COMPARAO DAS CARACTERSTICAS DOS SISTEMAS CONVECTIVOS OBSERVADOS NA AMAZNIA E NA FRICA

1
Characterization of tropical convective systems
Henri Laurent IRD/LTHE Cooperation with
Brazil CTA (Centro Técnico Aeroespacial) CPTEC
(Centro de Previsião do Tempo e Estudos
Climaticos) Cooperation with Africa AGHRYMET
center, Niamey (Niger)
2
Motivations

• Tropical rainfall is mostly of convective origin
  (e.g., 90 in West Africa)
• Rainfall is the key parameter of climate in
  tropical regions
• convection is essential for atmospheric
  circulation (vertical transport of water and
  energy)
• impacts food production, flooding, ressources,
  health,..

3
Why to study the convective systems ?

• vector of the tropical precipitations
• cloud clusters at mesoscale link between
  general atmospheric circulation and hydrological
  scales
• atmospheric water cycle and energy balance

4
convective system studies
convective systems meso-scale 100 km
Monsoon ocean/continent. Chemistry, aerosols
Rainfall fields Cloud microphysics, aerosols
Retroactions with the surface Hurricane
development
large scale gt1000 km
Local scale 1-10 km
5
AMMA African Monsoon Multidisciplinary Analysis
6
Convective systems Amazonia - Africa
LBA Large-Scale Biosphere Atmosphere Amazon
Mesoscale Campaigns WET-AMC jan-fev
1999 DRYtoWET-AMC sep-oct 2002
(Hapex-Sahel 1992, EPSAT-Niger 1989-2000) AMMA
African Monsoon Multydisciplinary Analysis
Long Observing Period 2001-2010 Extended
Observing Period 2005-2007 4 Special
Observing Periods 2006
Objective understanding of monsoon
? improve climate and weather forecasts
7
Tracking of convective systems
Warm
Cold
IR10.8 Top Temperature MSG-1, 14 July 2003,
0200-0845 UTC, IR10.8
8
(No Transcript)
9
Distributions of convective systems
Importance of well organized systems (large/long
lived) for the total convective cloud cover
Mathon and Laurent., QJRMS., 2001
10
Importance of a few major convective
systems
Over West Africa, 50 cloud cover
systems gt 24 h
11
different distributions of convective systems
Over Amazonia shorter lifetime of convective
systems 50 cloud cover systems gt 12 h
Laurent et al., JGR, 2002
12
Diurnal cycle Amazonian wet season
WETAMC/LBA jan-fev 1999 (Silva Dias et al. JGR
2002)
? Short-lived CS, explosive convection
? Convection at minimum of total
cloud cover (energy)
Machado et al., JGR., 2002
13
comparison of CS African monsoon Amazonian
monsoon
? understanding of monsoons ? need to improve
convection in GCMs
14
Convective systems and precipitations

Sahel

• Niamey mesoscale network (since 1989)
• Classification of rainfall events (e.g.,
  Amani et al. Water res. Res., 1996)
• 90 to 95 of rainfall from mesoscale events
• Up to 80 of rainfall from major events with
  coherent propagation

? rain events (surface) / cloud events (satellite)
15
Organized convective systems (OCSs)

• OCS 12 of MCS
• OCS 78 of cloud cover (233 K)

Satellite events 83 of total rainfall Among
them - 94 OCS - 6 others
Mathon et al., J. Applied Meteo., 2002 Lebel et
al., JGR, 2003
16
annual rainfall ? number of events
17
Atmospheric Circulation ? convective systems
wind regimes during
WETAMC/LBA
Westerly regime (monsoon) large systems,
moderate rainfall, weak propagation Easterly
regime (break) explosive convection, shorter and
more intense rainfall, steady westerly
propagation Silva Dias et al., Rickenbach et al.,
Laurent et al., Machado et al., JGR 2002
18
MCS propagation
Rondônia state
wind 700 hPa
19
Tracking of convective systems (satellite) and
rain cells (radar)
Laurent et al., JGR, 2002
20
Divergence at top of convective systems
Relationship between high-level divergence and CS
expansion
Divergence
Convergence
21
(No Transcript)
22
Divergence at top of convective systems
Relationship between high-level divergence and CS
expansion
23
Relationship between initial expansion and
lifetime
? Application to nowcasting
24
Operational tracking of convective systems
Outcome of a cooperative project
Brazil-France Operational version of the CS
tracking methodology FORTRACC (Forecasting and
Tracking Convective Cloud Clusters) running at
CPTEC (Brazilian center for weather forecasting
and climate studies) www.cptec.inpe.br
25
www.cpetc.inpe.br
26
Summary

• Mesoscale convective systems from satellite data
• characterization of CS life cycle
• rainfall associated with CS
• interactions with atmospheric dynamics

• retroactions CS-surface

• Operational tracking of CS
• Nowcasting
• climatology