Changes In Vertical Profiles Research Articles

Variation Characteristics and Influencing Factors of Soil Moisture Content in the Lime Concretion Black Soil Region in Northern Anhui

Soil moisture content (SMC) is an important factor affecting crop growth. Based on the field SMC data measured at the Wudaogou experimental station from 1989 to 2019, two typical crop types, wheat and maize, were selected. By combining the groundwater depth, crop growth period, and meteorological factors in the same period, and using classical statistics and redundant analysis (RDA) methods, the characteristics and influencing factors of SMC changes in vertical profiles of different crops were compared and analyzed. The results showed that the SMC and average daily water storage of wheat were greater than that of maize. The crop growth mainly consumed 0–60 cm SMC. The SMC in this area was moderately variable; the SMC of 0–30 cm belongs to the active layer, and the SMC of 30–100 cm belongs to the sub-active layer. The RDA method identified ground temperature, groundwater depth, relative humidity, and the wheat growing period as the main factors affecting soil moisture variation in wheat fields; groundwater depth, relative humidity, and water vapor pressure differences were the main factors affecting soil moisture variation in maize fields. The results can provide a basis for accurate prediction of soil water dynamics and thus provide a reference for irrigation decision-makers.

Evaluation and Evolution of MAX-DOAS-observed Vertical NO2 Profiles in Urban Beijing

Multiaxis differential absorption spectroscopy (MAX-DOAS) is a newly developed advanced vertical profile detection method, but the vertical nitrogen dioxide (NO2) profiles measured by MAX-DOAS have not yet been fully verified. In this study, we perform MAX-DOAS and tower gradient observations to simultaneously acquire tropospheric NO2 observations in the Beijing urban area from 1 April to 31 May 2019. The average values of the tropospheric NO2 vertical column densities measured by MAX-DOAS and the tropospheric monitoring instrument are 15.8 × 1015 and 12.4 × 1015 molecules cm−2, respectively, and the correlation coefficient R reaches 0.87. The MAX-DOAS measurements are highly consistent with the tower-based in situ measurements, and the correlation coefficients R from the ground to the upper air are 0.89 (60 m), 0.87 (160 m), and 0.76 (280 m). MAX-DOAS accurately measures the trend of NO2 vertical profile changes, although a large underestimation occurs by a factor of two. By analyzing the NO2 vertical profile, the NO2 concentration reveals an exponential decrease with height. The NO2 vertical profile also coincides with the evolution of the boundary layer height. The study shows that the NO2 over Beijing mainly originates from local sources and occurs in the boundary layer, and its vertical evolution pattern has an important guiding significance to better understand nitrate production and ozone pollution.

Estimation of water quality dynamics under long-term anoxic state in organically polluted reservoir by field observations and improved ecosystem model

In closed water bodies with significant organic pollution, anoxification due to thermal stratification leads to the elution of nitrogen and phosphorus from the bottom sediment and the generation of sulfide, resulting in further degradation of the water environment. This study focuses on the water quality dynamics in an organically polluted reservoir exhibiting long-term anoxification using two approaches: (1) field observations of seasonal changes in vertical profiles of dissolved oxygen, nitrogen, phosphorus, and sulfide and (2) construction of a water quality prediction model based on an ecosystem model incorporated with anaerobic biochemical processes. Iron and sulfate reduction occurred simultaneously because nitrate–nitrogen was reduced by denitrifying bacteria after the anoxification, and iron reduction became the main factor of the increase in ammonium–nitrogen and phosphate–phosphorus. The redox state of the bottom sediment surface, when anoxification began to occur, greatly affected the water quality dynamics caused by gradual reductive reactions under anaerobic conditions. Furthermore, the calculation accuracy of ammonium–nitrogen, phosphate–phosphorus, and sulfide was highly improved by modifying the conventional model based on the field observations. The characteristics of water quality under anaerobic conditions were sufficiently reflected in the upgraded ecosystem model. The proposed water quality prediction model could be used to quantitatively estimate the water environment dynamics in organically polluted water bodies. The model could be developed further in the future to solve the problems caused by long-term anoxification.

Vertically resolved characteristics of air pollution during two severe winter haze episodes in urban Beijing, China

Abstract. We conducted the first real-time continuous vertical measurements of particle extinction (bext), gaseous NO2, and black carbon (BC) from ground level to 260 m during two severe winter haze episodes at an urban site in Beijing, China. Our results illustrated four distinct types of vertical profiles: (1) uniform vertical distributions (37 % of the time) with vertical differences less than 5 %, (2) higher values at lower altitudes (29 %), (3) higher values at higher altitudes (16 %), and (4) significant decreases at the heights of ∼ 100–150 m (14 %). Further analysis demonstrated that vertical convection as indicated by mixing layer height, temperature inversion, and local emissions are three major factors affecting the changes in vertical profiles. Particularly, the formation of type 4 was strongly associated with the stratified layer that was formed due to the interactions of different air masses and temperature inversions. Aerosol composition was substantially different below and above the transition heights with ∼ 20–30 % higher contributions of local sources (e.g., biomass burning and cooking) at lower altitudes. A more detailed evolution of vertical profiles and their relationship with the changes in source emissions, mixing layer height, and aerosol chemistry was illustrated by a case study. BC showed overall similar vertical profiles as those of bext (R2=0.92 and 0.69 in November and January, respectively). While NO2 was correlated with bext for most of the time, the vertical profiles of bext ∕ NO2 varied differently for different profiles, indicating the impact of chemical transformation on vertical profiles. Our results also showed that more comprehensive vertical measurements (e.g., more aerosol and gaseous species) at higher altitudes in the megacities are needed for a better understanding of the formation mechanisms and evolution of severe haze episodes in China.

On the Nature of the Transition Between Roll and Cellular Organization in the Convective Boundary Layer

Both observational and numerical studies of the convective boundary layer (CBL) have demonstrated that when surface heat fluxes are small and mean wind shear is strong, convective updrafts tend to organize into horizontal rolls aligned within 10–20\(^\circ \) of the geostrophic wind direction. However, under large surface heat fluxes and weak to negligible shear, convection tends to organize into open cells, similar to turbulent Rayleigh-Benard convection. Using a suite of 14 large-eddy simulations (LES) spanning a range of \(-z_i/L\) between zero (neutral) and 1041 (highly convective), where \(z_i\) is the CBL depth and L is the Obukhov length, the transition between roll- and cellular-type convection is investigated systematically for the first time using LES. Mean vertical profiles including velocity variances and turbulent transport efficiencies, as well the “roll factor,” which characterizes the rotational symmetry of the vertical velocity field, indicate the transition occurs gradually over a range of \(-z_i/L\); however, the most significant changes in vertical profiles and CBL organization occur from near-neutral conditions up to about \(-z_i/L \approx \) 15–20. Turbulent transport efficiencies and quadrant analysis are used to characterize the turbulent transport of momentum and heat with increasing \(-z_i/L\). It is found that turbulence transports heat efficiently from weakly to highly convective conditions; however, turbulent momentum transport becomes increasingly inefficient as \(-z_i/L\) increases.

Thermocline deepening boosts ecosystem metabolism: evidence from a large-scale lake enclosure experiment simulating a summer storm.

Extreme weather events can pervasively influence ecosystems. Observations in lakes indicate that severe storms in particular can have pronounced ecosystem-scale consequences, but the underlying mechanisms have not been rigorously assessed in experiments. One major effect of storms on lakes is the redistribution of mineral resources and plankton communities as a result of abrupt thermocline deepening. We aimed at elucidating the importance of this effect by mimicking in replicated large enclosures (each 9m in diameter, ca. 20m deep, ca. 1300m3 in volume) a mixing event caused by a severe natural storm that was previously observed in a deep clear-water lake. Metabolic rates were derived from diel changes in vertical profiles of dissolved oxygen concentrations using a Bayesian modelling approach, based on high-frequency measurements. Experimental thermocline deepening stimulated daily gross primary production (GPP) in surface waters by an average of 63% for >4weeks even though thermal stratification re-established within 5days. Ecosystem respiration (ER) was tightly coupled to GPP, exceeding that in control enclosures by 53% over the same period. As GPP responded more strongly than ER, net ecosystem productivity (NEP) of the entire water column was also increased. These protracted increases in ecosystem metabolism and autotrophy were driven by a proliferation of inedible filamentous cyanobacteria released from light and nutrient limitation after they were entrained from below the thermocline into the surface water. Thus, thermocline deepening by a single severe storm can induce prolonged responses of lake ecosystem metabolism independent of other storm-induced effects, such as inputs of terrestrial materials by increased catchment run-off. This highlights that future shifts in frequency, severity or timing of storms are an important component of climate change, whose impacts on lake thermal structure will superimpose upon climate trends to influence algal dynamics and organic matter cycling in clear-water lakes.

Estimation of roughness length Z0for Kalpakkam site

The accurate knowledge of the surface topographic parameters, which represent terrain characteristics of a site, is required in atmospheric dispersion modeling. The rough surface retards the wind flow from a smooth surface, which results in sharp decrease in wind speed, change in vertical profile along with atmospheric stability. Dispersion models require extrapolation of wind speed U Ref at measured height Z Ref to the wind speed U Stack at stack height Z Stack , based on power law wind profile. Wind speed profile can be evaluated using site specific surface scaling parameters roughness length Z 0 and friction velocity U * . In this paper, sector dependent Z 0 and U * for Kalpakkam site is evaluated for neutral category and the sector values of Z 0 are explained according to the terrain features. The maximum and minimum Z 0 was observed in SSE (0.84 m) and N (0.26 m) upwind sectors due to the presence of more number of residential buildings, sand dunes, and high traffic, in contrast to N sector where mostly agricultural farming lands are present. The site specific wind speed profile index P is calculated based on Z 0 for different sectors leads to better estimation of annual dilution factor and gamma dose on the part of neutral category computation. The surface scaling parameter mean surface drag coefficient C D was estimated to be 0.16, which implies urban environment at Kalpakkam site.

Numerical modelling of wave current interactions at a local scale

The present work is focused on the evaluation of wave–current interactions through numerical simulations of combined wave and current flows with the Code_Saturne (Archambeau et al., 2004), an advanced CFD solver based on the RANS (Reynolds Averaged Navier–Stokes) equations. The objectives of this paper are twofold. Firstly, changes in the mean horizontal velocity and the horizontal-velocity amplitude profiles are studied when waves are superposed on currents. The influence of various first and second order turbulence closure models is addressed. The results of the numerical simulations are compared to the experimental data of Klopman (1994) and Umeyama (2005). Secondly, a more detailed study of the shear stresses and the turbulence viscosity vertical profile changes is also pursued when waves and currents interact. This analysis is completed using the data from Umeyama (2005). A relationship between a non-dimensional parameter involving the turbulence viscosity and the Ursell number is subsequently proposed.

Summertime columnar content of atmospheric water vapor from ground‐based Sun‐sky radiometer measurements through a new in situ procedure

A new in situ technique for the retrieval of atmospheric water vapor content (i.e., precipitable water content) from Sun photometric direct solar irradiance measurements, taken at the 940 nm wavelength during clear‐sky conditions, is presented. The procedure is applied to summer data recorded in 2007, 2008, and 2009 with a Sun‐sky radiometer at the San Pietro Capofiume station in the Po valley, Italy. It is a preliminary development of the retrieval procedure providing the columnar water vapor content from measurements performed with PREDE Sun‐sky radiometers. The technique brings improvement and innovation by retrieving the best values of constants (a and b), characterizing atmospheric water vapor transmittance while reducing simulation errors, and potentially contains information on seasonal changes in vertical profiles of temperature, air pressure, and moisture at measurement sites. Initially, the in situ procedure needs at least 1 week of independent measurements of precipitable water content taken over a range of solar zenith angles simultaneously with radiometric measurements, but it was also tested for cases in which independent measurements are not available. In the latter, the procedure was started using monthly precipitable water content estimates derived from surface observations of relative humidity, pressure, and temperature. Time patterns and absolute values of precipitable water content retrieved using the in situ procedure were in good agreement with Moderate Resolution Imaging Spectroradiometer retrievals and radiosonde measurements, with correlation coefficients of 0.8–0.9 and low percentage median differences of 7%–13%.

Permeability as an important parameter for radon risk classification of foundation soils

Permeability of soils and rocks for gases is one of the main parameters for final radon risk classification of building sites. For the improvement of the method for radon risk classification it is recommended to complete in situ measurements of permeability and/or results derived from grain size analysis by an expert description of parameters of soils and rocks and their changes in vertical profile.

Distribution and ecological effect of mercury in Laogang landfill, Shanghai, China

Laogang landfill near Shanghai is the largest landfill in China, and receives about 10000 t of daily garbage per day. Samples of topsoil and plants were analyzed to evaluate mercury pollution from the landfill. For topsoil samples, there were significant correlations among total mercury (Hg T), combinative mercury (Hg c) and gaseous mercury (Hg G), and content of total organic carbon (TOC), but, no significantly relationship was found between Hg content and filling time. Hg content changes in vertical profiles with time showed that the average Hg T of profiles 1992, 1996, and 2000 was similar, but their average Hg G was quite different. Hg T was significantly correlated with Hg c in profile 1992 and 2000, and Hg T was significantly correlated with Hg G in profile 1996. Hg G/Hg T ratio in profile samples decreased in the order of (Hg G/Hg T) 1992>(Hg G/Hg T) 1996≫(Hg G/Hg T) 2000. A simple outline of Hg release in landfill could be drawn: with increasing of filling time, degradation undergoes different biodegradation, accordingly, gaseous mercury goes through small, more, and small proportion to total mercury. Distribution of Hg in plants was inhomogeneous, following the order of leaf>root>stem. The highest value of leaf may be associated with higher atmospheric Hg from landfill. Ligneous plants (e.g. Phyllostachys glanca, Prunus salicina and Ligustrum lucidum) are capable of enriching more Hg than herbaceous plants.

Resistance of two dentin-bonding agents and a dentin densensitizer to acid erosion in vitro

Objectives: To determine the resistance of two dentin-bonding agents (DBAs) and a dentin desensitizer to simulated dental erosion. Methods: Twenty teeth in each of three groups of selected premolars, with exposed cervical dentin, were treated with one of three dentin surface treatment systems: Gluma Desensitizer (Heraeus Kulzer (UK) Ltd), One Coat Bond (Whaledent (UK) Ltd), and Optibond FL (Kerr (UK) Ltd) and exposed to water (control) and an erosive challenge (Coca Cola ®) for 14 days. Sequential tracings of the specimens were taken, superimposed and the mean reduction in densensitizer or DBA thickness and or tooth loss determined. Results: A mean loss of 77 μm (s.d. 14.6 μm) of tooth tissue over the untreated sites following 14 days exposure to Coca Cola ® was observed. The application of DBAs, as opposed to Gluma Desensistizer alone, over exposed dentin surfaces afforded substantial protection against erosion by Coca Cola ® over the period of study. The mean change in vertical profile of teeth treated with a DBA was 20 μm (s.d. 14.7 μm), almost four times less than that seen over untreated sites. Significance: With the exception of Gluma Desensitizer, which was lost completely, One Coat Bond and Optibond FL demonstrated levels of acid dissolution resistance, which would be of potential value clinically.

Initial burial and subsequent degradation of sedimented phytoplankton: relative impact of macro- and meiobenthos

The initial burial (transfer through the sediment-water interface) and subsequent degradation of sedimented phytoplankton was examined in the laboratory in sediments containing meiofauna, both with and without macrofauna, over a 10-day period. Burial and degradation were monitored by following changes in vertical profiles of Chl a and phaeopigments in sediment columns with and without an addition of senescent Skeletonema costatum Greville (Cleve) cells to the sediment surface. The macrofauna present in the cores consisted of a subsurface deposit-feeder assemblage typical of organically enriched habitats. Upon diatom addition, the visual redox potential discontinuity (RPD) rose to or near the sediment surface. Chl a and phaeopigment levels increased 6 and 3 days after diatom addition, respectively, with no difference in concentrations in the presence or absence of macrofauna. These increases appeared to be confined to the top 5 mm of sediment. Overall, phaeopigment concentrations were higher in cores containing macrofauna. A minimum of 83 % of the added Chl a was transferred through the sediment-water interface in 10 days. In organically enriched habitats, the initial burial and subsequent degradation of sedimented phytoplankton appears to be a process dominated by the meiofaunal and microbial communities, and unaffected by subsurface deposit-feeding macrofauna.

Diurnal Variation in Physical Attributes Associated With Photosynthesis of a Tobacco Canopy

Diurnal changes in vertical profiles of sunlit foliage and distributions of the angle between the leaves and the sun were derived from computer representations of the actual foliage display of a tobacco crop. The crop was analysed at five stages of development. Diurnal variations in the proportion of sunlit leaf area were significant only at lower solar elevations. For a large part of the day, most of the foliage of small, isolated plants was directly lit, whereas the proportion of beam-lit foliage fell to approximately 0.4 in larger crops. The distributions of sunlit foliage with respect to the leaf-beam angle were used to assess the efficiency with which photosynthetically active radiation was captured by the component layers of the crop. At each stage of development, larger proportions of sunlit foliage at intermediate and higher leaf-beam angles coincided with higher solar elevations. These results are discussed in the context of the photosynthetic response of tobacco leaves. Sunlit leaf area and its distribution with respect to the leaf-beam angle were also estimated with a model of the foliage display of tobacco plants. The model accounted for the presence and influence of neighbouring plants in the crop. Comparisons between model estimates and those from geometrical representations of the crop are discussed in assessing model performance.

Influence of San Gabriel submarine canyon on narrow-shelf sediment dynamics, southern California

Variations in the concentration of total suspended particulate matter (TSM) collected 1 m above bottom, changes in vertical profiles of light transmission, and substrate textural patterns reveal a corridor for preferential sediment transport on San Pedro continental shelf, California. During the winter, this corridor, designated the preferential transport corridor (PTC), is defined by higher concentrations of TSM relative to the rest of the shelf and extends for 10–15 km from the inner shelf to the head of San Gabriel Submarine Canyon. Vertical profiles of light transmission within the PTC suggest density stratification throughout the water column and apparent mixing in the upper 15–20 m of water column on either side of the PTC. The PTC is not as fully developed during the summer. Excursions in isopleths of substrate textural variables perpendicular to isobaths in the PTC suggest that although the PTC is seasonally episodic, it recurs regularly over a longer period. A conceptual model attributes the PTC to modification of shelf circulation patterns by San Gabriel Canyon. Surface waves diverge over the canyon head resulting in differential wave set up at the shore face. This forces back turbid nearshore water for a distance of a few kilometers toward the canyon. At some point on the shelf, seaward nearshore flow overlaps offshore currents generated or modified by internal waves focused onto the shelf by the canyon and/or turbulent eddies produced by flow separation in currents moving across the canyon axis. At times, these subtle processes overprint tidal and wind-driven currents and thereby create the PTC. The model suggests that canyons heading several kilometers from shore can have a regulatory effect on narrow-shelf sediment dynamics.