composite analyses of tropical convective systems prior to tropical cyclogenesis
DESCRIPTION
Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis. Chip Helms Jason Dunion Lance Bosart University at Albany Cyclone Workshop 27 September 2013. Funding through NSF AGS-0849491 and NASA HSRP #NNX12AK63G. - PowerPoint PPT PresentationTRANSCRIPT
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27 Sept. 2013Future WorkResultsMethodologyMotivation
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Composite Analyses of Tropical Convective Systems Prior to
Tropical Cyclogenesis
Chip HelmsJason DunionLance Bosart
University at Albany
Cyclone Workshop27 September 2013
Funding through NSF AGS-0849491 and NASA HSRP #NNX12AK63G
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Vorticity Generation Tendency as aFunction of Buoyancy
Want to be able to include thermodynamics in vort. Tendency without invoking thermal wind balance.
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Motivation
Motivating Questions and Working Hypotheses
• Why do some marginal systems develop despite the presence of inhibiting factors?– External features enhance vorticity generation– Robust vorticity column dampens turbulent mixing
• Why do viable systems fail to develop?– Insufficient vorticity generation– Excess vorticity destruction– Conditions hostile to sustained deep convection
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Creating Subset Composites• Metrics represent system evolution
– System structure– Near-system environment
• Metrics define a phase space– Phase spaces have proven useful in past studies
• Wheeler and Hendon 2004; Hart 2006; McTaggart-Cowan et al. 2008
Methodology
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Vortex Tracker• Limited best track data for pre-genesis and
non-develop systems
• Based on NCEP vortex tracker (Marchok 2002)– Multiple fields to generate center fix– Link fixes using steering flow and previous motion
• Currently using Climate Forecast System Reanalysis (CFSR)
Methodology
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Vortex Tracker - Variables
100% = non-divergent cyclonic0% = irrotational
-100% = non-divergent anticyclonic
Methodology
NCEP vortex tracker Pre-genesis vortex trackerVariable Levels Variable Levels
Vorticity 850, 700 hPa Tangential Velocity 850 hPa
Pressure Surface MSLP gradient Surface
Pressure gradient Surface Vortex Idealization 850, 700, 500 hPa
Geo. height 850, 700 hPa
Wind 850, 700 hPa
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Idealized ExampleMethodology
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Merging CirculationsNon-developing SystemCape Verde TCs ????
Track ExamplesMethodology
850 hPa Vortex Idealization
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Mixed
Methodology
Pre-genesis Phase Space
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Phase Space: Organization Metrics
• 500-850 hPa center offset– Conflicting tilts lower composite detail– Genesis occurs shortly after vertical alignment
• Nolan (2007), Davis and Ahijevych (2012), Helms and Hart (2012)
• Tangential velocity (850, 500 hPa)– Tracks intensity of system
• Vortex idealization (850, 500 hPa)– Proxy for evolution of a closed circulation
Methodology
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Phase Space: Near-system Environment Metrics
• Deep layer environmental shear– High shear has a detrimental effect on genesis– Look for dev/nondev bifurcation in profiles
• RH (300-500, 500-850 hPa)– Important in a two ways
• Directly modifies the stability profile• Indirectly modifies stability profile via evaporative
cooling and inhibition of LHR
Methodology
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Phase Space: Mixed Metrics• Δθe between 850 hPa and tropopause
– Potential stability → near-system environment– Bulk diabatic heating → convective activity
• Thermal vorticity (200-850 hPa)– Warm core cyclone– Upper-level anticyclone
• synoptic scale feature or system-scale feature
Methodology
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Phase Space
2010 Atlantic Hurricane Season
Pre-genesis and Non-developing
Results
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Future Data Sources
• Reanalyses– ERA-Interim, NCEP/NCAR, MERRA
• Operational– GFS, ECMWF, CMC
• Observational– CIMSS satellite winds, dropsondes, satellites
Future Work
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Analysis Goals• Examine differences between dev/non-dev in variety
of composites– Kinematic, dynamic, and thermodynamic fields
• Examine how parameters vary with phase space location– SST, OHC, MPI (Emanuel 1988),
ventilation index (Tang and Emanuel 2012), genesis pathway (McTaggart-Cowan et al. 2008)
• Will allow us to explore why viable systems sometimes fail to develop and marginal systems sometimes succeed
Future Work
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Vorticity Tendency as aFunction of Buoyancy
Want to be able to include thermodynamics in vort. Tendency without invoking thermal wind balance.
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