Effect of Air-Sea Environmental Conditions and Interfacial Processes on Extremely Intense Typhoon Haiyan (2013)

Typhoon Haiyan (2013) intensified rapidly and reached a central pressure of 895hPa over the warm northwestern Pacific. To clarify why Haiyan became such an extraordinarily intense tropical cyclone (TC), we investigated the impacts of atmospheric and oceanic conditions and air-sea interfacial processes on Haiyan's intensity. We performed ensemble experiments with many different initial oceanic conditions and a 7-km-mesh atmosphere-wave-ocean coupled model. We also performed sensitivity experiments to examine the impacts of sea spray and use of a 2-km-mesh horizontal resolution. Also, analogous experiments were performed with Typhoon Mike (1990), which followed a similar track but was less intense than Haiyan. For both TCs, ocean coupling helped alleviate uncertainty in the simulated intensities caused by different preexisting oceanic conditions. Increases in air-sea latent heat fluxes helped increase the intensity of both TCs although the effect of sea spray depended on whitecap coverage. Preexisting oceanic conditions and air-sea interfacial processes directly affected the secondary circulation via changes in latent heat fluxes and near-surface moisture influxes. However, the 2-km-mesh resolution improved only Haiyan's simulation; the mean latent heat flux over the strength area was insufficient to simulate the intensity. It was easterly winds and specific humidity at 850 hPa that determined the small size, rapid translation, less sea surface cooling, and small decreases in latent heat fluxes beneath the frictional convergence area of simulated Haiyan. Understanding of the effect of preexisting oceanic conditions and air-sea interfacial processes on simulated TCs will serve as a guideline for improvement of the atmosphere-wave-ocean coupled model.