Reply to comment by Paul A. Hwang on "A study of the slope probability density function of the ocean waves from radar observations" by D. Hauser et al.

Abstract

In response to the comment of Hwang [2009], this paper presents an addendum to the study published by Hauser et al. [2008] on the mean square slopes (mss) derived from radar observations (at C-band and incidence angles between 7 and 21°). Different sea state conditions are sorted out (swell, wind sea, and mixed sea) and their possible impact on mean square slopes is analyzed. It is found that swell encountered in condition of moderate wind (6-12 m/s) seems to affect only weakly the radar-derived mean square slope and mainly in the crosswind direction. Under light wind (<6 m/s) where only swell conditions were encountered, the sensitivity of the mss to wind speed is much larger than in wind sea conditions (either pure or mixed). In wind sea cases, there is no significant difference for the mss-wind relationship between pure wind sea and mixed sea cases with dominant wind sea part. Compared to mss estimated from Hwang [2009] and Hwang [2005] parameterizations, the radar-derived mss are in good agreement for intermediate wind speed (4-7 m/s), but larger at light wind (<4 m/s) and smaller at moderate to strong wind (>7 m/s). This conclusion is the same whatever parameterization of Hwang is used (mixed sea or pure wind sea). Although the effect of swell cannot be excluded at light winds, sorting the radar data by type of sea conditions does not help to reconcile the mss calculated from Hwang [2005] parameterizations and the radar-derived ones at strong winds. The best agreement of the radar-derived mss remains with the mss derived from the Elfouhaily et al. [1997] parameterization. © 2009.