CLIVAR
AFRICA Panel meeting Abidjan 7-9 May 1998
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RECOMMENDATIONS FOR RESEARCH
GLOBAL TELECONNECTIONS
In this theme, a priority for
research is the better understanding of oceanic teleconnections to African
climate variability.
1.1 In respect of modelling
efforts:
-
develop the capability to predict
SST in the tropical Atlantic and Indian Ocean, comparable to the Pacific,
using a range of modelling techniques
-
conduct experiments to relate
oceanic dynamics and coupling mechanisms to circulation changes over Africa
(and test sensitivity of model resolution)
·
use diagnostic studies to verify the model-simulated annual cycle.
1.2
Empirical and diagnostic studies - inherently regional in character and
pursued jointly with numerical studies.
For particular attention
are key atmospheric and coupled structures:
- jets and atmospheric fluxes
- cellular patterns around
Africa and surrounding monsoons
- tropical zonal flows
and waves (Walker, MJO)
- extra-tropical flows
and linkages (NAO, frontal systems, etc)
- interaction with heat
lows in semi-arid zones
- wave propogation into
and from the continent
- forcing of tropical convection
- tropical cyclone genesis
and flow adjustments
- moisture advection including
vertical structure
- seasonality and the annual
cycle
·
identification of structures of variability in datasets, with focus on
scale interactions (eg. intra-annual) and non-linearity
1.3 Observations and Data
·
expand ocean observations over the tropics near Africa (eg. PIRATA, TRITON)
consistent with modelling needs for assimilation, noting that understanding
will depend on observations
-
call for enhancement of radiosonde
network in data voids (eg. Angola, Congo basin, Sudan, key ocean islands)
-
encourage reanalysis and verification
thereof, particularly in the tropics, to assist with diagnostic studies
-
inter-calibration of different
observing systems - for assimilation, monitoring, and model validation
-
create comprehensive data sets
- eg. atmospheric reanalysis, satellite remote sensed - as proxies for
rainfall and fluxes
paleo records - diaries,
oceanic core, etc
1.4 Process studies
-
field experiments, tropical
ocean-atmosphere-land interactions, including fluxes
-
upwelling and interaction with
overlying atmosphere
1.5 Capacity building
- making data sets available
- transfer of models
- interconnectivity with
other WCRP programmes to improve data dissemination
A plan of action is required
to link global and regional research projects involving:
- design of field studies
- model simulations and
sensitivity tests
- data set creation
- training, logistics,
meetings
- joint model and diagnostic
studies
- research exchange programmes
2. CONTINENTAL-SCALE PROCESSES
2.1 Modelling and numerical
experiments - focus on performance of high resolution regional climate
models in respect of:
- seasonal cycle and climatological
means
- intraseasonal variability
- synoptic weather systems
- convection statistics
- interannual to decadal
fluctuations
Model intercomparison should
be investigated for
-
systematic regional anomalies
, eg. near African lakes
-
incoherent patterns and diurnal
land surface processes
Simple models are needed
to improve understanding for inter-annual to decadal variability, background
state changes, etc. Regional models can be used to guide the design of
observing networks.
2.2 Empirical diagnostic
studies - call for research projects to use a mix of reanalysis and station
data to validate results. Suggested focus:
·
small scale boundary layer processes
·
nature of intra-seasonal variability and modulation by annual cycle
·
diagnosis of interannual and decadal variability
Describe teleconnections within
Africa in terms of historical rainfall, and in recent decades with reanalysis
products using dynamical variables.
2.3 Observations and Data
station network - building
of research data sets, yet maintaining realtime availability; need for
missing value indicator
-
daily rainfall data - in conjunction
with GPCP objectives, need to be archived to create seasonal data sets,
-
recognize importance of extreme
events in climate databases
-
include river streamflow, crop
yield, etc - beware of spatial coherence - processes are chaotic
satellite sensed data:
tropical rainfall monitoring
mission - should consider African needs and expertise in rainfall estimation
algorithms
Radiosondes - need to define
and maintain a minimum network
Reanalysis data is considered
crucial, but there is a need to validate with actual observations
Fine scale observations
may be needed to verify detailed modelling processes, comparison with existing
studies (eg. HAPEX) essential
Identify where field experiments
are needed, eg. Equatorial Africa Paleo-records:
should be used to place decadal variability in context - investigate travel
journals, tree rings, dust deposits, etc
2.3 Process Studies
African climatic variability
is unique in many ways. There is a need to go beyond ITCZ movement - to
describe the characteristics of convection and links to surrounding monsoon
circulation systems.
The size of Africa brings
unique land-atmosphere interactions particularly in the tropics. Its size
and symmetry around equator are important factors. There is a need for
regionalised studies to:
-
diagnose dynamical instabilities
and their interaction with jet streams and intraseasonal variability (what
generates long dry spells, convection bursts)
-
study on Principal Components
of interannual and intra-seasonal variability in the region (diagnostic)
-
understand teleconnection processes
which can assist capacity building efforts
2.4
Capacity Building
-
research interactions - collaborative
projects and two way exchange of scientists
-
uncover existing manuscripts
and recent internal research - upgrade and disseminate to international
community
-
develop a comprehensive list
of key papers for compilation in a WMO volume and distribution throughout
Africa.
-
numerical modelling - UNIX
knowledge lacking, however simple PC-based models should be distributed
with training efforts
PREDICTABILITY
3.1 Modelling and numerical
studies
-
establish capability to predict
Atlantic and Indian Ocean SST through various modelling techniques (ocean,
coupled, dynamical, empirical)
-
study impact of parameterisation
and value of ensemble forecast over Africa, particularly for areas where
deepest convection occurs and where there is a lack of data
3.2 Empirical and diagnostic
studies
-
assess error of estimation
(sampling density) in reanalysis fields over Africa and its impact on development
of predictive models
-
conduct diagnostic studies
to demonstrate and predict the ENSO teleconnection over Africa - build
on existing studies
3.3 Observations and Data
-
exploit remote sensing in diagnostic
and predictive activities to take into account the large areas and sparse
sampling over Africa.
Further develop calibration
and validation procedures for remote sensing data for use in predictive
models.
-
in order to better predict
SST in key areas, sustained ocean measurements are required (moored arrays
for subsurface structure, surface fluxes, etc)
-
improve observational network
on land, both surface and upper air to help better characterise continental
scale convection
-
continue support for data rescue,
archiving and quality control with view to improve forecast verification
-
improve telecommunication to
facilitate data flow and exchange, including value added products (important
for capacity building)
3.4 Process studies
-
regional field studies are
required to enable downscaling of predictions and evaluate limitations
of predictability (global modes like ENSO vs internal or local modes)
-
develop objective methods to
merge forecasts
3.5 Capacity building
-
increase internal capability
to provide predictive products, (eg. ACMAD, DMC, Univ interaction with
NMCs) through training and collaborative projects
-
develop human resources through
joint research which feeds back to the continent - eg. strengthen relevant
research institutions and networks in Africa
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