Between 07:00 and 08:00 UTC on the 4th July 2017, the South African icebreaker S.A. Agulhas II entered the Antarctic MIZ (62 South and 30 East) during an explosive polar cyclone. A system of two GigE monochrome industrial CMOS cameras with a 2/3 inch sensor was installed on the icebreaker. The cameras provide a field of view of the ocean surface around the port side of the ship. Images were recorded with resolution 2448x2048 pixels and a sampling rate 2 Hz during daylight on the 4th July 2017. The wave acquisition stereo-camera system (WASS; https://www.dais.unive.it/wass/) is used to reconstruct the water surface elevation. Reconstructed surface elevations are given as .nc files (6). The file name is “wass__20170704_hhmm.nc” where hh and mm denote the hour and minute in UTC of the start of each acquisition. X_grid and Y_grid are the grid in x and y direction, resolution 1000mm or 1m. Fps is the acquisition frequency, resolution 2Hz. Time is a dummy variable, time is reconstructed from start time and fps. Z is the surface elevation in space and time, in mm. Missing values are "Nan". Other variables are WASS control variables. Further details on the measurements and use of the data can be found at Alberello et al. “An extreme wave field in the winter Antarctic marginal ice zone during an explosive polar cyclone”.

Reconstructed nonlinear surface from WAMOS (marine radar) data collected during the 3rd leg of Antarctic Circumnavigation Expedition, from the end of January to the end of March 2017. WAMOS data (AAS_4434_ACE_WAMOS) are processed with the Higher Order Spectral Method (HOSM) to provide the nonlinear surface elevation and the corresponding spectrum of waves during ACE. A Montecarlo approach is adopted to reproduce the natural variability of the sea state and gain reliable statistics of the underlying nonlinear surface elevation. Details on the method can be found on Toffoli, Alessandro, et al. "Evolution of weakly nonlinear random directional waves: laboratory experiments and numerical simulations." Journal of Fluid Mechanics 664 (2010): 313-336. File structure: Folder name corresponds to the time stamp of the input spectrum (yyyyMMddhhmmss) from AAS_4434_ACE_WAMOS. Each folder contains: 1. The surface elevation for 250 random realisations at 10 instant in times from initialisation saved every 5 dominant wave periods apart (0,5,10,15,…,50 Tp). The ten digits name is structured as 0000NRRttt where NRR is the number of the random realisation (from 1 to 250) and ttt denotes the time index (from 0 to 10). 2. NEW_SPECTRUM.DAT the 2D spectrum (64x64) as a columnar vector of the initial spectrum read from the AAS_4434_ACE_WAMOS. 3. INPUT_SPECTRUM.DAT the 2D spectrum (256x256) as a columnar vector of the initial spectrum for the HOSM. 4. WAVENUMBERSX.DAT and WAVENUMBERSY.DAT the wavenumber in x and y respectively 5. PP_INFO.DAT contains the peak period (Tp) in seconds 6. RUN_INFO.DAT contains the resolution in x of the WAMOS spectrum (64), the resolution in y of the WAMOS spectrum (64), the delta x for the surface elevation in m, the delta y for the surface elevation in m. Subsequent parameters are flags for the HOSM method. Waves in the Southern Ocean are the biggest on the planet. They exert extreme stresses on the coastline of the Sub-Antarctic Islands, which affects coastal morphology and the delicate natural environment that the coastline offers. In Antarctic waters, the sea ice cover reflects a large proportion of the wave energy, creating a complicated sea state close to the ice edge. The remaining proportion of the wave energy penetrates deep into the ice-covered ocean and breaks the ice into relatively small floes. Then, the waves herd the floes and cause them to collide and raft. There is a lack of field data in the Sub-Antarctic and Antarctic Oceans. Thus, wave models are not well calibrated and perform poorly in these regions. Uncertainties relate to the difficulties to model the strong interactions between waves and currents (the Antarctic Circumpolar and tidal currents) and between waves and ice (reflected waves modify the incident field and ice floes affect transmission into the ice-covered ocean). Drawbacks in wave modelling undermine our understanding and ability to protect this delicate ocean and coastal environment.