caa a22 4500 605472548 CHVBK 20210128100338.0 cr unu---uuuuu 210128e20151201xx s 000 0 eng 10.1007/s00382-015-2528-y doi (NATIONALLICENCE)springer-10.1007/s00382-015-2528-y Understanding and modelling extra-tropical teleconnections with the Indo-Pacific region during the northern winter [Elektronische Daten] [Franco Molteni, Timothy Stockdale, Frédéric Vitart] Teleconnections originated by anomalous heat sources over the tropical Indo-Pacific oceans are investigated in this paper comparing observational results with numerical simulations run as part of the re-forecast set for the latest ECMWF seasonal forecasting system (System 4). We show that the traditional methodology of linearly relating circulation anomalies to SST anomalies, while appropriate for signals originated in central and east Pacific, fails to adequately identify the response to anomalous heating over the west Pacific and most of the Indian Ocean, because of the relatively weak (or even negative) correlation between SST and rainfall anomalies in these regions. Instead, if teleconnections are computed from covariances with rainfall anomalies, a stronger consistency is found between observed and modelled patterns, as well as between diagnostics derived from seasonal and intra-seasonal time scales. The main mode of inter-annual variability in Indo-Pacific rainfall associated with planetary-scale teleconnections is a tri-polar structure with two positively correlated centres in the western Indian Ocean and the central Pacific, and a third centre around the maritime continents which is anti-correlated with the other two. In the extratropical response, positive rainfall anomalies over the western and central Indian Ocean (WCIO) are connected with a negative height anomaly centred over Alaska and a positive North Atlantic oscillation (NAO) signal, in a way reminiscent of the Cold-Ocean-Warm-Land pattern. This teleconnection cannot be explained by the ENSO-forced component of Indian Ocean rainfall, and is in phase with signals associated with the Madden-Julian oscillation. Results from the System-4 re-forecasts show that the ECMWF coupled model reproduces the broad features of tropical and extratropical teleconnections with a good degree of fidelity. However, the model significantly over-estimates the correlation between rainfall anomalies in the WCIO with those over the western and central Pacific. The impact of this deficiency on the extratropical flow is to weaken the relationship between the NAO and Indian Ocean rainfall on the seasonal scale, and to affect the projection of the ENSO response on the NAO. Finally, we argue that reproducing the correct relationship between SST and rainfall anomalies in different part of the Indo-Pacific basin is also crucial for the correct simulation of inter-decadal variability. Particular care should be taken in interpreting results of AGCM simulations with prescribed SST, where the absence of feedbacks between convection and SST over the warm pool region affects the simulation of rainfall anomalies. Springer-Verlag Berlin Heidelberg, 2015 Teleconnections nationallicence Seasonal prediction nationallicence Indo-Pacific variability nationallicence Ocean-atmosphere interactions nationallicence Molteni Franco European Centre for Medium-Range Weather Forecasts, RG2 9AX, Shinfield Park, Reading, UK aut Stockdale Timothy European Centre for Medium-Range Weather Forecasts, RG2 9AX, Shinfield Park, Reading, UK aut Vitart Frédéric European Centre for Medium-Range Weather Forecasts, RG2 9AX, Shinfield Park, Reading, UK aut Climate Dynamics Springer Berlin Heidelberg 45/11-12(2015-12-01), 3119-3140 0930-7575 45:11-12<3119 2015 45 382 https://doi.org/10.1007/s00382-015-2528-y text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00382-015-2528-y text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Molteni Franco European Centre for Medium-Range Weather Forecasts, RG2 9AX, Shinfield Park, Reading, UK aut NATIONALLICENCE 700 1- Stockdale Timothy European Centre for Medium-Range Weather Forecasts, RG2 9AX, Shinfield Park, Reading, UK aut NATIONALLICENCE 700 1- Vitart Frédéric European Centre for Medium-Range Weather Forecasts, RG2 9AX, Shinfield Park, Reading, UK aut NATIONALLICENCE 773 0- Climate Dynamics Springer Berlin Heidelberg 45/11-12(2015-12-01), 3119-3140 0930-7575 45:11-12<3119 2015 45 382