Challenges for numerical
weather prediction in the
tropics: AMMA legacy
Aida Diongue NIANG
ANACIM
METEOROLOGY
Senegal
Outline
1. Performance of NWP in the tropics and in
Africa
2. Rainfall variability and impacts
3. AMMA programme and legacy
4. Implications for operational forecasting
5. Conclusion - Recommendations
évaluation AERES 15-17 janvier
2008
2
Poor NWP model performance in Tropical Africa
ECMWF
ECMWF
Stable Equitable Error
in Probability
Space
To monitor Precipitation forecast
the score measures the error in
‘probability space’ through use of
the climatological cumulative
distribution function
Rodwell et al, 2010
Rainfall errros in NWP and climate models
Similar errors in NWP and climate models:
Misrepresentation of key processes (NWP &
Climate models ): dry and moist convection, surface,
radiation, turbulence, aerosols…
From Met Office
NB: improvement of the model since
4
Scores Evolution for Tropics: wind field
•Wind RMS @72h is large ~5 m/s 850 hPa) and
increases with altitude (~8 m/s 250 hPa)
• Dispersion between models is ~1 to 2 m/s (850 to
250 hPa)
• Progresses are slow!
évaluation AERES 15-17 janvier
2008
From Jean-Philippe lafore,
Meteo-France and CNRS
Tropics: RMS errors against TEMP
observations through forecast range
• RMS error against TEMP observations increases fast with the
forecast range at the same rate for all models
évaluation AERES 15-17 janvier
2008
6
Model performance to predict AEWs in the WAM System
at 3 longitudes
• Very low score beyond 2 days
•More skill for western Sahel
•Impact on rainfall forecast
évaluation AERES 15-17 janvier
2008
Private communication by Gareth Berry et al. 2008
7
Rainfall Variability Over Sahel:
Anomalies departures from the mean (1905-2005)
20%
10%
0
-10%
-20%
Niger à Malanville: 106
km²\
Monsoon onset
Jump of max rainfall
[10E-10W]
Sultan et al., 2003
17/07/1997
Water Vapor Channel
Complexity of the West
African Monsoon System
Key features of the West African
Monsoon Climate System during
SAL
Boreal summer
Heat
Low
AEJ
ITCZ
Cold
Tongue
Chris Thorncroft
Scale interactions
Figure adapted from Redelsperger et al ,
BAMS 2006
Global
Global SST
Teleconnections
Remote effects of MJO
104 km
Regional
Monsoon Systems
Scale interactions
103km
AEWs
Major River Basins
Mesoscale
102km
Local
101km
Mesoscale
Convective
Systems Catchments
Intraseasonal scale
is a central scale for
the understanding of
Monsoon variability
and its impacts: S2S
Vegetation
Deep Conv
Soil
Cells
Pools
Vegetation
Shallow
Cells
Soil
Hour
Day
Diurnal
Cycle
Season
Seasonal
Cycle
Year
Interannual
Variability
Outline
1. Performance of NWP in the tropics and in
Africa
2. Rainfall variability and impacts
3. AMMA programme and legacy
4. Implications for operational forecasting
5. Conclusion - Recommendations
évaluation AERES 15-17 janvier
2008
11
Outline
1. Performance of NWP in the tropics and in
Africa
2. Rainfall variability and impacts
3. AMMA programme and legacy
4. Conclusion - Recommendations
évaluation AERES 15-17 janvier
2008
12
Decision
makers
Multidisciplinary
approach
Early warning systems, advices …
WEATHERFORECASTING & CLIMAT PREDICTION
Days
Weeks
Seaseson Interannual
Seamless Vision
Redelperger et al.
West African
Monsoon
Aerosols
Chemestry
Climate Change
IMPACTS
Water Ressources
Health
Agriculture
Observing
strategy (original)
Ocean-Atmosphere-Continental surface
measuremens
impacts data (surveys, …)
Multi-scale measurements (temporal & spatial)
(
Sal
(
Dakar
Gourma
(
(
Niamey
Ouaga
Multi-échelles dans le temps et dans
l’espace
Meteor
Ouém
é
Atalante
Déploiement SOP
(
Réseau Radio-sondages
6 Avions de
Recherche
Bouées PIRATA
Sites auxiliaires SOP
Sites de Méso-Echelle
3 bateaux
AMMA LEGACY
– Better understanding of the West African Monsoon
Publications: ~ 600 reffered / 10 special issues :
J. of Geophysical Research (2)/J. of Atmospheric Physics & Chemistry/J. of Hydrology/Quarterly
Journal & ASL (RMS)/Weather & Forecast & J. of Atmospheric Sciences (AMS) /Climate Dynamics
– Capacity Building
– PHD; ~ 160, 80 Aricans
– ~ 40 research units for 20 different countries
– Masters, Summer schools, workshop
– Observations of the WAM: improvement of the operational observation
network (soundings…), GPS, driftsondes, surface conditions, satellite,
research observations (lidar, radar, aircraft…)
 opportunity to evaluate NWP models
and the impact of observations
évaluation AERES 15-17 janvier
2008
15
AMMA: Impact of using the AMMA
radiosonde dataset
•
New radiosonde stations
•
Enhanced time sampling
•
Bias correction for RH
developed at ECMWF
(Agusti-Panareda et al)
•
Data impact studies
With various datasets,
With and without RH bias
correction
Number of soundings provided on GTS in 2006 and 2005
Period: 15 July- 15 September, 0 and 12 UTC
AMMA: Impact of using the AMMA
radiosonde dataset (2)
AMMABC: AMMA + RH bias correction
PreAMMA: with a 2005 network
NOAMMA: No Radiosonde data
CPC: Observations
• Positive impact of the assimilation of AMMA dataset
• Very poor performances of NOAMMA
• Best performance of AMMABC
Similar results
obtained at ECMWF
Monthly averaged RR
better with bias
correction
Faccani et al, 2009
Assimilation of AMSUB over land•
Impact on TCWV
Average over the period 1 Aug-14
Sep’06
•
•
Developments @ Météo-France
to assimilate surface sensitive satellite
humidity channels over land
(Karbou et al., 2006)
To improve the hydrological cycle over
the Tropics, in particular over the
AMMA region
(Karbou et al., 2009a/b,
TCWV diurnal cycle at TOMB
TCWV (EXP-CTL)
• Positive impact of the assimilation of AMSU over land
• Large impact over Tropics in Monsoon regions
• especially over Africa and in region with a poor data coverage
• Improvement of the diurnal cycle
évaluation AERES 15-17 janvier
2008
Karbou et al, 2009a, b
Outline
1. Performance of NWP in the tropics and in
Africa
2. Rainfall variability and impacts
3. AMMA programme and legacy
4. Implications for operational forecasting
5. Conclusion - Recommendations
évaluation AERES 15-17 janvier
2008
19
Forecast during the AMMA-SOP 2006
•
An unique experiment at ACMAD
(Support WM0, AMMA, Europe (FP6), MF, Médias-France)
– Operational forecast during 4 months (JJAS) in 2006
– 2 briefings/day to guide the field experiment
– 15 forecasters from 12 West African countries
•
Tools and methods
– Synergie Forecasting System (MF)
• 4 Stations at ACMAD fed with NWP products + Observations with the RETIM link
– AOC-Web site (Medias, MF) http://aoc.amma-international.org/
• VSAT internet link at ACMAD
• Reports, quicklooks, NWP products (ECMWF, UKMET, MF, NCEP, Morocco), diagnostics,
research models…
• MCS tracking: RDT from SAF-Nowcasting
•
– Development of a forecasting method WASA/F
– 2 weeks training for forecasters
Major learning
–
–
–
–
–

NWP skill is poor especially for convection
But NWP is very useful for the large scale mass and circulation
Need of observations, adequate NWP products and diagnostics
Need to combine several NWPs
Diversity of methods across West African Forecasters
Need to have a forecasters handbook
20
Forecasters’ Handbook project
Leaded by Parker (University of Leeds) and colleagues
• Collaborative programme with the aims of documenting existing good
practice in forecasting, and accelerating the translation of new research
results into operational forecasting practice.
• The document is close to completion and is expected to be published in
2015.
• The main challenge: to bridge the scientific gap between the theoretical
and operational side
• Various new tools for forecasters, including new conventions for plotting
of synthetic charts (the West African Synthetic Analysis/Forecast, or
WASA/WASF system) and new diagnostics with various case studies.
• THORPEX support , specifically by supporting two workshops, at the
International Centre for Theoretical Physics (ICTP) in 2009, and in Dakar in
March 2013
WASA- WASF (West African Synthetic Analysis /Forecast)
WASA du 06/08/06 06TU
Project
•
Collaboration between Senegal Weather
Service and CNRM/MOANA:
researchers and forecasters
•
A real-time website, simple but easily and
rapidly evolving, according to the
encountered needs and ideas
•
Use of websites providing complementary
information (broader context)
–
•
•
e.g. MJO: Wheeler’s website + NCEP
Regular reports (~2/week) and
discussions between Toulouse and Dakar.
Use of the products in operation al
forecasting
Paper in preparation for BAMS
http://isv.sedoo.fr
Summary and Recommendations
•
•
•
•
•
•
•
•
•
•
NWP skill over Tropics and especially over Africa is still poor as compared with extra-tropics
Due to the lack of observations and to the importance of the role played by the physics (dry
and moist convection, surface, radiation, turbulence, aerosols…)
Nevertheless large scale thermodynamical and dynamical structures that force convection
are better depicted and are very useful for forecasting weather
AMMA allowed to demonstrate the positive impact and the key importance of improving the
operational observation networks
Major progresses have been performed in recent years especially in the assimilation area
(microwave data)
Efforts to be made by countries to maintain orenhance observing systems
Nevertheless the forecast skill of the water cycle and of precipitation progresses very slowly
Lessons learned during the forecasting exercise and some research results being put in the
West African Forecasting guide
New Metrics and better diagnostics adapted to Tropics (and Africa) in the framework of
MISVA but need for more particularly for Ensemble prediction
Recommendations: Seamlessness means also that any place in the world get
advantage of improvement and availability of weather products to predict particularly
for HIW prediction by first easing access to NWP products .
évaluation AERES 15-17 janvier
2008
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