Atmospheric Modelling of Aerosols Long-Range Transport over the Himalayas

Abstract:

An Atmospheric Modelling System has been set up at International Centre for Integrated Mountain Development (ICIMOD) Headquarters in Kathmandu, Nepal, for the assessment of air quality in the Hindukush Himalaya region. The Weather Research and Forecasting with Chemistry (WRF-Chem) model version 3.6 is being implemented over a regional domain stretching across 4995 x 4455 km centred at Kathmandu, where an intensive field campaign, Sustainable Atmosphere for the Kathmandu Valley (SusKat) took place from December 2012 to February 2013. Seven stations around the valley collected data on meteorology and chemical parameters. WRF-Chem simulation are carried out for the winter time period at high horizontal resolution (1 km × 1 km), which is achieved by nesting the domain of interest, e.g. Kathmandu Valley, inside three coarser domains. Model validation is performed against the field data as well as satellite data, focusing on aerosols. The challenge of capturing the necessary atmospheric processes is discussed. The effort aims for a better understanding of atmospheric processes and aerosol impacts, as well as the impact of long-range transport, particularly of black carbon aerosol upon the radiative budget over the Himalayan glaciers. The rapid melting of Himalayan glaciers and snowfields, and the shrinkage of permafrost as noticed by glaciologists is a concern. Based on physically adjusted schemes, the WRF meteorological model performs well with Pearson correlation coefficients higher than 0.8 for temperature and solar radiation, although it has a tendency to overestimate wind speed. The WRF with chemistry is then used with local and regional emission databases, in combination and after comparison with the global inventory, as input for describing the long-range transport of aerosols. Improved aerosol prediction will allow us to provide crucial information needed for mitigation and adaptation strategies that save people’s lives across the Himalaya. The regional modelling tool is also being set up with an aim to capture aerosol interactions during fog formation, and to generate forecast during a field campaign of the increasing persistent winter fog that ICIMOD plans to coordinate across the Indo-Gangetic Plains during winters 2014-15 and 2015-16.