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1.
Following the collapse of the New York World Trade Center (WTC) towers on September 11, 2001, Local, State, and Federal agencies initiated numerous air monitoring activities to better understand the ongoing impacts of emissions from the disaster. The collapse of the World Trade Center towers and associated fires that lasted for several weeks resulted at times in a noticeable plume of material that was dispersed around the Metropolitan New York City (NYC) area. In general, the plume was only noticeable for a short period of time following September 11, and only apparent close to the World Trade Center site. A study of the estimated pathway which the plume of WTC material would likely follow was completed to support the United States Environmental Protection Agency’s 2002 initial exposure assessments. In this study, the WTC emissions were simulated using the CALMET-CALPUFF model in order to examine the general spatial and temporal dispersion patterns over NYC. This paper presents the results of the CALPUFF plume model in terms of plume dilution and location, since the exact source strength remains unknown. Independent observations of PM2.5 are used to support the general dispersion features calculated by the model. Results indicate that the simulated plume matched well with an abnormal increase (600–1000% of normal) in PM2.5 two nights after the WTC collapse as the plume rotated north to southeast, towards parts of NYC. Very little if any evidence of the plume signature was noted during a similar flow scenario a week after September 11. This leads to the conclusion that other than areas within a few kilometers from the WTC site, the PM2.5 plume was not observable over NYC’s background concentration after the first few days.  相似文献   

2.
A mesoscale model has been applied to calculate climatological means of the surface wind. A reliable average requires more than 40 model runs, which are differentiated by the direction and speed of the geostrophic wind under the assumption of neutral stratification. The frequency distributions of the geostrophic wind have been taken from observations of the 850-hPa winds at the radiosonde station in Prague for a 10-year period. The simulation results have been averaged over all sectors and speed classes of the geostrophic wind according to their frequencies. A comparison of the calculated mean wind speeds with observed ones shows deviations of about 0.4 ms−1 outside the mountains. The representation of steep topography and isolated mountains on the basis of a 3-km horizontal resolution of the simulations needs special treatment in order to reduce the gap of up to 4 ms−1 between observed and simulated mean wind speeds over mountains. Therefore, an empiric speed-up formula has been applied to the isolated mountains that otherwise would fall through the 3-km meshes. The corresponding deviations have been reduced to 1.5 ms−1.  相似文献   

3.
Observations from two SOund Detection And Ranging (SODAR) units, a 10 m micrometeorological tower and five Automated Surface Observing Stations (ASOS) were examined during several synoptic scale flow regimes over New York City after the World Trade Center disaster on September 11, 2001. An ARPS model numerical simulation was conducted to explore the complex mesoscale boundary layer structure over New York City. The numerical investigation examined the urban heat island, urban roughness effect and sea breeze structure over the New York City region. Estimated roughness lengths varied from 0.7 m with flow from the water to 4 m with flow through Manhattan. A nighttime mixed layer was observed over lower Manhattan, indicating the existence of an urban heat island. The ARPS model simulated a sea-breeze front moving through lower Manhattan during the study period consistent with the observations from the SODARs and the 10-m tower observations. Wind simulations showed a slowing and cyclonic turning of the 10-m air flow as the air moved over New York City from the ocean. Vertical profiles of simulated TKE and wind speeds showed a maximum in TKE over lower Manhattan during nighttime conditions. It appears that this TKE maximum is directly related to the influences of the urban heat island.  相似文献   

4.
Constraining physical parameters of tephra dispersion and deposition from explosive volcanic eruptions is a significant challenge, because of both the complexity of the relationship between tephra distribution and distance from the vent and the difficulties associated with direct and comprehensive real-time observations. Three andesitic subplinian explosions in January 2011 at Shinmoedake volcano, Japan, are used as a case study to validate selected empirical and theoretical models using observations and field data. Tephra volumes are estimated using relationships between dispersal area and tephra thickness or mass/area. A new cubic B-spline interpolation method is also examined. Magma discharge rate is estimated using theoretical plume models incorporating the effect of wind. Results are consistent with observed plume heights (6.4–7.3 km above the vent) and eruption durations. Estimated tephra volumes were 15–34?×?106 m3 for explosions on the afternoon of 26 January and morning of 27 January, and 5.0–7.6?×?106 m3 for the afternoon of 27 January; magma discharge rates were in the range 1–2?×?106 kg/s for all three explosions. Clast dispersal models estimated plume height at 7.1?±?1 km above the vent for each explosion. The three subplinian explosions occurred with approximately 12-h reposes and had similar mass discharge rates and plume heights but decreasing erupted magma volumes and durations.  相似文献   

5.
Deep CTD/transmissometer tows and water bottle sampling were used during 1985 to map the regional distribution of the neutrally-buoyant plumes emanating from each of two major vent fields on the Southern Symmetrical Segment (SSS) and Endeavour Segment (ES) of the Juan de Fuca Ridge. At both vent fields, emissions from point and diffuse hydrothermal sources coalesced into a single 200-m-thick plume elongated in the direction of current flow and with characteristic temperature anomalies of 0.02–0.05°C and light-attenuation anomalies of 0.01–0.08 m−1 (10–80 μg/l above background). Temperature anomalies in the core of each plume were uniform as far downcurrent as the plumes were mapped (10–15 km). Downcurrent light-attenuation trends were non-uniform and differed between plumes, apparently because different vent fluid chemistries at each field cause significant differences in the settling characteristics of the hydrothermal precipitates. Vent fluids from the SSS are metal-dominated and mostly precipitate very fine-grained hydrous Fe-oxides that remain suspended in the plume. Vent fluids from the ES are sulfur-dominated and precipitate a high proportion of coarser-grained Fe-sulfides that rapidly settle from the plume. The integrated flux of each vent field was estimated from measurements of the advective transport of each plume. Heat flux was 1700 ± 1100 MW from the ES and 580 ± 351 MW from the SSS. Particle flux varied from 546 ± 312 g/s to 204 ± 116 g/s at the ES depending on distance from the vent field, and was 92 ± 48 g/s from the SSS.  相似文献   

6.
A three-dimensional mesoscale numerical model is used to investigate mesoscale circulation over a Gulf Stream filament. Two numerical experiments are performed with different initial uniform ambient wind speeds (U=0.1 m s–1, 3.5 m s–1 and 7 m s–1) for a typical winter day. It is found that for both low and moderate winds, a closed mesoscale circulation forms over the Gulf Stream filament. When the Gulf Stream filament was removed, the model did not predict a mesoscale circulation. The modeled circulation over the filament is in agreement with the observations, suggesting that the atmospheric circulations over the filaments may be an important mechanism in the U.S. East Coast cyclogenesis.  相似文献   

7.
Marine circulation above the northern Brazilian continental shelf is subject to energetic forcing factors of various origins: high water buoyancy fluxes induced by the Amazon River freshwater discharge, a strong coastal current associated with a mesoscale current (North Brazil Current (NBC)), a forcing by semidiurnal tide and by Northeast or Southeast trade winds according to the season. Using a three-dimensional (3-D) hydrodynamic numerical model (MOBEEHDYCS), and realistic bathymetry and coastline of the northern Brazilian shelf, this paper aims at studying the influence of some specific physical processes on the morphology of the Amazon plume. The very large volume discharge (180 000 m3/s on average) and the weak effect of Coriolis force are additional characteristics of the studied system, which induce a particular dynamics. The various forcing factors are successively introduced into the model in order to simulate and to determine their respective influences upon the plume extent and the hydrodynamics at the shelf scale. Simulation reveal that the coastal current is at the origin of the permanent northwestward Amazon plume extension while wind effect can either reinforce or moderate this situation. The tide intervenes also to modify the position of the salinity front: a horizontal migration of salinity front is observed under its action.  相似文献   

8.
Vegetation constitutes one of the fundamental types of land use on Earth. The presence of trees in urban areas can decrease local winds and exchange sensible and latent heat with the surrounding environments, thus exerting notable influences on the urban microenvironment. A better understanding of the turbulent transfer of momentum and scalars around vegetation canopy could significantly contribute to improvement of the urban environment. This work develops a large-eddy simulation(LES) method that is applicable to model the flow and scalar transport over the forest canopy. We study the atmospheric flow over complex forested areas under typical weather conditions by coupling LES to the mesoscale model. Models of radiation and energy balance have been developed with explicit treatment of the vegetation canopy. By examining the flow over a forest canopy under a range of stability conditions, we found that buoyancy enhances or suppresses turbulent mixing in unstable or stable atmosphere respectively, with decreasing or increasing wind shear, respectively. From the multiscale modeling of the Beijing Olympic Forest Park, the present coupling scheme proves to better resolve the diurnal variations in wind speed,temperature, and relative humidity over complex urban terrains. The coupling scheme is superior to the traditional mesoscale model in terms of wind field simulation. This is mainly because the coupling scheme not only takes the influences of external mesoscale flow into consideration, but also resolves the heterogeneous urban surface at a fine scale by downscaling, thus better reproducing the complex flow and turbulent transport in the urban roughness sublayer.  相似文献   

9.
Observations of the Hudson River plume were taken in the spring of 2006 in conjunction with the Lagrangian Transport and Transformation Experiment using mooring arrays, shipboard observations, and satellite data. During this time period, the plume was subjected to a variety of wind, buoyant, and shelf forcings, which yield vastly different responses in plume structure including a downstream recirculating eddy. During weak and downwelling winds, the plume formed a narrow buoyant coastal current that propagated downstream near the internal wave speed. Freshwater transport during periods when the downwelling wind was closely aligned with the coast was near the river discharge values. During periods with a cross-shore component to the wind, freshwater transport in the coastal current estimated by the mooring array is less than the river discharge due to a widening of the plume that leads to the internal Rossby radius scaling for the plume width to be invalid. The offshore detachment of plume and formation of a downstream eddy that is observed surprisingly persisted for 2 weeks under a variety of wind forcing conditions. Comparison between mooring, shipboard, and satellite data reveal the downstream eddy is steady in time. Shipboard transects yield a freshwater content equal to the previous 3 days of river discharge. The feature itself was formed due to a large discharge following a strong onshore wind. The plume was then further modified by a brief upwelling wind and currents influenced by the Hudson Shelf Valley. The duration of the detachment and downstream eddy can be explained using a Wedderburn number which is largely consistent with the wind strength index described by Whitney and Garvine (J Geophys Res 110:C03014 1997).  相似文献   

10.
The traditional method of Synthetic Aperture Radar(SAR)wind field retrieval is based on an empirical relation between the near surface winds and the normalized radar backscatter cross section to estimate wind speeds,where this relation is called the geophysical model function(GMF).However,the accuracy rapidly decreases due to the impact of rainfall on the measurement of SAR and the saturation of backscattered intensity under the condition of tropical cyclone.Because of no available instrument synchronously monitoring rain rate on the satellite platform of SAR,we have to derive the precipitation of the SAR observation time from non-simultaneous passive microwave observations of rain in combination with geostationary IR images,and then use the model of rain correction to remove the impact of rain on SAR wind field measurements.For the saturation of radar backscatter cross section in high wind speed conditions,we develop an approach to estimate tropical cyclone parameters and wind fields based on the improved Holland model and the SAR image features of tropical cyclone.To retrieve the low-to-moderate wind speed,the wind direction of tropical cyclone is estimated from the SAR image using wavelet analysis.And then the maximum wind speed and the central pressure of tropical cyclone are calculated by a least square minimization of the difference between the improved Holland model and the low-to-moderate wind speed retrieved from SAR.In addition,wind fields are estimated from the improved Holland model using the above-mentioned parameters of tropical cyclone as input.To evaluate the accuracy of our approach,the SAR images of typhoon Aere,typhoon Khanun,and hurricane Ophelia are used to estimate tropical cyclone parameters and wind fields,which are compared with the best track data and reanalyzed wind fields of the Joint Typhoon Warning Center(JTWC)and the Hurricane Research Division(HRD).The results indicate that the tropical cyclone center,maximum wind speed,and central pressure are generally consistent with the best track data,and wind fields agree well with reanalyzed data from HRD.  相似文献   

11.
Validation of HRDI MLT winds with meteor radars   总被引：1，自引：0，他引：1  
A validation study of the mesospheric and lower-thermospheric (MLT) wind velocities measured by the High-Resolution Doppler Imager (HRDI) on board the Upper-Atmosphere Research Satellite (UARS) has been carried out, comparing with observations by meteor radars located at Shigaraki, Japan and Jakarta, Indonesia. The accuracy of the HRDI winds relative to the meteor radars is obtained by a series of simultaneous wind measurements at the time of UARS overpasses. Statistical tests on the difference in the wind vectors observed by HRDI and the meteor radars are applied to determine whether the wind speed has been overestimated by HRDI (or underestimated by the MF radars) as previously noticed in HRDI vs. MF radar comparisons. The techniques employed are the conventional t-test applied to the mean values of the paired wind vector components as well as wind speeds, and two nonparametric tests suitable for testing the paired wind speed. The square-root transformation has been applied before the Mests of the wind speed in order to fit the wind-speed distribution function to the normal distribution. The overall results show little evidence of overestimation by HRDI (underestimation by meteor radars) of wind velocities in the MLT region. Some exceptions are noticed, however, at the altitudes around 88 km, where statistical differences occasionally reach a level of significance of 0.01. The validation is extended to estimate the precision of the wind velocities by both HRDI and meteor radars. In the procedure, the structure function defined by the mean square difference of the observed anomalies is applied in the vertical direction for the profile data. This method assumes the isotropy and the homogeneity of variance for the physical quantity and the homogeneity of variance for the observational errors. The estimated precision is about 6m s– for the Shigaraki meteor radar, 15 m s–1 for the Jakarta meteor radar, and 20 m s–1 for HRDI at 90-km altitude. These values can be used ot confirm the statistical significance of the wind field obtained by averaging the observed winds.  相似文献   

12.
This study presents daily and seasonal variations of PAH concentrations in Erzurum atmosphere in summer season of 2008 and in winter seasons of 2008 and 2009. Sampling location at Erzurum urban center was selected to represent the effects of traffic (University junction). 18 PAH compounds were analyzed by GC–MS. Average total PAH concentration (gas + particulate) of 18 PAH compounds were measured during 2008 winter (431 ngm?3) and summer (103 ngm?3) seasons at the University junction. Daily and seasonal variations of PAH compounds were investigated and compared with other urban centers in the literature. Multiple linear regression and artificial neural network (ANN) models were constructed to determine the impacts of meteorological parameters on measured individual PAH concentrations. Results of the multiple linear regression and ANN models indicated that wind speed, wind direction and intensity of total solar radiation were the most significant factors for the measured concentrations of PAH compounds.  相似文献   

13.
A fundamental problem with all ground-based remotely sensed measurements of volcanic gas flux is the difficulty in accurately measuring the velocity of the gas plume. Since a representative wind speed and direction are used as proxies for the actual plume velocity, there can be considerable uncertainty in reported gas flux values. Here we present a method that uses at least two time-synchronized simultaneously recording UV spectrometers (FLYSPECs) placed a known distance apart. By analyzing the time varying structure of SO2 concentration signals at each instrument, the plume velocity can accurately be determined. Experiments were conducted on Kīlauea (USA) and Masaya (Nicaragua) volcanoes in March and August 2003 at plume velocities between 1 and 10 m s−1. Concurrent ground-based anemometer measurements differed from FLYSPEC-measured plume speeds by up to 320%. This multi-spectrometer method allows for the accurate remote measurement of plume velocity and can therefore greatly improve the precision of volcanic or industrial gas flux measurements. Editorial responsibility: A. Woods  相似文献   

14.
Wide-angle refraction and multichannel reflection seismic data show that oceanic crust along the Galápagos Spreading Center (GSC) between 97°W and 91°25′W thickens by 2.3 km as the Galápagos plume is approached from the west. This crustal thickening can account for ∼52% of the 700 m amplitude of the Galápagos swell. After correcting for changes in crustal thickness, the residual mantle Bouguer gravity anomaly associated with the Galápagos swell shows a minimum of −25 mGal near 92°15′W, the area where the GSC is intersected by the Wolf-Darwin volcanic lineament (WDL). The remaining depth and gravity anomalies indicate an eastward reduction of mantle density, estimated to be most prominent above a compensation depth of 50-100 km. Melting calculations assuming adiabatic, passive mantle upwelling predict the observed crustal thickening to arise from a small increase in mantle potential temperature of ∼30°C. The associated thermal expansion and increase in melt depletion reduce mantle densities, but to a degree that is insufficient to explain the geophysical observations. The largest density anomalies appear at the intersection of the GSC and the WDL. Our results therefore require the existence of compositionally buoyant mantle beneath the GSC near the Galápagos plume. Possible origins of this excess buoyancy include melt retained in the mantle as well as mantle depleted by melting in the upwelling plume beneath the Galápagos Islands that is later transported to the GSC. Our estimate for the buoyancy flux of the Galápagos plume (700 kg s−1) is lower than previous estimates, while the total crustal production rate of the Galápagos plume (5.5 m3s−1) is comparable to that of the Icelandic and Hawaiian plumes.  相似文献   

15.
— This paper examines the spatial and temporal distributions of the mixing height, ventilation coefficient (defined as the product of mixing height and surface wind speed), and cloud cover over the eastern United States during the summer of 1995, using the high-resolution meteorological data generated by MM5 (Version 1), a mesoscale model widely used in air quality studies. The ability of MM5 to simulate the key temporal and spatial features embedded in the time series of observations of temperature, wind speed, and moisture is assessed using spectral decomposition methods. Also, mixing heights estimated from the MM5 outputs are compared with those derived from observations at a few locations where data with high temporal resolution are available in the Northeast. In addition, the uncertainties associated with the estimation of the evolution of the boundary layer during the morning time are examined. The results indicate that nighttime mixing heights averaged <200?m, rising to 1 km by 10 EST, and to about 2.5?km in the afternoon. Ventilation coefficients followed a similar diurnal pattern, increasing from 500?m2/s at night?to 15,000?m2/s in the afternoon; the increase due to the growing mixing height and increasing surface wind speeds. Spatial variability of these parameters was relatively small (coefficient of variation=0.25) at?night and in the afternoon when conditions were quasi-stationary, but increased (to 0.5) during morning?and evening hours when mixing heights and wind speeds were changing rapidly. Analyses of surface ozone observations from about 400 sites throughout the eastern United States indicate that days with numerous stations reporting surface ozone concentrations in excess of 80 ppb (i.e., “high ozone” days) generally had less daytime cloud cover, lower surface wind speeds, higher mixing heights, and lower ventilation coefficients than did comparable “low ozone” days. Such meteorological features are consistent with a synoptic anticyclone centered over the mid-south region (Kentucky, Tennessee). Low ozone days were characterized by more disturbed weather conditions (low pressure systems, fronts, greater cloud cover, and precipitation events). Ozone observations at two elevated platforms (～400?m agl) in Garner, NC, and Chicago, IL, indicated that ozone concentrations aloft were about 40% larger on “high ozone” days than on “low ozone” days. On average, high levels of ozone persist aloft for about 2 to 3 days. Strong vertical mixing in the daytime can bring this pool of upper-level ozone downward to augment surface ozone production. Since ozone can be transported downwind several hundred kilometers from its source region over this time scale, depending on upper-level winds, effective ozone control strategies must take into consideration spatial scales ranging from local to regional, and time scales of the order of several days.  相似文献   

16.
The September 11, 2001 attack on the World Trade Center (WTC) resulted in a massive plume of dust and smoke that blanketed lower Manhattan and part of the Hudson-Raritan Estuary (HRE). The NOAA National Status and Trends Mussel Watch Program has long-term monitoring sites in the area and thus had an opportunity to assess the effect of the WTC attack on PAH and PCB contamination of the surrounding estuary. Seven additional sites were added in the Upper HRE to attain higher sampling resolution for comparison with regularly sampled Mussel Watch Project HRE sites. Elevated background levels of PCBs and PAHs in mussel tissue and sediments were high enough before the WTC attack that concentrations were not measurably changed by WTC derived contaminant input.  相似文献   

17.
The hydrostatic model SALSA is used to simulate a particular event observed during the Greenland Ice Margin EXperiment “GIMEX” (on July 12th, 1991). The time evolution of the large-scale flow was incorporated in the model through time dependent boundary conditions which were updated using the closest upwind sounding. A turbulent scheme for the stable boundary layer and an appropriate parametrization of the surface fluxes implemented in the same model, are used for this study. The simulation results are discussed and compared to the available observations. The computed turbulent fluxes are correctly estimated. The model predicts a mixing zone of about 1500 m high which is in good agreement with tundra site observations. Over the ice cap, the katabatic layer is correctly simulated by the model. Its height of 80–300 m is well estimated. The comparison between the simulation and observations taken at ice cap sites is reasonably valid. The ablation computed along the ice cap corresponds well to the values reconstructed of observations at sites 4 and 9. Finally, a sensibility study to a specified westward geostrophic wind (2 ms−1) shows that the consideration of this latter improves the simulated tundra wind evolution.  相似文献   

18.
《Continental Shelf Research》2005,25(9):1097-1114
South of the eastern end of Long Island (Montauk Point) along the Eastern U.S. coast, a coastal density front forms between the buoyant outflow plume of the Long Island Sound (LIS) and the denser shelf waters offshore. During a 2-day cruise in April 2002, measurements of the density and velocity structure of this front were obtained from high-resolution CTD and ADCP data. Transects show the front intersecting the bottom inshore of the 30 m isobath and shoaling offshore. Variability in the location of the front is small offshore of the 40 m isobath, yet tidal excursions of the front along the bottom are significant (5 km) inshore of this depth.The frontal structure of the LIS plume was similar to observations of bottom-trapped coastal density fronts and shelf break fronts. A coastal jet in the along front direction was the main feature of the mean velocity field and was found to be in thermal wind balance with the mean density field. Stronger than expected offshore velocities near the surface, most likely a result of wind forcing, were the only exception to these similarities. In addition, analysis of temperature and salinity gradients along isopycnals gives evidence of secondary cross-frontal circulation and detachment of the bottom boundary layer. Characteristics of the LIS plume are used to evaluate recent analytical models of bottom-trapped coastal density fronts and bottom-advected plume theory, finding good agreement.  相似文献   

19.
— Several radiation fog studies with emphasis on numerical simulation and prediction are reviewed. One of the earliest attempts started with a given surface diurnal variation of temperature and water vapor, and concluded by forecasting the onset of saturation at various levels; thus fog, by examining the spread of temperature and moisture in the vertical. The one-dimensional (1-D) models are still popular. Some of the recent numerical simulations use more than 100 levels in the vertical and treat various kinds of vegetation, aerosols, and soils with moisture contents. Some also employ a mesoscale model in conjunction with a 1-D model to consider the advective effects. In the following a simple 1-D numerical model was used to predict the onset of fog at Brunei, based on a desktop computer and routine surface observations of dry bulb temperature (T), dewpoint temperature (T d ), and wind speed at 1800 Local Time (LT). Optimism exists in improved predictions of fog and stratus as 1-D models incorporate many physical processes, and mesoscale models continue to improve in predicting advection and cloud cover.  相似文献   

20.
Huijie Xue  Yi Du 《Ocean Dynamics》2010,60(2):341-357
A high-resolution coastal ocean model was developed to simulate the temporal/spatial variability of the Kennebec–Androscoggin (K–A) river plume and the circulation in Casco Bay. The model results agree favorably with the moored and shipboard observations of velocity, temperature, and salinity. The surface salinity gradient was used to distinguish the plume from the ambient coastal water. The calculated plume thickness suggests that the K–A plume is surface trapped. Its horizontal scales correlate well with Q 0.25, where Q is the volume discharge of the rivers. Directional spreading is affected by the wind with the upwelling favorable wind transporting the plume water offshore. Both the wind and the tide also enhance mixing in the plume. The inclusion of a wetting-and-drying (WAD) scheme appears to enhance the mixing and entrainment processes near the estuary. The plume becomes thicker near the mouth of the estuary, the outflow velocity of the plume is weaker, and the radius of the river plume shrinks. The flow field in the model run with the WAD is noisier, not only in shallow areas of Casco Bay but also in the plume and even on the shelf. We speculate that the WAD processes can affect much larger areas than the intertidal zones, especially via a river plume that feeds into a coastal current.  相似文献   

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