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Principles of the Dvorak Method

Principles of the Dvorak Method. Andrew Burton, Severe Weather WA. Principles of the Dvorak Method. Overview. Origins. Measurements. Expectations. Pattern matching. Principles of the Dvorak Method. Overview. Origins. Measurements. Expectations. Pattern matching.

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Principles of the Dvorak Method

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  1. Principles of the Dvorak Method Andrew Burton, Severe Weather WA

  2. Principles of the Dvorak Method • Overview • Origins • Measurements • Expectations • Pattern matching APSATS 2002 Melbourne, Australia

  3. Principles of the Dvorak Method • Overview • Origins • Measurements • Expectations • Pattern matching APSATS 2002 Melbourne, Australia

  4. APSATS 2002 Melbourne, Australia

  5. Principles of the Dvorak Method Some Terminology The (only) Boring slide T Numbers for every occasion T = Tropical DT = Data T Number MET = Model Expected T No PT = Pattern T No FT = Final T No APSATS 2002 Melbourne, Australia

  6. Principles of the Dvorak Method Origins Operational use since 1973 Developed with North West Pacific and Atlantic data. Enhanced infrared technique 1978/1984 Ongoing development over 15 years. Probably the single most important tool in tropical cyclone analysis to date. APSATS 2002 Melbourne, Australia

  7. Principles of the Dvorak Method Locating the centre From Dvorak (1985): “The cloud system center is defined as the focal point of all the curved lines or bands of the cloud system. It can also be thought of as the point toward which the curved lines merge or spiral.” Centre not always obvious, especially at night. APSATS 2002 Melbourne, Australia

  8. Principles of the Dvorak Method Locating the centre • Low level centre • Use all available data – passive microwave to the rescue! • Maintain track continuity. • Centre location can influence intensity measurement APSATS 2002 Melbourne, Australia

  9. APSATS 2002 Melbourne, Australia

  10. Principles of the Dvorak Method • Pattern Types • Eye • Curved Band • Shear • Covered Centre APSATS 2002 Melbourne, Australia

  11. Principles of the Dvorak Method Intensity schematic APSATS 2002 Melbourne, Australia

  12. Principles of the Dvorak Method Eye patterns Method: Measure the warmest brightness temperature in the eye and the coldest surrounding temperature in the deep convection. Physical principle: strength of the thermal contrast between the eye and the surrounding convection indicates strength of the system APSATS 2002 Melbourne, Australia

  13. Principles of the Dvorak Method APSATS 2002 Melbourne, Australia

  14. Principles of the Dvorak Method APSATS 2002 Melbourne, Australia

  15. Principles of the Dvorak Method APSATS 2002 Melbourne, Australia

  16. Principles of the Dvorak Method Eye pattern using digital IR • Warmest eye pixel 16 °C • Coldest pixel 30 nmi from center -71 °C • Nomogram gives Eye no. =7 Hurricane Erika 1515 UTC 8 September 1997 APSATS 2002 Melbourne, Australia

  17. Principles of the Dvorak Method APSATS 2002 Melbourne, Australia

  18. APSATS 2002 Melbourne, Australia

  19. Principles of the Dvorak Method Curved bands Method: Measure the curvature of the band Physical principle: the “wrap-aroundness” of the convective bands indicates the vorticity associated with the system. APSATS 2002 Melbourne, Australia

  20. Principles of the Dvorak Method Curved Bands APSATS 2002 Melbourne, Australia

  21. Principles of the Dvorak Method TS Ivan 23/9/98 11:15 UTC APSATS 2002 Melbourne, Australia

  22. Measuring the arc length: Follow the convection, not cirrus blow-off Easier to do with VIS than Enhanced IR. You may have small breaks in convection and draw through Principles of the Dvorak Method Curved Bands APSATS 2002 Melbourne, Australia

  23. Log10 spiral overlay. Spiral should lie along the axis of the of the band, and roughly parallel the inside edge of the band. Measure the arc length. “Tightest inner curvature” “Cloud minimum wedge” Principles of the Dvorak Method Curved Bands LOG10 Spiral APSATS 2002 Melbourne, Australia

  24. Measuring the arc length: Can be very subjective. Inexperienced analysts tend to go too high (fooled by cirrus or outer bands). This storm is somewhere between 0.70 and 0.85. Principles of the Dvorak Method Curved Bands APSATS 2002 Melbourne, Australia

  25. Step 2A, Curved Band Note: Southern Hemisphere Example APSATS 2002 Melbourne, Australia

  26. Step 2A, Curved Band APSATS 2002 Melbourne, Australia

  27. Step 2A, Curved Band APSATS 2002 Melbourne, Australia

  28. Step 2A, Curved Band 0.70 0.80 0.60 0.50 0.40 0.10 0.30 0.20 APSATS 2002 Melbourne, Australia

  29. Step 2A, Curved Band A wrap of 0.80 would equal a Data T of T3.5 0.70 0.80 0.60 0.50 0.40 0.10 0.30 0.20 APSATS 2002 Melbourne, Australia

  30. We could have added an additional 0.05 for this portion of wrap, giving a total wrap of 0.85 0.70 0.80 0.60 0.50 0.40 0.10 0.30 0.20 APSATS 2002 Melbourne, Australia

  31. APSATS 2002 Melbourne, Australia

  32. Principles of the Dvorak Method Shear patterns Method: Measure the distance form the low level centre to the edge of the “dense overcast” Physical principle: greater involvement of the low level centre with the deep convection indicates a stronger system. APSATS 2002 Melbourne, Australia

  33. Principles of the Dvorak Method Shear patterns APSATS 2002 Melbourne, Australia

  34. Principles of the Dvorak Method APSATS 2002 Melbourne, Australia

  35. Principles of the Dvorak Method APSATS 2002 Melbourne, Australia

  36. Principles of the Dvorak Method APSATS 2002 Melbourne, Australia

  37. Principles of the Dvorak Method Shear pattern APSATS 2002 Melbourne, Australia

  38. Principles of the Dvorak Method Shear pattern 70nm = T1.5 APSATS 2002 Melbourne, Australia

  39. APSATS 2002 Melbourne, Australia

  40. Principles of the Dvorak Method Covered Centre Patterns IR=Embedded Centre (EC) VIS=Central Dense Overcast (CDO) APSATS 2002 Melbourne, Australia

  41. Principles of the Dvorak Method Central Dense Overcast Method: Appearance and size of the overcast + degree of banding. Physical principle?: The weakest link? Does size matter? “It is the pattern formed by the clouds of a tropical cyclone that is related to the cyclone’s intensity and not the amount of clouds in the pattern” - Dvorak 1984 Intensity measurement not dependent on centre location APSATS 2002 Melbourne, Australia

  42. Principles of the Dvorak Method A quick diversion on size APSATS 2002 Melbourne, Australia

  43. Principles of the Dvorak Method Central Dense Overcast APSATS 2002 Melbourne, Australia

  44. Principles of the Dvorak Method Embedded Centre Method: Measure coldest surrounding temperature. Physical principle: Greater involvement of low level centre with deep convection indicates a stronger system. APSATS 2002 Melbourne, Australia

  45. Principles of the Dvorak Method Embedded Centre • Restrictions on use. • Sensitive to centre location. • Methodology similar to eye patterns • Best used after disappearance of an eye. APSATS 2002 Melbourne, Australia

  46. Principles of the Dvorak Method Embedded Centre Just plain ugly! APSATS 2002 Melbourne, Australia

  47. Principles of the Dvorak Method Embedded Centre pattern – problematic Dependent on a temperature measurement related to a centre you can’t see. Dvorak temperature enhancement calibrated to North West Pacific. Cyclones occur at higher latitudes in NH. What might that mean for “southerners”? APSATS 2002 Melbourne, Australia

  48. APSATS 2002 Melbourne, Australia

  49. Principles of the Dvorak Method Reality check! TCs Elaine & Vance, March 1999 APSATS 2002 Melbourne, Australia

  50. APSATS 2002 Melbourne, Australia

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