Network over the Indian Monsoon Region

Abstract

The aerodynamic roughness length $(z_{0})$ is estimated here for four locations, Bangalore, Ranchi, Hyderabad and Tirunelveli of the Indian region, using micrometeorological measurements from the instrumentation network established during the programme, “Prediction of Regional Weather using Observational meso-Network and Atmospheric Modelling (PRWONAM)”. The average $z_{0}$ values estimated are $0.04 \pm 0.02$ and $0.06 \pm 0.03$ m for Bangalore for the summer and the winter seasons respectively; and $0.009 \pm 0.007$ and $0.04 \pm 0.02$ m for Ranchi. For Hyderabad and Tirunelveli locations, average $z_{0}$ values for the summer season are $0.8 \pm 0.1$ and $0.02 \pm 0.02$ m respectively. This value of $z_{0}$ for Hyderabad is consistent with the range 0.2–2.1 m quoted for fetches mainly covered with trees. The $z_{0}$ values for Bangalore, Ranchi and Tirunelveli are consistent with similar terrain pattern in the prevailing wind sectors at the experiment locations and are also in the range 0.006–0.08 m quoted in the literature for homogeneous land surfaces.

For the first time, the thermal roughness length $(z_\mathrm{h})$ is estimated for the Indian region. The average $z_\mathrm{h}$ estimated for Bangalore for the summer monsoon season is $0.006 \pm 0.006$ m, one order of magnitude smaller than the corresponding $z_{0}$. The ratio $z_{0}/z_\mathrm{h}$ is 6.8 for Bangalore, and comparable with values quoted in the literature.