Articles | Volume 8, issue 4
Geosci. Model Dev., 8, 1169–1195, 2015
https://doi.org/10.5194/gmd-8-1169-2015
Geosci. Model Dev., 8, 1169–1195, 2015
https://doi.org/10.5194/gmd-8-1169-2015

Model description paper 24 Apr 2015

Model description paper | 24 Apr 2015

Normal-mode function representation of global 3-D data sets: open-access software for the atmospheric research community

N. Žagar1, A. Kasahara2, K. Terasaki3, J. Tribbia2, and H. Tanaka3 N. Žagar et al.
  • 1University of Ljubljana, Faculty of Mathematics and Physics, Department of Physics, Ljubljana, Slovenia
  • 2National Center for Atmospheric Research, Climate and Global Dynamics Division, Boulder, Colorado, USA
  • 3University of Tsukuba, Center for Computational Sciences, Tsukuba, Japan

Abstract. This article presents new software for the analysis of global dynamical fields in (re)analyses, weather forecasts and climate models. A new diagnostic tool, developed within the MODES project, allows one to diagnose properties of balanced and inertio-gravity (IG) circulations across many scales. In particular, the IG spectrum, which has only recently become observable, can be studied simultaneously in the mass and wind fields while considering the whole model depth in contrast to the majority of studies.

The paper includes the theory of normal-mode function (NMF) expansion, technical details of the Fortran 90 code, examples of namelists which control the software execution and outputs of the software application on the ERA Interim reanalysis data set. The applied libraries and default compiler are from the open-source domain. A limited understanding of Fortran suffices for the successful implementation of the software.

The presented application of the software to the ERA Interim data set reveals several aspects of the large-scale circulation after it has been partitioned into the linearly balanced and IG components. The global energy distribution is dominated by the balanced energy while the IG modes contribute around 10% of the total wave energy. However, on sub-synoptic scales, IG energy dominates and it is associated with the main features of tropical variability on all scales. The presented energy distribution and features of the zonally averaged and equatorial circulation provide a reference for the validation of climate models.

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Short summary
The article presents MODES, a new software for the analysis of properties of balanced and inertio-gravity circulations across many scales in (re)analyses, weather forecasts and climate models. The software and real-time results based on ECMWF model can be found at http://meteo.fmf.uni-lj.si/MODES. Evaluation of models' ability to reproduce the unbalanced tropical circulation is expected to provide new insights on model performance that is helpful to diagnose deficiencies and define improvements.