The HiGEM Weather Paper

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The HiGEM Weather Paper

• Len Shaffrey
• NCAS-Climate, Department of Meterology,
  University of Reading

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The HiGEM Weather Paper

• The HiGEM overview paper has been accepted by
  Journal of Climate
• Revised version of the paper can be found at
  www.cgam.nerc.ac.uk/len/
• The weather and atmospheric variability paper is
  slowly coming together.
• What impact does increasing the horizontal
  resolution have on weather and atmospheric
  variability in a coupled climate model?
• The goal of the paper is to evaluate against
  observations and compare how well aspects weather
  and atmospheric variability are represented in
  the HiGEM1.2 and HadGEM1.2 control runs.

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The HiGEM Weather Paper

• The focus is on the coupled models, but where
  they provide insight into how the differences
  come about then the results from atmosphere-only
  runs are used as well.
• A list of topics to be (superficially!) covered
• Storm tracks
• Blocking
• North Atlantic Oscillation
• Madden Julian Oscillation
• Westerly wind bursts?
• Small-scale ocean atmosphere coupling in the
  extra-tropics?
• Others?
• Need to answer the So what? question. Its not
  enough to just describe the differences.

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Storm Tracks

• How well are the storm tracks are represented in
  HiGEM1.2 and HadGEM1.2?
• Different measures of storm tracks strength,
  Eulerian covariance vs Feature track densities
• The major NH storm tracks are reasonably well
  represented in both HadGEM1.2. and HiGEM1.2
• Either this section is brief description or it
  includes some of the work Jen has done on
  extreme storms?

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DJF 250hPa 2-6 day high-pass transient eddy
kinetic energy
HiGEM1.2
ERA-40
HadGEM1.2
Courtesy of Jen Catto
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Blocking

• The representation of blocking improves in
  HiGEM1.2
• The frequency of blocking increases in HiGEM1.2,
  particularly in wintertime.
• Lots of unanswered questions about how the
  blocking should evaluated in coupled climate
  models - but theyll have to wait for another
  paper.

Left) 250mb geopotential height and Right) theta
on PV2 from ECMWF analysis 21/09/98
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Blocking

• The representation of blocking improves in
  HiGEM1.2
• The frequency of blocking increases in HiGEM1.2,
  particularly in wintertime.
• Lots of unanswered questions about how the
  blocking should evaluated in coupled climate
  models - but theyll have to wait for another
  paper.

Left) 250mb geopotential height and Right) theta
on PV2 from ECMWF analysis 21/09/98
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Right TM DJF blocking frequencies for ERA-40,
HiGEM1.2 and HadGEM1.2 Below No of days with
blocking episodes (Blocks gt 9o longitude, gt5
days) in each NH sector.
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North Atlantic Oscillation

• A brief description of how well the NAO is
  represented in HiGEM1.2 and HadGEM1.2
• There is a slight improvement of the NAO in
  HiGEM1.2 versus HadGEM1.2.

HiGEM1.2
ERA-40
HadGEM1.2
Courtesy of Sarah Keeley
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Madden-Julian Oscillation

• The MJO is improved at higher resolution
• The propagation speed of the MJO in HiGEM1.2 is
  close to observed speed (too slow in HadGEM1.2)
• The distribution of the 20-100 day bandpass
  variance of OLR (Outgoing Longwave Radiation) is
  closer to observations in HiGEM1.2
• Why the improvement? Better basic state? Better
  representation of convection over MC? A bit of
  both?

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Courtesy of Pete Inness
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Small Scale Coupling
Annual mean windstress curl and SSTs from HiGEM1.2
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The HiGEM Weather Paper

• This is the plan in order to get it finished and
  submitted within 5 months.
• Finish the first five sections (which will
  definitely be in the paper)
• Introduction started
• Finalise blocking section
• Storm Track section - what exactly to include?
• NAO and MJO sections - figures already decided on
  - text to write
• At this point assess length of paper and decide
  what else to include
• Westerly wind bursts?
• Small scale coupling ?
• Then write concluding section.

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Blocking
DJF Blocking Frequency evaluated at each latitude
between 30N and 75N for HiGEM and ERA-40
(1979-2001)
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Blocking
DJF Blocking frequency based on 500mb
Geopotential Height index but evaluated at each
latitude between 30oN and 70oN for ERA-40
(1957-2001). Black line latitude of maximum
250mb total eke.
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Blocking
500mb geopotential height blocking index
(variable latitude) from HadGEM1, HadGAM1, HadAM3
and ERA-40 from Ringer et al. (2006)