Effects of Different Convection Models Upon the High-Latitude Ionosphere

It is well known that convection electric fields have an important effect on the ionosphere at high latitudes and that a quantitative understanding of their effect requires a knowledge of plasma convection over the entire high-latitude region. Two empirical models of plasma convection that have been proposed for use in studying the ionosphere are the Volland and Heelis models. Both of these models provide a similar description of two-celled ionospheric convection, but they differ in several ways, in particular, in the manner in which plasma flows over the central polar cap and near the polar cap boundary. In order to obtain a better understanding of the way in which these two models affect the ionosphere, two separate runs of our high-latitude, time-dependent ionospheric model were made, with only the convection models distinguishing the two runs. It was found that the two models lead to differences in the ionosphere but often the differences are subtle and are swamped by universal time effects. The most notable differences are in predictions of the height of the F2 peak and in the ion temperature, particularly along the evening polar cap boundary and in the cusp region. For these two parameters, the differences caused by the two different convection models dominate the universal time effects. One question that arises is whether one could examine measurements of plasma density and temperature and determine which of the two convection models most accurately represents actual ionospheric convection. Unfortunately, it is expected that when the effects of other ionospheric inputs are considered, such as the neutral wind, the uncertainties are sufficiently large that the characteristic differences between the Volland and Heelis convection models cannot be clearly identified in an examination of plasma density and temperature measurements

Irrigated water, polymer application in

In the past decade, water-soluble polyacrylamide (PAM) was identified as an environmentally safe and highly effective erosion preventing and infiltration enhancing polymer when applied in furrow irrigation water at 1 mg L-1 - 10 mg L-1 , i.e., 1 ppm- 10 ppm.[1-9] Various polymers and biopolymers have long been recognized as viable soil conditioners because they stabilize soil surface structure and pore continuity. The new strategy of adding the conditioner, high molecular weight anionic PAM, to irrigation water in the first several hours of irrigation implies a significant costs savings over traditional application methods, in which hundreds of kilograms per hectare of soil additives are tilled into the entire (15 cm deep) soil surface layer. By adding PAM to the irrigation water, soil structure is improved in the important 1-5 mm thick layer at the soil/water interface of the 25%-30% of field surface contacted by flowing water. In 1995, the U.S. Natural Resource Conservation Service (NRCS) published a PAM-use conservation practice standard for PAM-use in irrigation water." 01 A 3-year study[21 applying these standards showed that PAM at dosage rates of 1 kg ha-1 -2 kg ha-1 per irrigation eliminated 94% (80%-99% range) of sediment loss in furrow irrigation runoff, while increasing infiltration 15%-50%. Seasonal application rates using the NRCS standard typically total 3 kg ha -1 -5 kg ha-1 . As PAM-use is one of the most effective and economical technologies for reducing soil-runoff, it has branched into stabilization of construction sites and road cuts, with formal statewide application standards set in Wisconsin and several southern states. Recent studies with biopolymers such as charged polysaccharides,[11-143 whey," 51 and industrial cellulose derivatives[11.141 introduce potential biopolymer alternatives to PAM

Fate and efficacy of polyacrylamide applied in furrow irrigation: Full-advance and continuous treatments

Polyacrylamide (PAM) is applied to 400 000 irrigated hectares annually in the USA to control irrigation-induced erosion, yet the fate of dissolved PAM applied in irrigation water is not well documented. We determined the fate of PAM added to furrow streams under two treatments: Initial-10, 10 mg L-1 PAM product applied only during the initial hours of the irrigation, and Cont-1, 1.0 mg L—1 PAM product applied continuously during the entire irrigation. The study measured PAM concentrations in 167-m-long PAM-treated furrow streams and along a 530-m tail ditch that received this runoff. Soil was Portneuf silt loam (coarse-silty, mixed, superactive, mesic Durinodic Xeric Haplocalcid) with 1.5% slope. Samples were taken at three times during the irrigations, both during and after PAM application. Polyacrylamide was adsorbed to soil and removed from solution as the streams traversed the soil-lined channels. The removal rate increased with stream sediment concentration. Stream sediment concentrations were higher when PAM concentrations were <2 mg L-1 a.i., for early irrigations, and when untreated tributary ?ows combined with the stream. In these cases, PAM concentration decreased to undetectable levels over the ?ow lengths used in this study. When in?ows contained >6 mg L-1 PAM a.i., stream sediment concentrations were minimal and PAM concentrations did not change down the furrow, though they decreased to undetectable levels within 0.5 h after application ceased. One percent of applied PAM was lost in tail-ditch runoff. This loss could have been eliminated by treating only the furrow advance or not treating the last two irrigations

Model-Observation Comparison Study of Multiple Polar Cap Arcs

A quantitative model-observation comparison of multiple polar cap arcs has been conducted by using a time-dependent theoretical model of polar cap arcs. In particular, the electrodynamical features of multiple polar cap arcs with various spacings are simulated and the results are compared with the images obtained from the All-Sky Intensified Photometer at Qaanaaq. The results show that the observed and simulated arcs are quite similar, both spatially and temporally. The results support the theory proposed by Zhu et al. [1993a, 1994b] that the structure of polar cap arcs is mainly determined by the magnetosphere-ionosphere (M-I) coupling processes and that the spacing of multiple polar cap arcs is closely related to the hardness of the primary magnetospheric precipitation. It is found that for the multiple polar cap arcs with both narrow and wide spacings, the associated field-aligned currents are mainly closed by Pedersen currents. It is also found that a hard precipitation can lead to a highly structured secondary arc because of the nonlinear M-I coupling processes

What is the Source of Observed Annual Variations in Plasmaspheric Density?

Plasmaspheric densities have been observed previously to be higher in December than in June, with the ratio varying between 1.5 and 3.0 and with larger variations at lower L shells. In order to search for the cause of the observed annual variations, we have modeled plasmaspheric density, using a time-dependent hydrodynamic model. On an L = 2 field line with geomagnetic longitude equal to 300°, the modeled plasmaspheric densities were a factor of 1.5 times higher in December than in June. The modeled December to June density ratio was found to increase slightly with L shell, in contrast to observations; this discrepancy may be due to the fact that outer plasmaspheric flux tubes are never completely full. In addition, for an L = 2 field line with geomagnetic longitude equal to 120°, the modeled plasmaspheric density was higher in June than in December by a factor of about 1.2. Various numerical tests were also performed in order to examine the sensitivity of plasmaspheric density to various parameters. In particular, a large vertical neutral wind was applied in order to raise the O+ profile, which had the effect of raising plasmaspheric density by a factor of 6. This in conjunction with a theoretical analysis suggests that plasmaspheric density levels are very sensitive to O+ levels in the upper ionosphere. We conclude that annual variations in plasmaspheric density are due to similar variations in ionospheric O+

Biopolymer additives to reduce erosion-induced soil losses during irrigation

A series of biopolymers added to irrigation water were tested for their efficacy in reducing shear-induced erosion in a laboratory-scale mini-furrow. Suspensions of chitosan, starch xanthate, cellulose xanthate, and acid-hydrolyzed cellulose microfibrils, at concentrations of 20, 80, 80, and 120 ppm, respectively, reduced suspended solids by more than 80%. None of these biopolymers, however, exhibited the > 90% runoff sediment reduction shown by the present industry standard, synthetic polyacrylamide polymers, PAM. PAM is effective at concentrations as low as 5 ppm. In field tests, chitosan solutions were only marginally effective in reducing runoff from the end of a 137 m long furrow, with indications that results were dependent on the length of the furrow. Sediment runoff of some clay-rich Northern California soils was reduced by up to 85% by increasing the concentration of exchangeable calcium to > 2.5mM. Calcium improved the sedimentation of the polyelectrolytic polymers in this study

Design and calibration of percolation samplers for measuring polyacrylamide-amended furrow-irrigation effects on drainage water quality

Amending irrigation furrow inflows with polyacrylamide (PAM) at low concentrations (10 mg L -1 ) reduces irrigation-induced erosion by 94% and increases infiltration by 15%, relative to untreated furrows. We hypothesized that PAM erosion-control technology would allow irrigation managers to increase furrow inflows to speed furrow-stream advance, produce a more uniform water distribution down field, and reduce the leaching hazard at the upper end (due to reduced infiltration opportunity time and/or shorter sets). We developed, tested, and installed instruments in a furrow irrigated Portneuf silt loam (Co-Si, mixed, mesic, Durixerollic Calciorthids with 1.6% slope) to investigate this premise. Soils were instrumented with repeating pulse multivibrator (CS-615) soil water sensors, thermocouples, tensiometers, and percolation soil water samplers at upper and lower ends of the furrows. Percolation samplers consisted of a 23-cm-deep, 20-cm-dia. stainless-steel beaker with a 1 7-cm-long, 4-cm-dia., 0.5 bar air-entry ceramic cup imbedded in a 5-cm-deep silica flour layer, slurried into the beaker bottom. Water was collected under suction (~ 1.4x ambient) via teflon tubes. Percolation sampler design and testing, field installation, and study experimental design are discussed

Sprinkler irrigation runoff and erosion control with polyacrylamide - laboratory tests

Many semiarid and arid soils are prone to irrigation-induced erosion. Polyacrylamide (PAM) greatly reduces erosion from furrow irrigation. We hypothesized that PAM applied via sprinklers will provide erosion control and benefit water infiltration and aggregate stability. Screened (6.4 mm) Rad silt loam (coarse silty, mixed, superactive mesic Durinodic Xeric Haplocambid) was placed in 1.5 by 1.2 by 0.2 m steel boxes with 2.4% slope. An oscillating nozzle, 3 m above the soil, produced a median drop size of 1.2 mm diameter. We applied 0, 1, 2, 4, and 6 kg ha-1 PAM in 20 mm of water in the first irrigation, followed by two 20-mm water-only irrigations. In a second test, we applied 0, 2, and 4 kg ha-1 PAM in 8 mm of water in the first irrigation, followed by two 20-mm water-only irrigations. Two kilograms per hectare PAM in the first 20-mm irrigation reduced runoff 70% and soil loss 75% compared to control. Polyacrylamide in 8 mm of water was less effective. Polyacrylamide in the 20-mm irrigation did not affect tension infiltration; PAM in the 8-mm irrigation doubled tension infiltration following the third irrigation. Wet aggregate stability following the first irrigation was greater in all PAM treatments than on the check. With 2 kg ha-1 PAM in the 20-mm irrigation, it was 55%; in 8 mm, 77%. Polyacrylamide applied in the first irrigation at low rates effectively reduced runoff and erosion. Erosion was more effectively controlled than runoff

Polymer additives in irrigation water to reduce erosion and better manage water infiltration

Water-soluble polyacrylamide (PAM) was identified as an environmentally safe and highly effective erosion preventing and infiltration-enhancing polymer when applied in furrow irrigation water at 1-10 g m-3, i.e. 1-10 ppm. The agricultural use of polyacrylamide, PAM, as an additive in irrigation water has grown rapidly since commercial introduction in 1995 because it improves water infiltration and reduces erosion-induced soil losses up to 97%, saving tons of topsoil per hectare per year. Various polymers and biopolymers have long been recognized as viable soil conditioners because they stabilize soil surface structure and pore continuity. The new strategy of adding the conditioner, high molecular weight anionic PAM, to the irrigation water in the first several hours of irrigation enables a significant costs savings over traditional application methods of tilling soil conditoner into the entire (15 cm deep) soil surface layer. By adding PAM to the irrigation water, soil structure is Unproved in the all-important 1-5 mm thick layer at the soil/water interface of the 25 to 30% of field surface contacted by flowing water. Recent studies with biopolymers such as chitosan, charged polysaccharides, whey, and industrial cellulose derivatives show potential as biopolymer alternatives to PAM. Their success will depend on production economics

Polyacrylamide as an organic nitrogen source for soil microorganisms with potential effects on inorganic soil nitrogen in agricultural soil

Linear polyacrylamide (PAM) is gaining considerable acceptance as an effective anti-erosion additive in irrigation water. The potential effects of repeated PAM application on soil microbial ecology and the potential for biotransformation of this polymer in soils are not completely known. Untreated and PAM-treated soils (coarse-silty, mixed, mesic Durixerollic Calciorthids) were collected from agricultural fields near Kimberly, ID. Soils were analyzed to determine the effects of PAM treatment on bacterial counts and inorganic N concentrations and the potential for PAM biotransformation. Culturable heterotrophic bacterial numbers were significantly elevated in PAM-treated soil for the plot planted to potatoes; this effect was not observed in the plot planted to dry pink beans. Total bacterial numbers, determined by AODC, were not altered by PAM treatment in any of the soils sampled. Polyacrylamide-treated soil planted to potatoes contained significantly higher concentrations of NO3 and NH 3 (36.7 ± 2.20 and 1.30 ± 0.3 mg kg-1 , respectively) than did untreated soil (10.7 ± 2.30 and 0.50 ± 0.02 mg kg-1, respectively). For bean field soil there was no difference between treated and untreated soil inorganic N concentrations. Enrichment cultures generated from PAM-treated and untreated soils utilized PAM as sole N source, but not as sole C source. While the monomeric constituents of PAM, acrylamide and acrylic acid, both supported bacterial growth as sole C source, the PAM polymer did not. Enrichment cultures that used PAM for N exhibited amidase activity specific for PAM as well as smaller aliphatic amides. Utilization of PAM for N, but not for C, indicates that ultimately PAM may be converted into long chain polyacrylate, which may be further degraded by physical and biological mechanisms or be incorporated into organic matter