Post on 13-Mar-2020
Getting Organized Convection into
Climate Models
PROWESS International Conference
25th Anniversary of NCMRWF
February 17-20 2014
Mitch Moncrieff
NCAR Earth System Laboratory
Climate & Global Dynamics Division
Boulder, Colorado, USA
Weather Climate
MJO
30 - 90 days
Contents
• Dynamical system approach to organized convection parameterization
• Propagating orogenic MCS over the continental U.S.
• Madden - Julian Oscillation (MJO)
• Year of Tropical Convection (YOTC)
• Conclusions
• Underlying chaotic order, analogous to coherent structures in turbulent flow
• Upscale and downscale transport of energy and momentum
• Affects precipitation distribution, intensity, type
• Key part of the global water cycle
Organized convection
Cumulonimbus
O (10 km)
Supercell storm
O (100 km)
Tropical cyclone O (1000 km)
Madden-Julian Oscillation (MJO)
O (10000 km)
Mesoscale convective system (MCS) O (100 km)
Mesoscale Convective System (MCS)
• Provides about half the total tropical rainfall
• Long-lasting, propagates ~10m/s, with regional impact
• Transport properties distinct from turbulent cumulus mixing
• Affects structure of diabatic heating, convective and radiative
• Dynamically interactive, building block of larger-scale organization
Precipitation bias occurs within days … in regions of
large-scale convective organization
CAPT Program, LLNL
Fraction of rainfall from MCS
(TRMM satellite)
Tao & Moncrieff (2009)
MCSs are missing from traditional
climate models ...
• Cumulus parameterizations were not designed with organized
convection in mind ---
• MCS: Dynamical system distinct from cumulus convection
• Resolution of traditional climate models insufficient to simulate MCS
New Era: Mesoscale-permitting climate models:
O (10km) mesh
Physical resolution of numerical models is about an order of
magnitude coarser than its computational mesh, therefore:
i) O (100 m) mesh: cumulus parameterization not needed
ii) O (1 km) mesh: mesoscale organization resolved
iii) O (10 km) mesh: mesoscale organization permitted
Horizontal scale
Mesh
size
Cumulus
Scale-gap
~1 km ~100 km
Cumulus parameterization assumes a scale gap
Horizontal
scale
Cumulus
Mesoscale
Systems
~100 km ~1 km
But no scale gap in the real world
Mesh
size
Cumulus parameterization
MCS
Turbulent mixing
Single vertical column
L ~ 1-10 km
L < H
H ~ 10 km
L ~ 100 km
Slantwise quasi-
laminar flow
L >> H
H ~ 10 km
MCS as a Dynamical System Distinct from Cumulus
Dynamics of slantwise overturning
*c = U (z )
*z = z
( ,z )c, F
0
2 ( )z
z
FG dz
0z
Baroclinic generation of
vorticity
Vorticity
Shear
buoyancy
Steering level
latent heating
evaporative cooling
Convective Froude number:
Bernoulli Number:
0U (z) - c/p
Environmental shear
2
0U /CAPEcF
2102
U
2102
/E p U
Moncrieff (1992)
Propagating slantwise overturning
3 Categories of Energy: Potential, Kinetic, Pressure work
2102
( )UR
CAPE
c
2102
( )c
pE
U
E R
Representing MCS in Global Models:
Slantwise (Tilted) Heating in Shear Flow
Multi-scale Structural Paradigm
Propagating Orogenic MCS over US
Continent
Propagating MCS downstream of mountains
Laing and Fritsch (1997)
Continental US
W. Africa
Propagation and Diurnal Cycle
Afternoon
Next morning
~1000 km
Elevated heating:Start position /time of MCS
Mesoscale
descent
MCS – Family of
cumulonimbus
Vertical shear a) Organizes mesoscale dynamics
b) Controls propagation
C ~ 10 m/s
Simulated Propagating MCS:
Resolution Dependence and Observational Validation
3-km explicit NEXRAD analysis Carbone et al. (2002) 10-km Betts-Miller 10-km explicit
Moncrieff and Liu (2006)
Explicit vs Parameterized Precipitation
Parameterized Explicit Total
Superparameterized Community Atmospheric Model (SP-CAM)
Standard CAM - no MCS
SP- CAM - Propagating MCS
Second-baroclinic heating/cooling
communicated from CRM grid to
climate grid organized by vertical shear
Pritchard, Moncrieff and Somerville (2011)
Resolution Dependence of Convective Heating
30 km
10 km
3 km
Madden-Julian Oscillation (MJO)
Multi-scale Convective Organization
in Global Model Frameworks
A) Traditional climate models
B) High-resolution global NWP
C) Global cloud-system resolving models
D) Superparameterized global models
E) Multicloud parameterization
A) Tropical precipitation: Aqua-planet climate models
(5S - 5N average)
D. Williamson (NCAR), M. Blackburn (U. Reading)
“Truth”
Global Cloud-System
Resolving Model
(NICAM)
B) MJO Hindcasts for ECMWF IFS
Vitard et al (2011)
2004 2010 Analysis
C) Global cloud-system resolving models
The NICAM Team
MJO-like systems and MCS-like Organization
in NICAM (7km)
Miyakawa et al. (2012)
Mesoscale momentum transport
........... m m
convection
u uu w
t z t
Mesoscale Momentum Transport : 13000-section Average
Miyakawa et al. (2012)
Courtesy: Marat Khairoutdinov
D) Superparameterized MCS-like systems and MJO-like Organization
Courtesy Marat Khairoutdinov
E) Multi-cloud parameterization for the MJO:
Representing Slantwise Dynamics
Khouider and Majda (2006)
Dynamically active free atmosphere:
2 vertical modes
Passive boundary layer
• Deep convection
(P)
• Upper-tropospheric stratiform anvils & evaporatively driven
mesoscale downdrafts
(Hs)
• Lower tropospheric cumulus congestus & upper-tropospheric
radiative cooling
(Hc)
Khouider & Majda (2006)
Categories of Diabatic Heating
MJO-like Systems in AquaPlanet Climate Model
with Multi-cloud Parameterization
Ajayamohan, Khouider, Majda (2013)
WCRP/WWRP Year of Tropical
Convection (YOTC))
May ‘08 – Apr ’10
Focus Areas
MJO & CCEWs
Easterly Waves & TCs
Trop-ExtraTrop Interaction
Diurnal Cycle
Monsoons
yotc.ucar.edu
TARGETED APPROACH TO SEAMLESS PREDICTION
MJOs during
YOTC
(May ‘08 – Apr ‘10)
La Nina
conditions
El Nino
conditions
2
0
0
8
2
0
0
9
2
0
1
0
Moncrieff et al. (2012)
MJO Diabatic Heating Estimates: Reanalysis and TRMM
1. Climatology– multi-year simulations coupled or
atmosphere only
2. Short-range hindcasts – daily 48hr lead during
~20 days of the MJO
3. Medium-range hindcasts – daily 20-day lead
time
Vertical Structure and Diabatic Processes of
the MJO: Global Model Evaluation Project MJO Task Force/YOTC/GASS
Time step / 2 –Day Physics Errors
Daily / Weekly Forecast Errors
Long-Term Climate Simulation Errors
yotc.ucar.edu/mjo/vertical-structure-and-diabatic-heating-mjo
Conclusions: Organized Convection
• Organized convection is ubiquitous around the world, but missing
from climate models & incomplete in global weather models
• Single-column model used in cumulus parameterization fails to
represent organized dynamics
• Dynamical system approach: Vertical profile of diabatic/convective
heating is key to slantwise structure of diabatic heating and
organized convective momentum transport
• 10 km mesh for a global cliamte model is about the maximum for
the simulation of MCS having reasonable vertical structure and
propagation characteristics
• Multi-cloud parameterization approximating the dynamical system
approach in the form of slantwise heating successfully simulates
MJO-like features by representing MCS- and supercluster-like
features
•
Conclusions: YOTC
• YOTC, a targeted approach to seamless prediction, is focused
on organized tropical convection and its scale interactions
• Virtual global field-campaign framework complements actual
field campaigns and global-scale systems such as the MJO
• GEWEX Atmospheric System Study (GASS) utilizes the YOTC-
ECMWF database in the MJO Vertical Structure and Diabatic
Heating Evaluation project
• YOTC will formally finish at end of 2014, but research will
continue in other guizes, e.g.,
- WWRP Subseasonal- to-Seasonal (S2S) prediction project
- YOTC MJO Task Force has been moved to WGNE
http://yotc.ucar.edu
Thanks for your attention