Ensemble Dynamics and Bred Vectors

AbstractThe new concept of an ensemble bred vector (EBV) algorithm is introduced to assess the sensitivity of model outputs to changes in initial conditions for weather forecasting. The new algorithm is based on collective dynamics in essential ways. As such, it keeps important geometric features that are lost in the earlier bred vector (BV) algorithm. By construction, the EBV algorithm produces one or more dominant vectors and is less prone to spurious results than the BV algorithm. It retains the attractive features of the BV algorithm with regard to being able to handle legacy codes, with minimal additional coding.The performance of the EBV algorithm is investigated by comparing it to the BV algorithm as well as the finite-time Lyapunov vectors. With the help of a continuous-time adaptation of these algorithms, a theoretical justification is given to the observed fact that the vectors produced by the BV, EBV algorithms, and the finite-time Lyapunov vectors are similar for small amplitudes. The continuu...