DOI: 10.25919/yp77-v026
title: WHACS: Wave Hindcast for the Australian Climate Service

description: WHACS, the Wave Hindcast for the Australian Climate Service, is an ocean wave hindcast running from 1979 to the present* (*2023 at the time of publication). 
WHACS is designed to replace the CAWCR Wave Hindcast (Durrant, Hemer, Smith, Trenham & Greenslade (2019) http://hdl.handle.net/102.100.100/137152). 
A manuscript describing this dataset is in preparation, which will be linked to this metadata record in due course.

WHACS data was generated using the WAVEWATCHIII v6.07 wave model using ST6 physics, forced with ERA5 hourly winds and daily sea ice. The model was run on a spherical multi-cell (SMC) grid with a base resolution of 0.25 degrees in the polar regions and 0.125 degrees the non-polar global ocean, and a higher resolution of ~7km in the coastal zone globally.

The dataset comprises 4 components: the full SMC grid data; regridded data at 1/8deg globally; regridded data at 1/16deg in the Australian region, and spectral outputs.
Spectral wave output was produced at 11224 points: 286 buoys; 370 points on a global 10-degree grid; 10055 points from the coastal SMC grid in the Australian, New Zealand, Indian and Pacific Islands and the Maritime Continent regions; an additional 80 points around NZ; and 443 points that define the SCHISM-WWMIII based Coupled Coastal Hazard Prediction System (CCHaPS) hindcast. 

Examples of how to work with the data in Python are provided in "whacs_examples.ipynb" (see Supporting Files).

N.B. December 1978 was run as a model spin-up month, data should be reliable from January 1979.

SMC parameters: longitude; latitude; time; uwnd, vwnd (East- and Northward wind); hs (significant wave height); t01, t02, t0m1 (mean period T01, T02 and T0m1); fp (peak frequency); dir (mean direction); spr (directional spread); dp (peak direction); phs0; phs1; phs2; phs3 (significant wave height partitions); ptp0; ptp1; ptp2; ptp3 (peak period partitions); pdir0; pdir1; pdir2; pdir3 (mean direction partitions); pspr0; pspr1; pspr2; pspr3 (wave directional spreading partitions); pdp0; pdp1; pdp2; pdp3 (peak wave direction partitions); pqp0; pqp1; pqp2; pqp3 (wave peakedness partitions); ppe0; ppe1; ppe2; ppe3 (wave peak enhancement factor partitions); CgE (wave energy flux). 

Regridded parameters: longitude; latitude; time; hs (significant wave height); uwnd, vwnd (East- and Northward wind); t01, t02, t0m1 (mean period T01, T02 and T0m1); fp (peak frequency); dir (mean direction); dp (peak direction); phs0; phs1; phs2 (significant wave height partitions); ptp0; ptp1; ptp2 (peak period partitions); pdir0; pdir1; pdir2 (mean wave direction partitions); CgE (wave energy flux). 

Spectral wave parameters: efth (sea surface wave directional variance spectral density) including time; station; longitude; latitude; frequency; frequency1; frequency2 (centre, upper and lower bands); direction; dth (depth); wnd; wnddir (wind speed and direction 10m above surface). 

Some corrections were made to the data during post-processing: 
- CgE took negative values in sea ice regions due to numerical overflow in some cases. These values were reset to NaN or brought within range by changing the datatype from int16 to uint16. 
- fp took negative values sometimes due to a bug in this version of WW3 (https://github.com/NOAA-EMC/WW3/pull/741)
- Negative values of pqp* variables were reset to the maximum allowed, however such values would be considered nonphysical (https://github.com/NOAA-EMC/WW3/issues/210). If using partitioned Goda's peakedness parameter, please do so with caution.

Further note: WW3 spectral outputs are interpolated from the lower resolution grid and may not provide appropriately high quality information for spectral data to accurately represent the wave system near the coast (https://github.com/NOAA-EMC/WW3/issues/1233). Spectral outputs should be used with care particularly in coastal areas, spectral reconstruction from the SMC (not regridded) data may be more appropriate in some locations at some times.