Recent developments towards a seamless prediction in JMA global ensemble prediction system

Yoichiro Ota
11 am May 20 in Room 2155

In Japan Meteorological Agency (JMA), there are ongoing developments towards unifying existing three operational global ensemble prediction systems (EPS), i.e. Typhoon EPS, One-week EPS and One-month EPS into one global EPS. This new global EPS will cover the prediction of phenomena with various timescales from short-range to sub-seasonal. Among these developments, two topics will be mainly discussed in this talk. First topic will be the introduction of perturbations on Sea Surface Temperature (SST) as boundary conditions of the atmospheric model. The current operational EPS in JMA prescribes a common SST to all members which is derived as persistent anomaly from climatology. This could be a significant source of underdispersiveness in the ensemble forecasts. Statistically consistent way to generate perturbations on SST will be proposed and tested, with promising results leading to better spread-skill relations especially for lower-tropospheric fields in the Tropics and summer extra-tropics. Second topic will be the use of the Ensemble Kalman Filter (EnKF) for the generation of the initial perturbations. Current Typhoon EPS and One-week EPS use Singular Vectors (SVs) as the initial perturbations. After reviewing the characteristics of the EnKF perturbations, combined use of SVs and EnKF perturbations is proposed. Using the combination of the EnKF perturbations with SVs leads to improve the accuracy of short-range ensemble forecast than using only SVs, indicating that the EnKF perturbations approximate analysis error covariance better than SVs.