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A special category of extratropical cyclones: Diabatic Rossby Waves Aspects of their dynamics,

A special category of extratropical cyclones: Diabatic Rossby Waves Aspects of their dynamics, predictability and climatology. Outline. The concept of DRWs PV generation and destruction associated with DRWs DRW case studies Dec 2005 (N Atlantic) Nov 2007 (N Pacific)

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A special category of extratropical cyclones: Diabatic Rossby Waves Aspects of their dynamics,

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  1. A special category of extratropical cyclones: Diabatic Rossby Waves Aspects of their dynamics, predictability and climatology

  2. Outline • The concept of DRWs • PV generation and destruction associated with DRWs • DRW case studies • Dec 2005 (N Atlantic) • Nov 2007 (N Pacific) • Sep 2008 (N Pacific - a summer T-PARC case)

  3. “Classical picture”: top-down cyclogenesis Precursor or initial disturbance: upper-level trough upper-level trough (cf. positive PV anomaly at tropopause level) surface baroclinic zone Hoskins et al. 1985

  4. Synoptic situation at 00 UTC 26 Dec 1999 500-hPa chart: very intense, undisturbed jet stream ... ... at location of small-scale surface Low („Lothar“) Wernli et al. 2002

  5. The „Lothar“ storm: an example for bottom-up development? 2-pvu tropopause low-tropospheric pos. PV anomaly Europe

  6. z x Diabatic Rossby Waves The mechanism Schematic vertical cross-section along baroclinic zone: Low-level positive PV-anomaly over baroclinic zone Snyder and Lindzen 1991 (JAS) Parker and Thorpe 1995 (JAS)

  7. z X x Diabatic Rossby Waves The mechanism Schematic vertical cross-section along baroclinic zone: Low-level positive PV-anomaly over baroclinic zone Poleward ascending jet of warm & moist air Snyder and Lindzen 1991 (JAS) Parker and Thorpe 1995 (JAS)

  8. z x Diabatic Rossby Waves The mechanism Schematic vertical cross-section along baroclinic zone: H>0 D(PV)/Dt > 0 Low-level positive PV-anomaly over baroclinic zone Poleward ascending jet of warm air Diabatic heating  PV productiondownstream of PV vortex

  9. PV generation and destruction Calculate forward and backward trajectories from DRW (PV>1pvu) and look at diabatic PV rate neg. PV tendencies DRW PV>1pvu NE SW pos. PV tendencies

  10. PV generation and destruction Look backward: air parcels experience (mainly) PV generation -9h -6h -3h

  11. PV generation and destruction Look forward: air parcels experience (mainly) PV destruction +3h +6h +9h

  12. DRW case study Dec 2005 (N Atlantic) 18 Dec 2005 18 UTC GOES IR satellite image jet ECMWF analysis: PV mean 975-800hPa (colors) SLP contours Boettcher and Wernli 2011

  13. DRW case study Dec 2005 (N Atlantic) 19 Dec 2005 12 UTC GOES IR satellite image ECMWF analysis: PV mean 975-800hPa (colors) SLP contours

  14. DRW case study Dec 2005 (N Atlantic) 20 Dec 2005 12 UTC GOES IR satellite image deepening of 34hPa/24h ! ECMWF analysis: PV mean 975-800hPa (colors) SLP contours

  15. DRW case study Dec 2005 (N Atlantic) Analysis of operational ECMWF forecasts Consider 4 consecutive deterministic ECMWF forecasts starting at 00 & 12 UTC on 17 & 18 Dec 2005 (i.e. 0-36 hrs prior to DRW genesis) Question: How well is this DRW evolution predicted by ECMWF forecasts?

  16. fc17_00 18_18 fc17_12 2 pvu at 250 hPa fc18_12 fc18_00

  17. 20_00

  18. 20_12

  19. 20_18

  20. 21_00 1002 hPa 979 hPa 998 hPa 965 hPa

  21. DRW case study Nov 2007 (N Pacific) 26 Nov 18 UTC colors: PV vert. averaged 975-800 hPa SLP 30N PV production along intense baroclinic zone 20N Typhoon Mitag is moving towards Taiwan 10N Diploma thesis Christiane Hofmann

  22. DRW case study Nov 2007 (N Pacific) 27 Nov 06 UTC 30N DRW genesis 20N Typhoon Mitag is quasi-stationary

  23. DRW case study Nov 2007 (N Pacific) 28 Nov 00 UTC 30N DRW starts to propagate 20N Typhoon Mitag decays

  24. colors: PV on 850hPa SLP 2 pvu on 250hPa DRW case study Nov 2007 (N Pacific) 28 Nov 00 UTC 60N 40N first clear signal of DRW 20N

  25. DRW case study Nov 2007 (N Pacific) 29 Nov 12 UTC 60N 40N maximum intensity of DRW 20N

  26. colors: PV on 850hPa SLP 2 pvu on 250hPa DRW case study Nov 2007 (N Pacific) 01 Dec 00 UTC 60N 40N rapid propagation of DRW ~ 2000 km/day 20N

  27. DRW case study Nov 2007 (N Pacific) 02 Dec 00 UTC 60N 40N DRW crosses upper-level jet axis ~6000km downstream of its genesis region 20N

  28. DRW case study Nov 2007 (N Pacific) 02 Dec 12 UTC 60N 40N rapid intensification SLP decrease of 25 hPa/12 hrs 20N

  29. DRW case study Nov 2007 (N Pacific) 03 Dec 12 UTC 60N large-scale cyclone moves towards N American west coast 40N 20N

  30. DRW case study Nov 2007 (N Pacific) • “The great coastal gale of 2007” (Wikipedia) • hurricane-force wind gusts of up to 220 km/h at Holy Cross (WA) • and 208 km/h at Bay City (OR) • heavy rains, widespread record flooding • at least 18 deaths; damages: 1.18 billion US$ Satellite rainfall estimate > 150 mm in Washington 03 Dec 18 UTC

  31. DRW case study Sep 2008 (N Pacific) - an ET case of summer T-PARC 29 Sep 00 UTC 30N Typhoon Jangmi is north of Taiwan 20N

  32. DRW case study Sep 2008 (N Pacific) - an ET case of summer T-PARC 30 Sep 06 UTC PV production along intense baroclinic zone 30N Typhoon Jangmi undergoes ET 20N

  33. DRW case study Sep 2008 (N Pacific) - an ET case of summer T-PARC 01 Oct 00 UTC 30N DRW starts to propagate Typhoon Jangmi has become extratropical 20N

  34. DRW climatology 2001-2010 North Atlantic North Pacific Boettcher and Wernli 2013

  35. DRW climatology 2001-2010 Track density and genesis points (white: winter, black: summer) North Atlantic North Pacific

  36. DRW climatology 2001-2010 Genesis scenarios

  37. Summary • DRWs: fascinating and complex interaction of moist and dry dynamics! • DRWs are relatively rare; only few of them undergo explosive development • DRW mechanism involves PV generation & destruction • Initial amplitude and downstream baroclinicity are essential for their downstream propagation • In some cases very poor predictability of DRWs • Potential mechanism for DRW genesis • involves (ET of) Tropical cyclone south • of intense baroclinic environment

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