Vertical profiles of biological particle concentrations under convective conditions

Measurements of vertical profiles of pollen concentration from local and remote sources have been made during convective conditions with balloon-mounted rotating impaction samplers.The vertical profiles of local particles appear to be usually characterized by a decrease in the ground layer and by almost constant values aloft. A minimum often occurs at levels between 100 and 200 m.The concentration profiles of pollen from remote sources present a peak at heights of some hundred meters.By comparing the observed profiles with some published models of transport, it appears that: (i) because of differing eddy scales, turbulent transport affects the settling of pollen differently close to the ground than aloft; and (ii) turbulent anisotropies related to the dynamic and thermal structure of the atmosphere may affect the vertical distribution of particulate matter in the boundary layer.     

Estimating Heat Sources And Fluxes In Thermally Stratified Canopy Flows Using Higher-Order Closure Models

Over the past two decades, several inverse methods have been proposed to estimatescalar source and sink strengths from measured mean concentration profiles withinthe canopy volume (hereafter termed the `inverse' problem). These inverse methodscommonly assumed neutral atmospheric stability conditions for the entire canopyvolume. For non-neutral conditions, atmospheric stability corrections in inverseschemes were limited to adjusting the integral time scale or other flow statistics tomatch well-established surface-layer similarity relations above the canopy. Suchstability corrections do not explicitly consider the local stability effects within thecanopy volume. Currently, there is no satisfactory inverse scheme that explicitlyaccounts for local atmospheric stability for canopy turbulence. A Eulerian inversemethod that explicitly accounts for local atmospheric stability within the canopy isdeveloped using second-order closure principles. Field testing the method is conductedusing temperature measurements from two field experiments collected in an even-ageduniform loblolly pine forest. It is demonstrated that by accounting for local atmospheric stability in the inversion scheme, the agreement between modelled sensible heat flux calculations and measurements improve by 60% for stable conditions, 10% for near-neutral conditions and 20% for unstable conditions     

Internal gravity waves in a stably stratified boundary layer

Often, a combination of waves and turbulence is present in the stably stratified atmospheric boundary layer. The presence of waves manifest itself in the vertical profiles of variances of fluctuations and in low-frequency contributions to the power spectra. In this paper we study internal waves by means of a linear stability analysis of the mean profiles in a stably stratified boundary layer and compare the results with observed vertical variance profiles of fluctuating wind and temperature along a 200 m mast. The linear stability analysis shows that the observed mean flow is unstable for disturbances in a certain frequency and wavenumber domain. These disturbances are expected to the detectable in the measurements. It is shown that indeed the calculated unstable frequencies are present in the observed spectra. Furthermore, the shape of the measured vertical variance profiles, which increase with height, is explained well by the calculated vertical structure of the amplitude of unstable Kelvin-Helmholtz waves, confirming the contribution of waves to the variances. Because turbulence and waves have quite distinct transport properties, estimates of diffusion from measurements of variances would strongly overestimate this diffusion. Therefore it is important to distinguish between them.     

On equilibrium profiles of suspended particles

A power law is often used to represent the vertical profile of uniform suspended particles above a horizontally homogeneous surface. It serves as an analytical solution representing an equilibrium between vertical turbulent diffusion and gravitational settling, andcan be used to extract settling velocity information from observed particle number density profiles. In this note, we analyse this situation and use a numerical model to investigate the temporal change of particle number density and of the net vertical flux due to turbulent diffusion and gravitational settling. The results show that the net flux approaches zero very slowly for small particles (w_s/ u_* < 1), and show that the power law does not hold for small particles. If the power law is used to extract settling velocities from observed vertical distributions of particle number density in these cases, the estimated settling velocity may be unrealistically large.     

Inertial Effects on the Vertical Transport of Suspended Particles in a Turbulent Boundary Layer

In many atmospheric flows, a dispersed phase is actively suspended by turbulence, whose competition with gravitational settling ultimately dictates its vertical distribution. Examples of dispersed phases include snow, sea-spray droplets, dust, or sand, where individual elements of much larger density than the surrounding air are carried by turbulent motions after emission from the surface. In cases where the particle is assumed to deviate from local fluid motions only by its gravitational settling (i.e., they are inertialess), traditional flux balances predict a power-law dependence of particle concentration with height. It is unclear, however, how particle inertia influences this relationship, and this question is the focus of this work. Direct numerical simulations are conducted of turbulent open-channel flow, laden with Lagrangian particles of specified inertia; in this way the study focuses on the turbulent transport which occurs in the lowest few meters of the planetary boundary layer, in regions critical for connecting emission fluxes to the fluxes felt by the full-scale boundary layer. Simulations over a wide range of particle Stokes number, while holding the dimensionless settling velocity constant, are performed to understand the role of particle inertia on vertical dispersion. It is found that particles deviate from their inertialess behaviour in ways that are not easily captured by traditional theory; concentrations are reduced with increasing Stokes number. Furthermore, a similarity-based eddy diffusivity for particle concentration fails as particles experience inertial acceleration, precluding a closed-form solution for particle concentration as in the case of inertialess particles. The primary consequence of this result is that typical flux parametrizations connecting surface emission models (e.g., saltation models or sea-spray generation functions) to elevated boundary conditions may overestimate particle concentrations due to the reduced vertical transport caused by inertia in between; likewise particle emission may be underestimated if inferred from concentration measurements aloft.     

Global radiation within corn

Global and net solar radiation profiles were measured by traversing sensors at four heights in a square-sown plot and a row plot of field corn on four relatively cloudless days in August 1972. The fluxes and their vertical distributions are discussed. A numerical model of the short-wave radiation fluxes in a canopy is presented. Using leaf area index and fixed leaf radiative properties, calculated values of radiation are within 10% of measurements in most instances. The performance under predominantly beam or diffuse radiation is similar and model values of crop albedo compare well with values calculated from radiation measurements above the crops.     

A COMPARISON BETWEEN THE DOPPLER SODAR AND IN-SITU WIND MEASUREMENTS

In this paper,a comparison is made of the Doppler sodar wind measurement with the in-situ measurements on a 325 m meteorological tower.The results show that when the ratio of signal to noise is larger than 1,the mean wind speeds and directions obtained from the two techniques are well correlated,thus their profiles are close to each other.The mean value and root mean square of vertical velocity measured by the Doppler sodar are a little larger than those measured by a sonic anemometer at a height of 85 m,which is in agreement with the analysis by Gaynor et al.(1983).We notice that there are some differences in the observational results between the Doppler sodar and insitu measurements,especially when comparing the values measured at each time.Therefore,it is important to analyze the reason for the differences and to make corrections to the Doppler sodar measurements.     

BOUNDARY LAYER GROWTH AND LAPSE RATE CHANGES DETERMINED BY LIDAR AND SURFACE HEAT FLUX IN SOFIA*

In this study the results from a boundary layer experiment,conducted in autumn 1991 over a flat,build-up urban area in Southeast Sofia,together with some models for mixed layer growth rates are used to investigate the layered structure of the vertical atmospheric stability distribution in the Sofia Valley.Lidar measurements of aerosol layer heights and morning boundary layer development are combined with surface eddy correlation measurements of kinematic heat and moisture fluxes,profiles of temperature and humidity,wind speed and wind direction.A diagnostic method is presented for determining vertical lapse rates using surface meteorological measurements and lidar returns observed during the transition from nighttime stable stratification to daytime convective boundary layer after the sunrise.     

BOUNDARY LAYER GROWTH AND LAPSE RATE CHANGES DETERMINED BY LIDAR AND SURFACE HEAT FLUX IN SOFIA

In this study the results from a boundary layer experiment,conducted in autumn 1991 over a flat,build-up urbanarea in Southeast Sofia,together with some models for mixed layer growth rates are used to investigate the layered struc-ture of the vertical atmospheric stability distribution in the Sofia Valley.Lidar measurements of aerosol layer heightsand morning boundary layer development are combined with surface eddy correlation measurements of kinematic heatand moisture fluxes,profiles of temperature and humidity,wind speed and wind direction.A diagnostic method is pres-ented for determining vertical lapse rates using surface meteorological measurements and lidar returns observed duringthe transition from nighttime stable stratification to daytime convective boundary layer after the sunrise.     

The Turbulent Lagrangian Time Scale in Forest Canopies Constrained by Fluxes,Concentrations and Source Distributions

One-dimensional Lagrangian dispersion models, frequently used to relate in-canopy source/sink distributions of energy, water and trace gases to vertical concentration profiles, require estimates of the standard deviation of the vertical wind speed, which can be measured, and the Lagrangian time scale, T _L , which cannot. In this work we use non-linear parameter estimation to determine the vertical profile of the Lagrangian time scale that simultaneously optimises agreement between modelled and measured vertical profiles of temperature, water vapour and carbon dioxide concentrations within a 40-m tall temperate Eucalyptus forest in south-eastern Australia. Modelled temperature and concentration profiles are generated using Lagrangian dispersion theory combined with source/sink distributions of sensible heat, water vapour and CO₂. These distributions are derived from a multilayer Soil-Vegetation-Atmospheric-Transfer model subject to multiple constraints: (1) daytime eddy flux measurements of sensible heat, latent heat, and CO₂ above the canopy, (2) in-canopy lidar measurements of leaf area density distribution, and (3) chamber measurements of CO₂ ground fluxes. The resulting estimate of Lagrangian time scale within the canopy under near-neutral conditions is about 1.7 times higher than previous estimates and decreases towards zero at the ground. It represents an advance over previous estimates of T _L , which are largely unconstrained by measurements.     

The Høvsøre Tall Wind-Profile Experiment: A Description of Wind Profile Observations in the Atmospheric Boundary Layer

We present an analysis of data from a nearly 1-year measurement campaign performed at Høvsøre, Denmark, a coastal farmland area where the terrain is flat. Within the easterly sector upstream of the site, the terrain is nearly homogenous. This topography and conditions provide a good basis for the analysis of vertical wind-speed profiles under a wide range of atmospheric stability, turbulence, and forcing conditions. One of the objectives of the campaign was to serve as a benchmark for flow over flat terrain models. The observations consist of combined wind lidar and sonic anemometer measurements at a meteorological mast. The sonic measurements cover the first 100 m and the wind lidar measures above 100 m every 50 m in the vertical. Results of the analysis of observations of the horizontal wind-speed components in the range 10–1200 m and surface turbulence fluxes are illustrated in detail, combined with forcing conditions derived from mesoscale model simulations. Ten different cases are presented. The observed wind profiles approach well the simulated gradient and geostrophic winds close to the simulated boundary-layer height during both barotropic and baroclinic conditions, respectively, except for a low-level jet case, as expected. The simulated winds are also presented for completeness and show good agreement with the measurements, generally underpredicting the turning of the wind in both barotropic and baroclinic cases.     

NO<Subscript>3</Subscript> Vertical Profile Measurements from Remote Sensing Balloon-Borne Spectrometers and Comparison with Model Calculations

Eleven vertical profiles of stratospheric NO₃ have been obtained since 1992 using the AMON and SALOMON balloon-borne UV-visible spectrometers. The measurements are compared to the SLIMCAT 3D model and calculations based on the steady-state hypothesis for NO₃. The calculations cannot reproduce some parts of the profiles which exhibit strong concentration fluctuations over few kilometres, as a consequence of the dependence of NO₃ on local temperature variations. A statistical use of the data allows us to estimate the influence of the temperature dependence of the absorption cross-section on the data analysis, and the validity of the recommended reaction rates available in the literature. Discrepancies exist between the model based on recommended kinetics and observations at warmer temperatures. Nevertheless, the analysis is biased by local temperature inhomogeneities, and only a low-resolution vertical shape of the NO₃ profiles can be retrieved.     

用高分辨率FTIR测量不莱梅港地区HCl和HF在大气中的浓度分布

用高分辨率FTIR测量了Bremerhaven地区太阳红外光谱。通过逐线法及HITRAN数据库计算了拟合光谱,得出该地区HCl和HF的垂直浓度分布。     

用高分辨率FTIR测量不莱梅港地区HCl和HF在大气中的浓度分布

用高分辨率FTIR测量了Bremerhaven地区太阳红外光谱。通过逐线法及HITRAN数据库计算了拟合光谱,得出该地区HCl和HF的垂直浓度分布。     

A Comparison of Higher-Order Vertical Velocity Moments in the Convective Boundary Layer from Lidar with In Situ Measurements and Large-Eddy Simulation

We have analyzed measurements of vertical velocity w statistics with the NOAA high resolution Doppler lidar (HRDL) from about 390 m above the surface to the top of the convective boundary layer (CBL) over a relatively flat and uniform agricultural surface during the Lidars-in-Flat-Terrain (LIFT) experiment in 1996. The temporal resolution of the zenith-pointing lidar was about 1 s, and the range-gate resolution about 30 m. Vertical cross-sections of w were used to calculate second- to fourth-moment statistics of w as a function of height throughout most of the CBL. We compare the results with large-eddy simulations (LES) of the CBL and with in situ aircraft measurements. A major cause of the observed case-to-case variability in the vertical profiles of the higher moments is differences in stability. For example, for the most convective cases, the skewness from both LES and observations changes more with height than for cases with more shear, with the observations changing more with stability than the LES. We also found a decrease in skewness, particularly in the upper part of the CBL, with an increase in LES grid resolution.     

Rapid vertical sampling in stably stratified turbulent shear flows

A new method for obtaining instantaneous vertical profiles of two components of velocity and temperature in thermally stratified turbulent shear flows is presented. In this report, the design and construction of the traversing system will be discussed and results to date will be presented. The method is based on rapid vertical sampling whereby probe sensors are moved vertically at a high speed such that the measurement is approximately instantaneous. The system is designed to collect many measurements for the calculation of statistics such as vertical wave number spectra, mean square vertical gradients, and Thorpe scales. Results are presented for vertical profiles of temperature and compared to vertical profiles measured by single-point Eulerian time averages. The quality of the vertical profiles is found to be good over many profiles. Some comparisons are made between vertical measurements and standard single-point Eulerian measurements for three cases of stably stratified turbulent shear flow in which the initial microscale Reynolds number, Re_λ≈30. In case 1, the mean conditions are characterized by a gradient Richardson number, Ri_g=0.015, for which the flow is “unstable”, meaning the spatially evolving turbulent kinetic energy (E_k) grows. In case 2, Ri_g=0.095, for which the evolving turbulent kinetic energy is almost constant. In case 3, the flow is highly stable, where Ri_g=0.25 and E_k decays with spatial evolution. The measurements indicate anisotropy in the small scales for all cases. In particular, it is found that the ratio grows initially to a maximum and then decays with further evolution. Maximum Thorpe displacements are measured and compared to single-point measures of the vertical scales. It is found that vertical length scales derived from single-point measurements, such as the Ozmidov scale, L_O=(ε/N³)^1/2 and the overturn scale, L_t=θ′/(dT/dz), do not represent well the wide range of overturning scales which are actually present in the turbulence.     

A Method for Retrieving Vertical Ozone Profiles from Limb Scattered Measurements

A two-step method is employed in this study to retrieve vertical ozone profiles using scattered measure- ments from the limb of the atmosphere. The combination of the Differential Optical Absorption Spectroscopy (DOAS) and the Multiplicative Algebraic Reconstruction Technique (MART) is proposed. First, the limb radiance, measured over a range of tangent heights, is processed using the DOAS technique to recover the effective column densities of atmospheric ozone. Second, these effective column densities along the lines of sight (LOSs) are inverted using the MART coupled with a forward model SCIATRAN (radiative transfer model for SCIAMACHY) to derive the ozone profiles. This method is applied to Optical Spectrograph and Infra Red Imager System (OSIRIS) radiance, using the wavelength windows 571-617 nm. Vertical ozone profiles between 10 and 48 km are derived with a vertical resolution of 1 km. The results illustrate a good agreement with the cloud-free coincident SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) ozone measurements, with deviations less than ± 10% ( ± 5% for altitudes from 17 to 47 km). Furthermore, sensitivities of retrieved ozone to aerosol, cloud parameters and NO 2 concentration are also investigated.     

Estimation of sector roughness lengths and the effect on prediction of the vertical wind speed profile

An estimate of roughness length is required by some atmospheric models and is also used in the logarithmic profile to determine the increase of wind speed with height under neutral conditions. The choice of technique for determining roughness lengths is generally constrained by the available input data. Here, we compare sets of roughness lengths derived by different methods for the same site and evaluate their impact on the prediction of the vertical wind speed profile.Wind speed and direction data have been collected at four heights over a three-year period at the North Norfolk Wind Monitoring Site. Wind speed profiles were used to generate sector roughness lengths based on the logarithmic profile formula. This is the only direct way of determining roughness lengths. The simplest and cheapest method is to use maps with published tables giving roughness length estimates for different terrain types. Alternatively Wieringa (1976, 1986) and Beljaars (1987) give formulae for determining roughness lengths from wind speed gusts or standard deviations.The four sets of estimated roughness lengths vary considerably. They were used to estimate 34 m wind speeds from 12.7 m observations. The profile-derived roughnesses are used simply as a check on the prediction of the wind speed profiles. The terrain-derived roughness lengths give reasonable results. Gust-derived and standard deviation roughnesses both predict wind speeds which are lower than the observed ones. The error is greater in the case of standard deviation roughnesses. If stability corrections are applied in the prediction of the vertical wind speed profile, the results are considerably improved.     

The spatial structure of turbulence at production wavenumbers using orthonormal wavelets

Orthonormal wavelet expansions are applied to surface-layer measurements of vertical wind speed under various atmospheric, stability conditions. The orthonormal wavelet transform allows for the unfolding of these measurements into space and scale simultaneously to reveal the large intermittent behavior in space for the turbulent production wavenumbers. Both Fourier and wavelet power spectra indicated the existence of a –1 power law for the vertical velocity measurements at the production wavenumbers. The –1 power law in the turbulent production range was derived from surface-layer similarity theory. A dimensionless skewness, structure function is applied to the wavelet decomposed vertical velocity field to trace the destruction of the shear-or buoyancy-induced anisotropy under various stability conditions. The structure skewness function revealed shear- or buoyancy-induced eddy asymmetry dependence on stability at each scale within the –1 power-law wavenumber range with more isotropy during propagation from smaller to larger wavenumbers. The asymmetry of these events at the turbulent production wavenumbers appeared very localized in space, as well as in scale, and could be described with a simple eddy-overturning model. It is demonstrated that the wavelet transform is suitable for such analysis.