Download Papin_Team_Torn_9Feb2016

Subtropical Potential Vorticity Streamer Formation
and Variability in the North Atlantic Basin
Philippe Papin, Lance F. Bosart, Ryan D. Torn
University at Albany, Department of Atmospheric
and Environmental Sciences
Team Torn Meeting
9 February 2016
Motivation
• Subtropical Potential Vorticity (PV) streamer
• An elongated filament of high PV air
• Formation occurs in conjunction with Rossby wave breaking (RWB)
• Low PV air folds poleward over high PV air in Anticyclonic RWB
350-K PV (shaded, PVU)
0000 UTC 9 Jun 2013
Motivation
• Subtropical Potential Vorticity (PV) streamer
• An elongated filament of high PV air
• Formation occurs in conjunction with Rossby wave breaking (RWB)
• Low PV air folds poleward over high PV air in Anticyclonic RWB
350-K PV (shaded, PVU)
0000 UTC 9 Jun 2013
PV Streamer
Motivation
• Subtropical Potential Vorticity (PV) streamer
• An elongated filament of high PV air
• Formation occurs in conjunction with Rossby wave breaking (RWB)
• Low PV air folds poleward over high PV air in Anticyclonic RWB
350-K PV (shaded, PVU)
0000 UTC 9 Jun 2013
Low PV Air
High PV Air
Motivation
• PV streamers are associated with and modulate
• Corridors of high vertical wind shear (VWS)
• Moisture anomalies
 These environmental features impact Tropical Cyclone (TC) Activity
 Do changes in PV streamer activity affect TC Activity?
850-200 hPa Vertical Wind Shear Magnitude (shaded, ms-1) and direction (barbs, kt)
0000 UTC 9 Jun 2013
High VWS
Motivation
• PV streamers are associated with and modulate
• Corridors of high vertical wind shear (VWS)
• Moisture anomalies
 These environmental features impact Tropical Cyclone (TC) Activity
 Do changes in PV streamer activity affect TC Activity?
850-200 hPa Vertical Wind Shear Magnitude (shaded, ms-1) and direction (barbs, kt)
0000 UTC 9 Jun 2013
Motivation
• PV streamers are associated with and modulate
• Corridors of high vertical wind shear (VWS)
• Moisture anomalies
 These environmental features impact Tropical Cyclone (TC) Activity
 Do changes in PV streamer activity affect TC Activity?
350-K PV (shaded, PVU)
0000 UTC 1 Sep 2005
Small and Weak
0000 UTC 9 Jun 2013
Large and Intense
Objectives
1) Create a new climatology of PV streamers in the North Atlantic
basin emphasizing differences in size and intensity
•
Dataset: Climate Forecast System Reanalysis (CFSR)
2) Investigate preliminary results and interannual variability of PV
streamers
•
Size, intensity, and spatial distribution
3) Investigate relationship between PV streamer activity and TC
activity if it exists
•
Comparing PV streamer activity to Accumulated Cyclone Energy (ACE)
•
Sorted into different types of TCG in extra slides (per McTaggart-Cowan et al. 2013)
PV Streamer Identification
• Combine previous methodologies to identify PV streamer areas
directly linked to RWB
• Postel and Hitchman (1999)
 Only identified locations where RWB occurs
• Wernli and Sprenger (2007)
 PV streamers not explicitly linked to RWB, size criteria omitted large number of PV streamers
• Use isentropic surface that represents subtropical tropopause in
warm Season
• PV on the 350 K surface
• Calculate intensity of PV streamer as standardized PV anomaly relative to
climatology
• Identification algorithm run from 1979-2014 at 24 h increments
• Present results from 1 June – 30 November
• 0-70oN 120oW-20oE
• CFSR (CFSRv2 after 2010)
PV Streamer Identification
•
Identify 2-PVU contour on 350-K surface
350-K PV (shaded, PVU), and winds (barbs, kt)
0000 UTC 9 Jun 2013
PV Streamer Identification
•
Identify 2-PVU contour on 350-K surface
2-PVU contour on 350-K surface (blue contour)
0000 UTC 9 Jun 2013
PV Streamer Identification
•
Identify points along contour where meridional PV gradient reversal is observed
2-PVU contour on 350-K surface (blue contour), regions with meridional PV gradient reversal (red contour)
0000 UTC 9 Jun 2013
Points along contour where
meridional PV gradient
reversal is observed
Similar to Postal and Hitchman (1999)
PV Streamer Identification
•
•
Line identified orthogonal to first points of PV reversal
Ended when line crosses 2-PVU contour downstream
2-PVU contour on 350-K surface (blue contour), regions with meridional PV gradient reversal (red contour)
0000 UTC 9 Jun 2013
90
o
PV Streamer Identification
•
•
Line identified orthogonal to first points of PV reversal
Ended when line crosses 2-PVU contour downstream
PV streamer area (black shading), w (width between two points), p (along contour perimeter between two points)
0000 UTC 9 Jun 2013
90
o
p
PV Streamer Identification
•
Check if PV streamer candidate is large and elongated enough
Threshold Values: p must be 3 times > than w and p > 3000 km
PV streamer area (black shading), w (width between two points), p (along contour perimeter between two points)
0000 UTC 9 Jun 2013
Area = 8,569,380 km2
p =12,823 km
Similar but more inclusive than Wernli and Sprenger (2007)
PV Streamer Identification
•
Calculate the intensity of the PV streamer
PVstd_anom = (PV – PVmean) / PVsd
350-K Standardized PV Anomaly (shaded, Sigma), and 2-PVU contour (black contour)
0000 UTC 9 Jun 2013
[sigma]
Preliminary Results
Preliminary Results
• Climatology: PV streamer frequency in the North Atlantic
• 1979-2014 (1 Jun – 30 Nov)
N = 7191
Probability PV streamer is observed on any particular day (shading, %)
Preliminary Results
• Climatology: PV streamer frequency in the North Atlantic
• 1979-2014 (1 Jun – 30 Nov)
200-hPa Streamlines (arrows)
Preliminary Results
• Interannual variability of PV streamer frequency
• 1994 (1 Jun – 30 Nov)
Probability PV streamer is observed on any particular day (shading, %)
Preliminary Results
• Interannual variability of PV streamer frequency
• 1995 (1 Jun – 30 Nov)
Probability PV streamer is observed on any particular day (shading, %)
Preliminary Results
• PV streamer activity (19792014)
1 Jun – 30 Nov
• Annual PV streamer occurrence
has changed little in last 35
years
• PV streamer intensity exhibits
decreasing trend over last 35
years
Relationship to Tropical Cyclones?
• Use Accumulated Cyclone Energy
(ACE)
• Combines intensity and duration of
all TCs in given year
TC Activity negatively impacted by increased vertical wind shear and decreased
moisture anomalies
•
Associated with larger and stronger PV streamers
Preliminary Results
• Increased PV streamer activity
negatively affects TC activity
• Larger more intense PV streamers
correlated to reduction in TC activity
• Investigate top and bottom 8 TC
activity years (in terms of ACE)
1979-2010
Preliminary Results
• Increased PV streamer activity
negatively affects TC activity
• Larger more intense PV streamers
correlated to reduction in TC activity
• Investigate top and bottom 8 TC
activity years (in terms of ACE)
1979-2010
Preliminary Results
• Highest 8 years of ACE: 2005, 2004, 1995, 1998, 1999, 2003, 1996, 2010
Mean ACE: 192.3 kt2 104
PV streamer frequency as a departure from climatology (shaded, %)
Preliminary Results
• Lowest 8 years of ACE: 1983, 1982, 1994, 1987, 1991, 1986, 1993, 1997
Mean ACE: 32.8 kt2 104
PV streamer frequency as a departure from climatology (shaded, %)
Conclusions
• Created a new PV Streamer climatology
• Links RWB with downstream PV streamers
• Area and Intensity statistics obtained from each PV streamer identified
• Preliminary Results
• Large year to year variability in PV streamer activity
• Increased PV streamer activity results in reduced tropical cyclone activity
 R = -.61
• 8 highest ACE years reveal a decrease in PV streamer frequency, and 8
lowest ACE years reveal an increase in PV streamer frequency
 Between 10-30oN in the NATL basin
• Future Work
• Distinguish impact between different types of tropical cyclogenesis (TCG)
 Preliminary results suggest PV streamer impact greater with non-baroclinic TCG
Extra Slides
Scatter Plots of TC # versus PV
Streamer intensity metric
Total Yearly Atlantic TCs Versus PV Streamer Intensity Metric
Includes:
Nonbaroclinic cases
Low-level baroclinic cases
Trough Induced
Weak Tropical Transition
Strong Tropical Transition
From McTaggart Cowan et al.
2013 dataset
Total Yearly Atlantic Nonbaroclinic TCs Versus PV Streamer Intensity
Metric
Includes:
Nonbaroclinic cases
Low-level baroclinic cases
From McTaggart Cowan et al.
2013 dataset
Total Yearly Atlantic Baroclinic TCs Versus PV Streamer Intensity Metric
Includes:
Trough Induced
Weak Tropical Transition
Strong Tropical Transition
From McTaggart Cowan et al.
2013 dataset
Total Yearly Atlantic Baroclinic TCs Versus PV Streamer Intensity Metric
Includes:
Weak Tropical Transition
Strong Tropical Transition
From McTaggart Cowan et al.
2013 dataset
In Terms of ACE
TC ACE Versus PV Streamer Intensity Metric
Includes:
Nonbaroclinic cases
Low-level baroclinic cases
Trough Induced
Weak Tropical Transition
Strong Tropical Transition
From McTaggart Cowan et al.
2013 dataset
Nonbaroclinic TC ACE Versus PV Streamer Intensity Metric
Includes:
Nonbaroclinic cases
Low-level baroclinic cases
From McTaggart Cowan et al.
2013 dataset
Baroclinic TC ACE Versus PV Streamer Intensity Metric
Includes:
Trough Induced
Weak Tropical Transition
Strong Tropical Transition
From McTaggart Cowan et al.
2013 dataset
Baroclinic TC ACE Versus PV Streamer Intensity Metric
Includes:
Weak Tropical Transition
Strong Tropical Transition
From McTaggart Cowan et al.
2013 dataset
PV Streamer Identification Steps
Identify 2-PVU contour on 350-K surface
350-K PV (shaded, PVU), and winds (barbs, kt)
0000 UTC 9 Jun 2013
PV Streamer Identification Steps
PV Streamer Intensity
350-K PV (shaded, PVU), and 2-PVU contour (black contour)
0000 UTC 9 Jun 2013
Obtain total PV field for given time
PV Streamer Identification Steps
PV Streamer Intensity
350-K Mean PV (shaded, PVU), and 2-PVU contour (black contour)
0000 UTC 9 Jun 2013
Subtract Mean Climatological PV for given time
Preliminary Results
1 Jan – 31 Dec
• Nearly 10,000 350-K PV
streamers identified from 19792014
• Wide range of sizes and
intensities
• In future will composite top and
bottom intensity percentiles
• Majority of PV streamers occur
during TC season (June – Nov)
• Significant interannual variability
•1994: larger more intense PV streamers
•1995: smaller less intense PV streamers
Preliminary Results
1 Jun – 30 Nov
• Nearly 10,000 350-K PV
streamers identified from 19792014
• Wide range of sizes and
intensities
• In future will composite top and
bottom intensity percentiles
• Majority of PV streamers occur
during TC season (June – Nov)
• Significant interannual variability
•1994: larger more intense PV streamers
•1995: smaller less intense PV streamers
Preliminary Results
1 Jun – 30 Nov
• Nearly 10,000 350-K PV
streamers identified from 19792014
• Wide range of sizes and
intensities
• In future will composite top and
bottom intensity percentiles
1994
• Majority of PV streamers occur
during TC season (June – Nov)
• Significant interannual variability
•1994: larger more intense PV streamers
•1995: smaller less intense PV streamers
1995
Better way to quantify year to year
differences in PV streamer activity?
Integrate PV Streamer intensity by area and sum over TC season
“Seasonal PV Streamer Intensity Metric”
Motivation
• Changes in the size and intensity of PV streamers often affect
• Vertical Wind Shear (VWS) corridors
• Moisture anomalies
These environmental features impact Tropical Cyclone (TC) Activity
Do changes in PV streamer activity affect TC Activity? (has not yet been addressed)
850-200 hPa Vertical Wind Shear Magnitude (shaded, ms-1) and direction (barbs, kt)
0000 UTC 1 Sep 2005
Small and Weak
0000 UTC 9 Jun 2013
Large and Intense
Motivation
• Changes in the size and intensity of PV streamers often affect
• Vertical Wind Shear (VWS) corridors
• Moisture anomalies
These environmental features impact Tropical Cyclone (TC) Activity
Do changes in PV streamer activity affect TC Activity? (has not yet been addressed)
Standardized Precipitable Water Anomalies (shaded, sigma) and 40 mm contour (black contour, mm)
0000 UTC 1 Sep 2005
Small and Weak
0000 UTC 9 Jun 2013
Large and Intense
[sigma]