Effects of preexisting cyclonic eddies on upper ocean responses to Category 5 typhoons in the western North Pacific

This study examines the impacts of preexisting mesoscale cyclonic eddies (PCEs) on successive enhanced sea surface cooling in response to the passage of Super Typhoon Hai-Tang in the western North Pacific in 2005, using numerical simulation methods. We have done two numerical experiments: one with the presence of these PCEs resolved by the Hybrid Coordinate Ocean Model/Navy Coupled Ocean Data Assimilation system (EXP_HYC) and another with World Ocean Atlas 2001 climatology as initial conditions (EXP_WOA). The results show that the cooling response simulated by EXP_WOA is only half of that simulated by EXP_HYC, which is close to satellite observations. This suggests that an accurate representation of the upper dynamic conditions is required to estimate the sea surface cooling to a typhoon accurately. Subsequently, the effects of the PCEs on successive cooling response to most major typhoons are evaluated by conducting a systematical analysis with a focus on Category 5 typhoons occurring in the region from 2003 to 2008. Satellite altimeter sea surface height anomaly data and merged Tropical Rainfall Measuring Mission Microwave Imager/Advanced Microwave Scanning Radiometer for EOS microwave sea surface temperatures (SST) are used to characterize PCEs and cooling responses to those typhoons. The results identify the relationship between PCEs and successive enhanced SST cooling for most strong typhoons in the western North Pacific.