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-0304254 and #ATM-0553017 Bosart@atmos.albany.edu || Cordeira@atmos.albany.edu

2. Introduction (1 of 2) 18Z/29 12Z/30 19Z/1 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) (next presentation)

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

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

6. Data Sources Reanalysis Datasets 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] (a) 10  20 Oct(b) 15  25 Oct 11-day 300-hPa Streamfunction and Anomaly (  10 6 m 2 s  1 ) Initial quasi-zonal flow pattern featuring maritime flat ridges and North America/Central Pacific troughs

8. (c) 20  30 Oct(d) 25 Oct  4 Nov High-latitude ridge merger over Alaska and subsequent downstream development 11-day 300-hPa Streamfunction and Anomaly (  10 6 m 2 s  1 ) Part I: Hemispheric Overview [streamfunction]

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

10. PNA AO Alaskan ridge amplification Highest EC “activity” ? 1.Stationary eddy (vorticity) advection 2.Tropical convection 3.Transient eddy (vorticity) advection Franzke and Feldstein (2005) Given the three leading EOFs associated with PNA variability: Goal of Part II: Identify key North Pacific events on synoptic and intraseasonal timescales influencing the PNA variability from 11  23 October 1991 Part I: Hemispheric Overview [teleconnections]

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

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

13. 0000 UTC 15 October 0000 UTC 17 October DT , 30 mm PWAT, 925  850-hPa  OA 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” Tropical Convection  Transient Eddy Advection Part II: North Pacific Overview - Typhoons Orchid and Pat

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

15. 0000 UTC 21 October DT Analyses 18  20 October 1.East Asian cyclone ( ) influences high-latitude DT ridge response. 2.Low  / High PV air extraction into central Pacific. 0000 UTC 23 October DT Analyses 21  23 October 3.High-latitude ridge merger. Arctic intrusion of ~high  Air. 4.Central Pacific cyclone ( ) remains stationary. Persistent poleward advection of high  / low PV / high PWAT air. DT , 30 mm PWAT, 925  850-hPa  3. 4. Transient Eddy  Stationary Eddy Transient Eddy Advection Part II: North Pacific Overview - EC Influences

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

17. K Source: CLAUS 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 OKW ~2 m s  1 Brightness Temperature and 300-hPa Divergence [5  N  5  S] Tropical Convection Part II: North Pacific Overview - Tropical influences

18. 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) 180160140120100120140160100 Lag: 24 days // ~28 October Courtesy: Paul Roundy 60 0  60 40 20  40  20 W m  2 5 m s  1 300-hPa Z’ contour: 10m N N X N=7 [with 1991] Part II: North Pacific Overview - Tropical influences X

19. C’ P: (PS) Merger of C’ and D Fracture of B  C,D Fracture of C  C’,E 22 23 24 25 26 27 28 29 31 01 22 23 24 25 26 27 28 29 30 31 30 29 28 27 26 25 02 Fracture of F 26 27 29 G: (HG) P: Merger of D and G 30 28 1: Merger of E and F A A A A A B B B B B D C C D D G P P P P E E F F F F F F F 1 1: (EC1)  100  120  140  160  180 160  80  60  40 0 40 50 60 70 (a) Tracks of significant DT PV anomalies with PS and EC1 Key: Flow amplification influenced the tracks of “significant” PV anomalies Subsequent interactions between polar/arctic PV anomalies and low-latitude (tropical) moisture Summary: B -> C + D C -> C’ + E D + C’ -> D D + G -> P E + F -> 1 mm 23 Oct  4 Nov time-maximum precipitable water Arctic Circle Part III: Northern Hemisphere Impact [PV’ Tracks]

20. (a) Tracks of significant DT PV anomalies with PS mm 23 Oct  4 Nov time-maximum precipitable water 22 23 24 25 26 27 22 23 24 25 26 27 26 25 Fracture of F 26 A A A A A B B B B B C D F F F  140  160  180 160 40 50 60 70 Arctic Circle 27 29 28 G G G G P P P P D 29 31 30 01 02 P: PV’ associated with PS P: Merger of D and G 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 PS zoom

21. Key: Flow amplification influenced the tracks of “significant” PV anomalies Subsequent interactions between polar/arctic PV anomalies and low-latitude (tropical) moisture Part III: Northern Hemisphere Impact [PV’ Tracks] 25 26 27 28 29 30 31 01 04 03 02 31 01 30 H H H H H H I I I I 02 H H H  100  120  140  160 160  80  60  40 0 3030 40 50  20 60 70 mm 23 Oct  4 Nov time-maximum precipitable water Arctic Circle (b) Tracks of significant DT PV anomalies for EC2 I

22. Daily APE Climatology 10/1  11/15 APE [10 6 J m 2 ] Climatology (1954  2004 / 9-day smoothed) Part III: Northern Hemisphere Impact [APE] 1991 NH Available Potential Energy Acknowledgement: Eyad Atallah

23. Climatology APE [10 6 J m 2 ] APE variability consistent with NH evolution of regional synoptic patterns identified by Wintels and Gyakum (2000) Part III: Northern Hemisphere Impact [APE] Daily APE Climatology NH Available Potential Energy Climatology (1954  2004 / 9-day smoothed) Acknowledgement: Eyad Atallah Alaska Ridge Event PNA min / AO max PS EC1EC2 Typhoon ET E. Asian cyclone C. Pac. cyclone PNA max AO min

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. 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