Sea‐surface aerodynamic roughness

Abstract

This study surveys and evaluates similarity theory for estimating the sea‐surface drag coefficient with the bulk aerodynamic method. The most commonly used formulations of the aerodynamic roughness length, required by similarity theory, are examined using data sets from four different field programs. These relationships include the Charnock formulation and the wave age modified Charnock relationship. The goal is to assess the overall performance of simple formulations of the roughness length including cases where the Charnock formulation is not expected to apply, and to assess the errors resulting from application of the Charnock formulation to all conditions, as is done in many numerical models where an explicit wave model cannot be accommodated. This examination indicates that spurious self‐correlation explains more variance than actual physical relationships, even after eliminating weak wind cases. Frequent cases of anomalously low stress and very small values of the Charnock coefficient further reduce the usefulness of this formulation for the present data sets. Causes of the frequent very small values of the Charnock coefficient are briefly investigated.

Ten Years of Boundary-Layer and Wind-Power Meteorology at Høvsøre, Denmark

“…Here, we compare the observations of φ m with the extensive re-evaluation of the Businger-Dyer (2005) agrees well with the observations. Analysis of the degree of self-correlation between φ m and z/L for easterlies and 0 < z/L < 1, using the approach of Mahrt et al (2003), results in a linear correlation coefficient of 0.91 for the observations and an average value of 0.64 for 1000 trials of randomly-selected data from the observations. This indicates that, although the analysis is not dominated by self-correlation, it is not insignificant at Høvsøre.…”

Sea-surface roughness lengths in the midlatitude coastal zone

“…No strong evidence of a smooth flow regime was found in the VM06 datasets or in the many datasets examined by Mahrt et al (2003), perhaps due to the limited range of observed conditions in these datasets. A minimum roughness length is imposed (see below).…”

The influence of nonstationarity on the turbulent flux–gradient relationship for stable stratification

“…Examination of the dependence of the observed nondimensional gradients on stability must recognize serious contamination by self-correlation since the nondimensional gradients include scaling by u * , which also appears in z/L (Hicks 1981;Andreas 2002;Mahrt et al 2003). Such self-correlation between φ m , and z/L can exceed the physical correlation for stable conditions (Klipp and Mahrt 2004).…”