| dc.description.abstract | Aerosols can alter solar radiation in the earth’s atmosphere and have implications for future climate change. The Intergovernmental Panel on Climate Change (IPCC, 2007) has indicated that anthropogenic direct aerosol radiative forcing (ARF), which is estimated to be -0.5 Wm-2, has a large uncertainty. Liou et al. (2007) suggested the current challenges on the atmospheric radiative transfer model to be aerosol-radiative effect, surface complexity terrain-radiative effect, and wind-driven air-sea interface-radiative effect. We investigated atmospheric radiation and direct aerosol-radiative forcing at Lulin Atmospheric Background Station (LABS), Taiwan. We integrated measurements from the Kipp & Zonen solar instrument systems, the Aerosol Robotic Network (AERONET) Cimel sunphotometer (CIMELs), and a radiative transfer model (libRadtran) to estimate ARF. The good agreement between observation and simulation for clear-sky implies the model can represent solar radiation at the surface for the mountain site. We also discussed model and instrument uncertainties and analyzed data from 2010 to 2011 to clarify the characteristics of atmospheric radiation and aerosol optical properties at LABS. We applied three different methods (i.e., direct calculation, linearly interpolated, and model calculation) to estimate direct aerosol radiative forcing.
The results show that the mean downward shortwave ARFs at the surface are -14.6−-6.5 Wm-2 (Global), 11.0−14.1 Wm-2 (Diffuse), and -23.2−-17.1 Wm-2 (Direct), respectively. We observed the seasonal maximum values of ARFs in spring because of the higher aerosol optical depth (AOD). We estimated the aerosol radiative forcing efficiency (AREF; ARF/AOD) to be -237.8−-94.2, 167.8−191.8, and -350.2−-245.9 Wm-2τ-1 for Global, Diffuse, and Direct, respectively. We attributed the higher AREF values during June and September to aerosol with larger light absorption during this season.
In the future, we will attempt to improve our simulation results by using inputs of aerosol optical properties that are more accurate (e.g., obtained from in-situ). The empirical relationship between ARF and AOD from this study could also be used to estimate AOD, when surface radiation flux measurements are available. The AOD retrieved from the global distribution of radiometer measurements could benefit aerosol and radiation communities. | en_US |