1. Cascade
Scale interactions and organized convection in the tropical atmosphere
Project Manager: Steve Woolnough

2. Outline Motivation Cascade Project
Examples of scale interactions in organized tropical convection
Scientific and Technical Challenges
Cascade Project
The Science of Cascade
Project Structure

3. Organization of tropical convection
Tropical convection is organized across a wide range of scales associated with
Individual cloud systems
Squall lines and mesoscale convective complexes
African Easterly Waves, Tropical Cyclones, Equatorial Waves
Madden-Julian Oscillation, Monsoon circulations

4. Interactions between space and time scales of tropical convection
Diurnal Cycle
Seasonal Cycle
Monsoons
Modulates
activity
Upscale
organisation?
MJO
MJO Suppressed
Phase?
Mesoscale
systems
10-100’s km
Hours
100’s km
Days
1000’s km
Weeks
Extended
Predictability
(THORPEX)
El Nino &
Climate Change
(WCRP)
Monsoon
Onset?
Trigger
Synoptic
waves

5. Mean Climate over the Maritime Continent
Precipitation over the Maritime Continent plays a dominant role in driving the circulation over the Indo-Pacific Warm Pool
Modelled precipitation shows dry bias around the islands of the Maritime Continent
Large wet biases in Western Indian Ocean and West Pacific
Wet biases over the islands of the Maritime Continent
CMAP
HadGAM1
Difference
From Jane Strachan (Walker Institute)

6. Diurnal Cycle in the Maritime Continent
1100LT
1700LT
2300LT
0500LT
Observations from TRMM
Strong diurnal cycle in precipitation
Little or no precipitation over land during morning
Precipitation develops over land in late afternoon and into the late evening
Precipitation moves out over ocean during early hours of the morning
Convection in the Maritime Continent is strongly influenced by diurnal cycle and land-sea breezes
From Jane Strachan (Walker Institute)

7. Diurnal Cycle of Precipitation in HadGAM1
Maximum precipitation over land during morning
Precipitation dies out over land in late afternoon
Little or no precipitation over seas around Maritime Continent
Do weaknesses in the representation of key physical phenomena in the model impact the mean climate of the region?
1230LT
1830LT
0030LT
0630LT
From Jane Strachan (Walker Institute)

8. Organization of convection by equatorial waves
Observations (e.g. Wheeler and Kiladis 1999, Yang et al ) show convection is organized by large-scale equatorial waves
from Wheeler and Kiladis (J. Atmos. Sci, 1999)

9. Equatorial Waves in HadGAM
Observed
HadGAM1
By what processes are the convection and dynamics coupled?
How does the model represent these processes?

10. Lin et al. (J. Clim, 2006) (CGCMs)
MJO in Climate Models
Lin et al. (J. Clim, 2006) (CGCMs)
MJO variance approaches observed value in only 2 of 14 models
Ratio of eastward to westward variance is too small, consistent with lack of coherent eastward propagation
Variance in 13 of 14 models not associated with pronounced spectral peak.

11. Multiscale Organization in the MJO
Eastward propagating envelope of convection
Short lived, westward propagating systems within envelope
With individual mesoscale cloud systems embedded within them
from Chen et al. (J. Atmos. Sci, 1996)
from Rickenbach & Rutledge (J. Atmos. Sci, 1998)

12. Multiscale Organization in the MJO
What role do the different scales of organization play in the transports of heat, moisture and momentum by the convection?
How are these processes represented within conventional parametrization schemes?

13. Organized Convection in AEWs
Complex organization on synoptic and meso-scales
Strong temporal development linked to diurnal cycle
Triggering of convection by orography and convergence along cold pools
15Z
18Z

14. Scientific & Technical Challenges
How does convection organise itself across a range of time and space scales?
How are energy and momentum transferred?
Why do preferred structures emerge?
How can these be represented in global models?
But we cannot answer these questions using observations - so we must use models as pseudo ‘field experiments’.
This requires large domains and very high resolution so that the energy spectrum is not compromised.
Needs very significant computational resource, only just becoming available.

15. Cascade Project
Natural Environmental Research Council (NERC) Funded Consortium Project
Walker Institute, University of Reading
National Centre for Atmospheric Science
University of Leeds
University of East Anglia
Met Office
3½ year project which started on 1st October 2007

16. Proposal
Develop modelling framework for large domain (100 longitude by 30 latitude), high resolution (1-2 km) simulations.
Perform numerical case studies of organised convection over West Africa and the Indo-Pacific Warm Pool.
Evaluate these simulations using advanced satellite and in situ observations of cloud structures.
Analyse the simulations in terms of scale-dependent energy and momentum budgets.
Use idealised case studies to explore the links between convection and equatorial wave modes.
Bring this new understanding into the development of new representations of tropical convection for global weather and climate models.

17. Project Structure
WP1: Development of Modelling Tools and Infrastructure
WP2: Scale interactions in African Weather Systems
WP3: Organized Convection over the Indian Ocean and West Pacific Warm Pool
WP4: Model Evaluation against Observations
WP5: Synthesis of Results

18. Development of Modelling Tools and Infrastructure
Model Development (Met Office)
Met Office Unified Model
Build on existing work in the Met Office to develop 1km resolution LAM for use as forecasting tool and CRM research tool
Includes options for
3D turbulence scheme
5 phase microphysics scheme
Test small domain case studies
Modelling Infrastructure (Lois Steenman Clark, NCAS – CMS)
Optimatization
Scalability
Performance of I/O
Management of TB of data

19. Evidence of modelling capability:
Simulations of the diurnal cycle and land-sea breezes
over the Tiwi Islands in the Timor Sea
Evidence of modelling capability:
Realistic physical-dynamical coupling in 1 km version of the Unified Model

20. Evidence of model skill:
Simulations of the diurnal cycle and land-sea breezes
over the Tiwi Islands in the Timor Sea
Evidence of model skill:
Good agreement with radar observations

21. Scale Interactions in African Weather Systems
Diurnal Cycle of Convection (Tony Slingo, Walker Institute)
What mechanisms control the organization of convection by the diurnal cycle over varying land surface conditions and forcing regimes typical of North Africa?
MCSs and AEWs (Doug Parker, U of Leeds)
What is the role of MCSs, particular those forced by the diurnal cycle, in the dynamics of the regional and synoptic waves and vortices over Africa?

22. Organized Convection in the Indo-Pacific Warm Pool
Scale Interactions in the MJO (Steve Woolnough, Walker Institute)
How do the vertical heating profiles and momentum transports associated with convection influence the evolution of the MJO?
The diurnal cycle and the climate of the Maritime Continent (Adrian Matthews, UEA)
What role do the diurnal cycle and land-sea breezes play in determining the mean climate of the Maritime Continent?

23. Organized Convection in the Warm Pool
Idealized Simulations of organized convection and equatorial waves (Brian Hoskins, Mike Blackburn, Walker Institute)
How is convection organized by equatorial waves and how does it modify the structures predicted by the dry theory?

24. Case Study Methodology
Use the high resolution simulations as pseudo-observations to investigate
the energy and momentum budgets associated with organized convection
the interactions between the various scales of organization
Compare with low resolution simulations to identify weaknesses and missing processes in convection parametrization schemes

25. Model Evaluation against Advanced Observations
(Robin Hogan, Walker Institute)
Use geostationary Satellites to evaluate temporal development of organized cloud clusters
Use CloudSat, CALIPSO, and surface ARM sites to evaluate vertical structure of clouds

26. Synthesis of Results (Met Office)
Review the results from a parametrization perspective including
role of organized convection
Environmental influences on organization
Temporal evolution of convection
Test new parametrization ideas in low resolution simulations of case studies

27. Project Timeline Model Development, Porting and Optimization
Oct
’07
Apr
’08
’09
’10
‘11
Model Development, Porting and Optimization
African Case Studies
Case Identification and Model Configuration
Diurnal Cycle
AEW
Warm Pool Case Studies
MJO
Maritime Continent
Equatorial Waves
Model Evaluation against Observations
Synthesis of Results