Transcript Regional Climate Modeling: Where have we been and where

Towards Advanced Understanding and
Predictive Capability of Climate Change
in the Arctic
using a High-Resolution
Regional Arctic Climate System Model (RAMC)
– an overview
Participants:
Wieslaw Maslowski (PI)
John Cassano (co-PI)
William Gutowski (co-PI)
Dennis Lettenmeier (co-PI)
- Naval Postgraduate School
- University of Colorado
- Iowa State University
- University of Washington
Sponsor: DOE Climate Change Prediction Program (CCPP)
Period of Performance: 09/01/2007 - 08/31/2011
Rationale
Changes in the Arctic sea ice cover have significant
ramifications to the entire region and beyond,
including:
- Ocean thermohaline circulation
- Heat / energy budget
- Climate
- Ecosystems
- Native communities
- Natural resource exploration
- Commercial transportation
Rationale - continued
1. Global climate models have errors in representing northward
fluxes of heat and moisture, sea ice distribution, and export of
freshwater into the North Atlantic. Those parameters control
both regional Arctic and global climate variability and their
realistic representation requires dedicated high-resolution
modeling studies and it is critical to improved climate
predictions
2. Existing regional Arctic models do not account for important
sea-ice-atmosphere-land-hydrology feedbacks as they typically
simulate either the atmospheric state using simplified lower
boundary conditions for the ice/ocean or predict ice-ocean
variability using prescribed atmospheric forcing.
3. A Regional high-resolution Arctic Climate system Model
(RACM), can address these deficiencies and improve predictive
skill of climate models. High resolution is defined as of order
10-km or less for ice/ocean and 50-km or less for
atmosphere/land/hydrology components.
Primary science objective
To synthesize understanding of past and present states
and thus improve decadal to centennial prediction of
future Arctic climate and its influence on global climate.
Specific objectives
1. Determine and quantify the coupled Arctic climate
system processes responsible for the recent
observed and future projected changes in the ice
pack, regional hydrological cycle, and freshwater
export into the North Atlantic
2. Assess decadal system scenarios of a seasonally
/ partially ice free Arctic Ocean, including their
timing
3. Address the general circulation model (GCM)
limitations in predicting Arctic climate through the
identification
of
physical
and
numerical
requirements of future GCMs
Implementation
• Develop a state-of-the-art Regional Arctic Climate
system Model (RACM) including high-resolution
state-of-the-art atmosphere, ocean, sea ice, and
land hydrology components and
• Perform multi-decadal numerical experiments
using high performance computers to minimize
uncertainties and fundamentally improve current
predictions of climate change in the northern polar
regions
Proposed climate model
components and resolution
•
•
•
•
•
Atmosphere - Polar WRF
(gridcell ≤50km)
Land Hydrology - VIC / CLM / Noah (≤50km)
Sea Ice - LANL/CICE
(gridcell ≤10km)
Ocean - LANL/POP
(gridcell ≤10km)
Flux Coupler
(based on NCAR/CCSM global model coupler)
Proposed Arctic climate system model domain and elevations
(red box represents the domain of ocean and sea ice models)
Pan-Arctic region to include:
- all sea ice covered ocean in the northern hemisphere
- Arctic river drainage
- critical inter-ocean exchange and transport
- large-scale atmospheric weather patterns (AO, NAO, PDO)
Proposed Work
Proceed in three overlapping phases:
• Climate system component studies via one-way
coupling experiments (conducted under existing
complementary funding)
• Development of the Regional Arctic Climate
System Model (RACM)
• Physical feedback and future scenarios studies
focusing on changes in Arctic sea ice using the
fully coupled model
Research Questions
The primary research questions focus on the central role of the Arctic Ocean’s sea
ice as a mediator in atmosphere-ocean interaction and as a sensitive indicator
of Arctic climate-system change
• What have been the main ocean / sea ice / atmosphere processes and Arctic
system feedbacks that have led to the observed retreat of Arctic sea ice cover
over the past 50 years?
• What effect will the retreat of sea ice cover and warming of the upper ocean
through 2007 have on atmospheric circulation and fluxes? How will these
changes to the atmosphere feedback to further modify the ocean and sea ice
state of the Arctic?
• What is the relative control of the lower latitude variability (as defined along our
regional model lateral boundaries) compared to the internal system interactions
within the Arctic?
• Can the retreat of the Arctic ice pack pass a tipping point that propels summer
ice cover to complete collapse?
• If so, how long will it take to arrive at a seasonally ice free Arctic Ocean and
what physical processes will be responsible for moving the Arctic towards this
new state?
• If not, what changes are needed to reverse the present trend of sea ice retreat?
Planned Coupled RACM Model Experiments
1. ERA40/ECMWF atmospheric initial/lateral
boundary conditions and ocean/sea ice restarted
from end of 48-year spin up with PHC lateral
boundary conditions (1958-2007) with 1/12o
ocean/ice and 50-km atmosphere/land models
2. Four future climate scenarios with ‘near-future’,
‘warm’, ‘cold’, and ‘neutral’ lateral boundary
forcing data from GCM output (25-year
simulation for each scenario restarted from end
of 1 and configured the same as in 1)
Computational resource requirements
1. ARSC - FY08 allocation
- Platform:
Sun Cluster (Midnight)
- FY08:
1 Mln proc-hrs
2. DOE/INCITE proposal (pending)
- Platform:
Cray XT4 (Jaguar) at
DOE/ORNL
- Year 1:
3 Mln proc-hrs
- Year 2:
4 Mln proc-hrs
- Year 3:
4 Mln proc-hrs