Impact of Cartosat-1 Orography in 330 M Unified Model Forecast

The newly introduced high-resolution (330 m) regional model, Delhi Model (DM), at the National Centre for Medium Range Weather Forecasting targets winter time fog/visibility forecast over Delhi, India. The pre-sent study focuses on the benefits of enhanced oro-graphic features in DM, through a new data set deve-loped using the Indian Space Research Organisation Cartosat-1 orography (Cartosat-run), against those from the NASA Shuttle Radar Topography Mission Digital Elevation Model employed previously (SRTM-run). The early morning visibilities from the Cartosat-runs were lower compared to the SRTM-runs, which could be linked to an enhanced downdraft (negative vertical velocity) in the former, helping form a shallow and stratified boundary layer. The evolution and vari-ability of ‘ventilation index’ in the model domain is regulated by the local wind circulation changes within the shallow boundary layer which in turn is modulat-ed by the orography representation. The DM forecast-ed ventilation index has been projected to be a potential indicator of the atmosphere dispersion of airborne pollutants over Delhi.