Could mid-latitude weather forecasts be improved by better knowledge of the polar atmosphere?

• Main Authors: Kasper, Marta, Semmler, Tido, Jung, Thomas, Serrar, Soumia
• Format: Conference Object
• Language: unknown
• Published: 2014
• Subjects: Antarc*; Antarctic
• Online Access: https://epic.awi.de/id/eprint/36136/; https://epic.awi.de/id/eprint/36136/1/Polar_midlatitude.pdf; https://hdl.handle.net/10013/epic.44040; https://hdl.handle.net/10013/epic.44040.d001

To determine the impacts of a perfectly simulated Arctic/Antarctic atmosphere on mid-latitude weather forecasts, we carried out relaxation experiments with the Integrated Forecast System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). We conducted pairs of experiments initialized from different start dates between 1979 and 2012 of the INTERIM reanalysis data from ECMWF. Each pair contains a control hindcast (CTL) and a hindcast strongly relaxed to the reanalysis data (REL) in the Arctic north of 75 N and in the Antarctic south of 75 S. We determined the root mean square errors (RMSE's) for each grid point of the CTL and REL hindcasts with reference to the reanalysis data averaged over all CTL and REL hindcasts, respectively. Over the Northern mid-latitudes between 40 and 60 N hindcasts are improved especially over Eastern Europe and Asia (ca. 10% RMSE reduction), a region with little maritime influence. Over the Southern mid-latitudes improvements are generally smaller (ca. 4% RMSE reduction) and regionally roughly equally distributed between 40 and 60 S, but in winter and spring improvements of similar magnitude extend to the lower latitudes of Southern Australia. Over both hemispheres improvements are weaker in summer compared to the other three seasons. Generally, in weather situations with anomalous meridional wind components from the polar regions into the mid-latitudes improvements are pronounced. This has implications for the predictability of mid-latitude weather in a future climate with a changed large-scale circulation.