CORRESPONDENCE Comments on ‘‘Symmetric and Asymmetric Structures of Hurricane Boundary Layer in Coupled Atmosphere–Wave–Ocean Models and Observations’’

In a recent paper, Lee and Chen (2012, hereafter LC12) presented numerical simulations of symmetric and asymmetric hurricane boundary layer structures in a fully coupled atmosphere–wave–ocean model and used these simulations to compare aspects of the boundary layer structure against an analysis of observations. One of their main conclusions was that ‘‘the azimuthally averaged inflow layer tends to misrepresent the overall inflow structure in tropical cyclones, especially the asymmetric structure’’ (p. 3593). Another main conclusion was that the complicated asymmetric three-dimensional boundary layer structures (attributed by them to be) due in part to the air–sea and wind– wave coupling ‘‘make it difficult to parameterize the atmosphere–wave–ocean coupling effects without a fully coupled model’’ (p. 3593). After careful examination of their study, we have a number of questions regarding their methodology, their interpretations (including their interpretations of previous literature), and their conclusions. Specifically, we inquire about aspects of the methodology for defining the dynamical boundary layer depth, the selection of the boundary layer scheme, and we question the conclusions inferred. In addition to the foregoing concerns, inaccuracies in their literature review are noted and inconsistencies between their conclusions and reported results are identified. For many decades, physical processes across the air– sea interface and within the atmospheric boundary layer have been known to be essential for the development and maintenance of a tropical cyclone (Ooyama 1969; Emanuel 1986, 1995; Smith et al. 2009; Smith and Montgomery 2010; Bryan and Rotunno 2009; Bryan 2012). However, the boundary layer is the least-observed part of a storm—in particular, its turbulence structure. With the advent of the global positioning system (GPS) dropsonde (Hock and Franklin 1999), the mean boundary layer structure has been progressively studied. Previous studies have concentrated mostly on determining the boundary layer structure in an individual storm (e.g., Kepert 2006a,b; Montgomery et al. 2006; Bell and Montgomery 2008; Barnes 2008; Zhang et al. 2009; Zhang 2010)with the hope that these findings generalize to other storms. Recently, Zhang et al. (2011, hereafter Z11) conducted a composite analysis of the axisymmetric boundary layer structure based on hundreds of GPS Corresponding author address: Dr. Jun Zhang, NOAA/AOML/ Hurricane Research Division with University of Miami/CIMAS, 4301 Rickenbacker Causeway, Miami, FL 33149. E-mail: [email protected] 2782 JOURNAL OF THE ATMOSPHER IC SC IENCES VOLUME 71