Climate Impacts of Carbonaceous Aerosols over the Indian Subcontinent using a Regional Climate Model, RegCM4

Abstract:

Aerosol feedback continues to be a major source of uncertainty in climate forcing. Modelling of aerosol feedback is challenging because of uncertainties in emission inventory and aerosol processes parameterized in the climate models. In this work, we address both these aspects with a focus on the Indian monsoon region. First, we implement a regional emission inventory in the regional climate model RegCM4.6 and then implement a dynamic ageing scheme for carbonaceous aerosols in the model to improve the aerosol life cycle processes. We configure the model over the South Asian CORDEX domain at 25 km resolution for 11 years (2005-2015). The first year has been left as spin-up time and analysis has been done for the remaining 10 years to understand the climate feedback of the carbonaceous aerosols. Two sets of experiments have been carried out for this study – (i) Expt_1 includes anthropogenic aerosols (BC + OC + SO2) without any radiative feedback and (ii) Expt_2 with aerosol feedback. We show that the model performance in simulating the aerosol and meteorological fields improve after incorporating the regional emission inventory and the dynamic ageing scheme. The climate feedback is examined in terms of the changes in the meteorology (temperature, humidity, precipitation) over the study domain. We also demonstrate the changes in aerosol loading as a result of this feedback processes (i.e. how the aerosol optical depth changes when the aerosol feedback is switched on). Our results suggest that the models must improve the aerosol processes along with the periodic update of the emission inventory to reduce the uncertainty in climate feedback estimates at a regional scale.