A database containing sub-seasonal to seasonal forecasts from 11 operational 30 centres is available to the research community and will help advance our understanding of 31 the sub-seasonal to seasonal time range.Abstract 51 52Demands are growing rapidly in the operational prediction and applications communities for 53 forecasts that fill the gap between medium-range weather and long-range or seasonal 54

[1] This paper presents the aerosol modeling now part of the ECMWF Integrated Forecasting System (IFS). It includes new prognostic variables for the mass of sea salt, dust, organic matter and black carbon, and sulphate aerosols, interactive with both the dynamics and the physics of the model. It details the various parameterizations used in the IFS to account for the presence of tropospheric aerosols. Details are given of the various formulations and data sets for the sources of the different aerosols and of the parameterizations describing their sinks. Comparisons of monthly mean and daily aerosol quantities like optical depths against satellite and surface observations are presented. The capability of the forecast model to simulate aerosol events is illustrated through comparisons of dust plume events. The ECMWF IFS provides a good description of the horizontal distribution and temporal variability of the main aerosol types. The forecastonly model described here generally gives the total aerosol optical depth within 0.12 of the relevant observations and can therefore provide the background trajectory information for the aerosol assimilation system described in part 2 of this paper.

ABSTRACT:A combined medium-range and monthly-forecasting forecasting system is now operational at the European Centre for Medium-Range Weather Forecasts. Previously, these two systems were run separately. The new combined system provides skillful predictions of small-scale, severe-weather events in the early forecast range, accurate large-scale forecast guidance up to day 15 twice a day, and large-scale guidance up to day 32 once a week. In addition, the daily medium-range forecasts starting at 0000 utc are now coupled to an ocean general-circulation model after day 10 and persisted sea-surface temperature (SST) anomalies instead of persisted SSTs are applied when the atmospheric model is run in uncoupled mode. Average results indicate that the monthly forecasting scores are slightly higher in the Extratropics with this new combined system. In particular, the new system seems to produce better monthly forecasts for extreme events such as the 2003 heatwave over Europe or the 2007 wet summer over England. However, the monthly forecasting scores in the Tropics are slightly lower than with the previous system, most likely because of the lack of ocean-atmosphere coupling during the first ten days of the forecasts. This demonstrates that ocean-atmosphere coupling may be needed in medium-range forecasting and future plans include coupling the atmosphere to the ocean model from day 0. Average results based on 30 cases indicate that the medium-range forecasts benefit from the introduction of the ocean-atmosphere coupling after day 10, most especially the prediction of low-level temperature in the Tropics.