Tuesday 28 May 2013: CliMathNet seminar: Data assimilation and modelling the carbon cycle
Philip Aston and Sylvain Delahaies - University of Surrey
Harrison 209 16:00-17:00
In the first part of this talk (Aston), we describe the qualitative behaviour of one of the simplest car- bon cycle models, the Data Assimilation Linked Ecosystem Carbon (DALEC) model, which is a simple vegetation model of processes involved in the carbon cycle of forests. We review the dynamical structure of the model. Our analysis shows that the dynamics of both evergreen and deciduous forests in DALEC are dependent on a few key parameters and it is possible to find a limit point where there is stable sustainable behaviour on one side but unsustainable conditions on the other side. The fact that typical parameter values reside close to this limit point highlights the difficulty of predicting even the correct trend without sufficient data and has implications for the use of data assimilation methods.
In the second part of the talk (Delahaies), will review techniques from four-dimensional variational data assimilation applied to DALEC. Using synthetic flux tower measurements together with a linearization of DALEC model, we show that the assimilation problem is highly ill-posed, and that parameters related to slow processes are not observable. We study the impact of regularization methods (TSVD, Tikhonov, and random Gaussian matrices) on the quality of the analysis and on the reduction of the uncertainty.
(This seminar is delivered by videoconference)