Jennifer Catto

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Extra-tropical cyclones in HiGEM - Structure

• Jennifer Catto
• Supervisors Len Shaffrey and Kevin Hodges

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Outline

• Compositing and lifecycles
• Methodology
• Results
• Vertical Structures
• Conclusions so far
• HiGAM SST experiment
• Motivation
• Scientific questions
• Method

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Composite Analysis - Methodology

• Step 1 Identify tracks using Kevins tracking
  program

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Composite Analysis - Methodology

• Step 2 Choose at what stage in the lifecycle to
  composite the tracks e.g.
• Maximum tendency
• Maximum intensity
• Maximum precipitation
• Minimum pressure
• and identify where this occurs

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Composite Analysis - Methodology

• Step 3 Extract the 20o radius around this point
  and note the direction of propagation of the
  storms.

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Composite Analysis - Methodology

• Step 4 Rotate these areas to the same direction
  of propagation and average them.

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Composites Analysis Positions of tracks
HiGEM1.2
HadGEM1.2
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Composites Analysis Results 1 Wind, pressure
and temperature for Atlantic
Colours wind speed (m/s)
HadGEM1.2
HiGEM1.2
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Composites Analysis Results 1 Wind, pressure
and temperature for Atlantic
Colours wind speed (m/s)
ERA-40
HiGEM1.2
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Composites Analysis Results 3 Vertical
Velocity for Atlantic
HadGEM1.2
HiGEM1.2
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Composites Analysis Results 3 Vertical
Velocity for Atlantic
ERA-40
HiGEM1.2
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Composites Analysis Differences between
Atlantic and Pacific
Colours wind speed (m/s)
Pacific
Atlantic
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Composites Analysis Differences between
Atlantic and Pacific
Atlantic
Pacific
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Lifecycles - Methodology
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Lifecycles Results
Atlantic
Solid lines HiGEM Dashed lines
HadGEM Dot-dash lines ERA-40
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Lifecycles Results
Pacific
Solid lines HiGEM Dashed lines
HadGEM Dot-Dash lines ERA-40
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Vertical Structures - Atlantic
HiGEM1.2
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Vertical Structures
HadGEM1.2
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Conclusions so far

• Storm structures in HiGEM1.2 compare better with
  ERA-40 than those in HadGEM1.2
• The resolution has a large effect on the maximum
  intensity that storms attain.
• Differences between the Atlantic and the Pacific
  picked up well by the models.

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Future Work HiGAM SST experiment Motivation 1
HiGEM1.2
HiGAM1.2
Track Density
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Future Work HiGAM SST experiment Motivation 2
Track Density Difference
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Future Work HiGAM SST experiment Motivation 3
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HiGAM SST experiment

• Questions
• Is it the tighter SST gradient in the Kuroshio
  current that causes the excess cyclones in the
  Pacific basin in HiGEM?
• What effect do the higher resolution SSTs have on
  the storms in HiGAM?
• Is there any effect on the storm structures?
• Method
• Include a constant DJF SST anomaly in the
  midlatitude Pacific.
• Ensemble of 20 winter simulations starting in
  October.

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HiGAM SST experiment - Method
Will allow us to identify which (if any) storms
are affected by changes in SSTs applied to the
model.
Track density plots showing densities associated
with genesis in different regions.
HiGAM1.2
HiGEM1.2