The GCOM-C Mission and Eight Years of Continuous Global Observations with the SGLI: Estimation of Aerosol Optical Properties and Radiative Forcing from Large-Scale Wildfires

The Second-generation Global Imager (SGLI) onboard the Global Change Observation Mission–Climate (GCOM-C) is a polar-orbiting satellite launched by Japan Aerospace Exploration Agency (JAXA) on 23 December 2017. SGLI is a multi-wavelength optical radiometer with 19 spectral bands ranging from the near-ultraviolet to the thermal infrared. It provides unique observation capabilities, including polarization, multi-directional, and near-ultraviolet measurements, with a spatial resolution of up to 250 m and a swath width exceeding 1,000 km.

Assessing the climate influence of wildfires requires continuous observation of aerosols released by biomass burning, as well as quantitative evaluation of their optical characteristics and radiative impacts. In this work, we investigated large wildfire events occurring since 2018 across multiple regions, including Brazil, Angola, Australia, California, Siberia, and Southeast Asia. Based on observations from SGLI, we examined temporal variations in key aerosol optical parameters—namely aerosol optical thickness (AOT), Ångström exponent (AE), and single scattering albedo (SSA)—supplemented by complementary satellite and ground-based measurements.

Examination of the relationships between SSA and AE suggests that aerosol optical behavior is strongly influenced by ambient relative humidity and the dominant vegetation types involved in combustion, in agreement with earlier findings. In addition, variations in net incoming radiation at the top of the atmosphere were evaluated during periods of intense fire activity to quantify the direct radiative effects of biomass-burning aerosols. The analysis indicates pronounced negative radiative forcing, corresponding to a cooling effect, over oceanic areas, reaching −78 W m⁻² for Australia and −96 W m⁻² for California. In contrast, radiative forcing over land remains comparatively small, with values on the order of −10 W m⁻² across all examined regions.

These findings highlight the necessity of accounting for regional differences in aerosol optical properties and surface reflectance when estimating wildfire-related radiative forcing and when evaluating the future climatic implications of this short-lived climate forcer.