Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis

4 Nov. 2013Future WorkResultsMethodologyMotivation

Chip Helms Composite Analyses of Tropical Convective Systems 1

Composite Analyses of Tropical Convective Systems Prior to

Tropical Cyclogenesis

Chip HelmsJason DunionLance Bosart

University at Albany

Cyclone Research Group4 November 2013

Funding through NSF AGS-0849491 and NASA HSRP #NNX12AK63G



Motivation

Motivating Questions and Working Hypotheses

• Why do some marginal systems develop despite the presence of inhibiting factors?

• Why do viable systems fail to develop?



Relating Vorticity and Buoyancy

Goal: Include thermodynamics in vorticity tendency without invoking thermal wind balance.



Motivation

Genesis Process Hypothesis

Tropopause

500 hPa

SurfaceWave 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

+PV, +

Latent Heat Release

Radiative Cooling/HeatingShear



Motivation

Genesis Process Hypothesis

Tropopause

500 hPa

Surface

− 𝑫𝟐

𝑫𝒕𝟐Mid-Level Vortex

+/-

Low-Level Vortex

Shear

− 𝑫𝟐

𝑫𝒕𝟐-B +B− 𝑫

𝟐𝑫𝒕𝟐

− 𝑫𝟐

𝑫𝒕𝟐+B

+y+x

+𝑫𝟐𝑫𝒕𝟐

− 𝜕𝑣𝜕 𝑧𝜕𝐵𝜕 𝑥 +

𝜕𝑢𝜕 𝑧

𝜕𝐵𝜕 𝑦 +(+ 𝑓 ) 𝜕𝐵𝜕 𝑧

− 𝑫𝟐

𝑫𝒕𝟐

Night: -B / Day: +B

-/?− 𝑫

𝟐𝑫𝒕𝟐

− 𝑫𝟐

𝑫𝒕𝟐− 𝑫

𝟐𝑫𝒕𝟐

+/- +/-+/-

− 𝑫𝟐

𝑫𝒕𝟐

− 𝑫𝟐

𝑫𝒕𝟐

− 𝑫𝟐

𝑫𝒕𝟐− 𝑫𝟐𝑫𝒕𝟐



Creating Subset Composites• Metrics represent system evolution

– System structure– Near-system environment

• Metrics define a phase space

Methodology



Vortex Tracker• 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



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



Idealized ExampleMethodology



Merging CirculationsNon-developing SystemCape Verde TCs ????

Track ExamplesMethodology

850 hPa Vortex Idealization



Phase Space

2010 Atlantic Hurricane Season

Pre-genesis and Non-developing

Results



Future Data Sources

• Reanalyses– ERA-Interim, NCEP/NCAR, MERRA

• Operational– GFS, ECMWF, CMC

• Observational– CIMSS satellite winds, dropsondes, satellites

Future Work



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



END

Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis

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