Dice Question Streamline Icon: https://streamlinehq.com

Cause of discrete jumps in SHAP values for 43 nm irradiance

Determine the mechanism responsible for the discrete jumps observed in SHAP values at specific FISM2 43 nm irradiance thresholds in the TreeSHAP dependence plot for the Random Forest Atmospheric Neutral Density Model (RANDM) that predicts thermospheric neutral density at 400 km altitude.

Information Square Streamline Icon: https://streamlinehq.com

Background

The paper applies TreeSHAP to interpret a Random Forest model (RANDM) that predicts thermospheric neutral density from solar irradiance (FISM2 spectral bands), geomagnetic indices (SYM-H, AE), and spatial parameters (magnetic local time, satellite latitude). The 43 nm FISM2 band shows the strongest main effect on density predictions.

In the dependence plot for the 43 nm band, the authors observe discrete jumps in SHAP values at certain irradiance levels. They explicitly note that the reason for these discontinuities is unknown, identifying a methodological or physical ambiguity in how feature contributions change with irradiance within the model.

References

Interestingly, there appear to be discrete ``jumps'' in SHAP values at certain irradiance thresholds. The reason for this is unknown, and suggests a direction for future research.

— Elucidating the Grey Atmosphere: SHAP Value Analysis of a Random Forest Atmospheric Neutral Density Model (2509.26299 - Bard et al., 30 Sep 2025) in Section 3.2 (Interaction Effects between Features), paragraph discussing Figure 6a (Main Feature for 43 nm)