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Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis

Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis. Chip Helms Tropical Lunch 26 April 2013. Motivatio n. Cyclone Tracy (1974). Genesis: 12/21. Landfall: 12/24 110 kts ( Saffir -Simpson Cat. 3). Image courtesy Wikipedia. Motivatio n.

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Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis

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  1. Composite Analyses of Tropical Convective Systems Prior to Tropical Cyclogenesis Chip Helms Tropical Lunch 26 April 2013

  2. Motivation Cyclone Tracy (1974) Genesis: 12/21 Landfall: 12/24 110 kts (Saffir-Simpson Cat. 3) Image courtesy Wikipedia

  3. Motivation Methods for Studying TC Genesis • Case Study • Allow for detailed analysis • May not be representative of population • Composite Study • Identify prominent features in set of cases • Lose details in compositing process

  4. Motivation Example: Non-developing system Zonal Cross-sections 8/18/2010 ~14 UTC 8/17/2010 ~13 UTC Pressure [hPa] Pressure [hPa] Longitude [°E] Longitude [°E] Mid-levels will appear weaker in composite

  5. Methodology Solution: Composite on a Subset • Select a subset of cases with similar structure • More homogenous subset provides more detail in composites • Create subsets using phase space • Position in phase space indicates current state of important, yet highly variable structures • Composite all cases located in a given volume of the phase space • Retain more detail (like case studies) • Representative results (like composite studies)

  6. Methodology Data • CFSRv2, HURDAT2+INVESTs • Convenient for testing methodology • CFSR: Uniform in time • INVEST files contain a selection bias as not every disturbance triggers an INVEST • INVEST files only available since 2005 • Use best track as first guess position • Find 500 hPa and 850 hPa center by minimizing difference between tangential and total winds

  7. Methodology Phase Space Work in Progress 500 hPa center position relative to 850 hPa Center N = 5817 All HURDAT Systems 2005-2012 ALL INVESTs

  8. Results INVESTs+Pre-Genesis 2010 N=516, Red=15 16<σ<22 No 80% Contour

  9. Results INVESTs+Pre-Genesis 2010 N=107, Red=6 8<σ<22 80% Contour Was 16<σ<22

  10. Results INVESTs+Pre-Genesis 2010 N=25, Red=6 8<σ<22 Was 16<σ<22

  11. Results INVESTs+Pre-Genesis 2010 N=45, Red=6 6<σ<22 Was 16<σ<22

  12. Results INVESTs+Pre-Genesis 2010 N=16, Red=4 6<σ<18 Was 16<σ<22

  13. Results System Evolution: Sandy (2012) 850 vs 500 hPa Tangential Velocity

  14. Results Unwrapping TCs

  15. Future Work Primary Future Work • Create an algorithm to identify pre-genesis systems without relying on best track • Test and finalize phase space variables • Examine composites • e.g. Devvs Non-dev • System evolution in phase space

  16. Future Work Side Project Future Work • Create real-time phase space diagrams • Generate a climatology of phase space Genesis Productivity (% dev in each volume) • Apply to forecast times to provide a forecast diagnosis of genesis probability • Create real-time unwrapped figures

  17. END

  18. EXTRA SLIDES

  19. Results Year: 2010 N=516, Red=15

  20. Results Year: 2010 N=107, Red=6

  21. Results Year: 2010 N=25, Red=6

  22. Results Year: 2010 N=45, Red=6

  23. Results Year: 2010 N=16, Red=4

  24. Results All HURDAT 2005-2012

  25. Results INVEST/Pre-Genesis Systems Max Freq: 41 ~ 2.5%

  26. Results Tropical Depressions

  27. Results Tropical Storms

  28. Results Hurricanes

  29. Results Post Extra-Tropical Transition

  30. Results Sandy (2012)

  31. Results Sandy (2012): 10/18 – 10/21

  32. Results Sandy (2012): 10/22 – 10/25

  33. Results Sandy (2012): 10/26 – 10/29

  34. Results Sandy (2012): 10/30 – 10/31

  35. REMOVED SLIDES

  36. Prior Work Theory Simpson et al. (1997) and Ritchie and Holland (1997) Concentration term Stratiform Latent Heating Mergers of PV anomalies add PV while averaging thermal properties MCS Stretching term New PV Anomaly Out of balance with thermal structure Warm anomaly growth not detailed by theory, but would be accomplished by forced subsidence or increased LHR + PV Anomaly + Evaporative Cooling Forced Convergence Forced Ascent and Evaporative Cooling Act to cool sub-cloud layer

  37. Pre-Genesis Phase Space 200-850 hPa 500-850 hPa 500 hPa 850 hPa Displacement of 500 hPa center Displacement vs Tilt Direction Displacement vs Shear Stronger Mid Vortex Stronger Low Vortex 500-850 hPa Shear vs 500-850 hPaVorticity Difference Vorticityvs Divergence ~Bulk Lapse Rate vs Upper Level Moisture N = 5817 All HURDAT Systems 2005-2012 500 hPa Vλvs 850 hPaVλ Upper-level T’ vs Spec. Hum.

  38. Motivation Example: Non-developing system

  39. Motivation Genesis: 6/23 Cyclone Tracy (1974) Genesis: 12/21 Image courtesy Clark Evans Landfall: 12/24 110 kts (Saffir-Simpson Cat. 3) Image courtesy Wikipedia

  40. Motivation Issues with Traditional Composites • Mid-level features will appear weaker • High variability in system tilt • Vertically-aligned systems tend to be stronger • Composites will favor upright systems

  41. Methodology Methodology/Data • Locate center at 850 and 500 hPa 1) Maximum Vλ (0.5° search grid) 2) Minimum Difference of Vλand V (0.25°) 3) Minimum Difference of Vλ and V (0.10°) • Datasets: CFSRv2, HURDAT2+INVESTs • Convenient for testing methodology • CFSR: Uniform in time • Complete with all the selection bias caveats of the INVEST files

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