chris davis (ncar) collaborators: lance bosart ron mctaggart-cowan andy heymsfield
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The Tropical Transition of Cyclones: Science Issues and Critical Observations or TC Genesis: A Global Problem. Chris Davis (NCAR) Collaborators: Lance Bosart Ron McTaggart-Cowan Andy Heymsfield Michael Montgomery Jason Dunion. What is Tropical Transition?. - PowerPoint PPT PresentationTRANSCRIPT
The Tropical Transition of Cyclones: Science Issues and Critical Observations
orTC Genesis: A Global Problem
Chris Davis (NCAR)
Collaborators:Lance Bosart
Ron McTaggart-CowanAndy Heymsfield
Michael MontgomeryJason Dunion
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
Strong Baroclinic Precursors
Images courtesy of NRL: http://www.nrlmry.navy.mil/tc_pages/tc_home.html
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
Results – Genesis Locations
Strong TT Weak TT Tr Induced
TropicalWave InducedPerturbed
Development of Maria 2005, Wind on DT, at 950 hPa
00 Z 30 Aug 00 Z 01 Sep
00 Z 02 Sep00 Z 31 Aug
Potential Temperature on PV=1.5 PVURed Contours = 900 hPa Relative Vorticity (1, 2, 4, and 8x10-5 s-1)
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
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
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 (phys probes), aerosol lidar: cloud physics and dust concentration
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
WATTAGE Western Atlantic Tropical Transition and Genesis Experiment
45,000 ft.
30,000 ft.
15,000 ft.
10,000 ft.
2,000 ft.
500 ft.
Stage 1: C-130 cloud physics module
Stage 2: C-130 PBL module0ºC
45,000 ft.
30,000 ft.
15,000 ft.
10,000 ft.
2,000 ft.
500 ft.
Stage 1: C-130 cloud physics module
Stage 2: C-130 PBL module0ºC
L
100-200 km
300-400 km
(a) (c)(b) (d)
NCAR G-IV
NOAA G-IV
NASA DC-8
NCAR C-130
NRL P-3
NOAA P-3
UAVs
P-3/C-130 flight tracks
HIAPER flight tracks
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