27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems1 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 and NASA HSRP #NNX12AK63G

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems2 Motivation – Gabrielle (2013)

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems3 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

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems4 Previous Studies McBride and Zehr (1981) on developing systems –More pronounced upper-level warm anomaly –Stronger large-scale low-level vorticity –Lower vertical wind shear –Stronger upper-level divergence Lee (1989) on developing systems –Slightly lower environmental MSLP –Larger mid-level cyclonic circulations –Stronger low-level convergence –Moistening at mid-levels important –Environmental favorability dominant until just prior to genesis –Internal dynamics become dominant during final spin up

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems5 Methodology General approaches to studying genesis –Case Studies: Detailed analyses, may not be representative –Composite Studies Representative features, loss of detail Solution: Hybrid approach –Composite subsets with similar structure and environments

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems6 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

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems7 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)

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems8 Vortex Tracker - Variables NCEP vortex trackerPre-genesis vortex tracker VariableLevelsVariableLevels Vorticity850, 700 hPaTangential Velocity850 hPa PressureSurfaceMSLP gradientSurface Pressure gradientSurfaceVortex Idealization850, 700, 500 hPa Geo. height850, 700 hPa Wind850, 700 hPa

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems9 Idealized Example

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems10 Merging CirculationsNon-developing SystemCape Verde TCs???? Track Examples 850 hPa Vortex Idealization

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems11 Mixed Organizational Environmental Mixed Organizational Pre-genesis Phase Space

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems12 Phase Space: Organization Metrics 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

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems13 Phase Space: Near-system Environment Metrics

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems14 Phase Space: Mixed Metrics Δθ e between 850 hPa and tropopause –Potential stability → near-system environment –Bulk diabatic heating → convective activity Thermal vorticity ( hPa) –Warm core cyclone –Upper-level anticyclone synoptic scale feature or system-scale feature

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems15 Phase Space 2010 Atlantic Hurricane Season Pre-genesis and Non-developing

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems16 Future Data Sources Reanalyses –ERA-Interim, NCEP/NCAR, MERRA Operational –GFS, ECMWF, CMC Observational –CIMSS satellite winds, dropsondes, satellites

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems17 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

27 Sept Future WorkResultsMethodologyMotivation Chip HelmsComposite Analyses of Tropical Convective Systems18 END