Several semi-idealized numerical experiments are conducted to investigate the sensitivity of intensity of Typhoon Shanshan (2006) to changes of sea surface temperature (SST) over different radial extents.It is found that the increase of SST within the range 1.5–3.5 times the radius of maximum wind (RMW),defined as theeffective radius (ER),contributes greatly to the increase of TC intensity and the reduction of TC inner-core size,whereas the increase of SST farther outside the ER reduces TC intensity and increases TC inner-core size.Moreover,as the absolute SST over the whole domain increases,the TC is not much stronger but larger.These results suggest that the change of relative SST within the ER has a stronger impact on TC intensity than that of the absolute SST.Further analyses reveal that the different effects of SST within and outside ER on TC intensity rely on a number of factors that directly or indirectly influence the TC development.As SST increases within (outside) ER,more (less) surface enthalpy flux (SEF) enters eyewall and less (more) SEF enters the area of outer spiral rainbands,enhanced (attenuated) latent heating occurs at a smaller (larger) radius,and the RMW and eyewall slope are all decreased.These lead to larger (smaller) radial gradients of pressure,and horizontal and vertical velocities,which contribute directly to a stronger (weaker) TC.It is thus concluded that how TC intensity responds to the change of absolute SST depends on the competition between the positive effects of SST within ER and the negative effects of SST outside ER.