STC Climatology (1979–2010)

~3 STCs/yearStrong TT

Weak TT

Trough induced

N = 105

STC Climatology (1979–2010)

N = 34

Strong TT

Weak TT

Trough induced

STC Climatology (1979–2010)

N = 56

Strong TT

Weak TT

Trough induced

STC Climatology (1979–2010)

N = 15

Strong TT

Weak TT

Trough induced

• Identify the most common upper-tropospheric features linked to STC formation in 1979–2010 climatology

• Separate STCs included in 1979–2010 climatology into five clusters representing the most common upper-tropospheric features linked to STC formation: 1) PV Streamer, 2) Cutoff, 3) Midlatitude Trough, 4) Subtropical Disturbance, and 5) Debris

• Perform a cyclone-relative composite analysis of the upper-tropospheric features linked to STC formation within each cluster

Upper-Tropospheric Precursors

Upper-Tropospheric Precursors

Clusters: 1) PV Streamer, 2) Cutoff, 3) Midlatitude Trough, 4) Subtropical Disturbance, and 5) Debris

Upper-Tropospheric Precursors

Clusters: 1) PV Streamer, 2) Cutoff, 3) Midlatitude Trough, 4) Subtropical Disturbance, and 5) Debris

AWB

350Kisentropicsurface

• STC formation is associated with a PV streamer injected into the subtropics by a precursor anticyclonic wave breaking (AWB) event

• PV streamer maintains a clear connection with the midlatitudes

Upper-Tropospheric Precursors

Clusters:

AWB350K

isentropicsurface

• STC formation is associated with a region of relatively high upper-tropospheric PV cut off in the subtropics by a precursor AWB event

• Upper-tropospheric cutoff is entirely removed from midlatitude flow

1) PV Streamer, 2) Cutoff, 3) Midlatitude Trough, 4) Subtropical Disturbance, and 5) Debris

Clusters:

Upper-Tropospheric Precursors

350Kisentropicsurface

• STC formation is associated with a broad midlatitude trough moving progressively toward the southeast

• Broad midlatitude trough is not associated with a precursor AWB event

1) PV Streamer, 2) Cutoff, 3) Midlatitude Trough, 4) Subtropical Disturbance, and 5) Debris

Clusters:

Upper-Tropospheric Precursors

350KisentropicsurfaceH

+

• STC formation is associated with a small-scale PV filament propagating around the northern edge of a subtropical anticyclone

• PV filament is smaller than streamers, cutoffs, and midlatitude troughs

1) PV Streamer, 2) Cutoff, 3) Midlatitude Trough, 4) Subtropical Disturbance, and 5) Debris

Clusters:

Upper-Tropospheric Precursors

350Kisentropicsurface

• STC formation is associated with residual PV debris deposited in the subtropics from a previous AWB event

• PV debris moves westward on southern edge of a broad subtropical ridge

1) PV Streamer, 2) Cutoff, 3) Midlatitude Trough, 4) Subtropical Disturbance, and 5) Debris

Debris

Cutoff

StreamerUnclassifiable

7.62%11.43%

20.95%

20.95%

29.52%

N = 105

(8)

(22)

(22)

(31)

(12)

Upper-Tropospheric Precursors

Subtropical Disturbance

9.52%(10) Midlatitude

Trough

N = 105

Upper-tropospheric Precursors

Streamer

Cutoff

Midlatitude Trough

Subtropical Disturbance

Debris

Unclassifiable

Streamer = 0.0%Cutoff = 0.0%

Midlat. Trough = 0.0%Subtrop. Dist. = 20.0%

Debris = 73.3% Unclassifiable = 6.7%

Streamer = 1.8%Cutoff = 16.1%

Midlat. Trough = 7.1%Subtrop. Dist. = 30.4%

Debris = 33.9% Unclassifiable = 10.7%

Upper-Tropospheric Precursors

Weak TT Trough InducedStrong TT

Streamer = 20.6%Cutoff = 38.2%

Midlat. Trough = 17.6%Subtrop. Dist. = 5.9%

Debris = 2.9% Unclassifiable = 14.7%

Upper-level disturbance with strong

lower-level thermal gradients

Upper-level disturbance with moderate

lower-level thermal gradients

Upper-level disturbance without appreciable lower-level thermal

gradients

N = 34 N = 56 N = 15