Large Aerosol Radiative Forcing due to the 1997 Indonesian Forest Fire

During the last decade, the feedback between El Niño and biomass burning caused the Indonesia's forest fire aerosols to be the second most significant source of anthropogenic aerosol over the tropical Indian Ocean after the South Asian Haze. In this paper, the estimates of the radiative forcing during the 1997 Indonesia's forest fire have been obtained by integrating satellite derived aerosol optical depths and cloud cover with in‐situ observations of single scattering albedo and a Monte‐Carlo Aerosol‐Cloud radiation model. The haze reduced the seasonal average solar radiation absorbed by the equatorial Indian ocean by as much as 30 to 60 W m −2 during September to November 1997, and increased the atmospheric solar heating by as much as 50% to 100% within the first 3 kilometers. The radiative forcing at the top of the atmosphere (TOA) was in the range of 5 to 15 W m −2 under cloudy skies. The significance of such large radiative flux changes to the tropical ocean‐atmosphere heat budget and climate needs to be examined with climate models.