Moana Project releases Hau-Moana: NZ atmospheric downscaling data

The first output from the Moana Project is available. The project team is pleased to release the Hau-Moana data set, the New Zealand atmospheric downscaling.

Project Leader Associate Professor Moninya Roughan is excited. “We are happy to have the first data product available already. The MetOcean Solutions team has been working hard to finish this first step of the Moana Project, paving the way for the work packages to come.”
 

Top panels show low-resolution atmospheric products available globally from CFSR. The lower panels show the benefit of increasing the resolution in an NZ specific context around regions of complex topography such as the Cook Strait. Higher resolution modelling increases the accuracy of the data.  

Top panels show low-resolution atmospheric products available globally from CFSR. The lower panels show the benefit of increasing the resolution in an NZ specific context around regions of complex topography such as the Cook Strait. Higher resolution modelling increases the accuracy of the data.
 

Oceanographer Rosa Trancoso presented the project at the 2017 NZ Physical Oceanography Workshop in Wellington in mid-August. “Hau-Moana came about because we needed more accurate wind fields to improve our ocean modelling,” she explains. “The global Climate Forecast System Reanalysis (CFSR) made public by the National Center of Environmental Prediction, is used globally, however it does not provide accurate wind fields for nearshore areas, particularly around NZ. For accurate ocean modelling, atmospheric forcing needs to account for coastal topographic effects, shoreline complexity, and ocean surface temperatures. New Zealand is subject to rapidly moving weather systems, and complex topography, which means that we require atmospheric forcing data at good spatial and temporal resolution.

For the downscaling, the team used 0.312 degrees for sea surface temperature (SST) and surface fields such as pressure, humidity, temperature, etc. The modelling was done using 12-hour independent runs, discarding the first five hours to allow for model spin-up. 

The outputs were validated against data from 33 coastal sites around New Zealand and two offshore sites.

The model was validated using weather data from 33 coastal and two offshore observation sites.

The model was validated using weather data from 33 coastal and two offshore observation sites.

“Overall, the validation shows the model to perform well,” adds Rosa. “This means that we now have a better atmospheric data set for New Zealand than we’ve ever had in the past. Hau-Moana version 1.0 is a first step towards a high-quality, high-resolution, long-term reference data set, which can be improved in the future. The dataset covers the period from 1979 to 2015, and we’re currently working on a comprehensive validation and a descriptive paper for publication in a scientific journal.”

NIWA Ocean Modeller Dr Mark Hadfield says that the Hau-Moana high-resolution wind field is a key component in improving modelled circulation in the Cook Strait.

The Hau-Moana data set is freely available upon request - contact us at info@moanaproject.org if you would like to access it. 

For more information about the Moana Project, visit the website: www.moanaproject.org

Higher-resolution atmospheric modelling improves modelling of waves and currents. Left-hand images show the CFSR and WRF model outputs for mean wind speed (m/s) (top) and mean significant wave height (m) (bottom); right-hand images show the difference between the two, with negative values in blue and positive values in red.

Higher-resolution atmospheric modelling improves modelling of waves and currents. Left-hand images show the CFSR and WRF model outputs for mean wind speed (m/s) (top) and mean significant wave height (m) (bottom); right-hand images show the difference between the two, with negative values in blue and positive values in red.