Chris Davis (NCAR) Collaborators: Lance Bosart Ron McTaggart-Cowan Andy Heymsfield

1. The Tropical Transition of Cyclones: Science Issues and Critical ObservationsorTC Genesis: A Global Problem Chris Davis (NCAR) Collaborators: Lance Bosart Ron McTaggart-Cowan Andy Heymsfield Michael Montgomery Jason Dunion

2. What is Tropical Transition? • TC formation induced by disturbances of extratropical origin (cold core) • Strong: • Baroclinic frontal cyclone • Weak: • Cold upper-tropospheric troughs or weak baroclinic waves • Mesoscale Convective Vortices Bracken and Bosart (2000, MWR): Modest shear may assist TC development

3. Strong Baroclinic Precursors Images courtesy of NRL: http://www.nrlmry.navy.mil/tc_pages/tc_home.html

4. Synoptic Climatology of Atlantic TC Genesis • Define storm-centred objective indicators of TT: • Upper level Q-vector convergence • Lower level thermal asymmetry • Datasets (1948-2004) • NCEP/NCAR Reanalysis • NHC Best Track • Compute linear back-trajectories for storm centre locations from T-0h (NHC tracking) to T-36h

5. Results – Genesis Locations Strong TT Weak TT Tr Induced Perturbed Wave Induced Tropical

6. Development of Maria 2005q, Wind on DT, z at 950 hPa 00 Z 30 Aug 00 Z 01 Sep 00 Z 31 Aug 00 Z 02 Sep Potential Temperature on PV=1.5 PVU Red Contours = 900 hPa Relative Vorticity (1, 2, 4, and 8x10-5 s-1)

8. Genesis Mechanisms: Theories in need of Observations • Synoptic-scale: • Disturbances from higher latitudes • Tropical waves • ITCZ and cross-equatorial flow • Mesoscale • MCVs organizing convection • Vortex merger • Mid-tropospheric moistening and downdraft reduction • Convective-scale vortices (VHTs) Observations required on multiple spatial scales

9. Genesis Hypotheses • Governed by the synoptic-scale (global model success) • Merger and/or downward migration of mid-tropospheric mesoscale vortices. • Upscale influence of intense convective-scale vortices. • Lower-mid-tropospheric relative humidity governs downdrafts and surface divergence • Cloud physics critically affects downdrafts – strongly influenced by aerosols (dust) • Prediction more limited by synoptic-scale errors than mesoscale errors. Note: The above are not mutually exclusive, but facilitate defining observing objectives

10. Key Observations • Radar: convection structure, vertical circulations, vortices on multiple scales (vortical hot towers, MCVs) • Aircraft (in situ) and dropsondes: Boundary-layer: water vapor, surface fluxes • Aircraft (in situ) and dropsondes: Mesoscale structure of RH in the lower-middle troposphere. • Long-range, high altitude aircraft: upper-tropospheric sub-synoptic-scale features (wind and temperature, deduce PV) • Aircraft (mphys probes), aerosol lidar: cloud physics and dust concentration

11. Observing Challenges • Multiple altitudes (12 km, 6-8 km; 3-4 km; BL) • Long duration (genesis is an abrupt process with relatively long quiescent periods) • Close coordination with satellites: major questions about next generation US platforms => international effort required • Many precursors, not many cyclones • Genesis often far at sea – aircraft ferry considerations

12. L WATTAGE Western Atlantic Tropical Transition and Genesis Experiment NCAR G-IV NOAA G-IV NASA DC-8 HIAPER flight tracks (a) (c) (b) (d) 300-400 km NCAR C-130 NRL P-3 NOAA P-3 UAVs 100-200 km P-3/C-130 flight tracks

13. Closing Remarks • TC formation has global similarities obscured by regional taxonomy. Need to uncover the similarities. • Observations of TC formation require new paradigm • Long duration, multiple scales, episodic • Synergy of aircraft, satellite and numerical models for deployment