CASCADE DOWNSTREAM WORKSHOP ON CONVECTION MODELLING A report from the meeting held at Reading University, Reading, UK, 7–8 October 2014
Editor: Chris Holloway Breakout Group Leaders and Other Key Contributers: Stephanie Bush, Peter Clark, Paul Field, Cathy Hohenegger, Nick Klingaman, Humphrey Lean, Adrian Lock, John Marsham, Gill Martin, Adrian Matthews, Doug Parker, Karsten Peters, Jon Petch, Bob Plant, Malcolm Roberts, Thorwald Stein, Alison Stirling, Pier Luigi Vidale, Simon Vosper, Stuart Webster, and Steve Woolnough SUMMARY The Cascade Downstream Workshop on Convection Modelling took place from 7-­‐8 October 2014 at the University of Reading. The meeting focussed on recent and planned research involving the "Cascade" project framework (using large-­‐domain simulations at convection-­‐permitting resolutions to learn more about convection across scales and improve model parameterizations). This is related to the “virtual laboratory” recommendation from the Dartington convection meeting in January 2013 (Holloway et al. 2014). There was a particular focus on planning future directions and collaborations. The meeting began with some overview of past and present Cascade work, particularly with a goal of making connections across different studies and research groups. There were also talks on current and planned work that is related to Cascade but not part of it, such as work on the Indian Monsoon, tropical cyclone simulations, work on extratropical convection in both weather and climate contexts, global explicit convection runs, aggregation studies, international research programmes, and model development plans. These were followed by breakout group discussions and large-­‐
group discussions of future work, collaborations, and challenges. The meeting agenda, with PDFs of presentations, can be found here: http://www.jwcrp.org.uk/events/cascade.asp SPECIFIC RECOMMENDATIONS Each breakout group was given a topic and asked to address questions 1–4 listed below regarding this topic. Groups 1 and 2: Using this framework to improve explicit convection and parameterized convection. Group 3: Developing global explicit convection models and climate change experiments. 1) What questions do we have that this framework can (or cannot) answer? a Emerging strengths/weaknesses b What is the added value, and where are more idealised approaches better? 2) How can we improve the design of this framework? a How should we design “climate change” experiments? b Is the design framework better for regional climate “downscaling”, process modelling, more idealised modelling, other purposes? c How can we design better experiments? d How should we design/manage the MetUM (one path, options, simplified versions)? 3)
4)
How can we get the most out of these experiments in terms of analysis and collaboration? a What problems/challenges do we face (HPC, data analysis, data storage and sharing) and how do we address these? b How do we best analyse these experiments to support parameterization diagnosis and development? c How best can we collaborate and maximise outcomes from these experiments and data? New ideas for projects. a International collaborations. b How to get funding? A number of potential science questions were discussed. These include many of the questions that were raised at the Dartington meeting (Holloway et al. 2014), including how to represent convection at relevant model scales including those in the “grey zone”, the degree to which the real world (and our models) are in quasi-­‐equilibrium at various scales, the amount and sources of convective “memory” in the system and how to represent this in models, how to represent subgrid mixing for different resolutions and regimes, the degree to which our models “converge” at high enough resolution (and how to define this), and how convection interacts with other parts of the Earth System such as the land, the ocean, and dust/aerosols. Other points include the need to study the effects of timestep variability of convection on larger scales and the need to investigate the sensitivities of current frameworks for studying weather and climate with explicit convection (such as limited-­‐area hindcasts, global hindcasts, and limited-­‐area future climate timeslice experiments) to boundary and initial conditions and related setup choices. There were also discussions about how much to emphasise tool development versus science questions, idealised versus realistic simulations, and free-­‐running climate simulations versus initialised simulations. Discussions also highlighted several issues regarding convective parameterization development. There were questions about fitting parameterization development in with the Met Office development cycle, and suggestions that this cycle be made available to the community. The design for the next dynamical core is also relevant to future plans, since a long-­‐term plan to modify convective parameterizations and other physics schemes may not be useful if it has been formulated for an outdated dynamical core. Parameterization development might include bottom-­‐up approaches (starting from explicit convection models at very high resolutions and then modifying their subgrid parameterizations to work at coarser resolutions) or top-­‐down approaches (starting from current parameterizations at coarser resolutions and testing their assumptions using higher-­‐resolution models and observations and modifying them so that they behave more like explicit convection models) or some combination of the two. Several main suggestions for future projects (and related issues) emerged from the breakout groups and other workshop discussions. These include the development of a global MetUM setup with approximately 4.5 km grid spacing, the application of DYMECS-­‐type analyses of LES-­‐scale simulations and observations at several well-­‐observed sites around the world, a suite of idealised models at a range of different resolutions and complexities to improve convective parameterizations, improved planning and development of analysis methods, and an annual meeting of the UK convection community. These suggestions are described below, along with names of people and proposals that are either involved or might be interested in being involved. The names are not meant to be exclusive, and new names (and new suggestions that came out of the meeting) are encouraged as part of the drafting of this report. 1)
2)
3)
Global 4.5 km model − 10-­‐year realistic runs (start with shorter runs, perhaps nudged to reanalysis) − treat above as a satellite mission, thrown out to the community to analyse (with some cautions) − aquaplanet runs − initialised runs − analysis issues (need to be able to extract smaller or coarser domains/scales) − conservation issues (energy, water) − PRIMAVERA Proposal (N2048 development) − People: Stu Webster, Pier Luigi Vidale, Malcolm Roberts, Doug Parker Convective-­‐scale simulations at well observed sites − Potential Sites: SGP ARM site (Oklahoma), Chilbolton, Singapore, Darwin, Kwajalein (Marshall Islands), CINDY-­‐DYNAMO field campaign (Indian Ocean) − Cloud-­‐scale dynamics, physics − UK supersite (any actions since Dartington meeting?) − CASIM proposal − People: Paul Field, Peter Clark, Thorwald Stein, Kirsty Hanley, Karsten Peters, Chris Holloway, Humphrey Lean, John Marsham Idealised simulations − 100 m – 50 km limited area simulations to develop convection parameterizations − Look at energy/momentum spectra, how do they look when small scales are un(der)resolved? − Look at gravity waves. − People: Steve Woolnough, Alison Stirling, John Marsham, Doug Parker 4)
Analysis methods − Coordinating/Steering Group − Plan analysis framework before running simulation? − Data sharing (do we need more than JASMIN?) − Data advertising − Need to extract regions, relevant space/time scales (e.g. coarse-­‐grained fields) − Possible idea for the NASA Challenge for analysis code − People: Cyril Morcrette, Karsten Peters 5)
Need for Annual UK Convection Meeting − Potential for MOAP money − People: Steve Woolnough, Doug Parker A related topic of discussion was funding issues: e.g., who would fund a global 4.5 km model, since it is not currently in the Met Office’s plans? Where would resources come from to support DYMECS-­‐type simulations at well observed sites in other parts of the world? How do we get resources to do extensive analysis, rather than just creating large model output data sets? One response to this was that creating technologically advanced runs will provide inspiration and support for later applications for funding. CONCLUSIONS The Cascade Downstream Workshop on Convection Modelling brought together a diverse group of scientists from academic centres and the Met Office studying atmospheric convection and working to improve the representation of convection in numerical models. There was a focus on using large-­‐domain explicit convection simulations to bridge the gap between small-­‐scale convective processes and global weather and climate models. There is a large amount of activity going on in the UK and internationally using this framework for convection in many different regions and for simulations at both NWP and climate time scales. Several specific recommendations emerged from discussions, including development of a 4.5 km global explicit convection version of the Met Office Unified Model, convective-­‐scale simulations at several well-­‐observed sites around the world, idealised simulations with a range of complexity, development of new analysis methods for high-­‐resolution model output, and an annual UK convection meeting. While there was disagreement about the relative importance of these recommendations and specific details of their implementation, there is support for each one from at least a significant segment of the UK convection community. It is hoped that this report can serve as a platform for collaboration among different groups and institutions on high-­‐resolution modelling of convection and as a basis for beginning actions on the recommendations mentioned above. Acknowledgments This workshop was funded through NERC Fellowship NE/I021012/1. Logistics support was provided by Julia De Faveri, and webpage support was provided by Jemma Gornall. Lastly, thanks for the participation of all attendees, who are listed at the end of this report. References Holloway, C. E., Petch, J. C., Beare, R. J., Bechtold, P., Craig, G. C., Derbyshire, S. H., Donner, L. J., Field, P. R., Gray, S. L., Marsham, J. H., Parker, D. J., Plant, R. S., Roberts, N. M., Schultz, D. M., Stirling, A. J. and Woolnough, S. J. (2014): Understanding and representing atmospheric convection across scales: recommendations from the meeting held at Dartington Hall, Devon, UK, 28–30 January 2013. Atmosph. Sci. Lett., 15: 348–353. doi: 10.1002/asl2.508 For reference, detailed summaries of discussions from the three breakout groups are provided in the Appendix below. There is also a full list of workshop attendees at the end. APPENDIX: DETAILED SUMMARY OF THE BREAK-­‐OUT SESSIONS BREAKOUT GROUP 1: USING THIS FRAMEWORK TO IMPROVE EXPLICIT CONVECTION AND
PARAMETERIZED CONVECTION IN MODELS -­‐
What questions do we want to answer? o
o
How should we treat convection at the horizontal resolutions we are likely to be using in the next 5-­‐10 years? 
O(1.5 km) resolutions with explicit convection 
O(20 km) resolutions with parameterized convection. Should we be using column-­‐
based physics at these resolutions? 
Does anyone still care about O(200 km) resolution models? We decided that they would be used for Earth System modelling for the next 5-­‐10 years, so we probably need to improve parameterizations for these scales as well. How close to equilibrium are our current schemes? Over what spatial and temporal scales does equilibrium apply? We need an overview of the effectiveness of equilibrium assumptions on many scales. Equilibrium probably depends upon 
Relationships between convection and dynamics 
Strength and type of forcing o
How does energy cycle through cloud to the large-­‐environment? This depends on relationships between the convective-­‐scale and large-­‐scale energy transfers. o
How should convective triggering differ between the land and ocean? What even is the “trigger” for an equilibrium scheme? There were some comments about the presence of local dis-­‐equilibrium even in the presence of large-­‐scale equilibrium. o
Given that we are moving toward a convection scheme with some representation of convective memory … 
Where in the real system does memory lie? 
What should our convective prognostics depend upon? Should they be advected? 
How should we partition memory between the boundary layer and the free troposphere? How should those two terms interact? -­‐
Design of future experiments and analysis o
o
What can we learn from the similarity between explicit-­‐ and parameterized-­‐convection simulations at the same resolution? What is different between parameterized and explicit convection at O(20 km) resolution? 
Cloud structure? 
Presence of gridpoint storms? 
Mean-­‐state biases? 
Response to perturbations (e.g., 2×CO2 or interactive land surface) Could we develop a new parameterization by starting from explicit convection and adding some mixing or smoothing, rather than trying to continually adapt and tweak the current scheme? 
What would happen if we switched off the parameterization at even coarser resolutions? 
o
o
o
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Two approaches to parameterization development: adapt the current scheme to behave more like explicit convection or adapt explicit convection to coarser resolutions by adding a simpler parameterization. How much can/do we trust “reference” high-­‐resolution simulations (e.g., LEMs, high-­‐
resolution explicit convection simulations) against which we are comparing our coarser-­‐
resolution explicit-­‐ and parameterized-­‐convection models? 
We validate them by comparing against observations and by looking for functional relationships between variables, as well as by using those reference configurations in operational settings (e.g., the 1.5 km UKV) 
We must be careful that our reference-­‐simulation results are not overly sensitive to particular parameter choices or under-­‐represented or over-­‐represented phenomena (e.g., cold pools). We should perform a set of idealised simulations at a broad range of resolutions, from O(100 m) to O(25 km) 
Analysis should focus on the spectrum of energy and momentum transports: how does the spectrum look when large parts of it are under-­‐resolved or un-­‐resolved? 
We should also focus on gravity waves, to understand how we should parameterize un-­‐resolved parts of the spectrum. We should not focus only on clouds. We should ensure, as far as possible, that our explicit-­‐ and parameterized-­‐convection simulations use similar representations of microphysics. We need to understand spatial and temporal variability of convection at the timestep level o
Does spatial and temporal intermittency matter? o
Is this intermittency undesirable, numerically or physically? o
How does this intermittency interact with the model dynamics? o
There are large differences in intermittency between parameterized-­‐ (very intermittent both temporally and spatially) and explicit-­‐ (very persistent temporally and spatially) convection simulations, but both focus large amounts of heating into a small number of gridpoints. o
We could conduct idealised or single-­‐column model experiments with noisy and smooth heating increments to investigate impacts of temporal intermittency. Recommendations o
Design experiments with a clear question in mind. Know what you want to get out of the experiment before you start. o
Involve collaborators at the design stage. o
Make sure relevant diagnostics needed to answer your question are included as far as possible, but keep in mind that you can re-­‐run relevant parts of the simulation with more diagnostics if necessary. o
Don’t run simulations just to make pretty pictures. Next-­‐generation models and parameterizations o
The next-­‐generation MetUM will have the ability to use variable resolution globally, making it possible to run global simulations with an embedded high-­‐resolution region. Would the physics behave similarly across these scales and between these regions? Evidence from similar simulations at NCAR suggests that it would not. o
We should develop a next-­‐generation convection scheme for the next-­‐generation dynamical core. 
With non-­‐column physics? 
Any new scheme should be developed using idealised model configurations. 
Now is a good time to develop a new scheme in conjunction with the new dynamics, rather than trying to adapt the existing parameterization to the new dynamics and then deciding to develop a new scheme anyway. BREAKOUT GROUP 2: USING THIS FRAMEWORK TO IMPROVE EXPLICIT CONVECTION AND
PARAMETERIZED CONVECTION IN MODELS (SAME AS BG1) •
Thoughts on experimental design o
o
o
Should validate lower resolution models with higher resolution models, which need to be high enough resolution to approximate truth (higher than 1.5 km), and validate higher resolution models with observations. 
Specific suggestion – DYMECS style study year round over Darwin or Kwajalein (Marshall Islands), may also want to run over several years to see interannual variability 
Could also do it over the Dynamo sites, or CPOL scan radar 
100 m German model plans •
Summer season – 3 months •
Would overlap with a network of observational sites •
Could use more focus on how they will use the data •
The vertical velocities, and their link to the large scale flow, are the main target in the big runs Design experiments with your question in mind 
What model output do you need? 
What tools will you need to analyse the data? 
Can you use tools to minimize the output you need? 
Can you add new stash to output exactly what you need (cloud fraction, for example) Flexibility in the MetUM setup would allow a wider range of specific experiment to test more specific questions 
Boundary conditions (equatorial channels, etc…) 
Idealized model (can specify surface fluxes, etc….) o
If examining the interaction of larger scale flow and the convection, need a large enough domain that you are not practically prescribing the vertical velocities. Equatorial channels discussed as an option for this. o
In order to make large experiments usable for other applications, a certain set of basic stash, at least any observable quantities, should be output as well as the stash needed for the question in mind. But always preferable to tailor an experiment for the question to be answered. Idealized models often require keeping less stash (i.e. only need zonal means for aquaplanet experiments, so can have as detailed a profile as you like) o
Ideas to build on Cascade – interactive ocean, KPP? •
Convection permitting development o
Sensitivities – Smagorinsky mixing, is it the same in the tropics and extratropics? o
Need model runs where you have good observations of the microphysics (same principle as above) – lidar, flights, etc…. o
Turbulence grey zone question o
When we run the MetUM, clearly the eddies resolved in the LES aren’t resolved in the MetUM. We use coarser vertical resolution than horizontal resolution, do we need higher vertical resolution? o
LES work – where do we converge? What resolution matters for what application? BREAKOUT GROUP 3: GLOBAL EXPLICIT CONVECTION MODELS AND CLIMATE CHANGE EXPERIMENTS Overall conclusion: •
Possible to do global convection-­‐permitting, ~4 km at equator with new Met Office machine o
Test with 1x upgrade, longer run with 5x o
Would need coordination – input from different communities o
Would need funding – possibly SPAG – to Met Office as well o
Would be a fantastic resource for a variety of communities all looking at one model – storm tracks, polar, monsons, Maritime Continent, tropical cyclones, ENSO, hydrological cycle o
Would be a link in the chain of hierarchy of global models, allowing global teleconnections, scale-­‐interactions o
Do this in conjunction/interacting with parameterization development – can learn about impacts of convective representation from global model Treat as satellite mission – choose period, simulation length, configuration, diagnostics and simply run, and then throw out to community to analyse (with some guidance on what is most of value/makes most sense, e.g. EURO4 can give crazy precip amounts). o
o
ECMWF "small earth" approach. Shrink the radius of Earth. 
Advantages: get the scale interactions. 
Technical difficulties? Other methods to get convection-­‐permitting “globally” 
Two-­‐way nesting to give very high resolution in specific area but also allow it to feed back up to larger scales 
Variable resolution 
o
•
Would be able to target certain areas thought to need high resolution or of particular interest to a project •
Disadvantages. Long set up time, HPC resource improvements might have made it redundant once it is sorted out, need to parameterizations to adapt Both would need development, testing etc -­‐ View 4 km global convection permitting model run as a new satellite project. 
See it as a national resource o
o
o
o
o

Do a long global run "early" with best estimates of relevant parameters, ancillaries etc. 
Make the data freely available to national and international community, let the analyses and projects flood in – straightforward with MASS-­‐JASMIN link 
These can then feed back into refinement of model setup for later runs 
Need a call for standard diagnostics 
Ability to rerun from restart points with extra user-­‐defined diagnostics 
Need to define new analysis techniques for multi-­‐scale interactions. Making a global run freely available to community may be a good way to generate interest and development of this. 
Put data at BADC on JASMIN, with the associated tools there for post processing 
Pier Luigi’s and Malcolm's UPSCALE project could be a model for this – currently ~20 groups analysing different aspects 
Compare high resolution global model multi-­‐scale "features" with those from pre-­‐existing limited-­‐area runs e.g. from Cascade, to see the effect of imposing lateral boundary conditions versus free running global configuration. Realistic parameters 
N4096 is 360 / 4096x2 = 0.044 deg longitude = 4.8 km at equator 
Spin up of dynamics is 24 hours, land surface / soil moisture is few days. 
Can run for a year fairly easily 
Pick a time period to coincide with e.g. YOTC, satellite availability. 
Cannot run for times too close to present day because of delays with getting ancillary files (land surface?) 
Can produce boundary files from this and drive regional models – same, higher and lower resolutions Complexity 
interactive dust, aerosols, other additions to “physical climate” model 
couple to KPP mixed layer ocean, full ocean later in time Science problems to be addressed 
Scale interactions, tropical convection and waves 
Dust modelling feedback onto large scales 
Global structures such as MJO and storm tracks. 
A year-­‐long run would provide enough data to do proper statistics 
Ambition for 30-­‐year integration, settle for 10? Building up to 4 km global 
Need some preliminary experiments running 4 km over different (large) regions over the globe to find problems 
Problem with pole. At "4 km", actual longitudinal resolution is ~100 m near pole. Explore reduced grid options. 
Could we apply the reduced grid to the output (to reduce data volume) rather than at the model stage (which would involve major development)? 
Aquaplanet experiments – are these useful to complement realistic runs, coming after to understand specific processes? National science meeting 
Bring all interested communities to feed into this run 
MJO, monsoon, maritime continent (Year of the Maritime Continent), dust/aerosol, polar meteorology, storm tracks, land-­‐atmosphere o
Future climate 
Using limited-­‐area convection permitting runs, maybe too early for global explicit convection 
Experimental design/methodology – are we happy with standard, using boundary forcing from a global timeslice? 
How to separate remote drivers from local forcing, radiative forcing •

o
Is it sensible to use present-­‐day boundary forcing and future composition? Value in short global simulations to look at fast responses – e.g. 4×CO2 – to compare to results from regional models Funding and organisation 
For both NERC and Met Office communities 
Need people 
Need support for data management, analysis methods, exchangeable scripts 
Need coordination, someone to step forward – •
pull messages together, •
coordinate groups, communicate with parameterization development, etc. •
bring in Process Evaluation Group (PEG) representatives •
convection already has a steering group, but maybe we need a wider group Attendees of Cascade Downstream workshop, 7-­8 October 2014 1.
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Surname
Bhowmick
Boing
Bush
Chamberlain
Clark
Eagle
Feist
Field
Halliwell
Hanley
Hart
Hawcroft
Hohenegger
Holloway
Kendon
Klingaman
Lean
Lister
Lock
Marsham
Martin
Matthews
Mohd Nor
Morcrette
Parker
Pearson
Peatman
Petch
Peters
Plant
Roberts
Roberts
Schiemann
Shipway
Stein
Stirling
Stratton
Vidale
Vosper
Webster
Willetts
Woodage
Woolnough
Yang
First name
Mansi
Steef
Stephanie
Jill
Peter
Chloe
Matt
Paul
Carol
Kirsty
Neil
Matt
Cathy
Chris
Lizzie
Nick
Humphrey
Grenville
Adrian
John
Gill
Adrian
Fadzil
Cyril
Doug
Kevin
Simon
Jon
Karsten
Bob
Malcolm
Nigel
Reinhard
Ben
Thorwald
Alison
Rachel
Pier Luigi
Simon
Stu
Peter
Margaret
Steve
Guiying
Affiliation
U. Leeds
U. Leeds
U. Reading
U. Reading
U. Reading
Met Office, Reading
U. Reading
Met Office, Exeter
Met Office, Reading
Met Office, Reading
U. Reading
U. Reading
MPI, Hamburg
U. Reading
Met Office, Exeter
U. Reading
Met Office, Reading
U. Reading
Met Office, Exeter
U. Leeds
Met Office, Exeter
U. East Anglia
U. Reading
Met Office, Exeter
U. Leeds
U. Reading
U. Reading
Met Office, Exeter
U. Monash
U. Reading
Met Office, Exeter
Met Office, Reading
U. Reading
Met Office, Exeter
U. Reading
Met Office, Exeter
Met Office, Exeter
U. Reading
Met Office, Exeter
Met Office, Exeter
U. Leeds
U. Reading
U. Reading
U. Reading