Impacts of sea spray on the boundary layer structure of Typhoon Imbudo

Abstract

High winds in a typhoon over the ocean can produce substantial amounts of spray in the lower part of the atmospheric boundary layer, which can modify the transfer of momentum, heat, and moisture across the air-sea interface. However, the consequent effects on the boundary layer structure and the evolution of the typhoon are largely unknown. The focus of this paper is on the role of sea spray on the storm intensity and the structure of the atmospheric boundary layer. The case study is Typhoon Imbudo in July 2003. The results show that sea spray tends to intensify storms by increasing the sea surface heat fluxes. Moreover, the effects of sea spray are mainly felt in boundary layer. Spray evaporation causes the atmospheric boundary layer to experience cooling and moistening. Sea spray can cause significant effects on the structure of boundary layer. The boundary-layer height over the eyewall area east to the center of Typhoon Imbudo was increased with a maximum up to about 550 m due to sea spray, which is closely related with the enhancements of the heat fluxes, upward motions, and horizontal winds in this region due to sea spray. Key words: sea spray, typhoon, boundary structure IntroductionTyphoon is one of the most destructive natural disasters affecting China. Each year coastal South China is impacted seriously by typhoons that form over the western Pacific and the South China Sea. Millions of people live along the coastline and are exposed to the threat from wind, rain, storm surges, and severe weather caused by western Pacific typhoons. During the last two decades, the theory of typhoon evolution has been investigated extensively. In particular, large efforts were focused on the effects of large-scale circulation, typhoon structure, and terrain, etc. on the evolution of the typhoon (see the review in Meng et al., 2002). By comparison, the role of air-sea interaction processes in western Pacific typhoons seems to have received less attention in the earlier studies.Indeed, typhoon, one of the most energetic weather events over the ocean, is a powerful engine that runs on the energy extracted from the ocean. The air-sea transfer of momentum and enthalpy has long been recognized as important elements for generating and maintaining hurricanes. Turbulent transfer processes over the ocean are commonly parameterized using Monin-Obukhov similarity theory. However, during high-wind, hurricane conditions, large amounts of sea spray are produced by bursting air bubbles in whitecaps and by tearing spume from the wave crests. Consequently, both turbulence and sea spray provide routes by which moisture, heat, and momentum cross the air-sea interface. Although the question as to whether or how sea spray affects the evolution of hurricanes has