Monitoring atmospheric composition & climate
Eruption of the Merapi volcano

MACC is monitoring the developments around the eruption of the Merapi volcano on Java. This page provides daily-updated model simulations from the MACC global system. There is also information about available satellite observations of the volcanic ash plume. For formal volcanic ash plume advisories we refer to the Darwin Volcanic Ash Advisory Centre.

Daily Global MACC plume forecasts

MACC plume forecast

The global MACC system produces daily simulations of an SO2-like tracer to reflect the extent of the volcanic ash plume. Output is available at 3-hourly intervals. Both current and past simulations can be accessed. The emission strength is constant and injected at a fixed height of 9 - 11 km, which does not necessarily reflect current true emissions. The results should therefore only be used as an indication.


MACC does not carry out observations itself, but tries to optimally combine its modelling systems with the available observations from satellites, aircraft, and ground-based networks. At the moment of the eruption the only observations in the MACC pre-operational system that showed at least some of the ash plume were the aerosol optical depth (AOD) retrievals from the MODIS instrument. However, MACC is now looking at all other observations that provide information on the extent of the plume over time to assess the situation retrospectively.

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MODIS visual imagery SACS SO2 alert service ULB IASI SO2 alerts

Data assimilation

The MACC global data assimilation system combines forecasts of the atmospheric composition computer model with available observations of reactive gases, greenhouse gases, and aerosols to provide the best estimate of the state of the atmosphere. Volcanic eruptions are challenging, because the release of sulphur dioxide and volcanic ash is sudden and unpredictable. Observations from satellites provide good estimates of the atmospheric concentrations, but are limited by cloud cover. MACC is exploring how to optimize its system to be able to react quickly and make maximum use of the model capabilities and the observations in the future. The two figures below show how aerosol information from the MODIS instrument (Aerosol Optical Depth) is used in the assimilation to provide a better analysis of the volcanic ash plume, which will lead to a better forecast. The current configuration does not have a volcanic source in the model, but the observations already help to define a realistic plume of total aerosol.

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3-hour forecast of aerosol optical depth Aerosol optical depth as observed by MODIS