Recorded presentationJ8.4
The Ambrose Jet: Climatology and Simulations of Warm-Season Coastally Enhanced Winds in the New York Bight Region
David R. Novak, NOAA/NWS, Camp Springs, MD; and B. A. Colle
The coastal regions of New York and New Jersey are often dominated by sea-breeze circulations during the spring and summer months. Occasionally these gentle sea breezes become relatively strong southerly wind events (> 11 m s-1) that may require marine advisories. These strong winds are best described as a jet, since the winds are spatially confined to the New Jersey and Long Island coasts (the New York Bight) and are vertically confined to the boundary layer (< 300 m). The Ambrose Light Station (ALSN6), located at the entrance of New York harbor, often samples this jet. Thus, the winds have been colloquially called the Ambrose Jet. This study investigates the climatology of Ambrose Jet events and the processes responsible for their occurrence.
An Ambrose Jet event was defined as the occurrence of southerly (160–210 degrees) maximum sustained winds (10 m height) exceeding 11 m s-1 at ALSN6. This wind speed threshold is one standard deviation greater than the mean wind speed at ALSN6 during 1997–2006. The sustained wind speed maximum must occur between 18 UTC and 03 UTC. To assure the wind maximum is spatially localized, the sustained wind at buoy 44025, located about 50 km to the east-southeast of ALSN6, must be <85% of the maximum sustained wind at ALSN6. Analysis of wind data during 1997–2006 revealed 134 Ambrose Jet events. There is a seasonal maximum in June and July, with a skew towards the spring months, suggesting that land-sea temperature contrast and the associated local pressure gradient are important to Ambrose Jet occurrence. The jet events exhibit a diurnal cycle, with light southwest winds during the 0600–1500 UTC period, backing to south-southeast and strengthening during the 1500–2100 UTC period. The winds become more southerly and reach a maximum generally in the 2100–0000 UTC period. The mean maximum intensity was 12.5 m s-1. After the peak intensity, the winds veer to a southwest direction as they weaken. The veering winds after 1500 UTC suggests the influence of the Coriolis force. A composite analysis shows that the Ambrose Jet is favored on relatively warm days within synoptic-scale southwest flow on the western flank of the Bermuda high.
An Ambrose Jet event on 2 June 2007 was realistically simulated down to 1.33-km grid spacing using the Weather Research and Forecasting (WRF) and Penn State–NCAR Mesoscale Models (MM5). Model sensitivity experiments were conducted to identify how aspects of the complex coastline curvature of New York Bight and the urban land characteristics of New York City modify the local pressure gradient and regulate the Ambrose Jet. A momentum budget also quantifies the role of pressure gradient, frictional, and Coriolis accelerations. Results of these experiments and budgets will be presented.
Joint Session 8, Coastal Mesoscale Circulations-I
Wednesday, 14 January 2009, 8:30 AM-10:00 AM, Room 128B
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