Numerical weather prediction (NWP) model analysis is often poor in in-situ data over ocean. This lack is crucial in case of tropical ocean where man can find tropical cyclones, and especially over Indian ocean. But satellite observation can improve analysis and forecast on tropical region, especially for tropical cyclones.

In our presentation, we will focus on the impact of ERS wind data in the assimilation cycle of French NWP ARPEG. We have tested these data on several tropical cyclones over Indian ocean. We will study this impact in 3D-var scheme, and will also compare with the 4D-var scheme, now in operation at Météo-France.

The main result is that, depict the position of the tropical cyclone is not as much improve as one can expect in the analysis, introduction of ERS wind improve most of the forecast. The impact is more sensitive in 4D-var assimilation, than in 3D-var.