composite analyses of tropical convective systems prior to tropical cyclogenesis
DESCRIPTION
Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis. Chip Helms Tropical Lunch 26 April 2013. Motivatio n. Cyclone Tracy (1974). Genesis: 12/21. Landfall: 12/24 110 kts ( Saffir -Simpson Cat. 3). Image courtesy Wikipedia. Motivatio n. - PowerPoint PPT PresentationTRANSCRIPT
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26 April 2013Future WorkResultsMethodologyMotivation
Chip Helms Composite Analyses of Tropical Convective Systems
Composite Analyses of Tropical Convective Systems Prior to
Tropical Cyclogenesis
Chip Helms
Tropical Lunch26 April 2013
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Cyclone Tracy (1974)
Genesis: 12/21
Landfall: 12/24110 kts
(Saffir-Simpson Cat. 3)
Image courtesy Wikipedia
Motivation
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Motivation
Methods for Studying TC Genesis
• Case Study– Allow for detailed analysis– May not be representative of population
• Composite Study– Identify prominent features in set of cases– Lose details in compositing process
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Motivation
Example: Non-developing system
8/18/2010 ~14 UTC8/17/2010 ~13 UTC
Longitude [°E] Longitude [°E]Mid-levels will appear weaker in composite
Pre
ssur
e [h
Pa]
Pre
ssur
e [h
Pa]
Zonal Cross-sections
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Solution: Composite on a Subset• Select a subset of cases with similar structure
– More homogenous subset provides more detail in composites
• Create subsets using phase space– Position in phase space indicates current state of
important, yet highly variable structures• Composite all cases located in a given
volume of the phase space– Retain more detail (like case studies)– Representative results (like composite studies)
Methodology
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Data• CFSRv2, HURDAT2+INVESTs
– Convenient for testing methodology– CFSR: Uniform in time– INVEST files contain a selection bias as not
every disturbance triggers an INVEST– INVEST files only available since 2005
• Use best track as first guess position– Find 500 hPa and 850 hPa center by minimizing
difference between tangential and total winds
Methodology
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Methodology
Phase Space
N = 5817All HURDAT Systems 2005-2012
ALL INVESTs
Work
in P
rogres
s
500 hPa center position relative to 850 hPa Center
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Results
N=516, Red=15
INVESTs+Pre-Genesis 2010
16<σ<22No 80% Contour
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Results
N=107, Red=6
80% Contour
Was 16<σ<22
8<σ<22
INVESTs+Pre-Genesis 2010
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Results
N=25, Red=6
Was 16<σ<22
8<σ<22
INVESTs+Pre-Genesis 2010
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Results
N=45, Red=6
Was 16<σ<22
6<σ<22
INVESTs+Pre-Genesis 2010
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Results
N=16, Red=4
6<σ<18
Was 16<σ<22
INVESTs+Pre-Genesis 2010
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System Evolution: Sandy (2012)Results
850 vs 500 hPa Tangential Velocity
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Unwrapping TCs
Results
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Primary Future Work
• Create an algorithm to identify pre-genesis systems without relying on best track
• Test and finalize phase space variables• Examine composites
– e.g. Dev vs Non-dev• System evolution in phase space
Future Work
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Side Project Future Work
• Create real-time phase space diagrams– Generate a climatology of phase space
Genesis Productivity (% dev in each volume)– Apply to forecast times to provide a forecast
diagnosis of genesis probability• Create real-time unwrapped figures
Future Work
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END
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EXTRA SLIDES
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Results
N=516, Red=15
Year: 2010
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Results
N=107, Red=6
Year: 2010
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Results
N=25, Red=6
Year: 2010
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Results
N=45, Red=6
Year: 2010
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Results
N=16, Red=4
Year: 2010
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All HURDAT 2005-2012Results
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INVEST/Pre-Genesis SystemsResults
Max Freq: 41 ~ 2.5%
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Tropical DepressionsResults
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Tropical StormsResults
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HurricanesResults
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Post Extra-Tropical TransitionResults
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Sandy (2012)Results
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Sandy (2012): 10/18 – 10/21Results
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Sandy (2012): 10/22 – 10/25Results
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Sandy (2012): 10/26 – 10/29Results
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Sandy (2012): 10/30 – 10/31Results
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REMOVED SLIDES
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TheorySimpson et al. (1997) and Ritchie and Holland (1997)
Prior Work
Evaporative Cooling
StratiformLatent
Heating
p
gfP )(
+ PV Anomaly
Mergers of PV anomalies add PV while averaging
thermal propertiesNew PV Anomaly
Out of balance with thermal structure
Forced Ascent andEvaporative Cooling
Act to cool sub-cloud layer
Warm anomaly growth not detailed by theory, but would be accomplished by forced subsidence or increased LHR
Forced Convergence+
pf
tVkV)(
p-f)(V
Concentration term
Stretching termMCS
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Pre-Genesis Phase Space
N = 5817All HURDAT Systems 2005-2012
Displacement of 500 hPa center
Displacementvs
Tilt Direction
Displacement vs Shear
500-850 hPa Shearvs
500-850 hPa Vorticity Difference
Vorticity vs Divergence ~Bulk Lapse Ratevs
Upper Level Moisture
Upper-level T’ vs Spec. Hum.500 hPa Vλ vs 850 hPa Vλ
Stronger Mid Vortex
Stronger Low Vortex
850 hPa 500 hPa
500-850 hPa 200-850 hPa
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Motivation
Example: Non-developing system
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Cyclone Tracy (1974)
Genesis: 12/21
Landfall: 12/24110 kts
(Saffir-Simpson Cat. 3)Image courtesy Wikipedia
Image courtesy Clark Evans
Genesis: 6/23
Motivation
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Motivation
Issues with Traditional Composites
• Mid-level features will appear weaker– High variability in system tilt
• Vertically-aligned systems tend to be stronger– Composites will favor upright systems
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Methodology/Data• Locate center at 850 and 500 hPa
1) Maximum Vλ (0.5° search grid)2) Minimum Difference of Vλ and V (0.25°)3) Minimum Difference of Vλ and V (0.10°)
• Datasets: CFSRv2, HURDAT2+INVESTs– Convenient for testing methodology– CFSR: Uniform in time– Complete with all the selection bias caveats of
the INVEST files
Methodology