MyWave-D3.4 - Inter-comparison of MetOffice and CNMCA ensemble prediction systems for Mediterranean Sea

Within the framework of MyWave project, work package n°3, U.K. MetOffice and CNMCA (Italian Meteorological Service) have developed and implemented two independent ensemble prediction systems for the Mediterranean Sea. The two systems, later addressed as UKMO and Nettuno, are described in DR 1. The main purpose of present report is the description of the tasks related to the verification and inter-comparison of Nettuno and UKMO EPS. The validation is based on the observations dataset reported in DR 2, which cover the six month period from July 1 to December 31 , 2013. Proceeding from DR 3 and DR 4, the basic principles on which this verification is based on is that the forecasts are validated "as they are", that is without any calibration or other kind of post processing based on the same verification scores (e.g. bias correction). This does not exclude that ensemble members are post-processed in order to account for observation uncertainty, since these are based on knowledge preceding the forecast/validation period. In chapter II we describe the measurement uncertainty estimations and their use for EPS verification purposes. The aim of chapter III is the assessment of the behaviour of the ensemble mean in the framework of adopting it as a deterministic forecast, instead of the control member. Note that Nettuno control member is the actual operational forecast for the Italian Meteorological Service. Chapter IV investigates and compares the ensemble spread characteristics of Nettuno and UKMO systems. The last chapter (V ) describes the scores related to the capacity of both EPS in predicting events probability, in term of reliability and resolution, presenting also two metrics particularly suited for forecast users. Finally we draw the conclusions in VI.