Christiane Jablonowski and Diana ThatcherUniversity of Michigan, Ann Arbor, USA

Physics-Dynamics Coupling Workshop (PDC14), Ensenada, Mexico, 12/3/2014

Physics-Dynamics Test Strategies:Bridging the Gap with Simplified Moist Test

Cases

The Talk at its Crossroads

EffectiveResolution:What should the scales be that thedynamical corepasses to thephysics(grid-point value,area-averaged,sub-sampled)? What are the believable scalesin the dynamics?

Test Strategies:Can we under-stand some aspects of the complexphysics-dynamicscoupling with simplified moist test cases?

Partly covered byPeter Lauritzen’s talk Topic of this talk

Effective Resolution Papers with Foci on Advection

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• Test strategies: It is important to be able to identify good coupling schemes from inferior ones early on in the development cycle. Once the theoretical analysis of the scheme is complete, how can further evidence be collected to ensure the chosen scheme performs as anticipated? The full NWP trial stage usually only offers limited scope for (costly) change. The difficulty is to design tests with sufficient signal and validity, without being too complex such that they are useful in the early development/evaluation phase.

Physics-Dynamics Coupling:Session Announcements

Test Cases: Hierarchy with Increasing Complexity

Some Desirable Design CriteriaTest cases should• be designed for hydrostatic and non-hydrostatic dynamical

cores on the sphere, ideally: for both shallow and deep atmosphere models

• be easy to apply: analytic initial data suitable for all gridsformulated for different vertical coordinates

• deal with moisture in a simple way• reveal information about the physics-dynamics coupling• be as easy as possible, but as complex as necessary• be cheap and easy to evaluate• be relevant to atmospheric phenomena• have a converged reference solution• find broad acceptance in the modeling community

Overview of the Approaches• Short-term deterministic assessments (15 days)

– Moist baroclinic waves with large-scale condensation– Moist baroclinic waves coupled to the `simple-physics’

package by Reed and Jablonowski (James, 2012)• Long-term ‘climate’ assessments (multiple years)

– Moist version of the Held-Suarez test with elements of the `simple-physics’ package

This talk’s goal:• Convince you that idealized physics processes lead to

reasonable atmospheric circulations.Long-term goal (partly covered in this talk):• Evaluate whether idealized physics processes mimic the

behavior of complex physics to aid our understanding.

Questions to Ask• What is our motivation to pursue idealized approaches?• Is it reasonable: How does a moist Held-Suarez (HS) aqua-

planet simulation compare to a full-physics CAM5 aqua-planet simulation?

• Intercomparison: How do the different CAM5 dynamical cores compare in moist HS and complex aqua-planet experiments?

• Unit testing: How does the moist HS configuration compare to aqua-planet simulations that omit some processes (like the deep convection parameterization)?

• Can we replicate some aspects of the complex physics-dynamics interactions with the moist HS setup?

• What do we learn about the physics-dynamics coupling?

Motivation: Results from the Aqua-Planet Experiment (APE)

• Aqua-planet model intercomparison revealed a huge spread in the GCM circulations and precipitation characteristics

• Impossible to tell whether the APE differences are due to physics parameterizations or the dynamical cores or both?

• Our test approaches level the playing field (identical physics).

Zonal-meantime-mean total precipitation rates (hemispherically averaged) in 16 GCMsin aqua-planet mode, see Blackburn at al. (2013)

Dynamics Physics

Process

Variable

Interaction

Adding Simple Large-Scale Condensation to the Dynamical Core

PBL mixing

Adding Simple Large-Scale Condensation• Add a specific humidity field q and transport it as a tracer• Compute condensation C tendencies to force q and the

temperature T whenever the relative humidity (RH) at a grid point exceeds a threshold (e.g. RH > 100%):

• The large-scale precipitation Pls removes the water instantaneously without a cloud stage

Reed and Jablonowski (James, 2012)

Baroclinic Wave: Moisture and Large-Scale Condensation

Dynamical Core Model Intercomparison Project (DCMIP) 42 Large-scale condensation in a moist version of theJablonowski-Williamson (2006) baroclinic wave leads to an intensification of the baroclinic wave here at day 9

CAM-FV 1°x1° L30, dx = 110 km

• It rains in the right spots (updraft areas associated with frontal zones)• Provides a first glimpse at the non-linear physics-dynamics

interactions in the presence of moisture

Dynamics Physics

Process

Variable

Interaction

Adding a Simple-Physics Package to the Dynamical Core

Reed and Jablonowski (James, 2012)

PBL mixing

Simple-Physics Package: Basic Ideas• Replace the full-physics with a simple-physics package• The simple-physics tendencies are

• The fluxes are either– the bulk aerodynamic surface fluxes (latent and sensible

heat, friction) or – mimic the turbulence in the boundary layer via a first-order

closure (K-theory with surface wind-speed dependent eddy diffusivities)

• C is large-scale condensation (no re-evaporation)

Reed and Jablonowski (James, 2012)

Moist Interactions: Baroclinic Wave

Dry

Large-scale condensation

Simple-Physics, no surface friction

Complex CAM5 physicsno surface friction

Simple-Physics, with surface friction

Complex CAM5 physicswith surface friction

Idealized moist baroclinic wave tests expose the behavior of simulations with complex physical parameterizations (here CAM5)

Tests based on Jablonowski and Williamson (2006), Simple-physics: Reed and Jablonowski (2012)

Surface pressure, day 9, CAM-FV 1°L30

hPa

without radiation

Dynamics Physics

Variable

Interaction

Moist Version of the Held-Suarez Test on an Aqua-Planet (prescribed SST)

Thatcher and Jablonowski (in prep.)Reed and Jablonowski (James, 2012)

H

Held-Suarez (modified):• Radiation: Newtonian

Temperature relaxation• Rayleigh friction (PBL

momentum mixing and surface friction)

Simple-Physics:• Surface fluxes of latent

sensible heat• PBL mixing of moisture

and temperature • Large-scale

condensation

Color coding:

PBL mixing

Moist Held-Suarez and Complex Aqua-Planet

Thatcher and Jablonowski, in preparation

Moist Held-Suarez with simple-physics Aqua-Planet with complex CAM5 physics

CAM-SE 1° L30: Reasonable - Moist Held-Suarez mimics Aqua-Planet

Temperature

Zonal wind

Moist Held-Suarez and Complex Aqua-Planet

Moist Held-Suarez with simple-physics Aqua-Planet with complex CAM5 physics

CAM-SE 1° L30: Reasonable - Moist Held-Suarez mimics Aqua-Planet

Thatcher and Jablonowski, in preparation

Less efficient upward moisturetransport, but distributionsare similar

Specific humidity

Relative Humidity

Moist Held-Suarez and Complex Aqua-PlanetCAM-SE 1° L30: Reasonable – Eddy transports are comparable

Aqua-Planet with complex CAM5 physicsMoist Held-Suarez with simple-physics

Eddy heat flux

Eddy kinetic energy

Moist Held-Suarez and Complex Aqua-PlanetCAM-SE 1° L30: Reasonable – Physics forcing magnitudes comparable

Aqua-Planet with complex CAM5 physicsMoist Held-Suarez with simple-physics

Deep convec-tion peaks higher up

Focus on the tropics

Large-scalecondensation

Temperature tendency

Moisture tendency

Moist Held-Suarez and Complex Aqua-Planet

Moist Held-Suarez with simple-physics

Aqua-Planet with complex CAM5 physicsCAM-SE 1° L30: Similar tropical wavesare apparent in the totalprecipitation rate (averaged between 5S-5N)in moist Held-Suarez (top) and Aqua-Planet (bottom)runs (here eastward traveling Kelvin waves)

Thatcher and Jablonowski, in preparation

Precipitation is less organized in the moist HS experiment due to simplicityof precipitation

mm/day

Same Kelvin wave phase speeds

Moist HS, Complex Aqua-Planet & Unit Testing• CAM-SE experiments with and without simple Betts-Miller

(BM) and complex Zhang-McFarlane (ZM) deep convection• Moist HS replicates complex Aqua-Planet (AP) behavior

With deep No deep Total precipitation rate

AP AP

MoistHS

MoistHS

BMdeep

ZMdeep AP

HS

Intercomparisons & Unit Testing• Easier unit testing: How does CLUBB (new CAM PBL mixing,

shallow convection, macrophysics) interact with the SE and SLD dycores and diffusion in CAM5 aqua-planet experiments?

SE SE SLD

Double versus single ITCZ

DoubleITCZ

Morediffusion

Intercomparisons: CAM5 dynamical coresThe Community Atmosphere Model (CAM) provides four different dynamical cores (based on the primitive equations):1. Semi-Lagrangian (SLD): two-time-level, semi-implicit semi-

Lagrangian spectral transform model, Gaussian grid2. Eulerian (EUL): three-time-level, semi-implicit Eulerian

spectral transform dycore, Gaussian grid3. Finite-Volume (FV): default dynamical core in CAM 5 & CAM

5.1, grid-point-based finite-volume discretization, explicit time-stepping scheme, latitude-longitude grid

4. Spectral Element (SE): new default dynamical core (CAM 5.3), based on continuous Galerkin spectral finite element method, designed for fully unstructured quadrilateral meshes (cubed-sphere grid), locally energy- and mass-conserving, explicit time-stepping scheme

Intercomparisons: CAM5 dynamical cores• The kinetic energy (KE) spectra of the moist HS

experiments replicate the KE spectra of the complex CAM5 aqua-planet runs (here with 110-150 km grid spacing)

Intercomparisons: CAM5 dynamical cores• Moist HS experiments can partly replicate the tropical

precipitation rate characteristics of complex CAM5 aqua-planet runs

Increasedprecip.

Increasedconvergence

Moist HS CAM5 Aqua-PlanetCAM5 Aqua-Planet,no deep convection

Intercomparisons: CAM5 dynamical cores• Meridional

Eddy moisturetransport: v’q’

• Indication that the spectraldynamical coresEUL and SLD show systematic tropicaldifferences in comparison togrid point models FV and SE in both moistHS and aqua-planet

Moist HS Aqua-Planet

SE

EUL

FV

SLD

Conclusions• The interactions between the dynamical core and moisture

processes can already be simulated with very simple model configurations, like large-scale condensation, simple-physics, or the moist HS test

• Some aspects of the complex GCM behaviors can be replicated with the simplified physics setups

• Tests give access to an easier understanding of the physics-dynamics coupling

• Using identical physics with various dynamical cores levels the playing field

• Approach allows unit testing of selected parameterizations or tests of the physics-dynamics coupling technique

• Test cases hold promise to be useful for community use

• Reed, K. A., and C. Jablonowski (2012), Idealized tropical cyclone simulations of intermediate complexity: a test case for AGCMs, J. Adv. Model. Earth Syst., Vol. 4, M04001, doi:10.1029/2011MS000099

• Jablonowski, C., and D. L. Williamson (2006), A Baroclinic Instability Test Case for Atmospheric Model Dynamical Cores, Quart. J. Roy. Met. Soc., Vol. 132, 2943-2975

• DCMIP shared workspace and DCMIP test case document:https://www.earthsystemcog.org/projects/dcmip-2012/test_cases

• Thatcher, D. R. and C. Jablonowski, A moist variant of the Held-Suarez test for atmospheric model dynamical cores: Aquaplanet comparison and sensitivity analysis, manuscript in preparation

References