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Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis. Chip Helms Cyclone Research Group 22 July 2013. Motivatio n. Questions. What makes a tropical convective system (TCS) fail to develop? Especially for TCS expected to develop - PowerPoint PPT Presentation
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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