Julie Pullen

Urban Canopy Modeling of the New York City Metropolitan Area: A Comparison and Validation of Single- and Multilayer Parameterizations

Abstract High-resolution numerical simulations are conducted using the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)1 with two different urban canopy parameterizations for a 23-day period in August 2005 for the New York City (NYC) metropolitan area. The control COAMPS simulations use the single-layer Weather Research and Forecasting (WRF) Urban Canopy Model (W-UCM) and sensitivity simulations use a multilayer urban parameterization based on Brown and Williams (BW-UCM). Both simulations use surface forcing from the WRF land surface model, Noah, and hourly sea surface temperature fields from the New York Harbor and Ocean Prediction System model hindcast. Mean statistics are computed for the 23-day period from 5 to 27 August (540-hourly observations) at five Meteorological Aviation Report stations for a nested 0.444-km horizontal resolution grid centered over the NYC metropolitan area. Both simulations show a cold mean urban canopy air temperature bias primarily due to an underestimation of n...

Bora event variability and the role of air‐sea feedback

1) was conducted to improve forecast momentum and heat flux fields, and to evaluate surface flux field differences for two consecutive bora events during February 2003. (COAMPS 1 is a registered trademark of the Naval Research Laboratory.) The strength, mean positions and extensions of the bora jets, and the atmospheric conditions driving them varied considerably between the two events. Bora 1 had 62% stronger heat flux and 51% larger momentum flux than bora 2. The latter displayed much greater diurnal variability characterized by inertial oscillations and the early morning strengthening of a west Adriatic barrier jet, beneath which a stronger west Adriatic ocean current developed. Elsewhere, surface ocean current differences between the two events were directly related to differences in wind stress curl generated by the position and strength of the individual bora jets. The mean heat flux bias was reduced by 72%, and heat flux RMSE reduced by 30% on average at four instrumented over-water sites in the two-way coupled simulation relative to the uncoupled control. Largest reductions in wind stress were found in the bora jets, while the biggest reductions in heat flux were found along the north and west coasts of the Adriatic. In bora 2, SST gradients impacted the wind stress curl along the north and west coasts, and in bora 1 wind stress curl was sensitive to the Istrian front position and strength. The two-way coupled simulation produced diminished surface current speeds of 12% over the northern Adriatic during both bora compared with a one-way coupled simulation.

Northern Adriatic Response to a Wintertime Bora Wind Event

During winters, the northern Adriatic Sea experiences frequent, intense cold-air outbreaks that drive oceanic heat loss and imprint complex but predictable patterns in the underlying waters. This strong, reliable forcing makes this region an excellent laboratory for observational and numerical investigations of air-sea interaction, sediment and biological transport, and mesoscale wind-driven flow. Narrow sea surface wind jets, commonly known as “bora,” occur when cold, dry air spills through gaps in the Dinaric Alps (the mountain range situated along the Adriatics eastern shore). Horizontal variations in these winds drive a mosaic of oceanic cyclonic and anticyclonic cells that draw coastal waters far into the middle basin. The winds also drive intense cooling and overturning, producing a sharp front between dense, vertically homogenous waters (North Adriatic Dense Water, or NAdDW) in the north and the lighter (colder, fresher), stratified waters of the Po River plume. Once subducted at the front, the NAdDW flows southward in a narrow vein following the isobaths (contours of constant depth) of the Italian coast. In addition to governing the basins general circulation, these processes also influence sediment transport and modulate biological and optical variability

Two-Way Air–Sea Coupling: A Study of the Adriatic

High-resolution numerical simulations of the Adriatic Sea using the Navy Coastal Ocean Model (NCOM) and Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) were conducted to examine the impact of the coupling strategy (one versus two way) on the ocean and atmosphere model skill, and to elucidate dynamical aspects of the coupled response. Simulations for 23 September–23 October 2002 utilized 2- and 4-km resolution grids for the ocean and atmosphere, respectively. During a strong wind and sea surface cooling event, cold water fringed the west and north coasts in the two-way coupled simulation (where the atmosphere interacted with SST generated by the ocean model) and attenuated by approximately 20% of the cross-basin extension of bora-driven upward heat fluxes relative to the one-way coupled simulation (where the atmosphere model was not influenced by the ocean model). An assessment of model results using remotely sensed and in situ measurements of ocean temperature along with overwater and coastal wind observations showed enhanced skill in the two-way coupled model. In particular, the two-way coupled model produced spatially complex SSTs after the cooling event that compared more favorably (using mean bias and rms error) with satellite multichannel SST (MCSST) and had a stabilizing effect on the atmosphere. As a consequence, mean mixing was suppressed by over 20% in the atmospheric boundary layer and more realistic mean 10-m wind speeds were produced during the monthlong two-way coupled simulation.

Modes of Feeding in Aggregations of Barnacles and the Shape of Aggregations

The interactions between the form of a barnacle aggregation, its flow environment, and the feeding behavior of each individual was determined in unidirectional flows; both models of barnacle aggregations and live barnacles were used. Hill-shaped aggregations of model barnacles captured significantly more particles than flat aggregations. In general, rows upstream of, and at the peak of, all hill-shaped profiles captured significantly more particles than downstream rows. Living barnacles located at, or upstream of, the peak of natural clusters captured significantly more food particles than did barnacles located downstream. Living barnacles located at, or upstream of, the highest point in a natural cluster fed passively, whereas barnacles downstream of the peak actively swept their cirral net against the flow. Flow was laminar up to the highest point in natural clusters, whereas flow was both reduced and turbulent over the downstream portions. Individual barnacles within a cluster differ in their feeding rates and net energy gains, and therefore differ in their growth such that, in unidirectional flow, the peak of a cluster will shift upstream over time; in oscillating flows, the clusters will develop a symmetrical profile.

Chaotic Advection in an Archipelago

Abstract Techniques from dynamical systems theory have been applied to study horizontal stirring of fluid in the Philippine Archipelago. The authors’ analysis is based on velocity fields produced by two high-resolution (3 and 6 km) numerical models. Particular attention is paid to identifying robust surface flow patterns and associating them with dominant Lagrangian coherent structures (LCSs). A recurrent wind-driven dipole in the lee of the coastline is considered in detail. The associated LCSs form a template for stirring, exchange, and biological transport in and around the dipole. Chaotic advection is argued to provide a relevant framework for interpreting mesoscale horizontal stirring processes in an archipelago as a whole. Implications for the formation of filaments, the production of tracer variance, and the scale at which stirring leads to mixing are discussed in connection with an observed temperature record.

Forecasting the New York City Urban Heat Island and Sea Breeze during Extreme Heat Events

AbstractTwo extreme heat events impacting the New York City (NYC), New York, metropolitan region during 7–10 June and 21–24 July 2011 are examined in detail using a combination of models and observations. The U.S. Navys Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) produces real-time forecasts across the region on a 1-km resolution grid and employs an urban canopy parameterization to account for the influence of the city on the atmosphere. Forecasts from the National Weather Services 12-km resolution North American Mesoscale (NAM) implementation of the Weather Research and Forecasting (WRF) model are also examined. The accuracy of the forecasts is evaluated using a land- and coastline-based observation network. Observed temperatures reached 39°C or more at central urban sites over several days and remained high overnight due to urban heat island (UHI) effects, with a typical nighttime urban–rural temperature difference of 4°–5°C. Examining model performance broadly over both heat events ...

Summertime Influence of SST on Surface Wind Stress off the U.S. West Coast from the U.S. Navy COAMPS Model

Abstract High-resolution mesoscale model sea surface temperature (SST) analyses and surface wind stress forecasts off the U.S. West Coast are analyzed on monthly time scales for robust signatures of air–sea interaction as the surface winds encounter ocean surface features such as SST fronts, filaments, and eddies. This interaction is manifest by the linear relationship, or coupling coefficient, between the downwind SST gradient and wind stress divergence and between the crosswind SST gradient and wind stress curl evident from analysis of fields averaged over 29 days. This study examines fields from the Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS) model, spanning the summer months, June–September, for four consecutive years, 2002–05. Relative to several models evaluated previously, coupling coefficients are much closer to those calculated from Quick Scatterometer (QuikSCAT) satellite measurements. In addition, the summertime correlation between the wind stress derivative field and its corr...

Atmospheric response to local upwelling in the vicinity of New York-New Jersey harbor

Abstract Multiply nested urbanized mesoscale model [Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS)] simulations of the New York–New Jersey metropolitan region are conducted for 4–11 July 2004. The simulations differ only in their specification of sea surface temperatures (SSTs) on nest 4 (1.33-km resolution) and nest 5 (0.44-km resolution). The “control SST” simulation (CONTROL-SST) uses an analyzed SST product, whereas the “New York Harbor Observing and Prediction System (NYHOPS) SST” simulation (NYHOPS-SST) uses hourly SSTs from the NYHOPS model hindcast. Upwelling-favorable (southerly) winds preceding the simulation time period and continuing for much of the first 5 days of the simulation generate cold water adjacent to the New Jersey coast and a cold eddy immediately outside of the harbor in the New York Bight. Both features are prominent in NYHOPS-SST but are not pronounced in CONTROL-SST. The upwelled water has a discernible influence on the overlying atmosphere by cooling near-surfac...

Coastal Ocean Forecasting: science foundation and user benefits

The advancement of Coastal Ocean Forecasting Systems (COFS) requires the support of continuous scientific progress addressing: (a) the primary mechanisms driving coastal circulation; (b) methods to achieve fully integrated coastal systems (observations and models), that are dynamically embedded in larger scale systems; and (c) methods to adequately represent air-sea and biophysical interactions. Issues of downscaling, data assimilation, atmosphere-wave-ocean couplings and ecosystem dynamics in the coastal ocean are discussed. These science topics are fundamental for successful COFS, which are connected to evolving downstream applications, dictated by the socioeconomic needs of rapidly increasing coastal populations.