Patterns of convection in Africa and opportunities for collaboration

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Patterns of convection in Africa and
opportunities for collaboration

• Arlene Laing
• National Center for Atmospheric Research

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MOTIVATION

• Prediction of warm season precipitation is
  encumbered on improving understanding of
  initiation and evolution of organized convection.
  Societal need for improved precipitation
  prediction in Africa.
• Radar-based studies in US found that organized
  convective precipitation displays coherence in
  propagation (Carbone et al 2002)
• Studies of East Asia, Australia, Europe used IR
  data to track cold cloud clusters and found
  similar coherence
• How similar or different is organized convection
  in Africa? What can be inferred about
  prediction of precipitation from the behavior of
  deep convection?

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Seasonal distribution of African MCCs
Laing and Fritsch, 1993
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Study Domains Period
20N
May - Aug
Main Focus May - August 5-year (1999 to
2003) 2-year Sep-Oct 1999, 2003 2-year NovDec
1999, 2003 Meteosat-7 IR, 30min
0
Sep-Oct
20S
Nov - Dec
0
20W
40E
20E
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Methods

• Brightness temperatures (lt 253K, 233K, 213K)
  identifies organized convection most likely to be
  precipitating
• Pixel colder than threshold constitutes event
  at given distance time coordinate (Hovmoller
  space)
• Caveats
• IR advantage high temporal tracking capability
• Problems Identification of warm rain,
  underestimation of early stage of convection,
  distinguishing between deep convection and thick
  cirrus

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Tropical N. Africa 16 30 June 2003
253K
233K
213K
16 18 20 22 24 26 28 30
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Seasonal Diurnal Distribution
Average Hourly Percentage of Cold Cloud, Tbb lt
253K
Pre- Monsoon 15 May30 Jun

• PREFERRED ZONES
• Initiation in lee of high terrain
• Local Propagating
• Convection
• Seasonal migration
• Land/Ocean Diurnal Cycles

Peak Monsoon 1 Jul15 Aug
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EPISODES 16 30 June 1999
Mean Diurnal Cycle of time with Tbb lt 233K
12 18 0 6 12 18 0 6
UTC
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Comparing Continents
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Link with other projects programs

• African Monsoon Multidisciplinary Analysis (AMMA)

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African Contacts Institutions

• Amadou Gaye, UCAD, Senegal, Co-Chair, AMMA Water
  Cycle
• Debo Adeyawa, (Federal University of Technology,
  Akure, Nigeria)
• Collaborator with Ed Zipser on studies of TRMM
  diurnal cycles and convective systems
• Arona Diedhiou, AGHRYMET, Niger, Co-Chair, PIAF

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UCAR Institutions(AMMA Water Cycle)

• SUNY Albany, Chris Thorncroft
• Howard University, Greg Jenkins
• U of Oklahoma, Peter Lamb
• MIT, Fatih Eltahir
• MIT, Earle Williams
• U of North Dakota, Paul Kucera

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SH AFRICA Summer (20S 35S)
1100 UTC 9 Dec
8 -11 Dec 2003
1500 UTC 9 Dec
1800 UTC 9 Dec
2000 UTC 9 Dec
2330 UTC 9 Dec
0430 UTC 10 Dec
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Links with other programs

• Peter Chen, WMO World Weather Watch
• WMO Severe Weather Forecasting Demonstration
  Project (SWFDP), with a few National
  Meteorological Services, regional centers
  centers that produce global products
• challenges we face is to provide the necessary
  training to support and sustain the use of
  certain NWP products that are not being used
  there, or products that could be better "tuned"
  for better performance in this region
• Glad to hear of this initiative, sharing info
  with Dr. Jack Hayes, Director of World Weather
  Watch
• Will use my research on southern African
  convection in project this year
• Chris Reason, University of Cape Town, South
  Africa

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COMET Contribution

• Joint proposal with UNEP to the UN Foundation for
  enhancing environmental literacy in Africa
• Use of broadcasters
• Partnership with NEETF (National Env. Edu.
  Training Foundation)
• COMET Modules in wide use
• With additional funds could adapt modules to be
  Africa-centered
• Tropical Meteorology Textbook (Laing and Evans)

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Summary Tropical N. Africa

• Organized convection over Africa occur as
  coherent sequences
• Similar phase speeds to other continents although
  average zonal span and duration are greater
  (larger longitudinal domain)
• Large fraction of episodes initiate in the lee of
  high terrain
• Propagation leads to delayed-phase shift in
  diurnal maximum
• Convection occur with moderate vertical shear of
  zonal wind
• Without steering winds, longevity, and spatial
  span of events are greatly diminished, and
  significant propagation ceases
• Imagery shows evidence of gravity currents and
  mesoscale convective vortices (MCVs). Some MCVs
  became tropical cyclones close to west coast of
  Africa (e.g., Cindy, Gert, Alberto)

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Summary Mid-latitude S. Africa

• Similar coherent pattern of convection
• Episodes of organized convection are less
  frequent than other domains
• Phase speeds less than other continents
• High terrain aids in convective initiation
• Regime with propagation exhibit delayed-phase
  shift in diurnal max
• Examining westerly wind shear to determine
  influence on propagation (propagating vs
  non-propagating regimes)

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Mean Diurnal Cycles (JJA)
2000
2001
6 12 18 0 6 12 18
6 12 18 0 6 12 18
UTC
UTC
of time Tbb lt 253K
2002
2003
6 12 18 0 6 12 18
6 12 18 0 6 12 18
UTC
UTC