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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 Tropical Lunch 19 February 2016 Mo#va#on • 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 Mo#va#on • 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 Mo#va#on • 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 Mo#va#on • PV streamers are associated with and modulate • Corridors of high ver<cal wind shear (VWS) • Moisture anomalies ² These environmental features impact Tropical Cyclone (TC) Activity ² Do changes in PV streamer activity affect TC Activity? 850-‐200 hPa Ver<cal Wind Shear Magnitude (shaded, ms-‐1) and direc<on (barbs, kt) 0000 UTC 9 Jun 2013 High VWS Mo#va#on • PV streamers are associated with and modulate • Corridors of high ver<cal wind shear (VWS) • Moisture anomalies ² These environmental features impact Tropical Cyclone (TC) Activity ² Do changes in PV streamer activity affect TC Activity? 850-‐200 hPa Ver<cal Wind Shear Magnitude (shaded, ms-‐1) and direc<on (barbs, kt) 0000 UTC 9 Jun 2013 ir ude A t # a l d i Dry M Mo#va#on • PV streamers are associated with and modulate • Corridors of high ver<cal wind shear (VWS) • Moisture anomalies ² These environmental features impact Tropical Cyclone (TC) Activity ² 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 Objec#ves 1) Create a new climatology of PV streamers in the North Atlan<c basin emphasizing differences in size and intensity • Dataset: Climate Forecast System Reanalysis (CFSR) 2) Inves<gate preliminary results and interannual variability of PV streamers • Size, intensity, and spa<al distribu<on 3) Inves<gate rela<onship between PV streamer ac<vity and TC ac<vity if it exists • • Comparing PV streamer ac<vity to Accumulated Cyclone Energy (ACE) Sorted into different types of TCG in extra slides (per McTaggart-‐Cowan et al. 2013) PV Streamer Iden#fica#on • Combine previous methodologies to iden<fy PV streamer areas directly linked to RWB • Postel and Hitchman (1999) ² Only iden<fied loca<ons where RWB occurs • Wernli and Sprenger (2007) ² PV streamers not explicitly linked to RWB, size criteria omi`ed 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 rela<ve to climatology • Iden<fica<on algorithm run from 1979-‐2014 at 24 h increments • Present results from 1 June – 30 November • 0-‐70oN 120oW-‐20oE PV Streamer Iden#fica#on • Iden<fy 2-‐PVU contour on 350-‐K surface 350-‐K PV (shaded, PVU), and winds (barbs, kt) 0000 UTC 9 Jun 2013 PV Streamer Iden#fica#on • Iden<fy 2-‐PVU contour on 350-‐K surface 2-‐PVU contour on 350-‐K surface (blue contour) 0000 UTC 9 Jun 2013 PV Streamer Iden#fica#on • Iden<fy 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 Iden#fica#on • • Line iden<fied 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 90o PV Streamer Iden#fica#on • • Line iden<fied 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 90o p PV Streamer Iden#fica#on • Check if PV streamer candidate is large and elongated enough Threshold Values: p must be 3 #mes > 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 Iden#fica#on • 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 aly m o V An a P e ag m Aver 0.31 sig + [sigma] Preliminary Results Preliminary Results • Climatology: PV streamer frequency in the North Atlan<c • 1979-‐2014 (1 Jun – 30 Nov) Probability PV streamer is observed on any par<cular day (shading, %) N = 7191 Preliminary Results • Climatology: PV streamer frequency in the North Atlan<c • 1979-‐2014 (1 Jun – 30 Nov) 200-‐hPa Streamlines (arrows) Mid O ugh o r T cean Preliminary Results • Interannual variability of PV streamer frequency • 1994 (1 Jun – 30 Nov) Probability PV streamer is observed on any par<cular day (shading, %) Preliminary Results • Interannual variability of PV streamer frequency • 1995 (1 Jun – 30 Nov) Probability PV streamer is observed on any par<cular day (shading, %) Preliminary Results • PV streamer ac<vity (1979-‐2014) • Annual PV streamer occurrence has changed li`le in last 35 years • PV streamer intensity exhibits decreasing trend over last 35 years 1 Jun – 30 Nov Preliminary Results • PV streamer ac<vity (1979-‐2014) 1 Jun – 30 Nov • Annual PV streamer occurrence has changed li`le in last 35 years • PV streamer intensity exhibits decreasing trend over last 35 years 40oN Average DT Pressure 20oN 80oW 20oW Climate Change Signal? Compare with pressure on dynamical tropopause Preliminary Results • PV streamer ac<vity (1979-‐2014) • Annual PV streamer occurrence has changed li`le in last 35 years • PV streamer intensity exhibits decreasing trend over last 35 years 1 Jun – 30 Nov r = +0.67 40oN Average DT Pressure 20oN 80oW 20oW • Decrease in PV streamer intensity consistent with higher tropopause Preliminary Results • PV streamer ac<vity (1979-‐2010) Rela#onship to Tropical Cyclones? • Use Accumulated Cyclone Energy (ACE) • Combines intensity and dura<on of all TCs in given year Hypothesis: TC Ac<vity nega<vely impacted by increased ver<cal wind shear and decreased moisture anomalies • Associated with larger and stronger PV streamers • Larger more intense PV streamers correlated to a reduc<on in TC ac<vity • Inves<gate top and bo`om 8 TC ac<vity years (in terms of ACE) Preliminary Results • PV streamer ac<vity (1979-‐2010) Rela#onship to Tropical Cyclones? • Use Accumulated Cyclone Energy (ACE) • Combines intensity and dura<on of all TCs in given year Hypothesis: TC Ac<vity nega<vely impacted by increased ver<cal wind shear and decreased moisture anomalies • Associated with larger and stronger PV streamers • Larger more intense PV streamers correlated to a reduc<on in TC ac<vity • Inves<gate top and bo`om 8 TC ac<vity years (in terms of ACE) 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 sta<s<cs obtained from each PV streamer iden<fied • Preliminary Results • Large year to year variability in PV streamer ac<vity • Increased PV streamer ac<vity results in reduced tropical cyclone ac<vity ² R = -‐0.62 • 8 highest ACE years reveal a decrease in PV streamer frequency, and 8 lowest ACE years reveal an increase in PV streamer frequency ² Between 10-‐30oN in the NATL basin • Future Work • Dis<nguish impact between different types of tropical cyclogenesis (TCG) ² Preliminary results suggest PV streamer impact greater with non-‐baroclinic TCG Extra Slides Preliminary Results • Point Correla<on of PV Streamer Frequency vs. ACE PV Streamer Intensity Metric minus 5yr Running Mean A`empt to remove decreasing PV streamer intensity trend in the CFSR climatology Sca`er Plots of TC # versus PV Streamer intensity metric Total Yearly Atlan<c TCs Versus PV Streamer Intensity Metric Includes: Nonbaroclinic cases Low-‐level baroclinic cases Trough Induced Weak Tropical Transi#on Strong Tropical Transi#on From McTaggart Cowan et al. 2013 dataset Total Yearly Atlan<c Nonbaroclinic TCs Versus PV Streamer Intensity Metric Includes: Nonbaroclinic cases Low-‐level baroclinic cases From McTaggart Cowan et al. 2013 dataset Total Yearly Atlan<c Baroclinic TCs Versus PV Streamer Intensity Metric Includes: Trough Induced Weak Tropical Transi#on Strong Tropical Transi#on From McTaggart Cowan et al. 2013 dataset Total Yearly Atlan<c Baroclinic TCs Versus PV Streamer Intensity Metric Includes: Weak Tropical Transi#on Strong Tropical Transi#on 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 Transi#on Strong Tropical Transi#on 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 Transi#on Strong Tropical Transi#on From McTaggart Cowan et al. 2013 dataset Baroclinic TC ACE Versus PV Streamer Intensity Metric Includes: Weak Tropical Transi#on Strong Tropical Transi#on From McTaggart Cowan et al. 2013 dataset PV Streamer Iden#fica#on Steps Iden<fy 2-‐PVU contour on 350-‐K surface 350-‐K PV (shaded, PVU), and winds (barbs, kt) 0000 UTC 9 Jun 2013 PV Streamer Iden#fica#on 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 <me PV Streamer Iden#fica#on 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 <me Preliminary Results 1 Jan – 31 Dec • Nearly 10,000 350-‐K PV streamers iden<fied from 1979-‐2014 • Wide range of sizes and intensi<es • In future will composite top and bo`om intensity percen<les • 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 iden<fied from 1979-‐2014 • Wide range of sizes and intensi<es • In future will composite top and bo`om intensity percen<les • 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 iden<fied from 1979-‐2014 • Wide range of sizes and intensi<es • In future will composite top and bo`om intensity percen<les • Majority of PV streamers occur during TC season (June – Nov) • Significant interannual variability 1994 1995 • 1994: larger more intense PV streamers • 1995: smaller less intense PV streamers Beder way to quan#fy year to year differences in PV streamer ac#vity? Integrate PV Streamer intensity by area and sum over TC season “Seasonal PV Streamer Intensity Metric” Mo#va#on • Changes in the size and intensity of PV streamers oqen affect • Vertical Wind Shear (VWS) corridors • Moisture anomalies ² These environmental features impact Tropical Cyclone (TC) Activity ² Do changes in PV streamer activity affect TC Activity? (has not yet been addressed) 850-‐200 hPa Ver<cal Wind Shear Magnitude (shaded, ms-‐1) and direc<on (barbs, kt) 0000 UTC 1 Sep 2005 Small and Weak 0000 UTC 9 Jun 2013 Large and Intense Mo#va#on • Changes in the size and intensity of PV streamers oqen affect • Vertical Wind Shear (VWS) corridors • Moisture anomalies ² These environmental features impact Tropical Cyclone (TC) Activity ² 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] Preliminary Results • PV streamer ac<vity (1979-‐2014) • Annual PV streamer occurrence has changed li`le in last 35 years • PV streamer intensity exhibits decreasing trend over last 35 years Apply 5 Year Running Mean 1 Jun – 30 Nov Preliminary Results 1 Jun – 30 Nov • PV streamer ac<vity (1979-‐2014) • Annual PV streamer occurrence has changed li`le in last 35 years • PV streamer intensity exhibits decreasing trend over last 35 years o 40 N Average DT Pressure 20oN 80oW 20oW Climate Change Signal? Compare with pressure on dynamical tropopause Preliminary Results • PV streamer ac<vity (1979-‐2014) • Annual PV streamer occurrence has changed li`le in last 35 years • PV streamer intensity exhibits decreasing trend over last 35 years Apply 5 Year Running Mean • Decrease in PV streamer intensity consistent with higher tropopause r = 0.86
