Assimilation of All-Sky TROPICS Constellation Radiance Data in the NASA Goddard Earth Observing System (GEOS)

Abstract

This study examines the impact of assimilating all-sky microwave radiances from the Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS) mission within the NASA Global Earth Observing System (GEOS) data assimilation and forecasting framework based on the Gridpoint Statistical Interpolation (GSI) system. Observing system experiments and Forecast Sensitivity to Observation Impact (FSOI) diagnostics were conducted, covering July through September 2023 for the experiments and August 2023 for the FSOI analysis. Results show that TROPICS radiances improve the representation of tropical moisture, temperature, and wind structures and reduce forecast error across multiple atmospheric fields. The strongest improvements occur in the lower and middle troposphere and persist through forecast day five. The constellation architecture plays a key role, with the four-satellite configuration producing larger and more spatially coherent benefits than any individual platform in idealized experiments, with smaller but consistent positive impacts in the full GEOS-FP system. Even within a radiance-rich observing system, TROPICS provides complementary information on moist convective processes. Consistency between deterministic forecast verification and FSOI diagnostics supports the robustness of these findings. Overall, small-satellite constellations with high revisit rates can add value to global numerical weather prediction by improving the depiction of tropical convection in modern data assimilation systems.