Clear sky direct radiative effects of aerosols over Southeast Asia based on satellite observations and radiative transfer calculations

a r t i c l e i n f o Keywords: Aerosol Radiative Effects Southeast Asia MODIS CERES Radiative transfer model Using the Moderate Resolution Imaging Spectroradiometer (MODIS), Clouds and the Earth's Radiant Energy System (CERES) instrument, and a radiative transfer model (RTM), we provide a quantitative assessment of regional cloud-free diurnally averaged shortwave Aerosol Radiative Effects (AREs) at the top of atmosphere (TOA) and at the surface over Southeast Asia (SEAS, 10°S–20 N and 90°E–130°E). The spatial and temporal variations of the annual ARE are calculated based on satellite and ground-based measurements, supplemented by radiative transfer simulations. During 2001–2010, our results indicate that the TOA diurnally averaged ARE is −5.6 ± 0.8 Wm −2 over land and −4.8 ± 0.7 Wm −2 over ocean, respectively. In contrast, the surface ARE is −13.8 ± 3.2 Wm −2 based on radiative transfer calculations. For aerosol layers of 2 km in height with midvisible optical depth of 1.41 and single scattering albedo of 0.91, the shortwave radiative heating can exceed 0.8 K/day. Our results indicate significant inter-annual variability of aerosol radiative properties, which is extremely large over major emission outflow regions like SEAS. This study suggests that an integrated system of satellite data, model calculations coupled with ground-based and meteorological data sets is needed to assess Aerosol Radiative Effects on regional earth-atmosphere energy budgets. Although the impact of greenhouse gases on climate has been extensively studied, the role of aerosols also has measurable and equally significant impact on climate (Kaufman, Tanre, & Boucher, 2002). However, scientific understanding of the radiative effects due to atmospheric aerosols from regional to global scales is still uncertain, especially in regions with complex emission sources and land ecosystems such as Southeast Asia (SEAS) (IPCC, 2007; Reid et al., 2013). Previous studies have indicated that natural and anthropogenic aerosols alter the radia-tive energy budget by scattering and absorbing incoming solar radiation (the direct radiative effect) and also modify cloud properties (the indi-Depending on aerosol properties and the underlying surface albedo, the top of atmosphere shortwave aerosol direct radiative effects (ARE toa) can be positive (warming effects) or negative (cooling effects). By absorbing incoming solar radiation, aerosols such as soot can both warm the atmosphere and cool the surface, whereas highly scattering type aerosols (e.g. sul-fate) can cool the Earth's surface by reflecting more solar insolation and thereby increasing the planetary albedo that globally averaged ARE toa values …