Dr. K. N. Liou, Distinguished Professor, Department of Atmospheric and Oceanic Sciences, Founding Director, Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles

Abstract: We illustrate evidence of mountain snowmelt produced by climate change and global warming, followed by a discussion of the role of anthropogenic light-absorbing black carbon (BC, soot) and dust particles in 3D intense mountain/snow areas within the context of direct radiative forcings and snow albedo reduction. We studied two specific mountain areas: the Sierra Nevada Mountains in the western United States and the Tibetan Plateau.

BC particles, which have highly complex and often inhomogeneous morphologies, are a type of aerosols that profoundly affect vertical heating profiles by directly absorbing sunlight in the atmosphere. The radiative transfer schemes that have been used in modern climate models have not taken into consideration the effects that these particles’ open/closed cell structures and the external/internal mixing states in snow grains have on the evaluation of snow albedo reduction. We introduce a new theoretical development for the construction of fractal and complex soot aggregates by mean of stochastic procedures from which their extinction efficiency, single-scattering albedo, and asymmetry factor can be evaluated on the basis of the geometric-optics and surface-wave approaches. We demonstrate that small soot particles on the order of 1 µm, internally mixed with snow grains of 50-100 µm, could effectively reduce snow albedo by as much as 5-10% (Liou et al. 2011).

Furthermore, we present a computational approach for solar radiative transfer based on 3D Monte Carlo photon tracing simulations designed specifically for application to mountains/snow fields in all sky conditions. This is followed by multiple regression analysis and parameterization for direct, diffuse, and coupled surface fluxes with reference to differences produced by 3D and plane-parallel radiative transfer models in a 10x10 km2 domain (Lee and Liou 2011). We subsequently investigate the impacts of 3D radiative transfer parameterization on the land surface energy budget and its potential feedback to regional climate using a coupled land atmosphere model, based on WRF and CLM, as the test bed (Gu, Liou, et al. 2012, in preparation).

Finally, we discuss the importance of BC and dust particles in the reduction of mountain/snow albedo vis-a-vis aerosols-snow-albedo feedback as a regional system that has an irreversible impact on climate and climate change.