Besides Assimilation and Retrieval: Innovative Quantitative Uses of Satellite Brightness Temperatures and Radiosonde Observations

Satellite brightness temperature (BT) observations contain rich information about the horizontal distributions of cloud and rainfall structures; while radiosonde observations provide high-vertical-resolution measurements of temperature, moisture, and wind in the atmosphere. Beyond their traditional use in assimilation and retrieval, this study demonstrates innovative quantitative uses of BT and radiosonde observations for evaluating high-resolution numerical weather prediction (NWP) simulations of tropical cyclones (TCs) and Southwest Vortices (SWVs).

First, we apply BT observations to document  the structural evolution of TCs and SWVs and to directly compare simulated hydrometeor distributions with satellite-observed cloud and precipitation features. These BT-based diagnostics provide objective constraints on model representation of convective initiation and development as well as the impact of diurnal variability.

Second, a BT-based threat-score (BT-TS) framework is introduced to assess the skill of rainfall forecasts with respect to satellite BT observations instead of rainfall observations traditionally used in TS evaluation. Using microwave humidity-sounder channels, the BT-TS metric performs well for assessing rainfall forecast in regions where precipitation observations are sparse or unavailable. The BT-TS forecast results highlight model deficiencies in timing, extent, and intensity of SWV-induced convective rainfall.

Third, radiosonde profiles are used to investigate lower-tropospheric processes critical for vortex evolution, focusing on planetary boundary layer (PBL) height and vertical variability under different vertical-resolution configurations. Verification with high-vertical-resolution (~5–6 m) profiles from 119 Chinese radiosonde stations during the summers of 2021–23 shows that accurately representing PBL height and lower-tropospheric thermodynamic variability requires approximately doubling  the number of ERA5 vertical levels.

Together, these BT- and radiosonde-based diagnostics provide a comprehensive observational framework for evaluating the structural evolution of TCs and mesoscale SWVs. Future work will leverage these insights to refine cloud microphysics schemes, optimize model vertical-resolution design, and enhance the predictability of convection-permitting NWP systems.