Extra-tropical Cyclones in Recent Re-Analyses
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Extra-tropical Cyclones in Recent Re-Analyses
Kevin HodgesLennart Bengtsson and Robert Lee
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Motivation
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• Extra-tropical cyclones:-1. Important components of the general
circulation.2. How should they be verified for distribution
and properties?a) Observations are highly inhomogeneous.b) No long term observational record.
• Re-analyses:-1. Best available, 4D, homogeneous data sets
constrained by observations.2. What are the uncertainties?
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New Re-Analyses• ERA-Interim (ECMWF)
– T255L60 (~80km) spectral, 4D Var., 1989-2009.• Modern Era Retrospective Re-Analysis
(MERRA)– 0.50x0.670L72(~74km) finite volume, Grid-point
Statistical Interpolation (GSI, 3D Var.), 1979-2009.
• Japanese 25 Year Re-Analysis (JRA25)– T106L40 (~125km) spectral, 3D Var., 1979-
2009. • NCEP Coupled Re-analysis
– T382L64 (~38km), GSI, 1979-2009.• 20th Century Re-Analysis
– Surface only observations, 1891-2008, ensemble kalmen filter, T63.
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Comparison Methodology• Identify and track cyclones –
synoptic.– MSLP – T63.– ξ850 – T42.
• Compare using:-– INTERIM as base (1989-2006).– Spatial statistics.– Intensity pdf’s.– Cyclone matching.– Composites.
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Spatial Statistics
NH, DJF
SH, JJA
Track Density
Genesis Density
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Older Re-analyses
Track Density Differences (1979-2002)NH SH
NCEP
-ERA
40JR
A25-
ERA4
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General Results
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Number per month
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INTERIM-JRA25
NH, DJF
SH, JJA
Track Density
Genesis Density
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INTERIM-MERRA
NH, DJF
SH, JJA
Track Density
Genesis Density
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INTERIM-NCEP
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NH, DJF
SH, JJA
Track Density
Genesis Density
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Intensity-MSLP
NH, DJF SH, JJA
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Intensity Winds, Vorticity
12NH SH
925hPa Winds
850hPa Vorticity
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Cyclone Matching
Vorticity,T42 IntensitiesMean seperation ≤ 40
Time overlap > 60% points
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Separation, Vorticity
NH DJF SH JJA
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JRA25-ERA40, 1979-2002.
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Intensity
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Observations-Quickscat
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Max. Intensities Instantaneous Differences
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Lifecycles
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ATHENA-Intensities
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T159 Intensities
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ATHENA-Distributions
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Future Work• Apply same methods directly to
satellite data to verify cyclone structure in NWP (directly) and climate models (statistically).
• Apply to other weather system types, e.g. TC including examining the transition of EW to TC; the extra-tropical transition of TC and polar lows.
• Extend to energetics.20