Tropical Cyclone Outer‐to‐Inner Brightness Temperature Ratio: A New Size‐Adaptive Parameter Reflecting Storm Intensity and Its Change

Abstract The intensity and size of a tropical cyclone (TC) are profoundly shaped by its internal convective distribution. However, comparing convective structures across TCs is challenging because fixed‐radius metrics cannot adapt to TC size variations. We introduce the Outer‐to‐Inner Brightness‐temperature Ratio (TBR), a size‐adaptive metric quantifying the relative convective strength between the inner and outer region. Analysis of Northwest Pacific TCs (2001–2017) reveals TBR is strongly correlated with intensity ( r ≈ 0.6), significantly higher than correlations considering only the inner ( r = −0.34) or outer region convection ( r = 0.24). TBR is also strongly linked to intensification, with the frequency of rapid intensification peaking within a narrow high‐TBR window (1.15–1.20). Furthermore, for the intensification stage, sustaining a high‐TBR state—a strong inner convection and quiescent outer region—is crucial for achieving a higher lifetime maximum intensity, a process linked to more efficient inward angular momentum transport. TBR provides a powerful tool linking size‐adaptive convection features to TC intensity and evolution.