Convection and waves on Earth and small aqua
planets: Achievements and challenges
Peter Bechtold, Michael Herman* , Noureddine Semane
* New Mexico Tech
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 1
Convection scheme evolution
1989-2002
Mass flux scheme
2003
2007
Night/elev. convection Tropical variability
2013
Diurnal Cycle
Tiedtke (1989, MWR) Basic mass flux scheme
Bechtold et al. (2004, QJRMS) Convection initiation at night
“ “
et al. (2008, QJRMS) Entrainment, sensitivity to environment moisture,
variability
“ GEWEX Den Haag Session 8: Water Cycle 15. July 2014
“
et al. (2014, JAS) Closure and diurnal cycle
Slide 2
Convection: Tropical variability, OLR spectra, MJO
EC- Analysis 20082013
NOAA-Satellite
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
EC- Seas Fc
Cy40r1=2014
EC- Seas Fc ERAIcycle=2006
Aqua planet
Slide 3
MJO composite U and q anomalies
EC
Analysis
Seas Fc Cy40r1
Cy40r1
U
q
The remaining MJO problem is likely related to an underestimation of the dry
anomaly ahead = a moist bias; consistent with overestimation of precip over
Maritime continent/West Pacific and easterly wind bias
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 4
Kelvin T anomalies
EC
Analysis
Seas Fc Cy40r1
T
Aqua planet
characteristic tilted Kelvin wave
structure – note different tilt in
stratosphere
same for Aqua planet
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Important: T-anomaly and
heating must be in phase at
200-300 hPa to generate
potential energy and convert
into kinetic
energy
Slide 5
CAPE evolution and convective equilibrium
an entraining density weighted CAPE=PCAPE
compute its temporal derivative
write prognostic equation formally as
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 7
Closure ‘Deep’ in Numerical Weather prediction
Need to take into account the imbalance between deep
convective motions and surface forcing , define:
Adv+Rad+surf buoyancy flux
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 9
Diurnal cycle of Precipitation Phase (LST) for JJA
courtesy Yukari Takayabu and team for TRMM data composite
TRMM
Cy40r1
until
November
2013
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 10
How does diurnal Precip scale over land?
TP=total precipitation HF=surface enthalpy flux BF=surface buoyancy flux
NOTE: in NEW = surface daytime precipitation scales as the surface buoyancy flux
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 11
AMMA Precipitation : DA cycle, Aug2006 [mm/day]
TRMM 3B42 3hrly
DA Cy40r1 default :
t+24h
AMMA reanalysis :
t+24h
JJA 2001-2009
Convective precipitation
difference
Why?
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 13
Conclusions
 With realistic convective heating (phase and profile) it is
possible to support most variabilities: Synoptic, tropical
waves, diurnal cycles, ……… stratospheric oscillations
challenges
 too strong SE Asian Summer Monsoon and precip in
WPacific warm pool and related wind bias in the Central
Pacific Ocean (shared by many models with realistic
entrainment)
 Lack of nigt-time mesoscale convection: organization
through wind-shear, upper-tropospheric system
dynamics, cold pool dynamics?
To come
 T2000 (8-10 km) in 2015; T4000 (5 km) in 2020
 Prepare convective scaling on small planet
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 14
Idealised squall line simulation small
AQUA planet T159/22.5=5 km
5 km
no
deep
After 20 min
5 km
deep
Sylvie Malardel
GEWEX Den Haag Session 8: Water Cycle 15. July 2014
Slide 15