Simulation of the MJO and its teleconnections in an ensemble of 46-day EPS hindcasts

Simulation of the MJO and its teleconnections in an ensemble of 46-day EPS hindcasts
Technical memorandum
Date Published
Secondary Title
ECMWF Technical Memoranda
Franco Molteni
Abstract A series of 15-member ensemble of 46-day EPS integrations starting on the 15th of each month from 1989 to 2008 has been completed with IFS cycle 32r3. The Madden Julian Oscillation (MJO) simulated by this set of hindcasts is diagnosed using an index based on combined EOFs of zonal winds at 200 and 850 hPa and Outgoing Longwave radiation (OLR). The model is able to maintain the amplitude of the MJO during the 46 days of integrations and it displays skill for up to about 20 days to predict the evolution of the MJO. However, the MJO simulated by the model has a too slow propagation. The impact of the MJO on tropical precipitation and tropical cyclone activity is generally consistent with analysis or observations. The simulated impact of the MJO on the Northern Extratropics weather displays similar patterns as in the analysis (20 years of ERA Interim). However, the impact of the MJO on the 500 hPa geopotential height is generally too strong over the North Pacific, and too weak over the Euro-Atlantic sector. In particular the impact of MJO on the NAO is weaker in the model than in ERA Interim. This problem is consistent with the slow MJO eastward propagation. The MJO simulated by the hindcasts has a significant impact on weekly mean probabilistic skill scores, particularly for the time range day 19-25. At this time range, the reliability of the probabilistic forecasts over Europe depends strongly on the presence of an MJO event in the initial conditions.
DOI 10.21957/g8y9swk43