length scale analysis of the transition from shallow to deep convection joão paulo a. martins (1)...
TRANSCRIPT
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
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)
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
Using MesoNH as an LES
Grid 600×600×128 240×240×128Horizontal Resolution 100 m 250 m
Start Time 0730 LTEnd Time 1330 LT
Vertical GridAbove 1500 m – stretching of 1.2% from 100m at
1500m to 500 m near model topTime-step 2 s
Boundary Conditions Cyclic
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 SchemeMomentum – Centered in time, 4th order
Thermodynamic and scalars – Piecewise Parabolic Method
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
Vapor Gotículas
Precipitação
Neve
Transition is delayed in higher resolution
Length Scale growth
ShallowConvectio
n
DeepConvection
Beginning of precipitation
• Turbulent Integral Length Scale, based on spectral analysis (e.g. Pino et. al, 2006)
Evolution of length scales on z/zi=0.5
x (km)
y (
km)
θv perturbation (K)
x (km)
θv perturbation (K)
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
Thank you for your atention!
Photo: João Martins