1. An Unusual Pathway to Oceanic Cyclogenesis Linking “Perfect Storms” in the North Atlantic Ocean Jason M. Cordeira and Lance F. Bosart Department of Earth and Atmospheric Sciences, University at Albany, Albany, NY NROW IX 7-8 November 2007 Supported by: NSF Grant ATM-0304254 Email: cordeira@atmos.albany.edu

2. The “Perfect Storm” of 1991 -Motivation(1/2) 30 30-Oct29-Oct28-Oct27-Oct31-Oct Buoy 44137 Max. Wave Height Canadian moored buoys Nova Scotia Strong winds –67 kt Chatham, MA –55 kt Blue Hill Observatory Coastal flooding / High waves –30 m Southeast of Nova Scotia (see below) –8 m offshore MA Sig. Wave Height Wind Speed

3. The “Perfect Storm” of 1991 -Motivation(2/2) Subsequent to the development of the Perfect Storm (PS1) a second strong cyclone (PS2) formed along the surface warm front in a region of deep moist convection (dmc)… L PS2 moved into the North Atlantic where it interacted with an upper-level potential vorticity (PV) anomaly and merged with an existing cyclone… dmc Tropical moisture MSLP:  50 hPa / 24 hours Hurricane Grace

4. Outline I.Brief large-scale overview II.PS1: MSLP/PV Continuity III.PS1: Intensification IV.PS2: MSLP Continuity V.PS2: Development and PV Continuity VI.PS2: Analysis of rapid deepening phase VII.Summarizing Analysis and Conclusions VIII.Future Work and Thoughts PS1 / Perfect Storm 1 PS2 / Perfect Storm 2 HG / Hurricane Grace PV / Potential Vorticity DT / Dynamic Tropopause (2.0 PVU) MSLP / Mean Sea Level Pressure All plots: 1.125  ECMWF-ERA40

5. The “Perfect Storms” of Research PS3 PS2 PS1 HG Unique Track Heavy Snow Role of HG Unique Track Tropical Transition Development from PS1 Rapid Deepening This presentation will focus on PS2: Development from PS1 and rapid deepening

6. Brief large-scale flow evolution 15  25 Oct25  04 Oct/Nov 500-hPa Geopotential height and anomaly (dam) PSs -Large-scale flow reconfiguration manifested by time-mean 500-hPa flow and the PNA index -Meridional amplification of the NA flow pattern

7. PS1 -MSLP Continuity PS1 Hurricane Grace 29 Oct 00Z 30 Oct 00Z 26/00 27/00 28/00 29/00 30/00 31/00 01/00 02/00 500-hPa Backward Trajectory MSLP  36h  72h Ending 30 Oct 12Z  36h

8. PS1 -PV Anomaly Continuity 29/00Z 29/12Z 30/00Z A C’ B PV1 Merger of C’ and D Fracture of B  C,D Fracture of C  C’,E 21 22 23 24 25 26 27 28 29 31 01 21 22 23 24 25 26 27 02 26 C D 30 26 27 28 29 PVHG Merger of PVHG and PV1 E DT  (K), 850-925  (  10 -4 s -1 )

9. PS1 -Intensification(1/3) 29 October: 00Z 12Z 850 hPa  (K), Wind Barb (kt), 2-D Frontogenesis (K km -1 3h -1 ) Frontogenesis Scale: Hurricane GracePS1

10. PS1 -Intensification(2/3) 30 October: 00Z 12Z 850 hPa  (K), Wind Barb (kt), 2-d Frontogenesis (K km -1 3h -1 ) Frontogenesis Scale: PS1

11. PS1 -Intensification(3/3) 850 hPa Height (dam),  (  10 -5 s -1 ), Wind barb (kt) 29/00Z29/12Z30/00Z Hurricane GracePS1

12. The “Perfect Storms” of 1991 -MSLP Continuity PS1 PS2 Hurricane Grace 29/00 30/00 31/00 01/00 26/00 27/00 28/00 29/00 31/00 01/00 02/00 Backward Trajectory 01/00Z 999 hPa 949 hPa 31/1130  36h  72h

13. PS2 - Development A. 1.Intense warm frontogenesis 2.Southerly moisture transport B. 3.Strong low-level vorticity generation. 4.Strong deformation zone Northeast Next: look at the role of deep moist convection in strengthening the low-level cyclonic vorticity maximum.

14. PS2 - Development (deep moist convection) 850 hPa Winds A A’ PV1 A A’ GIBBS VIS 29/12Z Take N  S cross section across surface warm front

15. Frontogenesis [K km -1 3h -1 ], θ [K], ω [μb s -1 ],  [  10 -5 s -1 ] AA’ 925 hPa θ e 340K PS2 - Development (deep moist convection) 29/12Z Warm / Moist Cold / Dry Ascending tropical air originating from H. Grace. Deep moist convection along surface warm front  latent heat release Diabatic heating  PV redistribution and low-level vorticity generation

16.  e [K], θ [K], ω [μb s -1 ],  [  10 -5 s -1 ] AA’ PS2 - Development (deep moist convection) 29/12Z Warm / Moist Cold / Dry Ascending tropical air originating from H. Grace. Deep moist convection along surface warm front  latent heat release Diabatic heating  PV redistribution and low-level vorticity generation

17. PS2 - Development (low-level vorticity generation) Diabatic heating: 1.generates a low-level positive PV anomaly 2.erodes upper tropospheric PV Low-level PV anomaly: 1.+  anomaly 2.+  anomaly Upper-level PV anomaly: 1.  anomaly 2.  anomaly Adapted: Martin 2006

18. A C’ B PV1 Merger of C’ and D Fracture of B  C,D 21 22 23 24 25 26 27 28 29 31 01 21 22 23 24 25 26 27 02 26 C D 27 29 PVHG Merger of PVHG and PV1 28 30 Perfect Storm 2 - PV Anomaly Continuity PV Anomaly E:  Fracture from C  Modest cyclogenesis to the west of GB (980 hPa) PV Anomaly F:  Arctic origin  Into North Atlantic behind “E”. How did PS2 respond to “F”? Recall:  PS2 formed as a low- level diabatically generated/enhanced vortex. F E PV2 Merger of E and F Fracture of C  C’,E 28 29 30 31 30 29 28 27 26 Fracture of F 24 25

19. PS2 - Rapid deepening MSLP PV (PVU),  (  10 -5 s -1 ),  (K) 29/12Z 10/2910/3010/3111/0111/02 DT  (K), 850-925  (  10 -5 s -1 ) F F NS

20. PS2 - Rapid deepening MSLP 10/2910/3010/3111/0111/02 PV (PVU),  (  10 -5 s -1 ),  (K) DT  (K), 850-925  (  10 -5 s -1 ) F F 29/18Z NS

21. PS2 - Rapid deepening MSLP 10/2910/3010/3111/0111/02 PV (PVU),  (  10 -5 s -1 ),  (K) DT  (K), 850-925  (  10 -5 s -1 ) F F E 30/00Z NS

22. PS2 - Rapid deepening MSLP 10/2910/3010/3111/0111/02 PV (PVU),  (  10 -5 s -1 ),  (K) DT  (K), 850-925  (  10 -5 s -1 ) F F E 30/06Z NWSE

23. PS2 - Rapid deepening MSLP 10/2910/3010/3111/0111/02 PV (PVU),  (  10 -5 s -1 ),  (K) DT  (K), 850-925  (  10 -5 s -1 ) F F E 30/12Z WE

24. PS2 - Rapid deepening MSLP 10/2910/3010/3111/0111/02 PV (PVU),  (  10 -5 s -1 ),  (K) DT  (K), 850-925  (  10 -5 s -1 ) F F E 30/18Z NS

25. PS2 - Rapid deepening MSLP 10/2910/3010/3111/0111/02 PV (PVU),  (  10 -5 s -1 ),  (K) DT  (K), 850-925  (  10 -5 s -1 ) F F E 31/00Z NWSE

26. Summary / Conclusions PS1 formed in confluent air streams representing midlatitude and tropical (HG) source regions. –Trajectory analysis and PV continuity 500-hPa Backward Trajectory Ending 30 Oct 12Z  36h  72h  36h

27. Deep moist convection along the surface warm front produced intense diabatic heating –PV redistribution and low-level PV generation –Strong low-level vorticity maximum - PS2 Summary / Conclusions 850 Z (dam),  (  10 -5 s -1 ) dmc Tropical moisture PS1 Schematic L PV1

28. . Strong tropospheric deformation steered PS1 westward and PS2 eastward into North Atlantic. Summary / Conclusions PS1PS2 850 hPa Z (dam),  (  10 -5 s -1 ), Wind barb (kt)DT  (K) and Wind (kt), 850-925  (  10 -4 s -1 ) PV1 F

29. . PS2 phases with upper-level PV anomaly F of Arctic origin –MSLP decreases 50 hPa / 24 hours Summary / Conclusions 30/12Z PV, ,  MSLP 10/29 10/3010/31 11/01 11/02 DT , L.L.  F F E

30. cordeira@atmos.albany.edu Thoughts…. What happens without Hurricane Grace? –Limited tropical moisture and low-level vorticity –How much deep moist convection results? –What is the resulting strength of PS1? –What is the resulting strength of PS2? Comments? Questions?