The horizontal convective rolls are a part of mesoscale system spread over a large area with fine features. A nested model with a widespread outer domain to accommodate large scale system and a high resolution inner domain to
account for the detailed structures would be the appropriate one in the present case study. It is to be mentioned here that a similar study of rolls in an urban heat island has recently been carried out by Miao and Chen (2008) using WRF. Their simulation for a cloud free condition has shown good agreement with wind profiler observation. In the present case, the study area is a coastal terrain and the condition is low wind speed with fair weather cumulus clouds.