Discussion of “Evidence for a critical wind velocity for air‐sea boundary processes” and “Change in the relationship between wind and surface water movement at higher wind speeds”

Abstract

It seems fortunate that two papers concerning the relationship between wind velocity and movement of the surface water appeared in the same issue. Since both papers show apparently different results, it seems necessary to point out difference in the methods used to obtain these results. The first paper shows evidence for a discontinuity of the wind‐water movement relationship between wind force groups 1 to 4 and 5 to 8 of the Beaufort scale, and a decrease of the ratio k, current velocity/wind velocity, for stronger winds. The second paper reports an indication for a possible increase of this ratio at wind forces above 3 Beaufort. A corne a of both papers, therefore, is called for. Lawford and Veley do not include wind forces above Beaufort 5, and as indicated in their Figures 1 and 2, many values for force 5 are extrapolations from current curves a t forces 1 to 4. If any discontinuity should occur between 4 and 5 or at a higher forces, it cannot be discovered or will be veiled. Whether any change in the ratio k occurs at force 3 as indicated by the curves for Varne and S.2 could not be detected at Amrum bank. The method used by Mandelbaum does not permit the interpolation of intermediate values. As pointed out by Lawford and Veley, the conversion of wind velocities estimated by the Beaufort scale to a unit scale of cm/sec or mi/hr is always inherently arbitrary. This conversion scale also depends on where the wind velocity is estimated, at the masthead; on deck of the vessel, three to four meters above the water surface; or directly at the water surface. As indicated by Mandelbaum (Fig. 1) the various attempts for such conversions differ greatly from each other. A slightly different position given to forces 4 and 5 light alter the appearance of the curves completely. The results of both papers have this same inherent uncertainty.