West African Monsoon

1
West African Monsoon Modeling and Evaluation
(WAMME) Project Yongkang Xue, Bill Lau, Kerry
Cook With contributions from many collaborators
  C20C Workshop Exeter, U.K. March 2007
2
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

3
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
4
Summer Precipitation climatologies in the coupled
ocean/ atmosphere GCMs
N. Vizy K. H. Cook, 2006
CRU 1961-1990 Clima-tology (New et al. 1999)
5
Summer AEJ climatologies in the coupled ocean/
atmosphere GCMs
600 hPa NCEP 1949-2000 Climatology
6
What is the Sahel/Guinean Coast Rainfall dipole
response?
Take for example the summer of 1984
Surface Temperature Anomalies (?C)
Precipitation Anomalies (mm/day)
7
Dipole Year Composites of Summer Rainfall
(mm/day) from various GCM and differenced from
the 1949-2000 summer climatology
8
(No Transcript)
9
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  
10
Diurnal cycle

• West African Monsoon exhibits strong diurnal
  cycle
• Due to surface heating in heat low

Meridional wind
Profiles from HAPEX-Sahel
Humidity
Dolman et al J Hydrol 1997 Parker et al QJRMS
2005 Produced by C. Taylor, 2005
11
(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.  
12
(No Transcript)
13
(No Transcript)
14
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?
15
Mediterranean SST effect

16
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
17
Rowell, 2003
18
(No Transcript)
19
Aerosol Dust Effect

20
(No Transcript)
21
850 mb wind, sea level pressure and rainfall
induced by direct effects of dust in the NASA
fvGCM
22
Land Cover Change Effect

23
Observed and simulated precipitation anomalies
(mm/mon)
JAS (80s-50s)
OND (80s-50s)
JAS (desert-cntrl)
OND (desert-cntrl)
24
(No Transcript)
25
(No Transcript)
26
(No Transcript)
27
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.
28
WAMME focus

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

29
(No Transcript)
30
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
Janicot AMMA data management Laurence Fleury
C20C Adam Scaife
31

• 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).