The “Ambrose” (New York Bight) Jet: Climatology and Simulations of Coastally Enhanced Winds

1. The “Ambrose” (New York Bight) Jet: Climatology and Simulations of Coastally Enhanced Winds Brian A. Colle School of Marine and Atmospheric Sciences, Stony Brook University- SUNY David Novak NOAA/ NWS Eastern Region Headquarters, Scientific Services Division, Bohemia, New York & Stony Brook University, State University of New York, Stony Brook, New York

2. 15 UTC PK13

3. 23 UTC G24 PK34

4. Motivation • Jet can result in: • Small craft advisory conditions • Heightened rip current threat • JFK air traffic changes (wind direction, speed, shear)

5. Study Questions • How frequently does the New York Bight (NYB) Jet occur? • What synoptic conditions favor the NYB Jet? • What dynamics are responsible for the NYB Jet formation and evolution? • Is the NYB Jet predictable?

6. Analyzed hourly data from Ambrose Light House (ALSN6) during 1997-2006. • Much of 2005 missing – so effective climatology period is nine years. Data • Used logarithmic wind profile eqn. assuming neutral stability conditions to reduce ASLN6 wind to 10 m height.

7. Direction Range: 160-210 (S-SW) • Timing:Maximum sustained wind recorded in 18-03 UTC period New York Bight Jet Definition • Intensity:one standard deviation over the climatological late afternoon (18 UTC-03 UTC) southerly (160-210) sustained wind max = 11 m/s (~22 kt) • Width:Neighboring Bouy 44025 must have a sustained wind speed < 85% of the ALSN6 sustained wind speed. Condition checked +/- 1 h the time of maximum sustained wind at Ambrose.

8. 134 NYB Jet events recorded in nine year period • Most frequent occurrence in April – July Climatology • Suggests land/sea temperature contrast is important

9. Compare average monthly NYC temperature max to average monthly ALSN6 sea temperature: Climatology • Temperature differences exceed 5 C during March-Aug. • Suggests land/sea temperature contrast is important

10. 28% of events meet or exceed Small Craft Advisory wind conditions [~13 m/s (25 kt) wind speed] Climatology • Only ~4% of events with wind > ~15 m/s (~30 kt)

11. Maximum wind in early evening, generally 2-3 h AFTER inland maximum temperature Climatology

12. Hodograph Light SW wind 8-12 h prior to max. Wind backs to SSE and strengthens 4-8 h prior to max. Wind veers and reaches maximum. Continues veering and weakening over next 12 h. Composite Hodograph T=0 T= +12 T= -12 Red (12 h before max) Blue (12 h after max)

13. Sequential NYB jet events were often observed • Seven occurrences of 2 consecutive days of events • Three occurrences of 3 consecutive days of events • Two occurrences of 4 consecutive days of events Sequential Events

14. 500 mb Height -- ALL • Dates when the jet started • Graphics created from CPC NARR Composite Page Synoptic Composite 585 MSLP – Small Craft Adv. days MSLP -- ALL 1011 1021 1020

15. June 2, 2007 • High temperatures around 90 F inland, 70s near the coast. • Ambrose 10 m sustained wind maximized at 25 kt at 22 UTC. Case Study 22Z 12Z

16. 1400 UTC

17. 1500 UTC

18. 1600 UTC

19. 1700 UTC

20. 1800 UTC

21. 1900 UTC

22. 2000 UTC

23. 2100 UTC

24. 2200 UTC

25. 2300 UTC

26. 0000 UTC

27. Jet core derived from TDWR was 34 kt at ~70 m (230 ft) ! Case Study

28. 1541 UTC Case Study

29. Jet derived from ACARS was ~35 kt at ~200 m (600 ft), and found at top of inversion Case Study 2206 UTC

30. WRFv2.2 • Initialized 00 UTC 2 June (~22 h prior to speed max) • NOGAPS initial/boundary conditions (NAM SST) • YSU PBL • Thermal Diffusion land scheme • 1.33 km resolution w/37 vertical levels Model Simulations • MM5v3.6 • Initialized 00 UTC 2 June (~22 h prior to speed max) • NOGAPS initial/boundary conditions (NAM SST) • Blackadar PBL • Thermal Diffusion land scheme • 1.33 km resolution w/37 vertical levels

31. Model maximum within 0.5 m/s (1 kt) observed. 1.33-km WRF vs. Obs 22Z 22Z • Similar timing of wind speed and direction, except too much veering after max in model. 12Z 12Z

32. 1200 UTC 1.33-km WRF Forecast • SLP • 100 m wind speed

33. 1500 UTC WRF Forecast • SLP • 100 m wind speed

34. 1800 UTC WRF Forecast • SLP • 100 m wind speed

35. 2100 UTC WRF Forecast • SLP • 100 m wind speed

36. 0000 UTC WRF Forecast • SLP • 100 m wind speed

37. 0300 UTC WRF Forecast • SLP • 100 m wind speed

38. 1000 m 2100 UTC WRF Forecast 800 600 400 Wind Speed (m/s) Theta (K) 200

39. 1000 m 2100 UTC WRF Forecast 800 600 400 Wind Speed (m/s) Theta (K) 200

40. 12 km Does Resolution Matter? 4 km 1.3 km 15 m/s 16 m/s 16 m/s 17 m/s

41. 1.33-km MM5 vs. Obs • Similar evolution, but jet 1-2h and too much veering after max in model. 23Z 23Z 12Z 12Z

42. Impact of Urban Heating 12Z CTL NOURBAN • Little or no impact from the additional urban heating

43. Impact of Long Island 12Z CTL NOLI • Jet extends northward, but no further increase in jet strength

44. Summary • The New York Bight (“Ambrose”) Jet ‘season’ is Mar-Aug, although it can occur any time of the year. • Approximately 15 events per year. • Maximum wind speeds exceed Small Craft Advisory criteria ~ 28% of the time. • Wind Speed Maximum nearly always observed between 21 and 00 UTC. • Serial events common.

45. Summary (cont.) • Jet favored on warm days in synoptic southwest flow on western flank of Bermuda high. SCA events had slightly stronger gradient and upstream disturbance. • Land/sea temperature contrast appear to be critical to formation. Heating from NYC and Long Island does not enhance jet. • 1.33 km WRF/MM5 capable of simulating key characteristics.