Cascade Scale interactions and organized convection in the tropical atmosphere Project Manager: Steve Woolnough Outline Motivation Cascade Project
Examples of scale interactions in organized tropical convection Scientific and Technical Challenges Cascade Project The Science of Cascade Project Structure 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 Interactions between space and time scales of tropical convection
Diurnal Cycle Seasonal Cycle Monsoons Modulates activity Upscale organisation? MJO MJO Suppressed Phase? Mesoscale systems 10-100s km Hours 100s km Days 1000s km Weeks Extended Predictability (THORPEX) El Nino & Climate Change (WCRP) Monsoon Onset? Trigger Synoptic waves 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) Diurnal Cycle in the Maritime Continent
1100LT 1700LT 2300LT 0500LT Observations from TRMM Strong diurnal cycle inprecipitation Little or no precipitation over landduring morning Precipitation develops over landin late afternoon and into the lateevening Precipitation moves out overocean during early hours of themorning Convection in the MaritimeContinent is stronglyinfluenced by diurnal cycleand land-sea breezes From Jane Strachan (Walker Institute) Diurnal Cycle of Precipitation in HadGAM1
Maximum precipitation overland during morning Precipitation dies out overland in late afternoon Little or no precipitation overseas around MaritimeContinent Do weaknesses in therepresentation of key physicalphenomena in the modelimpact the mean climate of theregion? 1230LT 1830LT 0030LT 0630LT From Jane Strachan (Walker Institute) 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) Equatorial Waves in HadGAM
Observed HadGAM1 By what processes are the convection and dynamics coupled? How does the model represent these processes? 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. 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) 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? 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 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. 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 3 year project which started on 1st October 2007 Proposal Develop modelling framework for large domain (100 longitude by 30latitude), 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. 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 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 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 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 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? 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? 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? 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 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 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 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