Using NOAA/AVHRR products to monitor El Niño impacts: Focus on Indonesia in 1997-98

Abstract

The development of the El Niño-Southern Oscillation (ENSO) in 1997-98, the most intense in this century, has been monitored by space- and ground-based observations. In this study, the authors present the signatures of ENSO impacts on the surface-atmosphere system, as detected in satellite products that are routinely derived at NOAA from measurements by a single instrument on board NOAA polar-orbiting satellites - the Advanced Very High Resolution Radiometer (AVHRR). The Indonesian archipelago was selected to demonstrate how AVHRR products can be synergistically used to monitor interannual variability, such as caused by ENSO, on regional and global scales. The authors examined month-to-month changes in surface-atmosphere conditions over the region during July 1997-June 1998. The major ENSO impact over the Indonesian archipelago was a prolonged dry period with anomalously low amounts of cloud, precipitation, and water vapor. The net effect of these changes was a significant increase in the absorbed short-wave and outgoing longwave radiation fluxes. ENSO-induced drought coincided with the slash-and-burn agricultural season, which resulted in persistent fires and smoke from biomass burning, covering larger areas, producing more smoke, remaining longer than during most dry seasons, and causing health hazards for millions of people in Southeast Asia. Analysis of the impact of fires on cloud microphysics confirms earlier suggestions that the effective cloud droplet size decreases due to smoke aerosols and cloud reflectivity increases due to higher concentration of small droplets. Analysis of areas with active fires showed a decrease in both surface albedo and fractional green vegetation as a result of intensive burning.