Relationship between Convection and Tropical Cyclone Size and Size Change Rate

This study examines the relationship between convection activity and size as well as the size change rate of Tropical Cyclones (TCs) over the Northwestern Pacific Ocean (NWP) from 2001 to 2022. TC size is defined by the radius of 34-kt wind (R34) provided by the Joint Typhoon Warning Center (JTWC) and is classified into small, medium, and large categories across different intensity stages. Deep convection and high clouds were identified using infrared brightness temperature (IR BT) thresholds of 64 knots), convective coverage is proportional to R34, whereas for tropical storms (TS), the relationship is weak. As TC intensity increases, deep convection remains concentrated within the inner core (~100 km from the centre), while convective expansion is driven mainly by the broadening and enhancement of high clouds in the outer core. The TC cases undergoing rapid growth (RG; defined as a 24-hour R34 increase ≥ 83 km) have a significantly smaller R34 than those experiencing slow or no expansion, which is attributed to the higher frequency of RG during the TS stage. The intensity and occurrence ratio of deep convection near R34 are identified as key factors influencing whether TCs undergo RG.