Comparing the medium-range weather forecast impacts of the Tomorrow.io Microwave Sounder and TROPICS in January 2025

Passive microwave (PMW) sounders in Low Earth Orbit (LEO) garner some of the largest observational impacts on daily weather forecasts from operational centers. The Tomorrow.io Microwave Sounder (TMS) is the next generation of NASA’s Time-Resolved Observations of Precipitation structure and storm Intensity with a Constellation of Smallsats (TROPICS). Driven by cost, latency, coverage, and the aging public fleet of PMW sounders, the TMS constellation of 6U Bus satellites will provide global revisit rates on the order of 30 minutes. The first six satellites launched through March 2025, and we anticipate fourteen satellites in orbit by early 2026. There are implications for nowcasting, numerical weather prediction (NWP), the long-term observation record, improved global coverage, intercalibration, and validation.

We evaluate real impacts of TMS and TROPICS on NWP with Observing System Experiments (OSEs) through 30 days of continual NWP and data assimilation (DA) cycling in January 2025. Our most recent CNTRL prototype system ingests multiple TMS and TROPICS instruments, at various orbital inclinations. We also ingest all other PMW sounders that are assimilated operationally in GDAS, alongside other conventional and remotely sensed observations. We will present the impact of denying one to several TMS and TROPICS instruments from CNTRL. Additionally, we will compare those impacts to those of higher-cost PMW sounders like the Advanced Technology Microwave Sounder (ATMS).

Our CNTRL end-to-end workflow is modeled after the NOAA Global Data Assimilation System (GDAS) and Global Forecast System (GFS) v16, with some modifications to account for the still-in-development Joint Effort for Data Assimilation Integration (JEDI) ecosystem. Forecasts and DA utilize a C768-L127 mesh of the Unified Forecast System Finite-Volume Cubed-Sphere (FV3-UFS) atmospheric model. We use FV3-JEDI’s 3D ensemble variational data assimilation (3DEnVar) with 30-member C192-L127 6-h forecasts. Ensemble forecasts are cold-started from the NOAA Global Ensemble Forecast System (GEFS) initial conditions. An earlier preliminary study assimilating a single TMS instrument during November 2024 achieved a global average 2-3% positive impact on 2-day forecasts of temperature, water vapor, and winds. Here we extend that investigation to the evolving TMS and TROPICS constellation.