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

Brian A. ColleSchool of Marine and Atmospheric Sciences, Stony Brook University- SUNY

David NovakNOAA/ NWS Eastern Region Headquarters, Scientific Services Division, Bohemia, New York & Stony Brook

University, State University of New York, Stony Brook, New York

15 UTC

PK13

23 UTC

PK34

G24

Motivation•Jet can result in:•Small craft advisory conditions

•Heightened rip current threat

•JFK air traffic changes (wind direction, speed, shear)

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?

Data•Analyzed hourly data from Ambrose Light House (ALSN6) during 1997-2006.

•Used logarithmic wind profile eqn. assuming neutral stability conditions to reduce ASLN6 wind to 10 m height.

•Much of 2005 missing – so effective climatology period is nine years.

New York Bight Jet Definition•Direction Range: 160-210 (S-SW)

•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.

•Timing: Maximum sustained wind recorded in 18-03 UTC period

Climatology•134 NYB Jet events recorded in nine year period•Most frequent occurrence in April – July

•Suggests land/sea temperature contrast is important

Climatology•Compare average monthly NYC temperature max to average monthly ALSN6 sea temperature:

•Temperature differences exceed 5 C during March-Aug.•Suggests land/sea temperature contrast is important

Climatology

•Only ~4% of events with wind > ~15 m/s (~30 kt)

•28% of events meet or exceed Small Craft Advisory wind conditions [~13 m/s (25 kt) wind speed]

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

Composite Hodograph

Red (12 h before max)Blue (12 h after max)

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.

Hodograph

T=0

T= -12

T= +12

Sequential Events

•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

Synoptic Composite• Dates when the jet started• Graphics created from CPC NARR Composite Page

500 mb Height -- ALL

MSLP -- ALL

585

1020

1011

1021

MSLP – Small Craft Adv. days

Case StudyJune 2, 2007

•High temperatures around 90 F inland, 70s near the coast.•Ambrose 10 m sustained wind maximized at 25 kt at 22 UTC.

22Z

12Z

1400 UTC

1500 UTC

1600 UTC

1700 UTC

1800 UTC

1900 UTC

2000 UTC

2100 UTC

2200 UTC

2300 UTC

0000 UTC

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

Case Study1541 UTC

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

2206 UTC

Model Simulations•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

• 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

1.33-km WRF vs. Obs

•Model maximum within 0.5 m/s (1 kt) observed.

•Similar timing of wind speed and direction, except too much veering after max in model.

22Z22Z

12Z

12Z

1.33-km WRF Forecast

•SLP•100 m wind speed

1200 UTC

WRF Forecast

•SLP•100 m wind speed

1500 UTC

WRF Forecast

•SLP•100 m wind speed

1800 UTC

WRF Forecast

•SLP•100 m wind speed

2100 UTC

WRF Forecast

•SLP•100 m wind speed

0000 UTC

WRF Forecast

•SLP•100 m wind speed

0300 UTC

WRF Forecast

Wind Speed (m/s)Theta (K)

400

200

600

800

1000 m2100 UTC

WRF Forecast

Wind Speed (m/s)Theta (K)

400

200

600

800

1000 m2100 UTC

Does Resolution Matter?12 km

1.3 km

15 m/s

16 m/s

17 m/s

4 km

16 m/s

1.33-km MM5 vs. Obs

• Similar evolution, but jet 1-2h and too much veering after max in model.

23Z23Z

12Z

12Z

Impact of Urban Heating

• Little or no impact from the additional urban heating

12Z

CTL NOURBAN

Impact of Long Island

• Jet extends northward, but no further increase in jet strength

12Z

CTL NOLI

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.

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.