Adaptive Mesh Refinement AMR Techniques for CAM3

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Adaptive Mesh Refinement (AMR) Techniques for CAM3

• Christiane Jablonowski
• National Center for Atmospheric Research
  (NCAR),Boulder, Colorado, USA

NCAR, June/28/2005
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Focus

• Why are we interested in multi-scale
  interactions?
• New mathematical and computational tool
• Adaptive Mesh Refinement (AMR) technique
• Block data structure on the sphere
• AMR examples with the Finite Volume (FV)
  dynamical core Static and dynamic adaptations
• 2D shallow water runs
• 3D dynamical core runs
• Summary and future opportunities

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High resolution Multi-scale interactions
10 km resolution
W. Ohfuchi, The Earth Simulator Center, Japan
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Adaptive Grids for Weather and Climate Models

• Available today (Jablonowski et al., sub. to
  MWR) Finite-volume dynamical core for NCARs
  Community Atmosphere Model (CAM) that can
  statically and dynamically adapt its horizontal
  resolution with respect to
• Regions of interest (static adaptations nested
  grids)
• Features of interest (dynamic adaptations for
  e.g. cyclones)
• In preparationAMR CAM3 with adaptive physics

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Adaptive Mesh Refinement in Spherical Geometry
Block data structure
Self-similar blocks with 3 ghost cells in x y
direction
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Weather - Climate Interface

• Target high resolution areas within the global
  domain
• Selected geographical regions (e.g. North
  America, Europe)
• Mountain ranges, land-sea boundaries
• Pacific warm pool, tropical convection
• Storm-tracks in midlatitudes, interaction with
  the tropics
• Tropical cyclones
• AMR
• Built-in, consistent regional models in the
  global domain for weather and climate research
• 2-way interaction

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AMR examples with the FV dynamical core
Finite Volume Dynamics Future dynamical core
for CAM / CCSM

• 2D shallow water tests
• Static refinements in regions of interest (Test
  case 2)
• Dynamic refinements Flow over a mountain (Test
  case 5)
• 3D dynamical core tests
• Static refinements along the storm track in
  midlatitudes

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2D Static adaptations Region of interest
Test case 2, ? 45

• Smooth flow in regimes with strong gradients

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2D Dynamic adaptations Vorticity criterion
Test case 5
15-day run
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Adaptation criteria Vorticity
Test case 5
Vorticity criterion detects regions with strong
curvature
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Adaptation criteria Gradients
Test case 5
Gradient criterion detects disconnected regions
of the wave train
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Baroclinic waves in the 3D regime
Coarse resolution does not resolve the wave
train
Idealized baroclinic wave test case (Jablonowski
and Williamson, submitted to MWR)
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Static adaptations in 3D

• 1 Refinement along the storm track improves the
  simulation

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Static adaptations in 3D

• 2 Refinements along the storm track capture the
  wave accurately

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Static adaptations in 3D

• 3 Refinements along the storm track

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Summary and future opportunities

• Static and dynamic refinements on the sphere
  work
• AMR is a current research topic for the
  atmospheric sciences
• Future outlook
• Static and dynamic adaptations are a viable
  option for short-term weather predictions
• track storms as they appear
• focus on forecast region of interest replace
  nested grids
• Static adaptations are feasible for long-term
  climate studies
• refine mountainous terrain, regional climate
  models
• Future steps Add physics package to the FV
  dynamical core

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Physics-Dynamics Coupling in the AMR dycoreOpen
questions

• Physics are tuned towards a specific resolution
• Unclear whether the physics parameterizations
  work well in an adaptive grid setting with
  varying resolution, e.g. convection
• Potential for numerical problems at fine-coarse
  grid interfaces
• Performance and time step issues ?
• Treatment of the lower boundary condition
• Re-initialization of orography data, land use
  data, roughness lengths, albedos,
• NCARs land surface model is currently not
  adaptive
• Neither is the Ocean and Ice component
• First tests will be done with the so-called
  Aqua-Planet