Articles | Volume 8, issue 6
Development and technical paper
03 Jun 2015
Development and technical paper |  | 03 Jun 2015

A spectral nudging method for the ACCESS1.3 atmospheric model

P. Uhe and M. Thatcher

Abstract. A convolution-based method of spectral nudging of atmospheric fields is developed in the Australian Community Climate and Earth Systems Simulator (ACCESS) version 1.3 which uses the UK Met Office Unified Model version 7.3 as its atmospheric component. The use of convolutions allow for flexibility in application to different atmospheric grids. An approximation using one-dimensional convolutions is applied, improving the time taken by the nudging scheme by 10–30 times compared with a version using a two-dimensional convolution, without measurably degrading its performance. Care needs to be taken in the order of the convolutions and the frequency of nudging to obtain the best outcome. The spectral nudging scheme is benchmarked against a Newtonian relaxation method, nudging winds and air temperature towards ERA-Interim reanalyses. We find that the convolution approach can produce results that are competitive with Newtonian relaxation in both the effectiveness and efficiency of the scheme, while giving the added flexibility of choosing which length scales to nudge.

Short summary
We describe a spectral nudging technique to constrain the large spatial structures of an atmospheric general circulation model (ACCESS1.3) towards an observational product (ERA-Interim). This has a number of applications for model development and scientific studies. This paper shows potential benefits of using the spectral nudging over the traditional Newtonian relaxation method.