Experimenting with the LETKF in a dispersion model coupled with the Lorenz 96 model.

CARRASCO, F.; RUIZ, J.; SAULO, C.; OSSES, A.

Montreal

Conferencia; World Weather Open Science Conference; 2014

This work is framed in the general objective of testing the Local Ensemble Transform Kalman Filter (LETKF) as an assimilation technique to improve the representation of sources and sinks of atmospheric constituents. As a first step, this work focuses on two main objectives: a) to quantify the impact of the assimilation of concentrations and b) to investigate the ability of the LETKF to estimate model dispersion parameters (e.g. emission sources). In both cases OSSE experiments using a toy dispersion model based on the Lorenz 96 model have been done. For the first objective the LETKF ability to constrain concentration, when the dispersion model is coupled with the atmospheric model and when the dispersion model is uncoupled with the dispersion model, are investigated. The impact of the number of concentration observations has also been analyzed in both situations. We found that assimilation with the coupled model leads to better performance, particularly when a limited number of concentration observations are available. For the second objective, different emission scenarios (e.g. punctual sources with known location and sources with a priori unknown spatial distribution) as well as their temporal variability has been considered. Results show that a successful representation of concentration and dispersion parameters is possible and that a more accurate estimation of the parameters is achieved when they are estimated in a coupled system.