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 Bechtold et al. (2004) OBS 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 CoolingSurface Fluxes

4. Using MesoNH as an LES Grid600×600×128240×240×128 Horizontal Resolution100 m250 m Start Time0730 LT End Time1330 LT Vertical Grid Above 1500 m – stretching of 1.2% from 100m at 1500m to 500 m near model top Time-step2 s Boundary ConditionsCyclic Sub-grid processes parameterizations TURBULENCE = 3D, 1 and ½ closure (Cuxart et al., 2000) CLOUD = ICE3 (6 classes of hydrometeors) (Pinty and Jabouille, 1998) Advection Scheme Momentum – Centered in time, 4 th order Thermodynamic and scalars – Piecewise Parabolic Method

6. 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

7. VaporGotículas PrecipitaçãoNeve Transition is delayed in higher resolution

8. Length Scale growth Shallow Convection Shallow Convection Deep Convection Deep Convection

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

11. x (km) y (km) θ v perturbation (K)

12. x (km) θ v perturbation (K)

13. 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

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