Title:A modified shallow water model for investigating convective-scale data assimilation.

Author: Tom Kent (School of Mathematics, University of Leeds)
Onno Bokhove (School of Mathematics, University of Leeds)
Steve Tobias (School of Mathematics, University of Leeds)

I outline a modified rotating shallow water model to represent an atmosphere with moist convection for use in inexpensive convective-scale data assimilation experiments. The key ingredients to the modification are the introduction of two threshold heights, akin to the level of free convection and onset of precipitation. When the fluid exceeds these heights, the classical dynamics are altered to include a representation of conditional instability and idealised moisture transport. By combining the nonlinearity due to advection in the shallow water equations and switches for the onset of convection, the proposed model captures two important dynamical processes of convecting and precipitating weather systems. Classical numerical experiments in shallow water theory, such as the Rossby geostrophic adjustment, are reproduced and used to illustrate the modified dynamics of the proposed model.

When using such intermediate-complexity ‘toy’ models for atmospheric data assimilation research, it is important to justify their relevance in the context of numerical weather prediction (NWP). For meaningful ensemble-based experiments, choosing the initial ensemble to have sufficient error-growth is key to providing an adequate estimation of forecast error. Furthermore, the observing system should be tuned to give a similar observational influence as in NWP. These properties are examined for the modified model in advance of its use in ensemble Kalman filtering.

GMAO Head: Steven Pawson Global Modeling and Assimilation Office NASA Goddard Space Flight Center

Curator: Nikki Privé Last Updated: Feb 9 2015