Friday 12 Jul 2013: CliMathNet Seminar: Inclusion of Linearized Moist Physics in NASA's Goddard Earth Observing System Data Assimilation Tools
Dan Holdaway - NASA Goddard Space Flight Center
Harrison 209 14:00-15:00
Variational data assimilation techniques in numerical weather prediction make use of the tangent linear and adjoint versions of the weather forecast model. Inclusion of the moist atmospheric processes, such as convection and precipitation, in the linear model is highly beneficial. Doing so allows the sensitivity to moisture to be effectively measured and enables the assimilation of observations of clouds and precipitation. However, the schemes developed to model the so called `moist physics' do not generally behave in a linear way. Many of the processes being represented are inherently nonlinear and artificial switches in the numerics are commonplace. Here we show a how the Jacobian, with various perturbation structures, can be used for analysing the linearity and stability for a given scheme. Using this method, linearised versions of the in situ moist physics schemes are developed and implemented in NASA's GEOS-5 data assimilation tools. The benefits of including moist physics are shown through observation impact experiments and in sensitivity studies.