10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Improved Prediction of Aerosol Optical and Chemical properties over the Indian Subcontinent from Constrained Aerosol Simulation
Bharath Kumar, SHUBHA VERMA, Olivier Boucher, Rong Wang, Indian Institute of Technology Kharagpur
Abstract Number: 1708 Working Group: Aerosol Modeling
Abstract Role of aerosols in influencing the hydrological cycle is evidenced through studies with aerosol-chemistry-climate models. These studies are required specifically for the Indian subcontinent, as monsoon precipitation being a crucial element of economic growth in India. However, a large divergence between simulated and observed aerosol distribution over the Indian region limits the accuracy in prediction ability of aerosol-climate interactions over the region. This divergence is typically large over the Indo-Gangetic plain, where the atmosphere is observed laden with a high pollutant level of aerosol load. Due to the inclusion of various complex physical-chemical atmospheric and aerosol processes in aerosol-chemistry-climate models, in conjunction with inherent uncertainty in inputs to the model, e.g. aerosol emissions and their properties, a systematic approach is, therefore, required to improve the prediction of aerosols.
With the aim of obtaining a better concurrence between model estimates and observations of atmospheric aerosol chemical constituents and predicting their spatial distribution as consistently as possible, we performed a free running aerosol simulation (freesimu) in a general circulation model (GCM), and further constrained the simulated with the observed aerosol optical depth (AOD). Constrained aerosol simulations are used to establish an alternate approach for estimating the atmospheric concentration by surpassing the error induced specifically due to emissions in source regions which prevails in case of the free running aerosol simulations. The present study was carried out during the pre-monsoon season and for the Tigerz experiment which was conducted at stations over the Indo-Gangetic plain (IGP) and the Himalayan foot-hills in northern India. Our formulation of the constrained aerosol simulation (constrsimu) was based upon an identification of the freesimu with the most consistent estimates of aerosol characteristic among the three freesimu (differing in the source of emissions and resolution) carried out in the GCM of Laboratoire de Météorologie Dynamique (LMD-ZT GCM).
Estimates from constrsimu revealed a good concurrence with the observed counterparts. Black carbon (BC), organic carbon (OC), and sulfate-other water soluble (Sul-ows) constituents estimated from constrsimu amounted to 70%–100% compared to that from freesimu being 20%–50% of their measured counterparts. Also, a good agreement between constrsimu estimated aerosol constituents and the respective observations confirmed the postulation of our formulation that the lack of anthropogenic emissions in aerosol simulation in GCM-indemiss being the primary reason for a large discrepancy between model and observations over the mainland India. Estimates from constrsimu were further used to examine the pattern of the distribution of pre-monsoon mean of aerosol species optical depth and concentration over the Indian subcontinent. Among the aerosol constituents, the pre-monsoon mean of dust concentration from constrsimu was considerably high over most of the Indian subcontinent, the anthropogenic aerosol constituents were, however, specifically predominant over the IGP. While the high value of observed AOD was found being mainly due to dust (>0.3) over the northern–northwestern IGP, it was due to Sul-ows (as high as 0.4) over the eastern IGP, eastern coastline, and the Bay of Bengal.
Improved prediction of aerosol constituents as obtained from constrsimu over the Indian subcontinent region gives an insight on prognostic improvement in free running aerosol simulations in the GCM. This information is also useful towards a more realistic estimation of aerosol-induced radiative perturbations and their climatic implications over the region.