Waving in the rain

TL;DR

This paper investigates the complex effects of rain on wind wave dynamics, revealing discrepancies between theoretical predictions and observational data, and suggesting a deeper connection between white-capping and wind input.

Contribution

It introduces a new analysis of rain's impact on wave spectra and challenges existing assumptions about wind-wave interactions and white-capping mechanisms.

Findings

Rain dampens shorter waves in the spectrum tail.

Operational models may overestimate wave growth under rain conditions.

White-capping's role in wind input is more complex than previously thought.

Abstract

We consider the effect of rain on wind wave generation and dissipation. Rain falling on a wavy surface may have a marked tendency to dampen the shorter waves in the tail of the spectrum, the related range increasing with the rain rate. Following the coupling between meteorological and wave models, we derive that on the whole this should imply stronger wind and higher waves in the most energetic part of the spectrum. This is supported by numerical experiments. However, a verification based on the comparison between operational model results and measured data suggests that the opposite is true. This leads to a keen analysis of the overall process, in particular on the role of the tail of the spectrum in modulating the wind input and the white-capping. We suggest that the relationship between white-capping and generation by wind is deeper and more implicative than presently generally assumed.