An Unusual Pathway to Oceanic Cyclogenesis Linking “Perfect Storms” in the North Atlantic Ocean

An Unusual Pathway to Oceanic CyclogenesisLinking “Perfect Storms” in the North Atlantic Ocean

Jason M. Cordeira and Lance F. BosartDepartment 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

The “Perfect Storm” of 1991 -Motivation (1/2)

30

30-Oct29-Oct28-Oct27-Oct 31-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 HeightWind Speed

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

Tropicalmoisture

MSLP: 50 hPa / 24 hours

HurricaneGrace

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 1PS2 / Perfect Storm 2HG / Hurricane Grace

PV / Potential VorticityDT / Dynamic Tropopause (2.0 PVU)MSLP / Mean Sea Level Pressure

All plots: 1.125 ECMWF-ERA40

The “Perfect Storms” of Research

PS3PS2

PS1

HG

Unique TrackHeavy Snow

Role of HGUnique TrackTropical Transition

Development from PS1Rapid Deepening

This presentation will focus on PS2: Development from PS1 and rapid deepening

Brief large-scale flow evolution

1525 Oct 2504 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

PS1 -MSLP Continuity

PS1

Hurricane Grace

29 Oct 00Z 30 Oct 00Z

26/00

27/00

28/00

29/00

29/00

30/00

31/00

01/00

02/00500-hPa Backward Trajectory

MSLP MSLP

36h

72h

Ending 30 Oct 12Z36h

PS1 -PV Anomaly Continuity

29/0

0Z29

/12Z

30/0

0Z

A

C’

B

PV1Merger of C’ and D

Fracture of B C,D

Fracture of C C’,E

21

22

23

24

25

2627

28

29

31

01

21

22

23

24

25

26

27

0226

C

D 30

2627

2829

PVHG

Merger of PVHG and PV1

E

DT (K), 850-925 (10-4 s-1)

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 Grace PS1

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

PS1 -Intensification (3/3)

850 hPa Height (dam), ( 10-5 s-1), Wind barb (kt)

29/00Z 29/12Z 30/00Z

Hurricane Grace PS1

The “Perfect Storms” of 1991 -MSLP Continuity

PS1

PS2

Hurricane Grace

29/00

30/00

30/00

31/00

01/00

26/00

27/00

28/00

29/00

31/00

01/00

02/00

Bac

kwar

d T

raje

ctor

y

01/00Z

999 hPa

949 hPa

31/1130

36h72h

72h

PS2 - Development

A.

1. Intense warm frontogenesis

2. Southerly moisture transport

B.

3. Strong low-level vorticity generation.

4. Strong deformation zone

Northeast

Northeast

Next: look at the role of deep moist convection in strengthening the low-level cyclonic vorticity maximum.

PS2 - Development (deep moist convection)

850 hPa Winds

A

A’

PV1

A

A’

GIBBS VIS

29/12ZTake NS cross section across surface warm front

Frontogenesis [K km-1 3h-1], θ [K], ω [μb s-1], [10-5 s-1]

A A’

925 hPa θe

340K

PS2 - Development (deep moist convection) 29/12Z

Warm / MoistCold / 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

e [K], θ [K], ω [μb s-1], [10-5 s-1]

A A’

PS2 - Development (deep moist convection) 29/12Z

Warm / MoistCold / 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

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. + anomaly2. + anomaly

Upper-level PV anomaly: 1. anomaly2. anomaly

Adapted: Martin 2006

A

C’

B

PV1Merger of C’ and D

Fracture of B C,D

21

22

23

24

25

2627

28

29

31

01

21

22

23

24

25

26

27

0226

C

D

2627

29PVHG

Merger of PVHG and PV1

28

30

Perfect Storm 2 - PV Anomaly Continuity

PV Anomaly E:Fracture from CModest cyclogenesis to the west of GB (980 hPa)

PV Anomaly F:Arctic originInto North Atlantic behind “E”.

How did PS2 respond to “F”?

Recall: PS2 formed as a low-level diabatically generated/enhanced vortex.

F

E

PV2Merger of E and F

Fracture of C C’,E

28

29

30

31

3029

2827

26

Fracture of F24

25

PS2 - Rapid deepening MSLP

PV (PVU), (10-5 s-1), (K)

29/12Z

10/29 10/30 10/31 11/01 11/02

DT (K), 850-925 (10-5 s-1)

F

F

N S

PS2 - Rapid deepening MSLP

10/29 10/30 10/31 11/01 11/02

PV (PVU), (10-5 s-1), (K)

DT (K), 850-925 (10-5 s-1)

F F

29/18ZN S

PS2 - Rapid deepening MSLP

10/29 10/30 10/31 11/01 11/02

PV (PVU), (10-5 s-1), (K)

DT (K), 850-925 (10-5 s-1)

FF

E

30/00ZN S

PS2 - Rapid deepening MSLP

10/29 10/30 10/31 11/01 11/02

PV (PVU), (10-5 s-1), (K)

DT (K), 850-925 (10-5 s-1)

FF

E

30/06ZNW SE

PS2 - Rapid deepening MSLP

10/29 10/30 10/31 11/01 11/02

PV (PVU), (10-5 s-1), (K)

DT (K), 850-925 (10-5 s-1)

F F

E

30/12ZW E

PS2 - Rapid deepening MSLP

10/29 10/30 10/31 11/01 11/02

PV (PVU), (10-5 s-1), (K)

DT (K), 850-925 (10-5 s-1)

FFE

30/18ZN S

PS2 - Rapid deepening MSLP

10/29 10/30 10/31 11/01 11/02

PV (PVU), (10-5 s-1), (K)

DT (K), 850-925 (10-5 s-1)

FF

E

31/00ZNW SE

Summary / Conclusions

• PS1 formed in confluent air streams representing midlatitude and tropical (HG) source regions.– Trajectory analysis and PV continuity

500-hPa Backward TrajectoryEnding 30 Oct 12Z

36h

72h

36h

• 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

Tropicalmoisture

PS1 Schematic

L

PV1

.

• Strong tropospheric deformation steered PS1 westward and PS2 eastward into North Atlantic.

Summary / Conclusions

PS1 PS2

850 hPa Z (dam), ( 10-5 s-1), Wind barb (kt) DT (K) and Wind (kt), 850-925 ( 10-4 s-1)

PV1

F

..

• 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 10/30 10/31 11/01 11/02

DT , L.L.

F

F

E

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?