1. The “Perfect Storms” of 1991:
Large Scale Antecedent Conditions
Lance F. Bosart and Jason M. Cordeira
Dept. of Earth and Atmospheric Sciences
University at Albany/SUNY
14th Cyclone Workshop
2126 September, 2008
Sainte-Adèle, Quebec ||
NSF Support #ATM and #ATM

2. The “Perfect Storm” (PS)
Introduction (1 of 2)
18Z/29
The “Perfect Storm” (PS)
28 October  2 November 1991
Merger of Hurricane Grace with extratropical cyclone (EC)
Warm seclusion and tropical transition into the “Unnamed Hurricane” (1991)
12 Deaths
Hurricane Force Winds
30-meter waves
$200+ Million Damage (1991)
12Z/30
(next presentation)
19Z/1

3. EC1 EC2 PS Hurricane Grace Introduction (2 of 2)
31/00
EC1
01/00
03/00
04/00
30/00
EC2
02/00
29/00
31/00
01/00
02/00 PS
30/00
01/00
29/00
Hurricane Grace
28/00
27/00
26/00
6h SLP Tracks and 500-hPa mean height 25 Oct.4 Nov. 1991
Highly active 10-day period featuring two additional and exceptional ECs

4. EC1 Atlantic Bomb 50 hPa / 24 h SLP
Introduction (2 of 2)
31/00
EC1 Atlantic Bomb 50 hPa / 24 h SLP
01/00
03/00
04/00
30/00
EC2 “Halloween Blizzard” 1-meter Snowstorm 57 cm Icestorm
02/00
29/00
31/00
01/00
02/00 PS
30/00
01/00
29/00
Hurricane Grace
28/00
27/00
26/00
6h SLP Tracks and 500-hPa mean height 25 Oct.4 Nov. 1991
Highly active 10-day period featuring two additional and exceptional ECs

5. Previous Research - Classification of the large-scale flow
With respect to the “Perfect Storm”:
Cameron and Parkes (1992)
Low-amplitude
500-hPa pattern and strong zonal flow
High-amplitude
500-hPa pattern and strong meridional flow
Nielsen-Gammon (2001)
Meridional flow evolution on the dynamic tropopause (DT) resulted from a combination of downstream development, cyclogenesis, and diabatic heating.

6. Data Sources Outline Reanalysis Datasets Teleconnection Indices
1.125 ECMWF-ERA40
2.5 NCEP-NCAR (anomaly calculation purposes)
Teleconnection Indices
Pacific North American (PNA): Calculated from NCEP-NCAR Reanalysis (courtesy Heather Archambault)
Arctic Oscillation (AO): Daily values downloaded from Climate Prediction Center (CPC)
Cloud cover / Ocean data
0.5 CLoud Archive Users Service (CLAUS) brightness temperature
Tropical Atmosphere Ocean (TAO) project buoy data archive
Outline
Part I: Hemispheric overview
Part II: North Pacific synoptic and intraseasonal variability
Part III: Hemispheric impact

7. Part I: Hemispheric Overview [streamfunction]
11-day 300-hPa Streamfunction and Anomaly (106 m2 s1)
(a) 1020 Oct
(b) 1525 Oct
Initial quasi-zonal flow pattern featuring maritime flat ridges and North America/Central Pacific troughs

8. Part I: Hemispheric Overview [streamfunction]
11-day 300-hPa Streamfunction and Anomaly (106 m2 s1)
(c) 2030 Oct
(d) 25 Oct4 Nov
High-latitude ridge merger over Alaska and subsequent downstream development

9. Alaskan ridge amplification
Part I: Hemispheric Overview [teleconnections]
Alaskan ridge amplification AO
PSECs
PNA
Highest EC “activity”
PNA (Octobers 19482007): Largest ( to ) transition and Lowest index value
AO (Octobers 19482007): 4th largest ( to ) transition and 6th lowest index value

10. Alaskan ridge amplification
Part I: Hemispheric Overview [teleconnections]
Given the three leading EOFs associated with PNA variability:
Alaskan ridge amplification
Stationary eddy (vorticity) advection
Tropical convection
Transient eddy (vorticity) advection
Franzke and Feldstein (2005) ?
Goal of Part II:
Identify key North Pacific events on synoptic and intraseasonal timescales influencing the PNA variability from 1123 October 1991
Highest EC “activity” AO
PNA

11. 515 October Orchid 12Z/10 Pat 12Z/10
Part II: North Pacific Overview - Typhoons Orchid and Pat
515 October
925-hPa  12Z/15
Orchid 12Z/10
Pat 12Z/10 TD TS
: every 2.5105 from 2.5105 s1 TY
Time Minimum Brightness Temperature (K) EC
CLAUS

12. Part II: North Pacific Overview - Typhoons Orchid and Pat
DT Analyses 1517 October
Orchid and Pat merge ( ) and “cross” the DT Jet axis ( )
0000 UTC 15 October
0000 UTC 17 October
DT , 30 mm PWAT, 925850-hPa 
Tropical Convection  Transient Eddy Advection

13. OA OA Part II: North Pacific Overview - Typhoons Orchid and Pat
DT Analyses 1517 October
Orchid and Pat merge ( ) and “cross” the DT Jet axis ( )
Diabatically-influenced outflow anticyclone (OA)
Anticyclonic wave breaking
Establishes North Pacific “wave guide”
0000 UTC 15 October OA
0000 UTC 17 October OA
DT , 30 mm PWAT, 925850-hPa 
Tropical Convection  Transient Eddy Advection

14. Part II: North Pacific Overview - EC Influences
DT Analyses 1820 October
East Asian cyclone ( ) influences high-latitude DT ridge response.
Low  / high PV air extraction into central Pacific.
0000 UTC 18 October 1.
Transient Eddy Advection
0000 UTC 20 October 2.
DT , 30 mm PWAT, 925850-hPa 

15. Part II: North Pacific Overview - EC Influences
DT Analyses 1820 October
East Asian cyclone ( ) influences high-latitude DT ridge response.
Low  / High PV air extraction into central Pacific.
0000 UTC 21 October 3. 4.
Transient Eddy Advection
DT Analyses 2123 October
High-latitude ridge merger.
Arctic intrusion of ~high  Air.
Central Pacific cyclone ( ) remains stationary.
Persistent poleward advection of high  / low PV / high PWAT air.
0000 UTC 23 October 3. 4.
DT , 30 mm PWAT, 925850-hPa 
Transient Eddy  Stationary Eddy

16. Part II: North Pacific Overview - Tropical influences
1 October - 15 November
Active convection 1522 October in association with a convectively active MJO
Brightness Temperature and 300-hPa Divergence
[5N5S]
MJO
~6 m s1 K
CLAUS
Tropical Convection

17. Part II: North Pacific Overview - Tropical influences
1 October - 15 November
Active convection 1522 October in association with a convectively active MJO
Subsequent initiation of Oceanic Kelvin Wave (OKW) as illustrated by coupled atmospheric convection
Brightness Temperature and 300-hPa Divergence
[5N5S]
OKW
~2 m s1 K
Source: CLAUS
Tropical Convection

18. Part II: North Pacific Overview - Tropical influences
Was there a preconditioning of the midlatitude flow pattern by convection associated with the coupled atmospheric-ocean Kelvin wave?
Composite OLR and 300-hPa geopotential height/wind anomaly
1. Composited for similar OKWs crossing 180 longitude
2. 9-day average (synoptic filter)
100
120
140
160
180
160
140
120
100 X
5 m s1 N 60 40 X 20
Lag: 24 days // ~28 October N
300-hPa Z’ contour: 10m
20
40
60
Courtesy: Paul Roundy
N=7 [with 1991]
W m2

19. Part III: Northern Hemisphere Impact [PV’ Tracks]
Key:
Flow amplification influenced the tracks of “significant” PV anomalies
Subsequent interactions between polar/arctic PV anomalies and low-latitude (tropical) moisture
(a) Tracks of significant DT PV anomalies with PS and EC1
Arctic Circle
160 B
1: Merger of E and F A 22 F
Fracture of F
1: (EC1) 30
180 22 A 25 31 B F E 1 23 26 70 A F 23 27 F F 24 28 F 60 B 29
160 A
Fracture of C  C’,E 29 30 F 50 24 C 28 E B 25 27 C’ 40 25 A C 28 26 D D B P
P: (PS) 26 D 27
Merger of C’ and D 29
40 26 02
P: Merger of D and G
140 P 30
Fracture of B  C,D P 31 P G 01 29
Summary:
B -> C + D
C -> C’ + E
D + C’ -> D
D + G -> P
E + F -> 1 28 27
G: (HG)
120 mm
100
80
60
23 Oct 4 Nov time-maximum precipitable water

20. P: PV’ associated with PS G: PV’ associated with HG
Part III: Northern Hemisphere Impact [PV’ Tracks]
Key:
Flow amplification influenced the tracks of “significant” PV anomalies
Subsequent interactions between polar/arctic PV anomalies and low-latitude (tropical) moisture
(a) Tracks of significant DT PV anomalies with PS
P: PV’ associated with PS 28
Arctic Circle
160 D B A P 29 22 F
P: Merger of D and G
Fracture of F
180 22 A 25 B F 23 02 30
PS zoom 26 70 A F 23 P 27 24 60 31 B
160 P A G 50 P 24 01 B G 29 25 40 28
G: PV’ associated with HG A C 25 26 G B 27 26 D 27 26 G mm
140
23 Oct 4 Nov time-maximum precipitable water

21. Part III: Northern Hemisphere Impact [PV’ Tracks]
Key:
Flow amplification influenced the tracks of “significant” PV anomalies
Subsequent interactions between polar/arctic PV anomalies and low-latitude (tropical) moisture
(b) Tracks of significant DT PV anomalies for EC2
Arctic Circle H
160 25 H 26 I 70 H 30
20 27 H 60 28 I
160 50 H 40 31 29 04 30 I I H
40 01 03
140 I 30 02 02 H H 31 H 01
120 mm
100
80
60
23 Oct 4 Nov time-maximum precipitable water

22. Part III: Northern Hemisphere Impact [APE]
1991 NH Available Potential Energy
10/111/15
APE [106 J m2]
Climatology
Daily APE
Acknowledgement: Eyad Atallah
Climatology (19542004 / 9-day smoothed)

23. Part III: Northern Hemisphere Impact [APE]
Climatology
Climatology
NH Available Potential Energy
Daily APE AO
min
APE [106 J m2]
PNA max
Typhoon ET
E. Asian cyclone
C. Pac. cyclone
EC1
EC2
Alaska Ridge Event PNA min / AO max PS
Acknowledgement: Eyad Atallah
Climatology (19542004 / 9-day smoothed)
APE variability consistent with NH evolution of regional synoptic patterns identified by Wintels and Gyakum (2000)

24. Summary: Part I (Hemispheric Overview)
The “Perfect Storm” occurred during a highly active 10-day period that featured strong extratropical cyclogenesis
The active period was characterized by a climatological significant regime transition featuring noteworthy flow amplification and downstream development
originated over the western and central Pacific

25. Flow amplification was (likely) governed by
Summary: Part II (North Pacific Overview)
Flow amplification was (likely) governed by
“Wave guide” establishment courtesy Typhoons Orchid/Pat
High-latitude ridge amplification and downstream development
Tropical convection associated with the MJO and subsequent OKW

26. Summary: Part III (Northern Hemisphere Impact)
Flow amplification influenced the cross-latitudinal exchange of  / PV / PWAT critical to extratropical cyclogenesis
e.g. merging of polar/arctic and tropical/subtropical disturbances
The “Perfect Storm” period was characterized by the largest APE deficit of 1991