Dynamical MJO Hindcast Experiments: Sensitivity toInitial Conditions and Air-Sea Coupling

Yehui Chang, Siegfried Schubert, Max Suarez

Global Modeling and Assimilation OfficeNASA/Goddard Space Flight Center and

Duane Waliser

Jet Propulsion Laboratory, California Institute of Technology

October 21, 2008

OutlineMeasure the capacity of GEOS-5 to predict the MJO.Focus on the reasons for the temporal changes in MJO prediction skills.The experiments were for the period of 1979, Nov 1996 - Aug 1997 and 2002 where there were strong intraseasonal activities.

AGCMFinite-volume dynamical core (S.J. Lin)Moist physics (J. Bacmeister, S. Moorthi and M. Suarez)Physics integrated under the Earth System Modeling Framework (ESMF)Generalized vertical coord to 0.01 hPaCatchment land surface model (R. Koster)Prescribed aerosols (P. Colarco)Interactive ozonePrescribed SST, sea-ice Replay Apply Incremental Analysis Increments (IAU) to reduce shock of data insertion (Bloom et al.) IAU gradually forces the model integration throughout the 6 hour analysis periodGEOS-5 Atmospheric and Coupled Model Replay System Model predicted changeCorrection from DASTotal observed change Analysis CGCM GFDL ocean model (MOM4) A replay of the atmospheric data analysis in the CGCM. Has the potential to massively reduce initialization shocks Reanalysis MERRA NCEP, JRA-25, ERA

* Scout: coarse resolution, precursor of MERRA system * AGCM: replay Scout data to generate initial states

Models AGCM: GEOS-5 at 2X2.5X72Replay runs (Scout data) AGCM replay run: 1979, 1996-1997, 2002 35-day Hindcasts AGCM (1034 cases): 1979, Nov1996-Aug1997, 2002 ICs: daily 21z in 1979, 1996-1997, 2002 from replay runsDynamical MJO Hindcast Experiments: Sensitivity to Initial Conditions

Analysis toolUse Scout 200mb velocity potential from 1979, Nov 1996 Aug 1997 and 2002. Band pass 20-90 days between 30S 30N.EOF analysis. Hindcasts and verifications will be projected to two leading complex EOFs.

* Scout: coarse resolution, precursor of MERRA system * AGCM: replay Scout data to generate initial states

Models AGCM: GEOS5 at 2X2.5X72Replay runs (Scout data) AGCM replay run: 1979, 1996-1997, 2002 AGCM replay run (w/o Q IAU): 2002 35-day Hindcasts AGCM (1034 cases): 1979, Nov1996-Aug1997, 2002 AGCM ( 365 cases): 2002 (degraded Q in ICs) ICs: daily 21z in 1979, 1996-1997, 2002 from replay runsDynamical MJO Hindcast Experiments: Sensitivity to Initial Conditions (Q IAU)

Models AGCM: GEOS-5 at 2X2.5X72 GFDL MOM4 : 1/3x1 in tropics; 1x1 in extratropics; 50 layers Coupling every 30 minutes Sea ice extent taken as observed climatologyReplay runs (Scout data) AGCM replay run: 1979, 1996-1997, 2002 AGCM replay run (w/o Q IAU): 2002 CGCM replay run: 1979-2005 replay Scout data to initialize ocean and to generate the initial states35-day Hindcasts AGCM (1034 cases): 1979, Nov1996-Aug1997, 2002 AGCM ( 365 cases): 2002 (degraded Q ICs) CGCM ( 669 cases): Nov1996-Aug1997, 2002 ICs: daily 21z in 1979, 1996-1997, 2002 from replay runsDynamical MJO Hindcast Experiments: Sensitivity to Initial Conditions and Air-Sea Coupling

ICs lead to low forecasting skill

May 14, 1979 Apr 3, 1997Jun 27, 1979 May 3, 1997Aug 3, 1979 May 6, 2002Nov 22, 1979

ICs lead to low forecasting skill: cases 1 & 2

ICs lead to low forecasting skill: case 3

ICs lead to high forecasting skill

Apr 19, 1979 Feb 4, 1997 Apr 24, 2002Jun 8, 1979 May 15,1997 Jun 9, 2002

ICs lead to high forecasting skill: cases 1 & 2

ICs lead to high forecasting skill: case 3

Concluding Remarks:There are changes in the MJO forecasting skills between 1979 and 2002. Higher forecasting skills in 2002 appear to be resulting from the better moisture observations from the satellite. Both AGCM and CGCM predicted realistic MJO signals. Coupling tends to improve forecasting skills. Interactive air-sea coupling is essential in maintaining the intensity of the MJO in GEOS-5 coupled model.GEOS-5 exhibits the different forecasting skills on different phases of the MJO. It has less strength to develop the dry phase of the MJO over the Indian Ocean. Skills are enhanced when intended to develop the wet phase.The magnitudes of the surface latent heat fluxes in AGCM are much weaker than those in the coupled system. The phasing of the AGCM respond to the prescribed MJO SST anomalies and the associated surface flux anomalies are incorrectly simulated. This could be due to inadequacies in the model parameterizations. However, by forcing the atmospheric model with prescribed SST, it may be inherently difficult for AGCM to simulate realistic MJO. The study suggests that the following additional factors for improving MJO forecasts and simulation may be required: a) accurate initial conditions (e.g. wet and dry phases of an MJO over Indian Ocean); b) coupled to an ocean model to allow for air-sea interactions and realistic surface heat and moisture fluxes; c) improve the model physical package.

Version of GSI?