TM3-DAM, version 3, which is used to generate global ozone fields and forecasts, based on the GOME total ozone observations.
Assimilation improves the model state based on the information contained in the observations.
It provides the most probable state of the system, given the uncertainties in the observations and model forecast. The model is a modification of the chemistry-transport model TM3 . Analysis based on the model shows that the low ozone values are mainly caused by an exceptional atmospheric flow and a transport of ozone-poor air from the subtropics to higher latitudes. The event lasted only a few days, and after that the ozone layer in the Northern Hemisphere returned to normal values. Ozone columns in Dobson units.