Synoptic-Climatology of Episodic, Sub-seasonal Retractions of the Pacific Jet Sharon Jaffe, Jonathan E. Martin, and Daniel J. Vimont A synoptic and climatological perspective on these jet transitions Episodic meaning they occur sporadically Sub-seasonal meaning a time period of less than a season (also intra-seasonal) Retraction meaning the core of the jet “moves” westward, or breaks down on its eastern side. Outline: I: Background (Jet Stream Climatology & Storm Track) II: Background (Teleconnections & PNA Pattern) III: Motivation (Otkin & Martin 2004, Kevin Kodama) IV: Case Study (Winter 2005-6) V: Composite Analysis of Jet Transition VI: What’s next? 300-hPa Zonal Wind [ms-1], 1/30/2006 20 30 40 50 60 70 80

The zonal extent of the jet exerts significant influence on Hawaiian weather Large-scale circulation — (Chu et al., 1993) Wet winter in Hawaii (1981-2) many kona storms negative PNA/retracted jet Dry winter in Hawaii (1980-1) no kona storms positive PNA/extended jet Chu et al., 1993

Pacific Jet & Kona Storm Activity (Otkin & Martin, 2004) Pacific jet/PNA pattern act as a large-scale control on the transient synoptic disturbances in the central subtropical Pacific. Active periods are 2+ cyclones within 10 days Inactive Periods Active Periods Composite 300-hPa zonal wind Inactive subtropical cyclogenesis periods Composite 300-hPa zonal wind Active subtropical cyclogenesis periods Climatological mean jet stream is strongest in winter This is a MEAN jet (no messiness, no subtropical or polar parts) Discuss longitudinal position & seasonal cycle

What happened during Winter 2005-6 in Hawaii? December/January 2005-6 Record-breaking dryness 100 mm less rain than normal at Lihue (Kauai) 1100 mm less rain than normal at Mt Waialeale (Kevin Kodama, Senior Hydrologist, NWS Honolulu, personal correspondence) http://i.pbase.com/u18/linzwhang/large/8362672.1020221_IMG.jpg

What happened during Winter 2005-6 in Hawaii? December/January 2005-6 Record-breaking dryness 100 mm less rain than normal at Lihue (Kauai) 1100 mm less rain than normal at Mt Waialeale Normal-Extended Pacific jet (Kevin Kodama, Senior Hydrologist, NWS Honolulu, personal correspondence) 300-hPa Zonal Wind December-January 2005-2006 http://i.pbase.com/u18/linzwhang/large/8362672.1020221_IMG.jpg 300-hPa Zonal Wind 25 December 2005 40 50 60 70

What happened during Winter 2005-6 in Hawaii? February/March 2006 Unprecedented extended wet period 22 days of flash flood warnings Unusual Hawaiian tornado (Kevin Kodama, Senior Hydrologist, NWS Honolulu, personal correspondence) http://www.holidayinsuranceweb.com/Flash_flood_warning_issued_for_Hawaii_17059328.html http://www.carlschaad.com/blog/tornado/

What happened during Winter 2005-6 in Hawaii? February/March 2006 Unprecedented extended wet period 22 days of flash flood warnings Unusual Hawaiian tornado Retracted Pacific jet (Kevin Kodama, Senior Hydrologist, NWS Honolulu, personal correspondence) 300-hPa Zonal Wind February-March 2006 http://www.holidayinsuranceweb.com/Flash_flood_warning_issued_for_Hawaii_17059328.html 40 50 60 70 http://www.carlschaad.com/blog/tornado/

Our Goal: Characterize Rapid Jet Retractions Sudden retractions of the Pacific jet—a phenomenon we call a jet retraction event Data: NCEP/NCAR Reanalysis (http://www.cdc.noaa.gov) November-March, 1979-2007 (28 years) Smoothed variables with a 5 day running mean EXTENDED JET RETRACTED JET (4 February 2006) (16 February 2006) But the jet stream/baroclinic wave interaction has feedbacks going both ways: EDDIES LEAD THE JET -Eddies influence the jet position -Jet position feeds back slightly into the position of the eddies -Is it possible to say what started it?? 40 50 60 70

How to define a jet retraction event EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° 10+ day duration EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° 10+ day duration 33 events identified EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° 10+ day duration 33 events identified Objective Criterion Following Reiter (1961) Box-averaged zonal wind speed dips below climatology by at least 10 ms-1 EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° 10+ day duration 33 events identified Objective Criterion Following Reiter (1961) Box-averaged zonal wind speed dips below climatology by at least 10 ms-1 at least 20 ms -1 departure from climatology EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° 10+ day duration 33 events identified Objective Criterion Following Reiter (1961) Box-averaged zonal wind speed dips below climatology by at least 10 ms-1 at least 20 ms -1 departure from climatology 30 events identified EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° 10+ day duration 33 events identified Objective Criterion Following Reiter (1961) Box-averaged zonal wind speed dips below climatology by at least 10 ms-1 at least 20 ms -1 departure from climatology 30 events identified Use the overlap of two methods to be conservative EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

How to define a jet retraction event Subjective Criterion 40 ms-1 isotach of 300 hPa zonal wind displaced west of 180° 10+ day duration 33 events identified Objective Criterion Following Reiter (1961) Box-averaged zonal wind speed dips below climatology by at least 10 ms-1 at least 20 ms -1 departure from climatology 30 events identified Use the overlap of two methods to be conservative 19 events identified EXTENDED JET 4 Feb 2006 RETRACTED JET 16 Feb 2006 40 50 60 70

Composite Time Series of Jet Retraction Composite Box-Average Zonal Wind (departure from Climatology) [ms-1] Retraction Day Day (with respect to Retraction Day)

Pacific Jet Climatology (300-hPa Zonal Wind) November December January February March May April 40 50 60 70

Composite 300-hPa Zonal Wind PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite 500-hPa Geopotential Height Anomaly [m] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite 500-hPa Geopotential Height Anomaly [m] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite 500-hPa Geopotential Height Anomaly [m] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite 500-hPa Geopotential Height Anomaly [m] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite 500-hPa Geopotential Height Anomaly [m] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite 500-hPa Geopotential Height Anomaly [m] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite 500-hPa Geopotential Height Anomaly [m] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite SLP Anomaly [Pa] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite SLP Anomaly [Pa] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite SLP Anomaly [Pa] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite SLP Anomaly [Pa] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite SLP Anomaly [Pa] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite SLP Anomaly [Pa] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite SLP Anomaly [Pa] PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Composite Potential Vorticity Anomaly PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Summary of Composite Analysis Characteristics of Jet Retraction: Geopotential Height & SLP Transition from a dominant negative to dominant positive anomaly in Aleutian Region Stationary or meridionally-oriented structure transitions to wave train-like pattern Possible tropical influence PV Negative PV anomalies from Rocky Mountains and Mongolia merge over the central Pacific Subtropical Positive PV anomaly forms near Hawaii and south of the jet core Zonally elongated PV anomaly becomes more isotropic at jet exit Rex Block structure forms simultaneously to the retraction of the jet

Future Work What underlies Jet Retraction Events? Mean Flow vs. Eddy Activity Piecewise Tendency Diagnostic (Nielsen-Gammon & Lefevre, 1996) PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Future Work What underlies Jet Retraction Events? Mean Flow vs. Eddy Activity Piecewise Tendency Diagnostic (Nielsen-Gammon & Lefevre, 1996) Precursors and Downstream Consequences of Jet Retraction Events Downstream Development and Kona Storm Genesis (Moore et al., 2008) Examine PV & Local Energetics (Orlanski & Sheldon, 1993) PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Future Work What underlies Jet Retraction Events? Mean Flow vs. Eddy Activity Piecewise Tendency Diagnostic (Nielsen-Gammon & Lefevre, 1996) Precursors and Downstream Consequences of Jet Retraction Events Downstream Development and Kona Storm Genesis (Moore et al., 2008) Examine PV & Local Energetics (Orlanski & Sheldon, 1993) Possible Connections with Tropical Convection Anomalies Madden-Julian Oscillation? PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Future Work What underlies Jet Retraction Events? Mean Flow vs. Eddy Activity Piecewise Tendency Diagnostic (Nielsen-Gammon & Lefevre, 1996) Precursors and Downstream Consequences of Jet Retraction Events Downstream Development and Kona Storm Genesis (Moore et al., 2008) Examine PV & Local Energetics (Orlanski & Sheldon, 1993) Possible Connections with Tropical Convection Anomalies Madden-Julian Oscillation? Other Possible Connections Midwinter Suppression Southeast Asian Winter Monsoon & Cold Air Outbreaks PNA Pattern •Positive –Amplified wave pattern at 500 hPa –High heights over Hawaii & Intermountain region of North America –Enhanced Aleutian Low –Strong, zonally extended Pacific jet –Atmosphere is more barotropically stable: better predictability! •Negative –Zonal wave pattern at 500 hPa –High heights over North Pacific –Weak Aleutian Low -Retracted, weak Pacific jet

Questions?

What about the vertical structure? SLP 500-hPa Tilts westward with height -- Baroclinic Structure 500-hPa SLP

Possible link with Tropical Convection So far OLR gives inconclusive results Polarity and strength of ENSO signal influences extension of Pacific jet and weather in Hawaii — Chu, 1995 Only 55% kona storms follow the “correct” pattern of tropical convection (30 % “incorrect”) — Otkin & Martin, 2004

Link to FLIs link