Aerosol Forcing During INDOEX and ACE-Asia as Determined From Aircraft and Grou nd Measurements

A suite of radiometers was flown on the NCAR C-130 aircraft throughout the INDOEX and ACE-Asia experiments to measure broadband and spectral irradiances. Identical instruments were placed in the zenith and nadir positions, allowing net flux and optical depth to be determined. The radiative forcing efficiency (aerosol forcing per unit optical depth) was determined below the aerosol layer, i.e. at an altitude of about 40 meters. This was measured in the spectral range s 220 to 3910 nm (total solar forcing) and 680 to 3300 nm (near infrared) and in seven spectral channels covering contiguously the visible range from 400 to 700 nm. Surface measurements of solar insolation as well as aerosol column optical depth were made at Kaashidoo, Maldives (INDOEX) and at Cheju Island, South Korea (ACE-Asia). These measurements, in conjunction with aerosol-free model simulations, are used to determine the radiative forcing at the surface for the visible, near-infrared, and total solar spectral bandpasses. During INDOEX the diurnally averaged broadband surface aerosol radiative forcing was -72.2+/- 5.5 W m^-2 per unit optical depth at 500 nm with roughly half being contributed from the visible (-38.5+/- 4.0 W m^-2). The corresponding results during ACE-Asia were: broadband -73.1+/- 9.7 W m^-2, visible -41.7+/- 4.7 W m^-2, and near infrared -36.3+/- -5.6 W m^-2.