# Comparing a 41-year model hindcast with decades of wave measurements from the Baltic Sea

## TL;DR

This study compares a 41-year wave hindcast with measurements in the Baltic Sea, highlighting the effects of ice cover on wave statistics and model accuracy, especially during winter months and near the shore.

## Contribution

It provides a comprehensive validation of a long-term wave hindcast against measurements, including ice effects, and identifies model limitations near the shore and in high wave periods.

## Key findings

- 84% of large wave events occur between November and January
- Ice cover reduces mean significant wave height by 30% in the Bay of Bothnia
- Model accurately predicts wave heights except in narrow bays with high peaks

## Abstract

We present ice-free and ice-included statistics for the Baltic Sea using a wave hindcast validated against data from 13 wave measurement sites. In the hindcast 84% of wave events with a significant wave height over 7 m occurred between November and January. The effect of the ice cover is largest in the Bay of Bothnia, where the mean significant wave height is reduced by 30% when the ice time is included in the statistics. The difference between these two statistics are less than 0.05 m below a latitude of 59.5 degrees. The seasonal ice cover also causes measurement gaps by forcing an early recovery of the instruments. Including the time not captured by the wave buoy can affect the estimates for the significant wave height by roughly 20%. The impact below the 99th percentiles are still under 5%. The significant wave height is modelled accurately even close to the shore, but the highest peak periods are underestimated in a narrow bay. Sensitivity test show that this underestimation is most likely caused by an excessive refraction towards the shore. Reconsidering the role of the spatial resolution and the physical processes affecting the low-frequency waves is suggested as a possible solution.