1 22 July 2013 Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical...

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Composite Analyses of Tropical Convective Systems Prior to

Tropical Cyclogenesis

Chip Helms

Cyclone Research Group

22 July 2013

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Questions

• What makes a tropical convective system (TCS) fail to develop?– Especially for TCS expected to develop

• How often/easily do TCSs change from being unfavorable for development to being favorable?

• Is TCS structure a function of basin? Season? Mesoscale/Synoptic Scale Environments? Future development? Development pathway?– If so, what processes generate the relationship?

• What causes a TCS to become vertically aligned with time? Do all TCS do so? What about this vertical alignment makes the low levels rapidly spin-up? What causes this spin-up to fail in non-developing systems?

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Genesis Process Hypothesis

Tropopause

500 hPa

Surface

Wave Axis

Convergenceand ascentalong wave

Cooling (Melting, Evaporation, Radiation?)

Concentration of background vorticity produces low-level vortex

Deep convectionforms along

convergence line

Deep convection fuels formation of stratiform

sheild downshear

+PVMid-Level Vortex

Low-Level Vortex

Latent Heat Release

ShearHydrostatic response to

heating profile results in PV convergence

and a non-linear feedback due to

thermal wind balance

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Vertical Alignment Process

?

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Method Motivation

• Two general approaches to studying genesis– Case Studies

• Detailed analyses, may not be representative

– Composite Studies• Represenative features, loss of detail

• Solution: Composite on homogeneous subset– Select based on important, highly-variable

structures

• Make subset selections using phase space

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Methodology

Old Phase Space

N = 5817All HURDAT Systems 2005-2012

ALL INVESTs

15 Variables, 10 Plots

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Methodology

New Phase Space

12 Variables, 6 Plots

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Current Variables

• 500-850 hPa center displacement• 850, 500 hPa Mean Tangential Velocity• Mean 200-850 hPa Shear Vector

– Mean removes axisymmetric component of vortex

• 850,500 hPa Total Deformation– Mean derivatives to remove axisymmetric vortex

• 500,200 hPa Mean Relative Humidity• Mean Curl of 200-850 hPa Shear• Bulk Lapse Rate or Bulk Diabatics

Methodology

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Planned Variable Changes

• Remove mean relative humidities• Add mean total precipitable water• Add ‘Percent Idealized’

– Measure of how close the wind field is to purely tangential cyclonic flow

– Closed circulation has a lower value than a shear line

Methodology

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Moving Beyond NHC INVESTs

• Using INVEST files introduces a selection bias and reduces potential data ranges– Only NHC basins from 2005 onwards

• Vortex detection and tracking algorithm– Uses 850 hPa ‘Percent Idealized’ variable for

vortex identification• Positions found using overlapping 5°x 5° boxes

– Tracking based on Hart (2003) • Cyclone Phase Space vortex tracker

Methodology

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Example Vortex Identification

Methodology

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Idealized Example

Methodology

Percent Idealized Mean Vλ

+

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Tracking Algorithm (Hart 2003)• 5 Requirements:

1)

2) New position is the closest at time t to where cyclone was at time

3) Cyclone motion =

4) where5) Change in cyclone direction is within limits

determined by cyclone movement speed no restrictions

• System must last for 24 hours

Methodology

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Methodology

Example TrackingFirst Pass Tracks

Adjoint TracksExtensionsDeletion

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Future Work

• Run tracking algorithm– Extend to multiple data sets

• 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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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

END

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

EXTRA SLIDES

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Results

N=516, Red=15

Year: 2010

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Results

N=107, Red=6

Year: 2010

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Results

N=25, Red=6

Year: 2010

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Results

N=45, Red=6

Year: 2010

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Results

N=16, Red=4

Year: 2010

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

All HURDAT 2005-2012Results

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

INVEST/Pre-Genesis SystemsResults

Max Freq: 41 ~ 2.5%

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Tropical DepressionsResults

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Tropical StormsResults

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

HurricanesResults

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Post Extra-Tropical TransitionResults

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Sandy (2012)Results

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Sandy (2012): 10/18 – 10/21Results

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Sandy (2012): 10/22 – 10/25Results

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Sandy (2012): 10/26 – 10/29Results

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Sandy (2012): 10/30 – 10/31Results

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

REMOVED SLIDES

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

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 properties

New PV AnomalyOut 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

t

VkV)(

p-f)(V

Concentration term

Stretching termMCS

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

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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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Example: Non-developing system

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

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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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

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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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

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

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Genesis Process Hypothesis

Tropopause

500 hPa

Surface

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Genesis Process Hypothesis

Tropopause

500 hPa

Surface

Vort. Max

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22 July 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems

Motivation

Genesis Process Hypothesis

Tropopause

500 hPa

Surface