Directional distribution of the short wave estimated from HF ocean radars

Short‐wave directional distributions estimated using HF (high‐frequency) radar are compared with model predictions. The short‐wave directional distributions are estimated on the basis of HF radar using two‐ and four‐parameter parametric models to describe short‐wave directional distributions. The model‐predicted short‐wave directional distributions are computed using the energy balance equation. The nonlinear interaction source function in the energy balance equation is calculated from both the exact computation and the discrete interaction approximation (DIA). The predicted short‐wave directional distributions from the exact computation and the DIA are compared with those estimated using HF radar. The energy balance equation is simplified by neglecting the propagation term, and the validity of the simplification is investigated. It is found that the four‐parameter model is more accurate than the two‐parameter model to estimate short‐wave directional distribution using HF radar. The model‐predicted mean short‐wave directions with respect to wind directions are correlated with those estimated from the HF radar. The short‐wave direction change associated with a sudden wind shift can be reproduced both from the exact computation and the DIA. The predicted second‐order moments of short‐wave directional distributions are also correlated with those estimated from the HF radar. This result shows that the model can reproduce transient short‐wave directional distributions associated with changes of wind direction. The short‐wave directional distributions predicted by the exact computation are narrower than those predicted by the DIA and estimated using the HF radar. The simplification of the energy balance equation is not the main source of the short‐wave prediction error.