Effects Of Vertical Variations Research Articles

Studying the effect of vertical variation of wind speed and eddy diffusivity on the advection-diffusion equation

Studying the effect of vertical variation of wind speed and eddy diffusivity on the advection-diffusion equation

Effects of Vertical Variation in Vegetation Density on Wave Attenuation

AbstractA physical model experiment was used to investigate irregular wave attenuation through emergent vegetation with variations in stem heights. The experiment was conducted with six peak periods, six incident wave heights, and two schemes of vegetation. One scheme used uniform vegetation (constant stem height) and the other scheme approximated vegetation with larger biomass near the bottom and decreasing linearly to the surface, consistent with observed biomass patterns in the field. Although distributions were different, the total vertical projected area was kept constant between the two schemes. The cross shore variation of wave heights across the vegetation were measured, and losses due to sidewall and bottom friction effects were measured and removed from the wave attenuation in the vegetated cases to isolate the influence of vegetation. The normalized wave height attenuation for each case was fit to the decay equation to determine the difference of vegetation transmission coefficients Kv and damp...

Preservation of meandering river channels in uniformly aggrading channel belts

AbstractChannel belt deposits from meandering river systems commonly display an internal architecture of stacked depositional features with scoured basal contacts due to channel and bedform migration across a range of scales. Recognition and correct interpretation of these bounding surfaces is essential to reconstruction of palaeochannel dimensions and to flow modelling for hydrocarbon exploration. It is therefore crucial to understand the suite of processes that form and transfer these surfaces into the fluvial sedimentary record. Here, the numerical model ‘NAYS2D’ is used to simulate a highly sinuous meandering river with synthetic stratigraphic architectures that can be compared directly to the sedimentary record. Model results highlight the importance of spatial and temporal variations in channel depth and migration rate to the generation of channel and bar deposits. Addition of net uniform bed aggradation (due to excess sediment input) allows quantification of the preservation of meander morphology for a wide range of depositional conditions. The authors find that the effect of vertical variation in scouring due to channel migration is generally orders of magnitude larger than the effect of bed aggradation, which explains the limited impact bed aggradation has on preservation of meander morphology. Moreover, lateral differences in stratigraphy within the meander belt are much larger than the stratigraphic imprint of bed aggradation. Repeatedly produced alternations of point bar growth followed by cut‐off result in a vertical trend in channel and scour feature stacking. Importantly, this vertical stacking trend differs laterally within the meander belt. In the centre of the meander belt, the high reworking intensity results in many bounding surfaces and disturbed deposits. Closer to the margins, reworking is infrequent and thick deposits with a limited number of bounding surfaces are preserved. These marginal areas therefore have the highest preservation potential for complete channel deposits and are thus best suited for palaeochannel reconstruction.

Contribution of baroclinic mechanism in the formation of the depression during MONEX-79

A linear baroclinic stability analysis is performed for the basic vertical zonal wind profile prior to the formation of the depression during Bay of Bengal phase of MONEX-79 by utilizing a quasi- geostrophic, multilayer, numerical model. The preferred wavelength obtained from the growth rate spectrum is 1400 km for the channel width 1500 km, with an e-folding time 5.2 days. The wave structure in the vertical is computed and compared with the observed structure of the depression. Many common features are noticed between them. Further, the vertical structure of the preferred wave obtained from the modified wind profile, removing wind shear below the westerly maximum level, shows closer agreement to the depression structure than that obtained from the full profile. The effect of vertical variation of static stability in the lower layers on the growth of short unstable waves is studied. It is found that a decrease in static stability in the lower layers resulted in the increase in growth rate and decrease in the preferred wavelength.

Vertical-structure effects on planetary microwave brightness temperature measurements: Applications to the lunar regolith

The effects of vertical variations in density and dielectric constant on nadir-viewing microwave brightness temperatures are examined. Stratification models as well as models of a continuous increase in density with depth are analyzed. Specific applications address the vertical structure of the lunar frontside regolith, utilizing combined constraints from Apollo data, bistatic radar signatures, and Earth-based measurements of the lunar microwave brightness temperature. Results have been analyzed in terms of the effects on the zeroth and first harmonic of the lunar disk-center brightness temperature variation over a lunation, and their wavelength dependence. Lunation-mean brightness temperatures, which are diagnostic of emissivity and steady-state sub-surface temperatures, are sensitive to both near-surface soil density gradients and single high-impedance dielectric contrasts. Models of the rapid density increase in the upper 5–10 cm of the lunar regolith predict brightness temperature decreases of 2–10°K between λ 0 = 3 and 30 cm. The magnitude of this spectral variation depends upon the thickness of a postulated low-density surface coating layer, and the magnitude of the density gradient in the transition soil layer. Comparable decreases in brightness temperature can be produced by a stratified two-layer model of soil overlaying bedrock if the high-density substrate lies within 1–2 m of the surface. Multiple soil layering on a centimeter scale, such as is observed in the Apollo core samples, is not likely to induce spectral variations in mean brightness temperature due to rapid regional variations in layer depths and thicknesses. The fractional variation in disk-center brightness temperature over a lunation (first harmonic) can be altered by vertical-structure effects only for the case in which a larger and abrupt dielectric contrast exists within the upper surface layer where the significant diurnal variations in physical temperature occur. Soil density variations do not cause scattering effects sufficient to significantly alter the microwave emission weighting function within the diurnal layer. For the Moon, this layer consists of the upper 10 cm. Since no widespread rock substrate as shallow as 10 cm exists in the lunar frontside, only volume scattering effects, due to buried shallow rock fragments, can explain the apparent high electrical loss inferred from Earth-based measurements of the amplitude of lunation brightness temperature variations. Representative models of the lunar frontside vertical structure have also been examined for their effects of radar cross-section measurements and resultant inferences of bulk dielectric constant. Models of the near-surface density gradient predict a significant increase in the remotely inferred dielectric constant value from centimeter to meter wavelengths. Such a model is in general agreement with the dielectric constant spectrum inferred from Earth-based brightness temperature polarization measurements, but is difficult to reconcile with the Apollo bistatic radar results at λ 0 = 13 and 116 cm.

On the Wavelength of Maximum Baroclinic Instability

Abstract A four-level quasigeostrophic model of a baroclinic atmosphere is used to examine the instability of short (∼2000 km) baroclinic waves. It is determined that only a slight decrease in the low-level static stability or increase in the low-level wind shear relative to the stale stability and wind shear in the middle and upper troposphere can mean the difference between the maximum growth rate occurring at a wavelength of 4000 km (∼wavenumber 7) or 2000 km (∼wavenumber 15). Similar changes of static stability in the upper troposphere relative to the middle and lower troposphere have very little effect on the growth-rate spectrum. This effect of vertical variations in the static stability and wind shear on the growth-rate spectrum is consistent with the structure of the short wavelengths. Wavelengths 4000 km extend through the depth of the troposphere. Therefore, changes in the static stability of the basic zonal flow near the earth's...