Small‐scale structure of the midlatitude storm enhanced density plume during the 17 March 2015 St. Patrick’s Day storm

Kilometer‐scale density irregularities in the ionosphere can cause ionospheric scintillation—a phenomenon that degrades space‐based navigation and communication signals. During strong geomagnetic storms, the midlatitude ionosphere is primed to produce these ∼1–10 km small‐scale irregularities along the steep gradients between midlatitude storm enhanced density (SED) plumes and the adjacent low‐density trough. The length scales of irregularities on the order of 1–10 km are determined from a combination of spatial, temporal, and frequency analyses using single‐station ground‐based Global Positioning System total electron content (TEC) combined with radar plasma velocity measurements. Kilometer‐scale irregularities are detected along the boundaries of the SED plume and depleted density trough during the 17 March 2015 geomagnetic storm, but not equatorward of the plume or within the plume itself. Analysis using the fast Fourier transform of high‐pass filtered slant TEC suggests that the kilometer‐scale irregularities formed near the poleward gradients of SED plumes can have similar intensity and length scales to those typically found in the aurora but are shown to be distinct phenomena in spacecraft electron precipitation measurements.Key PointsKilometer‐scale density irregularities measured in single‐station GPS TEC data from the 17 March 2015 storm enhanced density plume systemLocation, intensity, and length scales are estimated from spatial, temporal, and frequency analyses of multiple instrument dataFormation regions for small‐scale irregularities with length scales of 3‐10 km are identified for plasma velocities of 500–1200 m s−1Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136745/1/jgra53295_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136745/2/jgra53295.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136745/3/jgra53295-sup-0001-supplementary.pd

Obesity Prevalence and Dietary Intake of Antioxidants in Native American Adolescents

Antioxidants are well known for possessing anti-inflammatory properties, which can reduce the risk of chronic disease and obesity. However, very little research has been done to examine antioxidant intake among adolescent minority populations such as Native American adolescents. Our study examined the significance of antioxidant intake among Native American adolescents at an urban residential high school in Southern California. Our study population consisted of 183 male and female Native American adolescents, 14-18 years of age, representing 43 tribes from across the United States. Students' primary source of meals was provided by the school food service. Based on the BMI calculations, the rate of obesity within our population was 38% for males and 40% for females, more than two-fold the national rate indicated by NHANESIII data. We used the Harvard School of Public Health Youth/Adolescent Questionnaire (HSPH YAQ), a semi-quantitative food frequency questionnaire, to examine antioxidant nutrient intake and evaluate the differences in the intake between normal and obese weight students. Statistical analysis of the results showed that intakes of vitamins C, E, and lycopene were the antioxidant nutrients found to be significantly different between normal and obese weight students and intakes of these nutrients were found to be higher among normal weight students (p-values = 0.02451, 0.00847, and 0.04928, respectively). These results suggest that dietary intake of antioxidants could be increased among Native American adolescents. Further research is needed to confirm our findings and identify effective ways for school food service to incorporate antioxidant rich foods into school menus

GPS TEC observations of dynamics of the mid‐latitude trough during substorms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95166/1/grl28288.pd

The Effect of F‐Layer Zonal Neutral Wind on the Monthly and Longitudinal Variability of Equatorial Ionosphere Irregularity and Drift Velocity

The effect of eastward zonal wind speed (EZWS) on vertical drift velocity (E × Bdrift) that mainly controls the equatorial ionospheric irregularities has been explained theoretically and through numerical models. However, its effect on the seasonal and longitudinal variations of E × B and the accompanying irregularities has not yet been investigated experimentally due to lack of F‐layer wind speed measurements. Observations of EZWS from GOCE and ion density and E × B from C/NOFS satellites for years 2011 and 2012 during quite times are used in this study. Monthly and longitudinal variations of the irregularity occurrence, E × B, and EZWS show similar patterns. We find that at most 50.85% of longitudinal variations of E × B can be explained by the longitudinal variability of EZWS only. When the EZWS exceeds 150 m/s, the longitudinal variation of EZWS, geomagnetic field strength, and Pedersen conductivity explain 56.40–69.20% of the longitudinal variation of E × B. In Atlantic, Africa, and Indian sectors, from 42.63% to 79.80% of the monthly variations of the E × B can be explained by the monthly variations of EZWS only. It is found also that EZWS and E × B may be linearly correlated during fall equinox and December solstice. The peak occurrence of irregularity in the Atlantic sector during November and December is due to the combined effect of large wind speed, solar terminator‐geomagnetic field alignment, and small geomagnetic field strength and Pedersen conductivity. Moreover, during June solstices, small EZWS corresponds to vertically downward E × B, which suggests that other factors dominate the E × B drift rather than the EZWS during these periods.Key PointsZonal neutral wind controls more the seasonal variations of E × B drift than the longitudinal variations of E × B driftAt most 50.85% of the longitudinal variations of E × B drift are accounted for by the eastward zonal neutral wind speed onlyZonal neutral wind speed and E × B drift may be linearly correlated during fall equinox and December solsticePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155994/1/jgra55709.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155994/2/jgra55709_am.pd

Experimental observation of magnetic bobbers for a new concept of magnetic solid-state memory

The use of chiral skyrmions, which are nanoscale vortex-like spin textures, as movable data bit carriers forms the basis of a recently proposed concept for magnetic solid-state memory. In this concept, skyrmions are considered to be unique localized spin textures, which are used to encode data through the quantization of different distances between identical skyrmions on a guiding nanostripe. However, the conservation of distances between highly mobile and interacting skyrmions is difficult to implement in practice. Here, we report the direct observation of another type of theoretically-predicted localized magnetic state, which is referred to as a chiral bobber (ChB), using quantitative off-axis electron holography. We show that ChBs can coexist together with skyrmions. Our results suggest a novel approach for data encoding, whereby a stream of binary data representing a sequence of ones and zeros can be encoded via a sequence of skyrmions and bobbers. The need to maintain defined distances between data bit carriers is then not required. The proposed concept of data encoding promises to expedite the realization of a new generation of magnetic solid-state memory

Partial Covering Arrays: Algorithms and Asymptotics

A covering array $\mathsf{CA}(N;t,k,v)$ is an $N\times k$ array with entries in $\{1, 2, \ldots , v\}$, for which every $N\times t$ subarray contains each $t$-tuple of $\{1, 2, \ldots , v\}^t$ among its rows. Covering arrays find application in interaction testing, including software and hardware testing, advanced materials development, and biological systems. A central question is to determine or bound $\mathsf{CAN}(t,k,v)$, the minimum number $N$ of rows of a $\mathsf{CA}(N;t,k,v)$. The well known bound $\mathsf{CAN}(t,k,v)=O((t-1)v^t\log k)$ is not too far from being asymptotically optimal. Sensible relaxations of the covering requirement arise when (1) the set $\{1, 2, \ldots , v\}^t$ need only be contained among the rows of at least $(1-\epsilon)\binom{k}{t}$ of the $N\times t$ subarrays and (2) the rows of every $N\times t$ subarray need only contain a (large) subset of $\{1, 2, \ldots , v\}^t$. In this paper, using probabilistic methods, significant improvements on the covering array upper bound are established for both relaxations, and for the conjunction of the two. In each case, a randomized algorithm constructs such arrays in expected polynomial time

Multi‐instrument observations of SED during 24–25 October 2011 storm: Implications for SED formation processes

We present multiple instrument observations of a storm‐enhanced density (SED) during the 24–25 October 2011 intense geomagnetic storm. Formation and the subsequent evolution of the SED and the midlatitude trough are revealed by global GPS vertical total electron content maps. In addition, we present high time resolution Poker Flat Incoherent Scatter Radar (PFISR) observations of ionospheric profiles within the SED. We divided the SED observed by PFISR into two parts. Both parts are characterized by elevated ionospheric peak height ( h m F 2 ) and total electron content, compared to quiet time values. However, the two parts of the SED have different characteristics in the electron temperature ( T e ), the F region peak density ( N m F 2 ), and convection flows. The first part of the SED is associated with enhanced T e in the lower F region and reduced T e in the upper F region and is collocated with northward convection flows. The N m F 2 was lower than quiet time values. The second part of the SED is associated with significantly increased N m F 2 , elevated T e at all altitudes and is located near the equatorward boundary of large northwestward flows. Based on these observations, we suggest that the mechanisms responsible for the formation of the two parts of the SED may be different. The first part is due to equatorward expansion of the convection pattern and the projection of northward convection flows in the vertical direction, which lifts the ionospheric plasma to higher altitudes and thus reduces the loss rate of plasma recombination. The second part is more complicated. Besides equatorward expansion of the convection pattern and large upward flows, evidences of other mechanisms, including horizontal advection due to fast flows, energetic particle precipitation, and enhanced thermospheric wind in the topside ionosphere, are also present. Estimates show that contribution from precipitating energetic protons is at most ~10% of the total F region density. The thermospheric wind also plays a minor role in this case. Key Points SED formation during 24–25 October 2011 geomagnetic storm studied PFISR observations within the SED shown Electric field plays a major role in the formation of SED in this stormPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102626/1/jgra50711.pd

On the generation/decay of the storm‐enhanced density plumes: Role of the convection flow and field‐aligned ion flow

Storm‐enhanced density (SED) plumes are prominent ionospheric electron density increases at the dayside middle and high latitudes. The generation and decay mechanisms of the plumes are still not clear. We present observations of SED plumes during six storms between 2010 and 2013 and comprehensively analyze the associated ionospheric parameters within the plumes, including vertical ion flow, field‐aligned ion flow and flux, plasma temperature, and field‐aligned currents, obtained from multiple instruments, including GPS total electron content (TEC), Poker Flat Incoherent Scatter Radar (PFISR), Super Dual Auroral Radar Network, and Active Magnetosphere and Planetary Electrodynamics Response Experiment. The TEC increase within the SED plumes at the PFISR site can be 1.4–5.5 times their quiet time value. The plumes are usually associated with northwestward E  ×  B flows ranging from a couple of hundred m s −1 to > 1 km s −1 . Upward vertical flows due to the projection of these E  ×  B drifts are mainly responsible for lifting the plasma in sunlit regions to higher altitude and thus leading to plume density enhancement. The upward vertical flows near the poleward part of the plumes are more persistent, while those near the equatorward part are more patchy. In addition, the plumes can be collocated with either upward or downward field‐aligned currents (FACs) but are usually observed equatorward of the peak of the Region 1 upward FAC, suggesting that the northwestward flows collocated with plumes can be either subauroral or auroral flows. Furthermore, during the decay phase of the plume, large downward ion flows, as large as ~200 m s −1 , and downward fluxes, as large as 10 14  m −2  s −1 , are often observed within the plumes. In our study of six storms, enhanced ambipolar diffusion due to an elevated pressure gradient is able to explain two of the four large downward flow/flux cases, but this mechanism is not sufficient for the other two cases where the flows are of larger magnitude. For the latter two cases, enhanced poleward thermospheric wind is suggested to be another mechanism for pushing the plasma downward along the field line. These downward flows should be an important mechanism for the decay of the SED plumes. Key Points Vertical plasma lifting leads to density increase during plume generation phase Large downward field‐aligned ion flow/flux seen during plume decay phase Complex‐induced plasma drifts seen indicating plumes' highly dynamic naturePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/1/StormB_tec_20121113.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/2/QuietTimeF_tec_20100821.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/3/StormD_tec_20120423.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/4/QuietTimeC_tec_20120928.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/5/SupplementaryMaterial_Figure3_quiet.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/6/QuietTimeE_tec_20110203.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/7/StormC_tec_20120930.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/8/StormA_tec_20130423.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/9/StormF_tec_20100803.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/10/jgra51348.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/11/SupplementaryMaterial_Figure4_quiet.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/12/QuietTimeA_tec_20130421.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/13/QuietTimeD_tec_20120429.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/14/QuietTimeB_tec_20121109.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109661/15/StormE_tec_20110204.pd

Electrodynamics of the high‐latitude trough: Its relationship with convection flows and field‐aligned currents

We present a detailed case study of the electrodynamics of a high‐latitude trough observed at ~ 12 UT (~1 MLT) on 8 March 2008 using multiple instruments, including incoherent scattering radar (ISR), GPS total electron content (TEC), magnetometers, and auroral imager. The electron density within the trough dropped as much as 80% within 6 minutes. This trough was collocated with a counterclockwise convection flow vortex, indicating divergent horizontal electric fields and currents. Together with a collocated dark area shown in auroral images, the observations provide strong evidence for an existence of downward field‐aligned currents (FACs) collocated with the high‐latitude trough. This is further supported by assimilative mapping of ionospheric electrodynamics results. In addition, the downward FACs formed at about the same time as a substorm onset and east of the Harang reversal, suggesting it is part of the substorm current wedge. It has long been a puzzle why this type of high‐latitude trough predominantly occurs just east of the Harang reversal in the postmidnight sector. We suggest that the high‐latitude trough is associated with the formation of downward FACs of the substorm current system, which usually occur just east of the Harang reversal. In addition, we find that the ionospheric electron temperature within the high latitude trough decreases in the F region while increasing in the E region. We discuss possible mechanisms responsible for the complex change in electron temperature, such as ion composition change and/or presence of downward FACs. Key Points Multi‐instrument study of the high‐latitude trough electrodynamics Trough is associated with anti‐clockwise flow vortex and substorm downward FACs Complex Te profile observed in the trough and due to downward FACsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98817/1/jgra50120.pd