West African Monsoon Modeling and Evaluation (WAMME)

Project

Yongkang Xue, Bill Lau, Kerry Cook

With contributions from many collaborators  

C20C WorkshopExeter, U.K. March 2007

CEOP Inter-Monsoon Studies (CIMS)

Objectives:

• To provide better understanding of fundamental physical processes (diurnal cycle, annual cycle, intraseasonal oscillations) in monsoon regions around the world

• To demonstrate the synergy and utility of CEOP data in providing a pathway for model physics evaluation and improvement

Issues in WAM (West African Monsoon):

1). The WA monsoon precipitation and associated important features, as well as impacts of oceanic and land processes, and aerosols are not well understood;

2). Dynamical models used for WAM prediction have problems simulating fundamental characteristics of rainfall such as the diurnal, seasonal, interannual , and intra-decadal cycles;

Summer Precipitation climatologies in the coupled ocean/ atmosphere GCMs

N. Vizy & K. H. Cook,

2006

CRU 1961-1990 Clima-tology (New et al. 1999)

Summer AEJ climatologies in the coupled ocean/ atmosphere GCMs

600 hPa NCEP 1949-2000 Climatology

What is the Sahel/Guinean Coast Rainfall dipole response?Take for example the summer of 1984

Surface Temperature Anomalies (C)

Precipitation Anomalies (mm/day)

Dipole Year Composites of Summer Rainfall (mm/day) from various GCM and differenced from the 1949-2000 summer climatology

WAMMY (West African Monsoon Modeling and Evaluation) focus:

(1) to evaluate the performance of current GCMs/RCMs in simulating WAM precipitation and relevant processes at diurnal, intraseasonal, interannual, and intradecadal scales, as well as its onset and withdrawal;

(2) to identify the common discrepancies and provide better understanding of fundamental physical processes in WAM;

 

Diurnal cycle• West African Monsoon exhibits strong diurnal cycle

– Due to surface heating in heat low

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Meridional wind

Humidity

Dolman et al J Hydrol 1997Parker et al QJRMS 2005Produced by C. Taylor, 2005

(3) to demonstrate the utility and synergy of CEOP and AMMA field data and remote sensing data in providing a pathway for model physics evaluation and improvement.

 

WAMMY focus:(4) to conduct sensitivity experiments to isolate

important key physical processes for diurnal, annual, interannual and interdecadal variations of WAM;

 For example, there was severe drought in the 1960s to 1980s. Since the 1980s it is an increase in the “continentality" of the WAM, reflected by a shift of the WAM convection towards land from the 1980s to 1990s, consistent with satellite derived leaf area index over the west Africa.

SST? Aerosol? Land?

Mediterranean SST effect

Sahel Rainfall vs. Tropical Indian Ocean SST

Rainfall index from Dai et al.(2004), SST from merged CRU surface temp dataset.Plot created by A. Dai/NCAR

Rowell, 2003

Aerosol Dust Effect

850 mb wind, sea level pressure and rainfall induced by direct effects of dust in the NASA fvGCM

Land Cover Change Effect

Observed and simulated precipitation anomalies (mm/mon)

JAS (80s-50s) OND (80s-50s)

JAS (desert-cntrl) OND (desert-cntrl)

Since the West African monsoon variability strongly affected by several external forcings and their interactions, WAMME will necessarily encompass vegetation-ocean-atmosphere-aerosol interactions and is an interdisciplinary project.

WAMME focus:

• (5) to evaluate the nested RCMs’ ability of downscaling West African regional climate simulations.

WAMME is an initiative of CIMS/CEOP and designed to bring together current and planned Earth observing satellites, existing suite of operational satellites, and observational and modeling assets of the GEWEX

continental scale experiments and the field observations of CLIVAR and other WCRP activities, to support key science objectives in climate prediction and monsoon

system studies. WAMMW will have close collaborations with AMMA, C20C, and relevant projects

http://www.wamme.geog.ucla.edu

Other International Projects’ Coordinators:CEOP: Sam Benedict, Amadou Gaye

AMMA-US: Chris Thorncroft AMMA GCM: Paolo Ruti, HOURDIN Frederic, Serge

JanicotAMMA data management: Laurence Fleury

C20C: Adam Scaife

• 1st Stage Experimental Design• 1) Initial conditions: NCEP-DOE Reanalysis II.

The model runs start from April 1, 2, 3, and 4 through October 31 for years 2000, 2003, 2004, and 2005, 2006(?). Each group downloads the initial data sets from the Reanalysis II web site and interpolates them to the models’ vertical coordinates and horizontal resolutions.

• 2). Surface boundary conditions: The SST and sea ice data are HadISST1 (Rayner et al. 2003).

• 3). ……