Decadal predictability and nearterm climate change experiments with HiGEM

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Decadal predictability and near-term climate
change experiments with HiGEM

• Len Shaffrey, NCAS Climate
• University of Reading
• Thanks to Doug Smith, Rowan Sutton, Pier-Luigi
  Vidale,
• Ed Hawkins, Dave Stevens

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HiGEM

• HiGEM is a partnership between the UK academic
  community and the Met Office to develop a 'high'
  resolution atmosphere ocean coupled climate
  model.
• HiGEM is based on the Met Office coupled climate
  model, HadGEM1, but with increased horizontal
  resolution.

Snapshot of the HiGEM Model

• In the atmosphere the horizontal resolution is
  increased to 1.25 degrees longitude by 0.83
  degrees latitude (90km). The parametrisations
  remain largely the same as in HadGEM1, including
  the simple interactive aerosol scheme.
• In the ocean the horizontal resolution is 1/3 by
  1/3 degree globally.

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HiGEM

• Centennial length control integrations of HiGEM
  have been completed on two computing platforms,
  the HPCx in the UK and the Earth Simulator in
  Japan.
• Some marked improvements
• Blocking in the Northern Hemisphere
• Position of the Gulf Stream
• Representation of the MJO
• Warm SST biases in the marine stratocumulus
  regions
• Some things don't improve
• Indian monsoon
• Some Tropical precipitation biases

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ENSO in HiGEM and HadGEM1
Observations (HadISST2)
El Nino DJF Sea Surface Temperature composites
from HadISST2, HadGEM1.2 and HiGEM1.2. Units
K The warming of the Tropical Pacific during an
El Nino event is well captured in HiGEM.
HadGEM1
HiGEM
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HiGEM

• Just completed porting HiGEM to a third computing
  platform (HECToR)
• On 128 processors the integration speed is 0.75
  model years/day, but the model doesn't scale well
  past this.
• The plan is to be involved in the decadal
  predictability experiment, preferably using
  anomaly assimilation (some variation of DePreSys,
  Smith et al 2007)
• Computing resources and people are constraints to
  producing the forecasts but, since anomaly
  assimilation requires a series of long
  integrations to produce the initial conditions
  and HiGEM is slow, the biggest constraint might
  be time...
• ..so we've already started working on the anomaly
  assimilation runs.
• Another possible constraint might be data volume
  and data handling.
• Already using the COSP simulator (offline)
• No aquaplanet version planned (at the moment)

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El Nino in HiGEM
Normalised Nino3 SST Power Spectra for HadISST,
HadGEM1.1 and HiGEM1.1
Both the spatial and temporal characteristics of
ENSO, and its remote teleconnections, are better
simulated in HiGEM relative to HadGEM Why does
the ENSO improve in HiGEM?
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Tropical Instability Waves

• Tropical Instability Waves in the Tropical
  Pacific Ocean are shear instabilities that grow
  in the equatorial current-counter current system
• They propagate slowly westwards (0.5ms-1)

Instantaneous SSTs in the Tropical Pacific Ocean
(Chelton et al. 2001)
Instantaneous SST from HiGEM
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Future Directions

• Understanding the value of resolution
• HiGEM being used to inform seasonal forecasting
  development in the Met Office (PACE - Sarah
  Keeley)
• Idealised climate change experiments underway

• Decadal forecasting? How to initialise the ocean?

From Smith et al. (2008)

• Model development - a high resolution version of
  HadGEM3?

The ORCA2 grid - no North Pole!
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Will increasing the resolution of climate models
allow us to better represent weather?
HiGEM
ERA-40
Courtesy of Jen Catto
Composite structures of the 50 most extreme
wintertime Northern Hemisphere storms in ERA-40
and HiGEM. Colours windspeed, Black lines
1000hPa isobars, Red lines 850hPa to 500hPa
temperature thickness
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El Nino in HiGEM
CMAP
El Nino DJF precipitation composites from CMAP,
HadGEM1.2 and HiGEM1.2. Units mm/day.
HadGEM1.2
HiGEM1.2
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El Nino in HiGEM
ERA-40
El Nino DJF mslp composites from ERA40, HadGEM1.2
and HiGEM1.2. Units hPa.
HadGEM1.2
HiGEM1.2
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Tropical Instability Waves

• Tropical Instability Waves in the Tropical
  Pacific Ocean are shear instabilities that grow
  in the equatorial current-counter current system
• They propagate slowly westwards (0.5ms-1)
• Satellite data shows the coupling between the SST
  fronts associated with the TIWs and the atmosphere

Instantaneous SSTs in the Tropical Pacific Ocean
(Chelton et al 2001)
Instantaneous surface wind stress divergence from
QuikSCAT winds
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Tropical Instability Waves in HiGEM
HadGEM
HiGEM
Instantaneous Sea Surface Temperatures (contours)
and surface windstress divergence (colours)
How important is the small-scale coupling between
ocean and the atmosphere in Tropical Instability
Waves for the climate and its variability?