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Wenshou Tian
,
Douglas J. Parker
,
Stephen Mobbs
,
Martin Hill
,
Charles A. D. Kilburn
, and
Darcy Ladd

Abstract

In this paper, high-frequency pressure time series measured by microbarographs are used to extract information on the existence and characteristics of convective rolls in the convective boundary layer. Rolls are identified in radar and satellite data, and it is shown that the pressure signals associated with the rolls have been detected in an array of microbarographs. The methodology of obtaining further information on roll characteristics from the array, notably orientation and drift velocity, is discussed in some detail. It is shown that the pressure time series contain signals representing the roll motion, approximately normal to the mean wind, and signals representing turbulent structures that drift along the mean wind direction. As the along-wind signals may dominate the time series, care is needed to identify the roll motion. Filtering of the higher-frequency along-wind signals can isolate the roll motion details. Also, a new approach using “beam-steering diagrams” to discriminate rolls from gravity waves and turbulent eddies is tested in both a numerical model and an observational case. In the beam-steering diagram, multiple centers of signal cross correlation can be used to identify different features in a single set of time series from an array of stations. The observations and model show that an array of microbarographs are able to resolve rolls if they are properly distributed with their spacing being tuned according to roll wavelength.

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New York City's Vulnerability to Coastal Flooding

Storm Surge Modeling of Past Cyclones

Brian A. Colle
,
Frank Buonaiuto
,
Malcolm J. Bowman
,
Robert E. Wilson
,
Roger Flood
,
Robert Hunter
,
Alexander Mintz
, and
Douglas Hill

New York City, New York (NYC), is extremely vulnerable to coastal flooding; thus, verification and improvements in storm surge models are needed in order to protect both life and property. This paper highlights the Stony Brook Storm Surge (SBSS) modeling system. It utilizes surface winds and sea level pressures from the fifth-generation Pennsylvania State University (PSU)-National Center for Atmospheric Research (NCAR) Mesoscale Model (MM5) or the Weather Research and Forecasting (WRF) model to drive the Advanced Circulation Model for Coastal Ocean Hydrodynamics (ADCIRC). For this study, the MM5 is utilized at 12-km grid spacing and ADCIRC is run on an unstructured grid down to ~10-m resolution in areas around Long Island and NYC.

This paper describes the SBSS and its performance across the NYC region during the 11–12 December 1992 nor'easter and Tropical Storm Floyd on 16–17 September 1999. During the 1992 event, east-northeasterly surface winds of 15–25 m s−1 (30–50 kts) persisted for nearly 24 h, while hurricane-force winds (35–40 m s−1) occurred for a few hours just south of western Long Island. This created a 1.0–1.5-m storm surge around NYC and western Long Island Sound over three tidal cycles. ADCIRC successfully simulated the peak water levels to within ~10%, and it realistically simulated some of the flooding across lower Manhattan. The surface winds for Tropical Storm Floyd were only 5–10 m s−1 weaker than the 1992 event, but no coastal flooding occurred during Floyd, because the storm approached during a low tide. Additional Floyd simulations were completed by shifting the storm's landfall to the spring high tide the previous week, and by doubling the wind speed to mimic a category-1 hurricane. A combination of the spring high tide and a category-1 hurricane scenario during Floyd would have resulted in moderate flooding at several locations around NYC.

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Christina S. McCluskey
,
Thomas C. J. Hill
,
Francesca Malfatti
,
Camille M. Sultana
,
Christopher Lee
,
Mitchell V. Santander
,
Charlotte M. Beall
,
Kathryn A. Moore
,
Gavin C. Cornwell
,
Douglas B. Collins
,
Kimberly A. Prather
,
Thilina Jayarathne
,
Elizabeth A. Stone
,
Farooq Azam
,
Sonia M. Kreidenweis
, and
Paul J. DeMott

Abstract

Emission rates and properties of ice nucleating particles (INPs) are required for proper representation of aerosol–cloud interactions in atmospheric models. Few investigations have quantified marine INP emissions, a potentially important INP source for remote oceanic regions. Previous studies have suggested INPs in sea spray aerosol (SSA) are linked to oceanic biological activity. This proposed link was explored in this study by measuring INP emissions from nascent SSA during phytoplankton blooms during two mesocosm experiments. In a Marine Aerosol Reference Tank (MART) experiment, a phytoplankton bloom was produced with chlorophyll-a (Chl a) concentrations reaching 39 μg L−1, while Chl a concentrations more representative of natural ocean conditions were obtained during the Investigation into Marine Particle Chemistry and Transfer Science (IMPACTS; peak Chl a of 5 μg L−1) campaign, conducted in the University of California, San Diego, wave flume. Dynamic trends in INP emissions occurred for INPs active at temperatures > −30°C. Increases in INPs active between −25° and −15°C lagged the peak in Chl a in both studies, suggesting a consistent population of INPs associated with the collapse of phytoplankton blooms. Trends in INP emissions were also compared to aerosol composition, abundances of microbes, and enzyme activity. In general, increases in INP concentrations corresponded to increases in organic species in SSA and the emissions of heterotrophic bacteria, suggesting that both microbes and biomolecules contribute to marine INP populations. INP trends were not directly correlated with a single biological marker in either study. Direct measurements of INP chemistry are needed to accurately identify particles types contributing to marine INP populations.

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