Ensemble prediction of transitions of the North Atlantic eddy‐driven jet

The North Atlantic jet stream: a look at preferred positions, paths and transitions

“…The last transition is consistent with that obtained from the extended EOF analysis. Frame et al (2011) observe, using ERA-40 extended winter forecast data, that forecasts initialised in the N jet cluster are less skilful than those initialized in C or S. This ties well with the least persistence of the N regime observed here. and a given covariance matrix C. Both covariance matrices are supposed to be full rank.…”

Persistent Circulation Regimes and Preferred Regime Transitions in the North Atlantic

“…This is not surprising because our method looks for metastable flow regimes. Our results are consistent with the prediction study by Frame et al (2011) that analyses the skill of ensemble forecasting systems in predicting transitions between the different jet regimes of Woollings et al (2010). Frame et al (2011) find positive predictive skill of Atlantic jet stream transitions with about 5-10 days of lead time.…”

Flow‐dependent predictability of the North Atlantic jet

“…This transition implies temporary disruption of the zonal flow and passage of trajectories through the less predictable region of PCspace associated with weak or split jets. The increased rate of spread associated with passage through this region may be the explanation for the observation of Frame et al [2011] that ensemble predictions of the location of the jet are less skillful when the initial conditions have the jet shifted to the north.…”

“…[8] Following Woollings et al [2010] and Frame et al [2011] the North Atlantic eddy-driven jet is defined from the zonal winds between 15 ı N and 75 ı N, zonally averaged between 60 ı W and 0 ı W, and vertically averaged between the 925 and 750 hPa pressure levels, to produce profiles of zonal wind as a function of latitude. Such "jet profiles" are calculated for each six hourly time-point in the ERA-40 data set.…”

“…Further evidence has been found that the skill in forecasting the jet appears to vary with these regimes, with the skill being lowest when the forecast starts with the jet in the north regime [Frame et al, 2011]. These differences in forecast skill could indicate the presence of flow-dependent predictability.…”