the “ambrose” (new york bight) jet: climatology and simulations of coastally enhanced winds
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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 - PowerPoint PPT PresentationTRANSCRIPT
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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
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15 UTC
PK13
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23 UTC
PK34
G24
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Motivation•Jet can result in:•Small craft advisory conditions
•Heightened rip current threat
•JFK air traffic changes (wind direction, speed, shear)
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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?
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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.
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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
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Climatology•134 NYB Jet events recorded in nine year period•Most frequent occurrence in April – July
•Suggests land/sea temperature contrast is important
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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
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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]
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Climatology•Maximum wind in early evening, generally 2-3 h AFTER inland maximum temperature
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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
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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
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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
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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
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1400 UTC
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1500 UTC
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1600 UTC
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1700 UTC
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1800 UTC
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1900 UTC
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2000 UTC
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2100 UTC
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2200 UTC
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2300 UTC
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0000 UTC
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Case Study•Jet core derived from TDWR was 34 kt at ~70 m (230 ft) !
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Case Study1541 UTC
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Case Study•Jet derived from ACARS was ~35 kt at ~200 m (600 ft), and found at top of inversion
2206 UTC
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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
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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
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1.33-km WRF Forecast
•SLP•100 m wind speed
1200 UTC
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WRF Forecast
•SLP•100 m wind speed
1500 UTC
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WRF Forecast
•SLP•100 m wind speed
1800 UTC
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WRF Forecast
•SLP•100 m wind speed
2100 UTC
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WRF Forecast
•SLP•100 m wind speed
0000 UTC
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WRF Forecast
•SLP•100 m wind speed
0300 UTC
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WRF Forecast
Wind Speed (m/s)Theta (K)
400
200
600
800
1000 m2100 UTC
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WRF Forecast
Wind Speed (m/s)Theta (K)
400
200
600
800
1000 m2100 UTC
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Does Resolution Matter?12 km
1.3 km
15 m/s
16 m/s
17 m/s
4 km
16 m/s
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1.33-km MM5 vs. Obs
• Similar evolution, but jet 1-2h and too much veering after max in model.
23Z23Z
12Z
12Z
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Impact of Urban Heating
• Little or no impact from the additional urban heating
12Z
CTL NOURBAN
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Impact of Long Island
• Jet extends northward, but no further increase in jet strength
12Z
CTL NOLI
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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.
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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.