Transcript Atmospheric Modeling in an Arctic System Model

Atmospheric Modeling
in an Arctic System Model
John J. Cassano
Cooperative Institute for Research in Environmental Sciences
and Department of Atmospheric and Oceanic Sciences
University of Colorado
Proposed Arctic System Model Domain
Why develop an ASM?
• The Arctic is a unique region that presents unique
challenges for climate modeling
– An Arctic specific model can use model components that are
developed specifically for polar regions and polar processes
• Polar clouds and radiative fluxes
• Boundary layer and surface flux processes
• Existing regional Arctic climate models do not
account for important feedbacks between Arctic
climate system components
– Current regional Arctic models simulate atmospheric state
but have specified ocean and ice properties
• Arctic regional models are not subject to low latitude
errors present in global climate models
– Simulations with an ASM can use “perfect” lateral boundary
conditions
– Can explore polar processes without feedbacks to lower
latitudes
Why develop an ASM?
• Increased horizontal resolution compared to
global climate models
– Approx. 1 order of magnitude increase in
horizontal resolution compared to global models
– Increased horizontal resolution allows for:
• Improved representation of topography and coastlines
• Improved representation of small-scale processes
– Extreme events and storms
• More realistic representation of interactions and feedback
processes among climate model components
• Better match between model resolution and:
– end user needs (e.g. policy decisions)
– resolution of other climate system component models
– field studies
What Scientific Questions can be
Addressed with an ASM?
• Feedback studies
– Atmosphere / land hydrology
• Changes in permafrost, soil hydrology, and atmospheric
circulation
– How will degrading permafrost alter near surface soil moisture?
– What impact will changes in soil moisture have on the
atmosphere?
– Will altered atmospheric state intensify or dampen initial soil
moisture changes due to permafrost degradation?
• Impact of extreme storm events on land hydrology
– Atmosphere / ice / ocean
• Role of small scale processes such as polar lows
– How does ice / ocean state impact polar low development?
– How do polar lows alter the ice / ocean system?
– Do these small scale processes impact larger scales?
What Scientific Questions can be
Addressed with an ASM?
• How do high-resolution simulations of the Arctic climate
system differ from global climate model simulations?
– Consider observed changes in Arctic sea ice
• How do ASM simulations differ from GCSM simulations?
• Are different feedback processes acting in the ASM and GCSM?
• What is the role of lower latitude variability vs internal Arctic
system processes on observed Arctic change?
– Experiments using lateral boundary forcing from multiple GCSMs
and from global reanalyses
Atmospheric Model Requirements
• Community model with active research and
development
• Suitable for high resolution (O 1-10 km)
simulations
• Capable of long duration climate simulations
• Model capable of being run on many different
computer platforms
• Optimized for polar applications
ASM Atmospheric Model: WRF
• Suitable for high resolution (O 1-10 km)
simulations
– Fully compressible, nonhydrostatic dynamics
– Significantly improved numerics and dynamics
compared to MM5
– Designed for high-resolution applications
• Large eddy simulation
• Cloud resolving model
• Mesoscale applications
ASM Atmospheric Model: WRF
• Capable of long duration climate simulations
– WRF is formulated for mass and scalar conservation
• No long term drift due to model numerics
– Complete atmospheric physics
• Radiation
• Surface fluxes and land surface
• Planetary boundary layer (PBL)
• Cloud microphysics
• Cumulus parameterization
• Multiple options are available for all physical processes
– WRF - Chem is currently under development
• Will allow coupled atmosphere - chemistry simulations
WRF Physics Interactions
From NCAR WRF tutorial
ASM Atmospheric Model: WRF
• Model capable of being run on many
different computer platforms
– WRF runs on Unix single, OpenMP, and MPI platforms
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IBM
Linux (PGI and Intel compilers)
SGI Origin and Altix
HP / Compaq / DEC
Cray
Sun
Mac (xlf compiler)
ASM Atmospheric Model: WRF
• Optimized for polar applications
– Prior atmospheric model development effort led to the
widely used Polar MM5
• Focus on:
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Cloud and radiation processes
PBL and surface fluxes
Treatment of ice covered land
Sea ice
– On-going development of Polar WRF
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Cassano research group at CU
Polar Meteorology Group - BPRC / OSU
NOAA ESRL - Boulder
NCAR - AMPS
Fairbanks - July 2006
WRF - RRTM
WRF - CAM
Bias: -0.1 mb
Bias: 0.8 mb
Corr: 0.98
Corr: 0.98
Barrow - January 2006
WRF - RRTM
WRF - CAM
Bias: 10.6 deg
Bias: 2.7 deg
SHEBA Site - January 1998
Courtesy of Keith Hines
BPRC / OSU
Questions or comments?
WRF Model Details
• Mass based
terrain following
vertical coordinate
From NCAR WRF Tutorial
WRF Model Details
• Uses Arakawa C-grid staggering
From NCAR WRF Tutorial
WRF Model Details
• Lateral boundary conditions
– Specified from reanalyses, global, or regional models
– Open, symmetric, or periodic for idealized simulations
• Top boundary conditions
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Constant pressure
Rayleigh damping
Absorbing upper layer
Gravity wave radiation condition (planned)
• Map projections
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Polar stereographic
Lambert conformal
Mercator
Cartesian geometry (idealized only)
WRF Model Details
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3rd order Runge-Kutte time integration
High-order advection scheme
Mass and scalar conserving numerics
One and two-way nesting options
Four dimensional data assimilation (FDDA)
Model physics
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Radiation
Surface
Planetary boundary layer (PBL)
Cloud microphysics
Cumulus
Radiation
• Provides:
– Atmospheric temperature tendency
– Surface radiative fluxes (SW and LW)
• Options:
– Longwave
• RRTM
• CAM3
• GFDL
– Shortwave
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MM5
Goddard
CAM3
GFDL
From NCAR WRF Tutorial
Surface
• Provides:
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Surface turbulent fluxes
Soil temperature and moisture
Snow cover
Sea ice temperature
• Options:
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Fluxes: Monin-Obukhov similarity theory
Noah LSM
NCEP Noah LSM
RUC LSM
From NCAR WRF Tutorial
Planetary Boundary Layer
• Provides:
– Boundary layer fluxes
– Vertical diffusion / mixing
• Options:
– YSU PBL
– Eta PBL
– GFS PBL
– MRF PBL
From NCAR WRF Tutorial
Cloud Microphysics
• Provides:
– Atmospheric heat and moisture tendencies
– Cloud and precipitation amount
– Surface rainfall
• Options:
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Kessler warm rain
Purdue - Lin
WSM 3-class
WSM 5-class
WSM 6-class
Ferrier (NAM)
Thompson
From NCAR WRF Tutorial
Cumulus
• Provides:
– Atmospheric heat and moisture tendencies
– Surface rainfall
• Options:
– Kain-Fritsch
– Betts-Miller-Janjic
– Grell-Devenyi Ensemble
– Simplified Arakawa Schubert GFS
From NCAR WRF Tutorial