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

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

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

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

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.

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

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

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

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

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

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

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

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

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 

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

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

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

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

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

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

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

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)

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)

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

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

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