The Hurricane Boundary Layer

Abstract

The planetary boundary layer (PBL) within the troposphere of the atmosphere regulates the transfer of heat, moisture, and momentum between the atmosphere and the surface through drag effects, turbulent diffusion, and mixing processes (Stull, 1988; Garrat, 1994). The PBL is the layer of the atmosphere closest to the Earth and is therefore directly influenced by effects of the surface (friction, heating, cooling, evapotranspiration, etc.). Therefore, almost all the weather generation processes originate in the PBL. It is variously defined as a continental PBL or marine boundary layer (MBL) according to its location and secondly, as stable, neutral, or unstable, depending upon the degree of turbulence. The Hurricane Boundary Layer (HBL) is a special class of the MBL that refers to the bottom layer of the atmosphere in tropical cyclones (TCs). However, there are features unique to the HBL that has made modelling and understanding it one of the largest challenges facing the tropical cyclone forecasting community. Until recently, the risks to humans and scientific equipment associated with the extreme conditions in the HBL prevented the collection of high-quality observations in the HBL. Secondly, numerical models did not possess adequate resolution to model the HBL processes. Also there is a lack of understanding on the connection between the HBL structure and tropical cyclone intensity changes.