The effects of oceanic barrier layer on the upper ocean response to tropical cyclones

Abstract Previous studies of the barrier layer (BL) and tropical cyclone (TC) intensification show controversial results. Some studies suggest that the BL is favorable for TC intensification, whereas others demonstrate that the BL has little impact. The present paper reconciles these previous results by showing that the influence of the BL on TC intensification is complex and dependent on the stages, TC intensity, TC forcing time, and ocean stratification. The influence can be divided into three different stages. First, when a TC is weak or the TC‐induced forcing cannot break through the mixed layer (ML), the presence of the BL leads to a thin ML, results in a large ML cooling, and reduces the effective TC heat potential (ETCHP) by distributing the air‐sea heat loss to the thin ML, thus suppressing TC growth. Second, when TC strengthens or wind forcing increases, the forcing becomes strong enough to break through the ML and penetrates into the BL. The entrainment of BL water, which is warmer than the cooled ML, compensates the surface heat loss and leads to an increase of the ML temperature, supporting TC growth. Third, when the TC‐induced forcing is strong enough to break through the BL base and penetrates to the thermocline, the BL reduces the magnitudes of cooling temperature and of decreasing ETCHP compared to those without the BL, which is also favorable for TC intensification. Thus, whether the BL intensifies TCs depends on the conditions associated with the upper layer ocean and TCs.