698 research outputs found
Carriers and sources of magnetopause current: MMS Case Study
No full textWe investigate the current carriers and current sources of an ion scale tangential magnetopause current layer using the Magnetospheric Multiscale four spacecraft data. Within this magnetopause current layer, ions and electrons equally contribute to the perpendicular current, while electrons carry nearly all the parallel current. The energy range of all these current carriers is predominantly from middle to high (>100 eV), where particles with higher energies are more efficient in producing the current. By comparing each term, two-fluid magnetohydrodynamic (MHD) theory is able to describe the current sources to a large degree because the sum of all the perpendicular currents from MHD theory could account for the currents observed. In addition, we find that the ion diamagnetic current is the main source of the total perpendicular current, while the curvature current can be neglected. Nevertheless, ions and electrons both carry comparable current due to the redistribution of the electric field and show features beyond the classic Chapman-Ferraro model, particularly on the front side of the boundary layer where the electric field reversal is most intense. We also show a second, comparative event in which ions do not satisfy MHD theory, while the electrons do. The small-scale, adiabatic parameter (square of curvature radius/gyroradius) supports our interpretation that this second event contains ion scale substructure. We suggest that comparing the predicted MHD current with plasma current can be a good method to judge whether the MHD theory is satisfied in each specific circumstance, especially for high-precision Magnetospheric Multiscale data.</p
Automated calibration of a flight particle spectrometer
No full textA system for calibrating both electron and ion imaging particle spectrometers was devised to calibrate flight instruments in a large vacuum facility in the Space Science Laboratory at the Marshall Space Flight Center. An IBM-compatible computer was used to control, via an IEEE 488 buss protocol, a two-axis gimbled table, constructed to fit inside the tank. Test settings of various diagnostic voltages were also acquired via the buss. These spectrometers constructed by the author at UCSD were calibrated in an automatic procedure programmed on the small computer. Data was up-loaded to the SSL VAX where a program was developed to plot the results
Petitions and memorials
No full textPetition of the subscribers, citizens of Georgetown, praying that the General Assembly would pass a law to enable Jonathan R. Torbert, David B. Smith, Edward Wooten, and Gustavus A. Ewing to close certain parts of three alleys in Georgetown. (Related Act is Document 1111-000-000_16962d
Genetic study of carotenoids in maize grain (Zea mays L.)
No full textPro-Vitamin A (proVA) carotenoids, which are converted into retinol (Vitamin A) in the human body, have been the subject of human nutrition studies and are a target for biofortification of staple crops. Historically, β-carotene has been the principal target for enhancing levels of proVA, yet there is recent interest in enhancing the proVA carotenoid β-cryptoxanthin. Studies have shown that β-cryptoxanthin has excellent bioavailability, and its use in maize may be nearly as effective as β-carotene in providing retinol. The primary aim of this study was to gain a better understanding of the genetic control of levels of β-cryptoxanthin, conversion of β-carotene into β-cryptoxanthin, conversion of β-cryptoxanthin into zeaxanthin, and flux into the β-branch of the carotenoid pathway. We studied a biparental population derived from inbreds with relatively high levels of β-cryptoxanthin and different ratios of β-cryptoxanthin to β-carotene. Three field replications of this F2:3 population were grown and the grain analyzed by liquid chromatography (LC) with diode array detection. Data from a previous study using two color assessment methods, visual score and chromameter readings, were included to associate and compare LC and color results. Composite interval mapping (CIM) identified 90 quantitative trait loci (QTL). Notably, we detected a QTL for Ratio 3 (β-carotene / [β-cryptoxanthin + zeaxanthin]) and Ratio 5 ([β-carotene + β-cryptoxanthin] / zeaxanthin) on chromosome 2 that contains candidate gene hydroxylase 4 (hyd4), which has not been previously associated with QTL for carotenoids in maize grain. A common finding for LC and chromameter data included a QTL on chromosome 5 for β-carotene, zeaxanthin, β-carotene + β-cryptoxanthin, β-branch proVA, cisβC, Total carotenoids, Ratio 1 (β-carotene / β-cryptoxanthin + zeaxanthin), h, h99 and b*. This region contains candidate gene lycopene β cyclase (lcyβ). This new information could potentially be used in biofortification breeding programs to increase the content of proVA and the total carotenoids in maize
Evolution of Kelvin-Helmholtz activity on the dusk flank magnetopause
No full textOur purpose is to characterize the evolution of the magnetopause Kelvin-Helmholtz
(KH) wave activity with changes in thickness of the adjacent boundary layer,
geomagnetic latitude and interplanetary magnetic field (IMF) orientation. As the IMF
turns northward, wave activity may be generated at the dayside before propagating
down the tail, where the boundary layer is expected to support longer wavelengths. We
use two-point observations on the dusk magnetopause at low latitudes, from Geotail on
the dayside and Cluster tailward of the dusk terminator. We quantify the wavelength,
power, wavefront steepness and propagation direction at Cluster. An estimate of the
thickness of the low-latitude boundary layer (LLBL) is obtained by correlating normal
distances to the magnetopause, derived from two empirical solar-wind-driven models,
with a systematic relationship (the "transition parameter") found between the electron
number density and temperature; the correlation factor is used to infer the temporal
evolution of the thickness of the locally sampled layer. We find that wavelengths are
controlled by the IMF clock angle, as expected when generated by the KH mechanism
at the dayside, although amplitudes, wavefront steepness and propagation directions are
more closely correlated with the layer thickness. A survey of parameter space provides
evidence of the contribution of the KH mechanism to the widening of the electron LLBL
Petitions and memorials
No full textPetition of the subscribers, citizens of Georgetown, praying that the General Assembly would pass a law to enable Jonathan R. Torbert, David B. Smith, Edward Wooten, and Gustavus A. Ewing to close certain parts of three alleys in Georgetown. (Related Act is Document 1111-000-000_16962d
Reply to comment by H. Hasegawa on "Evolution of Kelvin-Helmholtz activity on the dusk flank magnetopause"
No full textWe demonstrate, on experimental grounds, that the justifications for the comment by Hasegawa [2009], hereinafter
H09, on work done by Foullon et al. [2008], hereinafter F08, are not well founded
Two-Dimensional Velocity of the Magnetic Structure Observed on July 11, 2017 by the Magnetospheric Multiscale Spacecraft
No full textIn order to determine particle velocities and electric field in the frame of the magnetic structure, one first needs to determine the velocity of the magnetic structure in the frame of the spacecraft observations. Here, we demonstrate two methods to determine a two-dimensional magnetic structure velocity for the magnetic reconnection event observed in the magnetotail by the Magnetospheric Multiscale (MMS) spacecraft on July 11, 2017, Spatio-Temporal Difference (STD) and the recently developed polynomial reconstruction method. Both of these methods use the magnetic field measurements; the reconstruction technique also uses the current density measured by the particle instrument. We find rough agreement between the results of our methods and with other velocity determinations previously published. We also explain a number of features of STD and show that the polynomial reconstruction technique is most likely to be valid within a distance of 2 spacecraft spacings from the centroid of the MMS spacecraft. Both of these methods are susceptible to contamination by magnetometer calibration errors
Measuring the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event
No full textInternational audienceVelocities in magnetic reconnection events, such as those of particles, are best understood in the frame of reference of the magnetic structure that is ultimately responsible for the reconnection process. We discuss four different methods for evaluating the velocity of the magnetic structure, and use those methods to find the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event studied by Torbert et al. (Science, 2018). The four methods are timing analysis, the SpatioTemporal Difference (STD) method of Shi et al. (JGR, 2006), Electron Magnetohydrodynamic (EMHD) reconstruction (Sonnerup et al., JGR, 2016), and polynomial reconstruction of the magnetic field in the vicinity of the spacecraft using the magnetic field and particle current density as input to the model. The relative merits of the different techniques will be discussed, and the different results compared
Measuring the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event
No full textInternational audienceVelocities in magnetic reconnection events, such as those of particles, are best understood in the frame of reference of the magnetic structure that is ultimately responsible for the reconnection process. We discuss four different methods for evaluating the velocity of the magnetic structure, and use those methods to find the magnetic structure velocity for the 11 July 2017 magnetotail reconnection event studied by Torbert et al. (Science, 2018). The four methods are timing analysis, the SpatioTemporal Difference (STD) method of Shi et al. (JGR, 2006), Electron Magnetohydrodynamic (EMHD) reconstruction (Sonnerup et al., JGR, 2016), and polynomial reconstruction of the magnetic field in the vicinity of the spacecraft using the magnetic field and particle current density as input to the model. The relative merits of the different techniques will be discussed, and the different results compared
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