1. 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

2. 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)

3. 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)

4. 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 0000 UTC 9 Jun 2013 350-K PV (shaded, PVU)

5. Motivation 0000 UTC 9 Jun 2013 850-200 hPa Vertical Wind Shear Magnitude (shaded, ms -1 ) and direction (barbs, kt) 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?

6. Motivation 0000 UTC 9 Jun 2013 850-200 hPa Vertical Wind Shear Magnitude (shaded, ms -1 ) and direction (barbs, kt) 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?

7. 0000 UTC 1 Sep 2005 350-K PV (shaded, PVU) 0000 UTC 9 Jun 2013 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? Motivation

8. 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) Objectives

9. 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 0-70 o N 120 o W-20 o E CFSR (CFSRv2 after 2010) PV Streamer Identification

10. 0000 UTC 9 Jun 2013 350-K PV (shaded, PVU), and winds (barbs, kt) PV Streamer Identification Identify 2-PVU contour on 350-K surface

11. 2-PVU contour on 350-K surface (blue contour) Identify 2-PVU contour on 350-K surface 0000 UTC 9 Jun 2013 PV Streamer Identification

12. Identify points along contour where meridional PV gradient reversal is observed Points along contour where meridional PV gradient reversal is observed Similar to Postal and Hitchman (1999) 2-PVU contour on 350-K surface (blue contour), regions with meridional PV gradient reversal (red contour) 0000 UTC 9 Jun 2013 PV Streamer Identification

13. Line identified orthogonal to first points of PV reversal Ended when line crosses 2-PVU contour downstream 0000 UTC 9 Jun 2013 PV Streamer Identification 2-PVU contour on 350-K surface (blue contour), regions with meridional PV gradient reversal (red contour)

14. 0000 UTC 9 Jun 2013 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)

15. Similar but more inclusive than Wernli and Sprenger (2007) Check if PV streamer candidate is large and elongated enough Threshold Values: p must be 3 times > than w and p > 3000 km 0000 UTC 9 Jun 2013 PV Streamer Identification PV streamer area (black shading), w (width between two points), p (along contour perimeter between two points)

16. 350-K Standardized PV Anomaly (shaded, Sigma), and 2-PVU contour (black contour ) PV std_anom = (PV – PV mean ) / PV sd Calculate the intensity of the PV streamer [sigma] 0000 UTC 9 Jun 2013 PV Streamer Identification

17. Preliminary Results

18. 1979-2014 (1 Jun – 30 Nov ) Climatology: PV streamer frequency in the North Atlantic Preliminary Results Probability PV streamer is observed on any particular day (shading, %) N = 7191

19. Climatology: PV streamer frequency in the North Atlantic Preliminary Results 200-hPa Streamlines (arrows) 1979-2014 (1 Jun – 30 Nov )

20. Interannual variability of PV streamer frequency Preliminary Results 1994 (1 Jun – 30 Nov ) Probability PV streamer is observed on any particular day (shading, %)

21. Preliminary Results Interannual variability of PV streamer frequency 1995 (1 Jun – 30 Nov ) Probability PV streamer is observed on any particular day (shading, %)

22. 1 Jun – 30 Nov PV streamer activity (1979- 2014 ) 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 Preliminary Results TC Activity negatively impacted by increased vertical wind shear and decreased moisture anomalies Associated with larger and stronger PV streamers

23. 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) Preliminary Results 1979-2010

24. 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

25. Preliminary Results Mean ACE: 192.3 kt 2 10 4 PV streamer frequency as a departure from climatology (shaded, %) Highest 8 years of ACE: 2005, 2004, 1995, 1998, 1999, 2003, 1996, 2010

26. Lowest 8 years of ACE: 1983, 1982, 1994, 1987, 1991, 1986, 1993, 1997 Preliminary Results Mean ACE: 32.8 kt 2 10 4 PV streamer frequency as a departure from climatology (shaded, %)

27. 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 10-30 o N 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 Conclusions

28. Extra Slides

29. Scatter Plots of TC # versus PV Streamer intensity metric

30. Total Yearly Atlantic TCs Versus PV Streamer Intensity Metric From McTaggart Cowan et al. 2013 dataset Includes: Nonbaroclinic cases Low-level baroclinic cases Trough Induced Weak Tropical Transition Strong Tropical Transition

31. Total Yearly Atlantic Nonbaroclinic TCs Versus PV Streamer Intensity Metric Includes: Nonbaroclinic cases Low-level baroclinic cases From McTaggart Cowan et al. 2013 dataset

32. Total Yearly Atlantic Baroclinic TCs Versus PV Streamer Intensity Metric From McTaggart Cowan et al. 2013 dataset Includes: Trough Induced Weak Tropical Transition Strong Tropical Transition

33. Total Yearly Atlantic Baroclinic TCs Versus PV Streamer Intensity Metric From McTaggart Cowan et al. 2013 dataset Includes: Weak Tropical Transition Strong Tropical Transition

34. In Terms of ACE

35. TC ACE Versus PV Streamer Intensity Metric From McTaggart Cowan et al. 2013 dataset Includes: Nonbaroclinic cases Low-level baroclinic cases Trough Induced Weak Tropical Transition Strong Tropical Transition

36. Nonbaroclinic TC ACE Versus PV Streamer Intensity Metric Includes: Nonbaroclinic cases Low-level baroclinic cases From McTaggart Cowan et al. 2013 dataset

37. Includes: Trough Induced Weak Tropical Transition Strong Tropical Transition Baroclinic TC ACE Versus PV Streamer Intensity Metric

38. From McTaggart Cowan et al. 2013 dataset Includes: Weak Tropical Transition Strong Tropical Transition Baroclinic TC ACE Versus PV Streamer Intensity Metric

39. Identify 2-PVU contour on 350-K surface 350-K PV (shaded, PVU), and winds (barbs, kt) PV Streamer Identification Steps 0000 UTC 9 Jun 2013

40. 350-K PV (shaded, PVU), and 2-PVU contour (black contour) PV Streamer Intensity Obtain total PV field for given time PV Streamer Identification Steps

41. 0000 UTC 9 Jun 2013 350-K Mean PV (shaded, PVU), and 2-PVU contour (black contour) PV Streamer Intensity Subtract Mean Climatological PV for given time PV Streamer Identification Steps

42. 1 Jan – 31 Dec Preliminary Results Nearly 10,000 350-K PV streamers identified from 1979- 2014 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

43. 1 Jun – 30 Nov Nearly 10,000 350-K PV streamers identified from 1979- 2014 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

44. 1 Jun – 30 Nov 1994 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” Preliminary Results Nearly 10,000 350-K PV streamers identified from 1979- 2014 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

45. Motivation 0000 UTC 1 Sep 2005 0000 UTC 9 Jun 2013 Changes in the size and intensity of PV streamers often affect 850-200 hPa Vertical Wind Shear Magnitude (shaded, ms -1 ) and direction (barbs, kt) 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)

46. Motivation 0000 UTC 1 Sep 2005 0000 UTC 9 Jun 2013 Standardized Precipitable Water Anomalies (shaded, sigma) and 40 mm contour (black contour, mm) 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) [sigma]