194 research outputs found
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Estimates for wet and dry removals' contribution to the residence time for atmospheric pollutants in the eastern United States
The length of time that atmospheric pollutants released from low-level
sources in the midwestern United States can expect to remain in
the atmosphere is discussed. The pollution is assumed to be removed
from the atmosphere by dry deposition and precipitation scavenging.
Layer-average trajectories originating from Kansas City, Missouri are
used to determine the Lagrangian probability of dry and wet conditions.
The residence time of these pollutants is estimated based on parameterizations
for the effective scavenging rates during wet and dry conditions.
This investigation shows that, in summer, the probability that
precipitation is being experienced by the pollutant is twice as great as
the probability of precipitation at the origin of the pollution; this
same ratio of probabilities is three in winter. Therefore, when precipitation
scavenging is the more important removal mechanism, the statistics
for the length of wet and dry periods at the source region overestimate
the residence time by a factor of about two to three.
By taking into consideration the Lagrangian probability of wet and
dry periods, the relative importance of dry deposition and precipitation
scavenging is discussed as a function of the wet and dry removal rates.
It is seen that for a time- and vertical-average dry deposition velocity
as large as 1 cm/sec, then dry deposition would normally be the bore
important removal process for the meteorological conditions in the midwest
to eastern United States.
Estimates for the expected atmospheric lifetimes of aerosol particles
and trace gases are reported as functions of dry deposition velocities
and collection efficiencies (or washout ratios). For example, lead
particles of mass mean diameter ~0.5 μm, should have a residence time ~8
days in winter, and ~3 days in summer, based on available data for the
dry deposition velocity and washout ratio. In general, the residence time
can be expected to be about twice as long during the summer season than
the winter.
The winter, monthly average distribution of pollutant mass is shown,
based on the steady-state Gaussian approximation solution of the convective
diffusion equation. The calculations are based on a statistical
analysis of the 12 hourly positions of a series of trajectories. Thus,
monthly average "diffusion" and removal are incorporated into the
Gaussian model
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The Cospectral Gap and Turbulent Flux Calculations
An alternative method to Fourier analysis is discussed for studying the scale dependence of variances and covariances in atmospheric boundary layer time series. Unlike Fourier decomposition, the scale dependence based on multiresolution decomposition depends on the scale of the fluctuations and not the periodicity. An example calculation is presented in detail.
Multiresolution decomposition is applied to tower datasets to study the cospectral gap scale, which is the timescale that separates turbulent and mesoscale fluxes of heat, moisture, and momentum between the atmosphere and the surface. It is desirable to partition the flux because turbulent fluxes are related to the local wind shear and temperature stratification through similarity theory, while mesoscale fluxes are not. Use of the gap timescale to calculate the eddy correlation flux removes contamination by mesoscale motions, and therefore improves similarity relationships compared to the usual approach of using a constant averaging timescale.
A simple model is developed to predict the gap scale. The goal here is to develop a practical formulation based on readily available variables rather than a theory for the transporting eddy scales. The gap scale increases with height, increases with instability, and decreases sharply with increasing stability. With strong stratification and weak winds, the gap scale is on the order of a few minutes or less. Implementation of the gap approach involves calculating an eddy correlation flux using the modeled gap timescale to define the turbulent fluctuations (e.g., w′ and T′). The turbulent fluxes (e.g., w′T′) are then averaged over 1 h to reduce random sampling errors
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Quality Control and Flux Sampling Problems for Tower and Aircraft Data
A series of automated tests is developed for tower and aircraft time series to identify instrumentation problems, flux sampling problems, and physically plausible but unusual situations. The automated procedures serve as a safety net for quality controlling data. A number of special flags are developed representing a variety of potential problems such as inconsistencies between different tower levels and the flux error due to fluctuations of aircraft height.
The tests are implemented by specifying critical values for parameters representing each specific error. The critical values are developed empirically from experience of applying the tests to real turbulent time series. When these values are exceeded, the record is flagged for further inspection and comparison with the rest of the concurrent data. The inspection step is necessary to either verify an instrumentation problem or identify physically plausible behavior. The set of tests is applied to tower data from the Risø Air Sea Experiment and Microfronts95 and aircraft data from the Boreal Ecosystem–Atmosphere Study
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Evaluation of the air-sea bulk formula and sea-surface temperature variability from observations
Eddy‐correlation fluxes are compared to air‐sea fluxes predicted by a widely used bulk flux formulation without wave‐state effects. Systematic discrepancies are found. For example, the model approximately equates the roughness lengths for heat and moisture; however, the observed roughness length for heat (zoh) exceeds that for moisture (zoq) by an order of magnitude or more, except in the strongest wind‐speed conditions. This is apparently due to the dynamic nature of temperature, which dominates buoyancy generation of turbulence in these data sets. The observed correlation between temperature and vertical velocity fluctuations generally exceeds that for moisture. For 10‐m wind speeds above a threshold value of 12 m s−1, zoq exceeds zoh apparently owing to enhanced moisture flux associated with the onset of wave breaking coupled with advection of cold dry air from land. In near‐collapsed turbulence, the observed momentum flux is smaller than predicted, and there is no clear indication of a smooth flow viscous regime. The scatter between observed and bulk fluxes generally decreases with averaging the observed fluxes over greater length scales even with variations in sea‐surface temperature (SST). The reduction in random flux sampling errors more than compensates for capturing increased surface heterogeneity with increasing averaging scale. Since similarity theory does not apply to heterogeneous surfaces, the bulk model does break down in the extreme case where the averaging window includes a sharp SST front. The response of the flow to changes in SST is presented for different amplitudes of SST variability. The change in vertical structure and acceleration of the low‐level wind over warm pools is discussed
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Observations of non-dimensional wind shear in the coastal zone
Vertical profiles of the time-averaged wind stress, wind speed and buoyancy flux from the off-shore tower site in the Risø Air Sea Experiment are used to evaluate similarity theory in the coastal zone. The observed dependence of the non-dimensional wind shear on stability is compared to the traditional parametrization. Relationships between the non-dimensional shear, development of internal boundary layers and wave state are explored. We find that the largest-scale turbulent eddies are suppressed in shallow convective internal boundary layers, leading to larger non-dimensional shear than that of the traditional prediction based only on stability. In shallow stable boundary layers, elevated generation of turbulence leads to smaller non-dimensional shear compared to the traditional prediction. Over young growing waves in stable stratification, the observed non-dimensional shear is less than that over older more mature waves in otherwise similar conditions. The non-dimensional shear is a function of wave state for stable conditions even though the observations are well above the wave boundary layer. We conclude that development of shallow internal boundary layers and young growing-wave fields, both of which are common in the coastal zone, can lead to substantial departures of the non-dimensional shear from the prediction based only on stability.Keywords: Turbulence, Similarity theory, Boundary laye
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Sensitivity of a subregional scale atmospheric inverse CO 2 modeling framework to boundary conditions
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95175/1/jgrd16614.pd
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Atmospheric inverse modeling to constrain regional‐scale CO 2 budgets at high spatial and temporal resolution
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95480/1/jgrd15697.pd
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Low-Level Wind Maxima and Structure of the Stably Stratified Boundary Layer in the Coastal Zone
A Rutan Aircraft Factory Long-EZ aircraft flew numerous low-level slant soundings on two summer days in
2001 off the northeastern coast of the United States. The soundings are analyzed here to study the nonstationary
vertical structure of the wind, temperature, and turbulence. An error analysis indicates that fluxes
computed from the aircraft slant soundings are unreliable. The first day is characterized by a weakly stable
boundary layer in onshore flow capped by an inversion. A low-level wind maximum formed at about 100 m
above the sea surface. The second day is characterized by stronger stability due to advection of warm air from
the upwind land surface. On this more stable day, the wind maxima are very sharp and the speed and height of
the wind maxima increase with distance from the coast. Although trends in the vertical structure are weak,
variations between subsequent soundings are large on time scales of tens of minutes or less. The vertical
structure of the wind and turbulence is considerably more nonstationary than the temperature structure,
although the existence of the wind maximum is persistent. Causes of the wind maxima and their variability are
examined but are not completely resolved.This is the publisher’s final pdf. The published article is copyrighted by the American Meteorological Society and can be found at: http://journals.ametsoc.org/loi/apme
Environmental proactivity and firms' performance: Mediation effect of competitive advantages in Spanish wineries
The main aim of this paper is to show the extent to which environmental proactivity is able to generate competitive advantages in a firm in order to improve their economic-financial performance by introducing the role of managerial perception into the analysis. This study focuses on Spanish wineries and their environmental practices and covers a total of 4598 wineries with a sample of 142 valid responses during the month of November 2015. The results can be summarized as follows. Firstly, there is positive environmental proactivity in terms of obtaining both cost-based and differentiation-based competitive advantages. Likewise, this proactivity has a positive impact on the manager’s perception of performance. Secondly, obtaining differentiation-based competitive advantages has a positive impact on the manager’s perception of performance although a negative impact on performance itself. There is, however, no significant evidence of the impact of cost-based competitive advantages on financial performance nor on the perception of performance itself, nor the impact of environmental proactivity on financial performance
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