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Length Scale analysis of the transition from shallow to deep convection

Study on diurnal cycle of tropical convection, analyzing length scales during transition, precipitation onset variations, and impact of cold pool dynamics on thermodynamic variables.

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Length Scale analysis of the transition from shallow to deep convection

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  1. Length Scale analysis of the transition from shallow to deep convection João Paulo A. Martins(1) Pedro M. A. Miranda(1) Pedro M. M. Soares(1) João Teixeira (2) (1)University of Lisbon - CGUL/IDL (2) Jet Propulsion Laboratory/California Institute of Technology

  2. Motivation • Diurnal cycle of tropical convection: • Most GCMs (or SCMs) fail to get the right timing of precipitation • New approaches are needed (e.g. Rio et al 2009) • EDMF Shallow Convection • Enhanced Emanuel (1991) Deep Convection Scheme (new trigger functions) • Cold pool parameterization OBS Bechtold et al. (2004) Rio et al. (2009)

  3. TRMM-LBA Shallow to deep convection case study • Grabowski et al. (2006) (GCSS-WG4 Case 4)– SCM/CRM intercomparison - observations made during the TRMM-LBA, Rondonia, Brazil, February 23, 1999. • The case considered is a daytime convective development over land • 7h30 to 13h30 LT Rad Cooling Surface Fluxes

  4. Using MesoNH as an LES

  5. Results in fair agreement with previous studies of the case • Higher horizontal resolution: • BL is higher • Clouds form earlier but reach less higher altitudes • Precipitation rate is lower

  6. Vapor Gotículas Precipitação Neve Transition is delayed in higher resolution

  7. Length Scale growth Shallow Convection Deep Convection

  8. Evolution of length scales on z/zi=0.5 • Turbulent Integral Length Scale, based on spectral analysis (e.g. Pino et. al, 2006) Beginning of precipitation

  9. θv perturbation (K) y (km) x (km)

  10. θv perturbation (K) x (km)

  11. Summary • The transition from shallow to deep convection was simulated by an LES model (two different resolutions) • Precipitation onset is delayed and deep convection is weaker with higher resolution (100 m) • Length scales are analyzed with an integral spectral method • Vertical velocity lengh scale is proportional to PBL height in time and in altitude • Theta length scales increases significantly in PBL from precipitation onset • Results suggest cold pool dynamics strongly influences length scales of thermodynamic variables inside PBL

  12. Thank you for your atention! Photo: João Martins

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