Lidar Observations of the Typhoon Boundary Layer Within the Outer Rainbands

Abstract

The typhoon boundary layer within the two super typhoons Dujuan and Soudelor is observed using ground-based Doppler lidar up to a height of 240 m, and primarily in the outer rain-bands. The mean wind-speed profiles are analyzed over 1-h intervals and two longer intervals, representing the stages of the typhoons’ approach and departure, respectively. In agreement with surface-layer parametrizations related to finite mixing-length theory, the hourly mean wind-speed profiles demonstrate that the scaling parameter $$u_{*o}$$ /fc, where $$u_{*o}$$ denotes the surface friction velocity, and fc denotes the Coriolis parameter, determines the depth the surface layer, and governs the boundary-layer formation in the mixed layer. With large values of $$u_{*o}$$ /fc, the dominance of surface friction extends the logarithmic layer to the uppermost level of the present observations. In contrast, with small $$u_{*o}$$ /fc values, the effect of the Coriolis parameter increases the wind speed with respect to the logarithmic profile above the surface layer. That the averaged wind-speed profiles may be described by finite mixing-length theory, the empirical Deaves and Harris model, as well as the power-law profile, suggest these approaches are appropriate for simulations of the typhoon boundary layer.