HR: 11:15h
AN: A32A-04    [Abstracts]
TI: Predictability and Prediction of the Intraseasonal Oscillation With the ECHAM5 GCM
AU: * Liess, S
EM: stefan.liess@stonybrook.edu
AF: Institute for Terrestrial and Planetary Atmospheres, State University of New York at Stony Brook Endeavour Hall Rm.177, Stony Brook, NY 11794-5000 United States
AU: Waliser, D E
EM: duane.waliser@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, MS 183-501 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: Schubert, S D
EM: schubert@gmao.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Earth Sciences Directorate Code 910.3 , Greenbelt, MD 20771 United States
AU: Kirchner, I
EM: Ingo.Kirchner@met.fu-berlin.de
AF: Freie Universität Berlin, Institut für Meteorologie Carl-Heinrich-Becker-Weg 6-10 , Berlin, 12165 Germany
AB: The present study analyzes the predictability and prediction of the intraseasonal oscillation (ISO) during northern summer. The ECHAM5 atmospheric general circulation model (GCM) is utilized to assess the ISO predictability and to predict observed ISOs. In the former case, the three strongest ISO events of a 10-year control simulation forced with climatological SSTs are predicted by a 14-member ensemble forecast. In the latter case, three strong ISO events observed during the years 1990, 1992 and 1996 are predicted. In each case, the leading extended empirical orthogonal functions of precipitation are used to define four different phases of the ISO. Fourteen-member ensembles of 90-day hindcasts are run for each phase of the three strongest ISO events. For the predictability study, initial conditions for each ensemble are created from the control simulation using a breeding method. For the prediction of observed events, the GCM is nudged every six hours toward ERA40 dynamics and SSTs. During the forecast period nudging is turned off and climatological SST is used. Different initial condictions are obtained by variations in the nudging coefficients. The signal-to-noise ratio is analyzed over a region that covers the core of the Asian summer monsoon activity. Theoretical predictability of more than 20 days is found for 200 hPa zonal wind. Precipitation is predictable for more than two weeks. A spatial analysis of the predictability of different phases of the ISO reveals that the area of high predictability follows the westward propagating subtropical Rossby-waves during the active and break phases of the monsoon, and additionally it follows the eastward propagating ISO during the active phase. This predictability is considerably higher than for numerical forecasts of typical weather variations, particularly for the Tropics, indicating that useful forecasts of monsoon active and break events may be possible with lead times of more than two weeks for precipitation and more than 20 days for the dynamics. A closer look at the breeding method used here to initialize the hindcasts, shows the importance of appropriate ensemble experiment designs. Analysis of the prediction skill study is ongoing and results will be presented at the meeting.
DE: 3314 Convective processes
DE: 3319 General circulation
DE: 3337 Numerical modeling and data assimilation
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly