Group seminar on 30. January, 14:15 CET
The influence of the tropics on extra-tropical predictions
Chen Wang
Tropically forced extratropical teleconnections represents a pathway for tropical errors in the initial state to propagate and affect longer-range forecast in the midlatitudes. Although numerical weather prediction sees development in both tropical forecasts skills and extratropical extended-range forecast, it is not clear how the latter benefits from the former. In this seminar I will begin with a presentation of prior studies demonstrating the tropical-extratropical teleconnections and that reducing tropical forecast errors benefits extratropical forecasts. Nudging experiments reveal that enhanced week 2-3 extratropical forecast skills with improved tropical initial conditions. I will also present TIGAR data assimilation experiments, which provides unique insight to the propagation. In the TIGAR DA system, we consider the mass-wind relationship associated with tropical Rossby and non-Rossby modes by using these modes as control variables. By assimilating exclusively tropical observations, we show the varying scales of error reduction in both tropical analysis and extratropical forecasts.