The interaction between transpolar arcs and cusp spots

Transpolar arcs and cusp spots are both auroral phenomena which occur when the interplanetary magnetic field is northward. Transpolar arcs are associated with magnetic reconnection in the magnetotail, which closes magnetic flux and results in a “wedge” of closed flux which remains trapped, embedded in the magnetotail lobe. The cusp spot is an indicator of lobe reconnection at the high-latitude magnetopause; in its simplest case, lobe reconnection redistributes open flux without resulting in any net change in the open flux content of the magnetosphere. We present observations of the two phenomena interacting—i.e., a transpolar arc intersecting a cusp spot during part of its lifetime. The significance of this observation is that lobe reconnection can have the effect of opening closed magnetotail flux. We argue that such events should not be rare

Management Guidelines for Controlling Sediments, Nutrients, and Adsorbed Biocides in Surface Irrigation Return Flows

Sediments in irrigation return flows arise mostly from furrow erosion, and nearly all nutrients and biocides in surface irrigation return flows, except those applied directly to the water, are adsorbed to the sediments. Therefore, controlling erosion and sediment loss in these surface return flows also controls the nutrients and biocides. There are three general management approaches for controlling sediments in return flows. The first is to eliminate surface runoff by using irrigation methods that produce no runoff. These methods include properly designed and operated sprinkler systems; basin, trickle, and some border and level furrow methods. The second approach is to eliminate or reduce erosion by controlling the slope in the direction of irrigation, the furrow stream size, the run length, the irrigation frequency and duration, and tillage practices. The third is to remove sediments from surface return flows by controlling the tailwater and utilizing sediment retention basins. All three approaches are applicable and necessary for adequate control in most irrigated areas. Available technology needs to be integrated and applied to these approaches. Research to develop improved irrigation systems and methods, improved irrigation water distribution systems, and better field management practices, and research on design and operational criteria for sediment retention basins are needed

Influence of Off-Sun-Earth Line Distance on the Accuracy of L1 Solar Wind Monitoring

Upstream solar wind measurements from near the L1 Lagrangian point are commonly used to investigate solar wind-magnetosphere coupling. The off-Sun-Earth line distance of such solar wind monitors can be large, up to 100 RE. We investigate how the correlation between measurements of the interplanetary magnetic field and associated ionospheric responses deteriorates as the off-Sun-Earth line distance increases. Specifically, we use the magnitude and polarity of the dayside region 0 field-aligned currents (R0 FACs) as a measure of interplanetary magnetic field (IMF) BY-associated magnetic tension effects on newly-reconnected field lines, related to the Svalgaard-Mansurov effect. The R0 FACs are derived from Advanced Magnetosphere and Planetary Electrodynamics Response Experiment measurements by a principal component analysis, for the years 2010–2016. We perform cross-correlation analyses between time-series of IMF BY, measured by the Wind spacecraft and propagated to the nose of the bow shock by the OMNI technique, and these R0 FAC measurements. Typically, in the summer hemisphere, cross-correlation coefficients between 0.6 and 0.9 are found. However, there is a reduction of order 0.1–0.15 in correlation coefficient between periods when Wind is close to (within 45 RE) and distant from (beyond 70 RE) the Sun-Earth line. We find a time-lag of around 17 min between predictions of the arrival of IMF features at the bow shock and their effect in the ionosphere, irrespective of the location of Wind.publishedVersio

Lobe Reconnection and Cusp-Aligned Auroral Arcs

Following the St. Patrick's Day (17 March) geomagnetic storm of 2013, the interplanetary magnetic field had near-zero clock angle for almost two days. Throughout this period multiple cusp-aligned auroral arcs formed in the polar regions; we present observations of, and provide a new explanation for, this poorly understood phenomenon. The arcs were observed by auroral imagers onboard satellites of the Defense Meteorological Satellite Program. Ionospheric flow measurements and observations of energetic particles from the same satellites show that the arcs were produced by inverted-V precipitation associated with upward field-aligned currents (FACs) at shears in the convection pattern. The large-scale convection pattern revealed by the Super Dual Auroral Radar Network and the corresponding FAC pattern observed by the Active Magnetosphere and Planetary Electrodynamics Response Experiment suggest that dual-lobe reconnection was ongoing to produce significant closure of the magnetosphere. However, we propose that once the magnetosphere became nearly closed complicated lobe reconnection geometries arose that produced interleaving of regions of open and closed magnetic flux and spatial and temporal structure in the convection pattern that evolved on timescales shorter than the orbital period of the DMSP spacecraft. This new model naturally explains many features of cusp-aligned arcs, including why they focus in from the nightside toward the cusp region.publishedVersio

Seasonal and diurnal variations in AMPERE observations of the Birkeland currents compared to modeled results

We reduce measurements made by the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to give the total Birkeland (field-aligned) current flowing in both hemispheres in monthly and hourly bins. We analyze these totals using 6 years of data (2010–2015) to examine solar zenith angle-driven variations in the total Birkeland current flowing in both hemispheres, simultaneously, for the first time. A diurnal variation is identified in the total Birkeland current flowing, consistent with variations in the solar zenith angle. A seasonal variation is also identified, with more current flowing in the Northern (Southern) Hemisphere during Bartels rotations in northern (southern) summer. For months close to equinox, more current is found to flow in the Northern Hemisphere, contrary to our expectations. We also conduct the first test of the Milan (2013) model for estimating Birkeland current magnitudes, with modifications made to account for solar contributions to ionospheric conductance based on the observed variation of the Birkeland currents with season and time of day. The modified model, using the value of ?D averaged by Bartels rotation (scaled by 1.7), is found to agree with the observed AMPERE currents, with a correlation of 0.87 in the Northern Hemisphere and 0.86 in the Southern Hemisphere. The improvement over the correlation with dayside reconnection rate is demonstrated to be a significant improvement to the model. The correlation of the residuals is found to be consistent with more current flowing in the Northern Hemisphere. This new observation of systematically larger current flowing in the Northern Hemisphere is discussed in the context of previous results which suggest that the Northern Hemisphere may react more strongly to dayside reconnection than the Southern Hemisphere

Book review of 'the people make the place: dynamic linkages between individuals and organizations edited by D. Brent Smith'

The People Make the Place is a festschrift celebrating the work of industrial/organizational psychologist Benjamin Schneider. It contains 11 specially written chapters each addressing a different element of Schneider’s work. The twelfth chapter, written by the honored scholar, summarizes the contributions and uses the opportunity to clarify many of the ideas surrounding attraction-selection-attrition (ASA) theory

Interconnected Self-Propagating Photopolymer Waveguides: An Alternative to Stereolithography for Rapid Formation of Lattice-Based Open-Cellular Materials

Recently, a new technique has been developed to create unique open-cellular materials with micro-scale truss, or lattice features ranging from tens to hundreds of microns. These materials are formed from a three-dimensional, interconnected array of self-propagating photopolymer waveguides. By utilizing this self-propagating effect, three-dimensional open-cellular polymer materials can be formed in seconds. In addition, intrinsic to the process is the ability to control specific micro-lattice parameters which ultimately affect the bulk material properties. Unlike stereolithography, this new fabrication technique is rapid (~ minutes to form an entire part) and relies on a single two-dimensional exposure surface to form three-dimensional structures (thickness > 25 mm possible). This combination of speed and planar scalability opens the possibility for large-scale mass manufacturing. The utility of these new materials range from lightweight energy absorbing structures to thermal management materials to bio-scaffolds.Mechanical Engineerin

Sediment-Phosphorus Relations in Surface Runoff from Irrigated Lands

Phosphorus and sediment concentrations were measured in irrigation and drainage waters, and phosphorus and sediment inflows and outflows computed. Relationships between phosphorus and sediment were developed. Total phosphorus and orthophosphate concentrations measured in nonfiltered samples are closely related to the sediment concentration, but dissolved orthophosphate measured in samples filtered through 0.45 µm membrane filters is independent of the sediment concentration. A net sediment inflow was found on one large tract where sediment settles in drains and the amount of surface runoff is low, but a net sediment outflow was found for another tract with steeper drains and from which more surface runoff returned to the river. Net phosphorus inflows were measured on both tracts. Particle size segregation takes place in irrigation and drainage waters whenever the flow velocity is slow enough to allow suspended sediment to settle, and the quantity of phosphorus per unit of sediment remaining suspended increases. Actually, much more phosphorus settles with that portion of the sediment that settles than remains in suspension where sediments are eroded from silt loam or loam soils. Thus, conditions favoring settling are phosphorus conserving conditions

Total Salt, Specific Ion, and Fertilizer Element Concentrations and Balances in the Irrigation and Drainage Waters of the Twin Falls Tract in Southern Idaho

Public interest in environmental quality has aroused concern and speculation about the effects of irrigation and the application of fertilizers on the quality of surface and ground waters. The Environmental Pollution Panel of the President's Science Advisory Committee, and other groups, have recommended that high priority be given to investigating the sources of total salts, specific ions, and nutrients that enter surface and ground waters. One source is drainage from irrigated areas or irrigation return flows. More information is needed about the quality of irrigation return flows under various management systems and climatic environments and on representative soil types. Such information is basic for determining practices to improve the quality of return flows and in planning new irrigation projects. The NO?-N, PO?-P, and total salt concentrations were measured in irrigation and drainage waters on the Twin Falls Canal Company irrigation tract in southern Idaho. This information was combined with a water balance to estimate input-output balances for these components, and results have been reported. The input-output balances for other specific ionic components have been computed for the irrigation and drainage waters of that tract. Results from these investigations and detailed information on specific ion concentrations, temperature and flow characteristics of drainage tunnels, tile-relief well complexes, and large surface drains are reported herein

Water Soluble NO3-Nitrogen, PO4-Phosphorus, and Total Salt Balanced on a Large Irrigation Tract

Return flow from a 82,030-ha (202,700-acre) tract of calcareous silt loam soils irrigated with water diverted from the Snake River in southern Idaho increased the downstream total soluble salt and NO?-N loads, but decreased the downstream PO?-P load. Under the existing water management practice, 50% of the total input water returned to the Snake River as subsurface drainage. Net total soluble salt output was 2.4 metric tons/ha (1.0 English ton/acre) and, on the average, was considerably greater than necessary to maintain a salt balance. Net NO?-N output was 33 kg/ha (30 lb/acre). Only about 30% as much PO?-P left the tract via drainage water as entered the tract in irrigation water. As water passed through the soil, PO?-P was removed by chemical reactions in the soil, thus decreasing the concentration in the subsurface drainage water and decreasing the downstream PO?-P load. Applied P fertilizer was not leached into the drainage water