Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis

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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


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Results

N=25, Red=6

Was 16<σ<22

8<σ<22


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Results

N=45, Red=6

Was 16<σ<22

6<σ<22


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Results

N=16, Red=4

6<σ<18

Was 16<σ<22


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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

Documents

Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis