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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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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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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Motivation

Vertical Alignment Process

?

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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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Methodology

Old Phase Space

N = 5817All HURDAT Systems 2005-2012

ALL INVESTs

15 Variables, 10 Plots

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Methodology

New Phase Space

12 Variables, 6 Plots

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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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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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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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Example Vortex Identification

Methodology

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Idealized Example

Methodology

Percent Idealized Mean Vλ

+

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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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Methodology

Example TrackingFirst Pass Tracks

Adjoint TracksExtensionsDeletion

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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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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 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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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

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Motivation


Tropopause

500 hPa

Surface

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Motivation


Tropopause

500 hPa

Surface

Vort. Max

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Motivation


Tropopause

500 hPa

Surface

1 22 july 2013 future workresultsmethodologymotivation chip helmscomposite analyses of tropical...

Documents

tropical convective

case study

future development

greatest level

compositing study

general sense

tcs structure

large number of cases