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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) 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,.. 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 Monsoon ocean/continent. Chemistry, aerosols Rainfall fields Cloud microphysics, aerosols Retroactions with the surface Hurricane development convective system studies convective systems meso-scale ~ 100 km Local scale ~1-10 km large scale ~ >1000 km AMMA: African Monsoon Multidisciplinary Analysis Objective: understanding of monsoon ? improve climate and weather forecasts 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 Warm Cold IR10.8 Top Temperature MSG-1, 14 July 2003, 02:00-08:45 UTC, IR10.8 Tracking of convective systems Importance of well organized systems (large/long lived) for the total convective cloud cover Mathon and Laurent., QJRMS., 2001 Distributions of convective systems Importance of a few major convective systems Over West Africa, 50 % cloud cover ~ systems > 24 h Over Amazonia: shorter lifetime of convective systems 50 % cloud cover ~ systems > 12 h Laurent et al., JGR, 2002 different distributions of convective systems 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 Diurnal cycle: Amazonian wet season ? understanding of monsoons ? need to improve convection in GCMs comparison of CS: African monsoon – Amazonian monsoon 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 Convective systems and precipitations  Sahel ? rain events (surface) / cloud events (satellite) OCS = 12 % of MCS OCS = 78 % of cloud cover (233 K) Mathon et al., J. Applied Meteo., 2002 Lebel et al., JGR, 2003 Organized convective systems (OCSs) Satellite events = 83% of total rainfall Among them: - 94% OCS - 6% others annual rainfall ? number of events 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 MCS propagation wind 700 hPa Rondônia state Tracking of convective systems (satellite) and rain cells (radar) Laurent et al., JGR, 2002 Relationship between high-level divergence and CS expansion Divergence Convergence Divergence at top of convective systems Divergence at top of convective systems Relationship between high-level divergence and CS expansion ? Application to nowcasting Relationship between initial expansion and lifetime 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 www.cpetc.inpe.br 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 Summary